Discharge lamp lighting apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a discharge lamp lighting apparatus which lights a discharge lamp by a high frequency current generated by a switching element.

2. Prior Art

FIG. 34

is a circuit diagram showing a construction of a conventional discharge lamp lighting apparatus. In

FIG. 34

, a reference symbol IV denotes an inverter circuit which is connected to a direct current power supply E, and switches a direct current of the direct current power supply E so that the direct current is converted into a high frequency current, an LAC

1

denotes a discharge lamp load circuit for lighting a discharge lamp LA by a high frequency current generated by the inverter circuit IV, and an NP

1

denotes a protective circuit which detects a fault of the discharge lamp load circuit LAC

1

, and outputs a control signal for stopping an operation of the inverter circuit IV.

The following is a detailed description on each of the above circuits.

The inverter circuit IV includes a starting circuit, a pair of MOS-FETs Q

1

and Q

2

(hereinafter, referred to as switching element Q

1

and Q

2

), an inverter control circuit IC

1

(hereinafter, referred to as IV control circuit IC

1

), and a frequency control circuit FC

1

. More specifically, the starting circuit is constructed in a manner that a starting resistor R

1

and a control power supply capacitor C

1

are connected in series and a constant voltage diode DZ

1

is connected in parallel with the control power supply capacitor C

1

. The pair of switching elements Q

1

and Q

2

are connected in series between both electrodes of the direct current power supply E. The inverter control circuit IC

1

controls the switching elements Q

1

and Q

2

. The frequency control circuit FC

1

sets a switching frequency of the switching elements Q

1

and Q

2

via the IV control circuit IC

1

. The IV control circuit IC

1

has terminals; more specifically, a power supply terminal

1

(hereinafter, referred to as terminal

1

) is connected to the control power supply capacitor C

1

, output terminals

2

,

3

and

4

(hereinafter, referred to as terminals

2

,

3

and

4

) are connected to the switching elements Q

1

and Q

2

, and oscillation control terminals

6

and

7

(hereinafter, referred to as terminals

6

and

7

) are connected to the frequency control circuit FC

1

. Moreover, the frequency control circuit FC

1

is composed of a main oscillation resistor R

2

and an oscillation capacitor C

2

which are connected between a negative electrode of the direct current power supply E and the terminals

6

and

7

of the IV control circuit IC

1

, respectively. In this manner, the IV control circuit IC

1

oscillates at a frequency f=K* (current flowing from the terminal

6

of the IV control circuit, which has a constant direct current potential) with respect to a constant K determined by a capacitance of the oscillation capacitor C

2

, and thereby, the switching elements Q

1

and Q

2

make a switching operation at the frequency f.

Next, the following is a description on the discharge lamp load circuit LAC

1

.

As shown in

FIG. 34

, the discharge lamp load circuit LAC

1

is composed of a ballast chock T

1

, a discharge lamp LA having electrodes F

1

and F

2

, and a coupling capacitor C

4

which are connected in series between both terminals of the switching element Q

2

, and further of a starting capacitor C

3

connected in parallel with the discharge lamp LA.

On the other hand, the protective circuit NP

1

is so constructed that the protective circuit NP

1

detects a peak-to-peak voltage (Vmax−Vmin) of a waveform of high frequency voltage between the electrode F

1

side terminal of the ballast chock T

1

and a negative electrode of the direct current power supply E by detection capacitors C

5

and C

6

connected to the discharge lamp load circuit LAC

1

, diodes D

1

and D

2

and a capacitor C

7

. Then, when a direct current voltage generated in both terminals of the capacitor C

7

exceeds a Zener voltage of a constant voltage diode DZ

2

, the protective circuit NP

1

outputs a signal to an oscillation stop terminal

5

(hereinafter, referred to as terminal

5

) of the IV control circuit IC

1

connected to the protective circuit NP

1

so that a switching operation of the switching elements Q

1

and Q

2

is stopped. In this case, when the discharge lamp LA is normally lighting, the direct current voltage of the capacitor C

7

is set so as to become lower than a Zener voltage of the constant voltage diode DZ

2

. Therefor, the protective circuit NP

1

is not operated. Moreover, a resistor R

4

is used for discharging a charge stored in the capacitor C

7

when a power supply is turned off, and a resistor R

16

and a capacitor C

11

divide and control a voltage inputted to the terminal

5

, and smooth an external high frequency noise, to prevent a malfunction of the IV control circuit IC

1

.

Next, the following is a description on an operation of a conventional discharge lamp lighting apparatus.

The discharge lamp is started up, and then, when a current is supplied to the inverter circuit IV from the direct current power supply E, the control power supply capacitor C

1

is charged by a starting current flowing through the starting resistor R

1

from the direct current power supply E. When a voltage of the terminal

1

of the IV control circuit IC reaches a predetermined operating voltage, the IV control circuit IC

1

oscillates at a frequency f determined by the frequency control circuit FC

1

so that a high frequency signal is outputted to the switching elements Q

1

and Q

2

from its terminals

2

and

4

. Then, the switching elements Q

1

and Q

2

are alternately turned on and off, and thereby, a high frequency current is supplied to the discharge lamp load circuit LAC

1

. By the high frequency current, a series circuit comprising the ballast chock T

1

and the starting capacitor C

3

(for the coupling capacitor C

4

is designed so as to have a capacitance several times as much as that of the starting capacitor C

3

, the coupling capacitor C

4

has no influence on the following resonance phenomenon) generates an LC resonance. Subsequently, a high voltage is generated in the starting capacitor C

3

, that is, between both terminals of the discharge lamp LA. Thus, the discharge lamp LA is started, and continues to light at a frequency f. In this case, the control power supply capacitor C

1

is connected in parallel with the constant voltage diode DZ

1

, so that a voltage applied to the terminals

1

of the IV control circuit IC

1

is limited by a Zener voltage of the constant voltage diode DZ

1

.

Next, the following is a description on an operation of a conventional protective circuit NP

1

.

When the discharge lamp LA is lighting, a high frequency voltage as shown in

FIG. 35

is generated between the electrode F

1

side terminal of the ballast chock T

1

and a negative electrode of the direct current power supply E. The high frequency voltage is generated so as to be overlapped with a constant direct current voltage. In the protective circuit NP

1

, a peak-to-peak voltage (Vmax—Vmin) is detected by the detection capacitors C

5

and C

6

and the diodes D

1

and D

2

which are connected between the ballast chock T

1

and the direct current power supply E, and further, is converted into a direct current voltage by the capacitor C

7

, and thus, is inputted to the constant voltage diode DZ

2

. In this case, when the discharge lamp LA is normally lighting, the direct current voltage of the capacitor C

7

is set so as to become less than a Zener voltage of the constant voltage diode DZ

2

; therefore, no oscillation stop signal is outputted to the IV control circuit IC

1

from the protective circuit NP

1

.

However, for example, in the case where the discharge lamp LA is rectified and lighting in the end of its file, a high frequency lamp voltage of the discharge lamp LA rises up; for this reason, a voltage of the capacitor C

7

becomes higher than the Zener voltage of the constant voltage diode DZ

2

. Whereupon the protective circuit NP

1

outputs an oscillation stop signal to the terminal

5

of the IV control circuit IC

1

, and further, by the oscillation stop of the IV control circuit IC

1

, a switching operation of the switching elements Q

1

and Q

2

is also stopped. As a result, that prevents the switching elements Q

1

and Q

2

from being abnormally exothermic, and a temperature in the vicinity of the electrodes F

1

and F

2

of the discharge lamp LA from becoming abnormally high to break down the discharge lamp LA. In this case, the oscillation stop state of the IV control circuit IC

1

is reset at the time when a voltage of the control power supply capacitor C

1

becomes less than a predetermined voltage, and an oscillation is started at the time when a voltage of the control power supply capacitor C

1

becomes more than the predetermined voltage.

Moreover, in the case where a high resonance voltage is generated in the starting capacitor C

3

, a large current flows through the ballast chock T

1

and the starting capacitor C

3

. Therefore, in the case where the discharge lamp LA is not lighting because of being defective or in the end of life, a voltage between terminals of the starting capacitor C

3

is continuously kept abnormally high, and a direct current voltage of the capacitor C

7

becomes higher than a Zener voltage of the constant voltage diode DZ

2

. Thus, in the same manner as described above, the protective circuit NP

1

outputs an oscillation stop signal to the terminal

5

so as to stop an oscillation of the inverter circuit IV. As a result, it is possible to prevent an excessive current from continuously flowing through the ballast chock T

1

and the starting capacitor C

3

and the ballast chock T

1

and the starting capacitor C

3

from being broken down.

Moreover, in the case where the discharge lamp LA is dismounted during lighting, a resonance current flows through a series circuit comprising the ballast chock T

1

and the detection capacitors C

5

and C

6

, and thereby, the direct current voltage of the capacitor C

7

becomes higher than the Zener voltage of the constant voltage diode DZ

2

. For this reason, the protective circuit NP

1

outputs an oscillation stop signal to the terminal

5

so as to stop an oscillation of the inverter circuit IV. In this manner, in the case where the discharge lamp LA is dismounted during lighting, the oscillation of the inverter circuit IV is stopped, and then, no high frequency current flows through the discharge lamp load circuit LAC

1

; therefore, no high frequency voltage is generated terminals in a socket of the discharge lamp LA. As a result, it is possible to prevent accidents such as a ground fault occurring in lamp replacement.

However, the above conventional discharge lamp lighting apparatus shown in

FIG. 34

has the following problems. The discharge lamp lighting apparatus detects a voltage difference between the maximum value and the minimum value of a high frequency voltage waveform between the electrode F

1

side terminal of the ballast chock T

1

and the negative electrode of the direct current power supply E. Then, by taking advantage of the fact that the above voltage difference becomes higher in abnormal cases (rectification lighting, no-lighting, no-load) than that in the case where the discharge lamp LA is normally lighting, an oscillation of the inverter circuit IV is stopped; for this reason, it is very difficult to make a circuit constant design for determining a protection level of the protective circuit NP

1

. Namely, in order to enhance a reliability of the protective circuit NP

1

, a sufficient margin needs to be left so that the protective circuit NP

1

does not output an oscillation stop signal during normal lighting of the discharge lamp LA, and on the other hand, a sufficient margin needs to be set so that the protective circuit NP

1

securely outputs an oscillation stop signal during abnormal lighting of the discharge lamp LA. As is evident from the circuit diagram shown in

FIG. 34

, the voltage difference detected by the protective circuit NP

1

is, after all, a voltage applied to the discharge lamp LA (i.e., both terminals of the starting capacitor C

3

). In general, considering that a lamp voltage of the discharge lamp LA greatly varies according to a different between individual products and an environmental temperature, there is a problem, in this fault detecting system of the conventional protective circuit NP

1

that the aforesaid two design margins cannot be set sufficiently large. In particular, in the discharge lamp lighting apparatus having a dimming function, a lamp voltage greatly rises when a lamp current of the discharge lamp LA is lowered to reduce a lumen output. Therefore, as a design of the protective circuit NP

1

is very difficult, there is a problem that the above protective circuit NP

1

cannot be actually applied to the discharge lamp lighting apparatus having a dimming function.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the above problems. It is, therefore, a first object of the present invention to provide a discharge lamp lighting apparatus which can take a sufficient design margin of a protective circuit, and can make high a reliability of the protective circuit and readily make a design of the protective circuit by securely distinguishing a normal lighting state from an abnormal lighting state.

Further, a second object of the present invention is to provide a discharge lamp lighting apparatus which can detect various faults of discharge lamp lighting apparatus, such as rectification lighting, no-lighting, and a no-load state, and can securely control an operation of an inverter circuit.

Further, a third object of the present invention is to provide a discharge lamp lighting apparatus having a preheat function of an electrode of a discharge lamp, which can securely light the discharge lamp and can securely control an operation of an inverter circuit in a fault state.

Further, a fourth object of the present invention is to provide a discharge lamp lighting apparatus which can securely light a discharge lamp in the case where an operating point in a steady state of the discharge lamp approaches or passes a resonance frequency of a discharge lamp load circuit, and can securely control an operation of an inverter circuit in a fault state.

Further, a fifth object of the present invention is to provide a discharge lamp lighting apparatus which can securely restart a discharge lamp after power supply is reset even in the case of an instantaneous failure of power supply, and can securely control an operation of an inverter circuit in a fault state.

Further, a sixth object of the present invention is to provide a discharge lamp lighting apparatus having a dimming function of a discharge lamp, which can take a sufficient design margin of a protective circuit securely light the discharge lamp by securely distinguishing a normal lighting state from an abnormal lighting state, securely control an operation of an inverter circuit in a fault state and have protective circuit having a high reliability.

Further, a seventh object of the present invention is to provide a discharge lamp lighting apparatus which has a low electrode loss consumed in an electrode of a discharge lamp, and has a high energy efficiency.

In order to achieve the above objects, the present invention provides a discharge lamp lighting apparatus comprising: a direct current power supply; a switching element for switching a direct current supplied from the direct current power supply so as to generate a high frequency current; a discharge lamp load circuit which is constructed in a manner that a discharge lamp and a coupling capacitor are connected in series, and the discharge lamp is lit by a high frequency current generated by the switching element; a protective circuit which detects a voltage generated in the coupling capacitor, and output a control signal; and a switching element control circuit for controlling the switching element by the control signal outputted from the protective circuit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the protective circuit is composed of: a voltage detecting unit for detecting a voltage generated in the coupling capacitor, and converting the detected voltage into a direct current voltage; a comparator unit for comparing the direct current voltage detected and converted by the voltage detecting unit with a reference voltage; and a control signal output unit for generating and outputting a control signal on the basis of the comparative result made by the comparator unit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a voltage inputted to the voltage detecting unit from the coupling capacitor, and is constructed so as to output a voltage divided by the divided resistor and the constant voltage diode to the comparator unit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the comparator unit has at least two different reference voltages, and is a window type comparator which is constructed so as to compare a direct current voltage outputted from the voltage detecting unit with the at least two reference voltages.

Further, the present invention provides the discharge lamp lighting apparatus wherein the direct current voltage outputted from the voltage detecting unit is compared with two different reference voltages by the comparator unit, and when the voltage becomes lower than a reference voltage on a low voltage side or becomes higher than a reference voltage on a high voltage side, the control signal output unit outputs a stop signal or an output reducing signal of the switching element to the switching element control circuit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the reference voltage of the comparator unit is set so as to be variable.

Further, the present invention provides the discharge lamp lighting apparatus wherein a plurality of discharge lamp load circuits having a coupling capacitor and a discharge lamp are driven by a high frequency current outputted from the switching element, and said protective circuit is provided with voltage detecting units each for detecting a voltage generated in the coupling capacitor of each of the discharge lamp load circuits, and converting the detected voltage into a direct current voltage; comparator units each for comparing the direct current voltage detected and converted by the voltage detecting unit with a reference voltage; and a control signal output unit for collecting outputs from the comparator units provided for the plurality of discharge lamp load circuits so as to generate a single control signal, and outputting the single control signal to the switching element control circuit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the protective circuit is provided with a mask circuit for masking a control signal outputted from the protective circuit for a predetermined time.

Further, the present invention provides the discharge lamp lighting apparatus wherein the apparatus further includes an over resonance detection circuit for detecting a high frequency current supplied to the discharge lamp load circuit and outputting a control signal to the switching element control circuit, so that the switching element is controlled by the control signal from the protective circuit and the control signal from the over resonance detection circuit via the switching element control circuit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the apparatus further includes an over resonance detection circuit for detecting a high frequency current supplied to the discharge lamp load circuit and outputting a control signal to the switching element control circuit, so that when the high frequency current detected by the over resonance detection circuit reaches a predetermined current value, even during a masking time of the protective circuit, the over resonance detection circuit outputs a stop signal or an output reducing signal of the switching element to the switching element control circuit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the apparatus further includes a service interruption in the case restoring circuit for automatically resetting the mask circuit when a feed from the direct current power supply is shut off, so that after the feed is restored, the mask circuit is operated so as to mask a control signal outputted from the protective circuit to the switching element control circuit for a predetermined time.

Moreover, the present invention provides a discharge lamp lighting apparatus comprising: a direct current power supply; a switching element for switching a direct current supplied from the direct current power supply so as to generate a high frequency current; a discharge lamp load circuit which is constructed in a manner that a discharge lamp and a coupling capacitor are connected in series, and the discharge lamp is lit by a high frequency current generated by the switching element; a switching element control circuit for controlling the switching element; and a plurality of starting capacitors which are connected in parallel with the discharge lamp, at least one of the starting capacitors being connected to the switching element side with respect to the discharge lamp.

Further, the present invention provides the discharge lamp lighting apparatus wherein a plurality of discharge lamp load circuits each having a coupling capacitor and a discharge lamp are driven by a high frequency current outputted from the switching element, and the protective circuit is provided with a first voltage detecting unit for detecting a stepped-up voltage of each coupling capacitor of the discharge lamp load circuit, and converting the detected voltage into a direct current voltage; a second voltage detecting unit for detecting a dropped voltage of each coupling capacitor, and converting the detected voltage into a direct current voltage; a first comparator unit for comparing the stepped-up direct current voltage detected by the first voltage detecting unit with a reference voltage; a second comparator unit for comparing the drop direct current voltage detected and converted by the second voltage detecting unit with a reference voltage; and a control signal output unit for generating a control signal on the basis of an output from any of the first or second comparator units, and outputting the single control signal to the switching element control circuit.

Further, the present invention provides the discharge lamp lighting apparatus wherein the first voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a voltage of each coupling capacitor, and reverse current blocking diodes interposed between the divided resistor and each coupling capacitor, and outputs the voltage divided by the divided resistor and the constant voltage diode to the first comparator unit, and the second voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a predetermined voltage, and reverse current blocking diodes interposed between the divided resistor and each coupling capacitor, and outputs the voltage divided by the divided resistor and the constant voltage diode to the second comparator unit in the case where any voltage of each coupling capacitor is higher than the predetermined voltage, and further, is constructed in a manner that in the case where any voltage of each coupling capacitor is lower than the predetermined voltage, the predetermined voltage is applied to a coupling capacitor having a lower voltage via the reverse current blocking diode.

Further, the present invention provides the discharge lamp lighting apparatus wherein one end of each reverse current blocking diode of the second voltage detecting unit is connected to a starting capacitor side of the discharge lamp.

Further, the present invention provides the discharge lamp lighting apparatus wherein the first voltage detecting unit includes divided resistors and constant voltage diodes each for dividing a voltage of each coupling capacitor, and reverse current blocking diodes interposed between the constant voltage diodes and the first comparator unit, and outputs the voltage divided by the divided resistor and the constant voltage to the first comparator unit via the diode reverse current blocking diodes, and the second voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a predetermined voltage, and reverse current blocking diodes interposed between the constant voltage diode and each of the constant voltage diodes of the first voltage detecting unit, and outputs the voltage divided by the divided resistor and the constant voltage diode to the second comparator unit in the case where any voltage of each coupling capacitor is higher than the predetermined voltage, and further, is constructed in a manner that in the case where any voltage of each coupling capacitor is lower than the predetermined voltage, the predetermined voltage is applied to a coupling capacitor having a lower voltage via the reverse current blocking diode, the divided resistor of the first voltage detecting unit and the constant voltage diode.

As is evident from the above description, the present invention has the aforesaid construction; and therefore, has the following effects.

More specifically, the present invention provides a discharge lamp lighting apparatus comprising: a direct current power supply; a switching element for switching a direct current supplied from the direct current power supply so as to generate a high frequency current; a discharge lamp load circuit which is constructed in a manner that a discharge lamp and a coupling capacitor are connected in series, and the discharge lamp is lit by a high frequency current generated by the switching element; a switching element control circuit for controlling the switching element. Further, the discharge lamp lighting apparatus includes a protective circuit which detects a voltage generated in the coupling capacitor, and output a control signal. Therefore, it is possible to securely distinguish a normal lighting state from an abnormal lighting state, and to stably light the discharge lamp in the normal lighting state. Moreover, it is possible to obtain a discharge lamp lighting apparatus which can control an oscillation of an inverter circuit in a fault state by securely operating the protective circuit, and has a high reliability.

Further, the protective circuit is composed of: a voltage detecting unit for detecting a voltage generated in the coupling capacitor, and converting the detected voltage into a direct current voltage; a comparator unit for comparing the direct current voltage detected by the voltage detecting unit with a reference voltage; and a control signal output unit for generating and outputting a control signal on the basis of the comparative result made by the comparator unit. Moreover, the comparator unit has at least two different reference voltages, and is a window type comparator which is constructed so as to compare a direct current voltage outputted from the voltage detecting unit with at least two reference voltages. Therefore, it is possible to detect a fault not only in a rectification lighting 1 state that a detection voltage steps up as compared with the fully normal lighting state, but also in a rectification lighting 2 state that a detection voltage steps up as compared with the fully normal lighting state and in a no-lighting state, and thus, to detect various faults generated in the discharge lamp.

The voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a voltage inputted to the voltage detecting unit from the coupling capacitor, and is constructed so as to output a voltage divided by the divided resistor and the constant voltage diode to the comparator unit. Therefore, it is possible to largely set a difference in a reference voltage between the normal lighting state and the abnormal state, and thus, to further improve a reliability of the protective circuit.

The direct current voltage outputted from the voltage detecting unit is compared with two different reference voltages by the comparator unit, and when the voltage becomes lower than a reference voltage on a low voltage side or becomes higher than a reference voltage on a high voltage side, the control signal output unit outputs a stop signal or output reducing signal of the switching element to the switching element control circuit. Therefore, it is possible to securely detect various faults generated in the discharge lamp, and by stopping or reducing an output to the discharge lamp, it is possible to prevent a breakdown or ground fault of the discharge lamp, the discharge lamp load circuit or the like.

The reference voltage of the comparator is set so as to be variable. Therefore, it is possible to more precisely set a reference value in accordance with a characteristic of the discharge lamp.

Each of the plurality of discharge lamp load circuits is provided with a voltage detecting unit for detecting a voltage generated in the coupling capacitor, and converting the detected voltage into a direct current voltage; a comparator unit for comparing the direct current voltage detected by the voltage detecting unit with a reference voltage; and a control signal output unit for collecting an output from the comparator units provided in the plurality of discharge lamp load circuits so as to generate a single control signal, and outputting the single control signal to the switching element control circuit. Therefore, it is possible to detect a fault at the point of time when any discharge lamps are in a fault state, and to reduce the number of components of the control signal output unit.

The protective circuit is provided with a mask circuit for masking a control signal outputted from the protective circuit for a predetermined time. Therefore, it is possible to obtain a discharge lamp lighting apparatus which can securely light a normal discharge lamp, and can securely stop an oscillation in a fault state. Moreover, the protective circuit is applicable to a discharge lamp lighting apparatus having a preheat function of preheating an electrode of the discharge lamp.

The discharge lamp lighting apparatus further includes an over resonance detection circuit which detects a high frequency current supplied to the discharge lamp load circuit and outputs a control signal to the switching element control circuit, and is constructed so that the switching element is controlled by the control signal from the protective circuit and the control signal from the over resonance detection circuit via the switching element control circuit. Therefore, it is possible to more precisely detect a fault, and to further improve a reliability of the protective circuit. Moreover, it is possible to apply the protective circuit to a discharge lamp lighting apparatus which is constructed in a manner that an oscillation frequency of the inverter circuit approaches a resonance frequency f

0

.

The discharge lamp lighting apparatus further includes a service interruption restoring circuit for automatically resetting the mask circuit when a feed from the direct current power supply is shut off, and after the feed is restored, the mask circuit is operated so as to mask a control signal outputted from the protective circuit to the switching element for a predetermined time. Therefore, even in the case where a service interruption takes place, after the service interruption is restored, it is possible to again operate the mask circuit, and to securely light the discharge lamp again simultaneously with when the power supply is restored.

Moreover, the present invention provides a discharge lamp lighting apparatus comprising: a direct current power supply; a switching element for switching a direct current supplied from the direct current power supply so as to generate a high frequency current; a discharge lamp load circuit which is constructed in a manner that a discharge lamp and a coupling capacitor are connected in series, and the discharge lamp is lit by a high frequency current generated by the switching element; a switching element control circuit for controlling the switching element. Further, the discharge lamp lighting apparatus includes a plurality of starting capacitors which are connected in parallel with the discharge lamp, at least one of the starting capacitors being connected to the switching element side with respect to the discharge lamp. Therefore, it is possible to make small an electrode loss consumed in the electrode of the discharge lamp, and thus, to improve an energy efficiency.

The plurality of discharge lamp load circuits having a coupling capacitor and a discharge lamp are driven by a high frequency current outputted from the switching element, and each of the plurality of discharge lamp load circuits is provided with a first voltage detecting unit for detecting a step-up voltage of each coupling capacitor, and converting the detected voltage into a direct current voltage; a second voltage detecting unit for detecting a drop voltage of each coupling capacitor, and converting the detected voltage into a direct current voltage; a first comparator unit for comparing the step-up direct current voltage detected by the first voltage detecting unit with a reference voltage; a second comparator unit for comparing the drop direct current voltage detected by the second voltage detecting unit with a reference voltage; and a control signal output unit for generating a control signal on the basis of an output from any of the first or second comparator units, and for outputting the single control signal to the switching element control circuit. Therefore, it is possible to detect a fault at the point of time when any of the discharge lamps is in a fault state, and to reduce the number of components as compared with the case where the comparator unit and the voltage detecting unit are independently provided in accordance with an increase of the discharge lamp load circuit.

The first voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a voltage of each coupling capacitor, and a reverse current blocking diode interposed between the divided resistor and each coupling capacitor, and outputs the voltage divided by the divided resistor and the constant voltage diode to the first comparator unit, and the second voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a predetermined voltage, and a reverse current blocking diode interposed between the divided resistor and each coupling capacitor, and outputs the voltage divided by the divided resistor and the constant voltage diode to the second comparator unit in the case where any voltage of each coupling capacitor is higher than the predetermined voltage, and further, is constructed in a manner that the predetermined voltage is applied to a coupling capacitor having a lower voltage via the reverse current blocking diode in the case where any voltage of each coupling capacitor is lower than the predetermined voltage. Therefore, even if the number of the discharge lamp load circuits is increased, the voltage detecting unit for detecting a voltage of each coupling capacitor is divided into the first voltage detecting unit for detecting a step-up voltage and the second voltage detecting unit for detecting a drop voltage, and thereby, it is possible to reduce the number of components of the voltage detecting unit by increasing the number of the divided resistors and the reverse current blocking diodes. Moreover, even if the number of the discharge lamp load circuits is increased, it is possible to detect the presence of the discharge lamp which is in the following states; more specifically, in a state such that any of the plurality of discharge lamps is in a fault state, that is, in a rectification lighting 1 state such that a detection voltage steps up as compared with the fully normal lighting state, in a rectification lighting 2 state such that a detection voltage drops as compared with the fully normal lighting state, and a detection voltage becomes 0 V by the removal of the discharge lamp. Moreover, it is possible to detect various faults of the discharge lamp.

In addition, the first voltage detecting unit outputs the voltage divided by the divided resistor and the constant voltage diode to the first comparator unit, and the second voltage detecting unit outputs the voltage divided by the divided resistor and the constant voltage diode to the second comparator unit in the case where any voltage of each coupling capacitor is higher than the predetermined voltage. Therefore, it is possible to largely set a difference in a reference voltage between the normal lighting state and the abnormal lighting state in the first and second comparator units, and thus, further improve a reliability of the protective circuit.

One end of the reverse current blocking diode of the second voltage detecting unit is connected to a starting capacitor side of the discharge lamp. Therefore, when the number of the discharge lamp load circuits is increased, in the case where any of the discharge lamps is dismounted, a circuit of the coupling capacitor of the discharge lamp and the reverse current blocking diode is shut off; as a result, the discharge lamp all becomes a normal state in the second voltage detecting unit, and the presence of the discharge lamp is not detected, and thereby, it is possible to make a detection in only case where any of the plural discharge lamps is in an abnormal state and a normal state.

The first voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a voltage of each coupling capacitor, and a reverse current blocking diode interposed between each constant voltage diode and the first comparator unit, and outputs the voltage divided by the divided resistor and the constant voltage to the first comparator unit via the diode reverse current blocking diode, and the second voltage detecting unit includes a divided resistor and a constant voltage diode for dividing a predetermined voltage, and a reverse current blocking diode interposed between the constant voltage diode and each constant voltage diode of the first voltage detecting unit, and further, a direct current voltage of each coupling capacitor is dived by a divided circuit comprising the divided resistor and the constant voltage diode, and the divided voltage is inputted to the first comparator unit via each reverse current blocking diode, and a direct current voltage of a direct current power supply is dived by a divided circuit comprising the divided resistor and the constant voltage diode, and the divided voltage is inputted to each coupling capacitor via each reverse current blocking diode. Therefore, it is possible to use a reverse current blocking diode having a low withstand voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a first embodiment of the present invention;

FIG. 2

is a voltage waveform chart between terminals of a switching element showing an operation of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 3

is an equivalent circuit diagram showing a fully normal lighting state of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 4

is a lamp current waveform chart of a fully normal lighting state and a rectification lighting state of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 5

is an equivalent circuit diagram showing a rectification lighting state of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 6

is an equivalent circuit diagram showing a rectification lighting state of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 7

is an equivalent circuit diagram showing a no-lighting state of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 8

is a comparative chart showing a change of potential of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 9

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a second embodiment of the present invention;

FIG. 10

is an equivalent circuit diagram showing a fully normal lighting state of the discharge lamp lighting apparatus according to the second embodiment of the present invention;

FIG. 11

is an equivalent circuit diagram showing a rectification lighting state of the discharge lamp lighting apparatus according to the second embodiment of the present invention;

FIG. 12

is an equivalent circuit diagram showing a rectification lighting state of the discharge lamp lighting apparatus according to the second embodiment of the present invention;

FIG. 13

is an equivalent circuit diagram showing a no-lighting state of the discharge lamp lighting apparatus according to the second embodiment of the present invention;

FIG. 14

is a comparative view showing a change of potential of the discharge lamp lighting apparatuses according to the first and second embodiments of the present invention;

FIG. 15

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a third embodiment of the present invention;

FIG. 16

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a fourth embodiment of the present invention;

FIG. 17

is an equivalent circuit diagram showing a reduced lumen output lighting state of the discharge lamp lighting apparatus according to the fourth embodiment of the present invention;

FIG. 18

is an equivalent circuit diagram showing a reduced lumen output lighting state of the discharge lamp lighting apparatus according to the first embodiment of the present invention;

FIG. 19

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a fifth embodiment of the present invention;

FIG. 20

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a sixth embodiment of the present invention;

FIG. 21

is a view showing an LC serial resonance curve showing a circuit operation of the discharge lamp lighting apparatus according to the sixth embodiment of the present invention;

FIG. 22

is a view showing a lamp voltage waveform showing a circuit operation of the discharge lamp lighting apparatus according to the sixth embodiment of the present invention and a transistor operation;

FIG. 23

is a view showing a lamp voltage waveform showing a circuit operation of the discharge lamp lighting apparatus according to the sixth embodiment of the present invention and a transistor operation;

FIG. 24

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a seventh embodiment of the present invention;

FIG. 25

is a view showing an LC serial resonance curve showing a circuit operation of the discharge lamp lighting apparatus according to the seventh embodiment of the present invention;

FIG. 26

is a view showing a high frequency current waveform of the discharge lamp lighting apparatus according to the seventh embodiment of the present invention;

FIG. 27

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to an eighth embodiment of the present invention;

FIG. 28

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a ninth embodiment of the present invention;

FIG. 29

is a view showing a voltage waveform between terminals of a switching element of the discharge lamp lighting apparatus according to the ninth embodiment of the present invention;

FIG. 30

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a tenth embodiment of the present invention;

FIG. 31

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to an eleventh embodiment of the present invention;

FIG. 32

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a twelfth embodiment of the present invention;

FIG. 33

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a thirteenth embodiment of the present invention;

FIG. 34

is a circuit diagram showing a construction of a conventional discharge lamp lighting apparatus; and

FIG. 35

is a voltage waveform chart showing an operation of the conventional discharge lamp lighting apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

FIRST EMBODIMENT

FIG. 1

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a first embodiment of the present invention. Like reference numerals are used to designate the same portion as the conventional discharge lamp lighting apparatus described in

FIG. 34

or the portion corresponding thereto, and the details are omitted.

The discharge lamp lighting apparatus of the first embodiment shown in

FIG. 1

is different from the conventional discharge lamp lighting apparatus shown in

FIG. 34

in a construction of the protective circuit and in a detecting object for detecting a fault. More specifically, in this first embodiment, a protective circuit NP

2

detects a voltage between both terminals of a coupling capacitor C

4

, and thereby, a fault of the discharge lamp load circuit LAC

1

is detected, and then, a control signal is outputted to the IV control circuit IC

1

. Thus, the protective circuit NP

2

includes: a voltage detecting unit VIN for detecting a direct current voltage between both terminals of the coupling capacitor C

4

; a comparator unit COMP for comparing the direct current voltage detected by the voltage detecting unit VIN with a reference voltage; and a control signal output unit VOUT for generating and outputting a control signal on the basis of the comparative result made by the comparator unit COMP.

The following is a description on a detailed construction of each unit constituting the above protective circuit NP

2

.

First, the voltage detecting unit VIN includes detection resistors R

10

and R

1

l for dividing the voltage between both terminals of the coupling capacitor C

4

, and a capacitor C

10

for removing a high frequency ripple component of the divided voltage. A detected voltage converted into a direct current is outputted to the comparator unit COMP. The comparator unit COMP includes two comparator IC

2

and IC

3

, and is constructed as a window type comparator in a manner that, two reference voltages are prepared by dividing a direct current voltage of the control power supply capacitor C

1

with the resistors R

12

, R

13

and R

14

, a voltage of a connecting point of the resistors R

12

and R

13

for determining a high threshold value is inputted to a non-inverting input terminal of the comparator IC

2

, a voltage of a connecting point of the resistors R

13

and R

14

for determining a low threshold value is inputted to an inverting input terminal of the comparator IC

3

, and further, the detected voltage from the voltage detecting unit VIN is inputted to an inverting input terminal of the comparator IC

2

and an non-inverting input terminal of the comparator IC

3

. An output terminals of either comparator IC

2

or IC

3

is an open collector, and both output terminals are connected to a base of a transistor Q

3

. A collector terminal of the transistor Q

3

is connected to the terminal

5

of the IV control circuit IC

1

, a parallel circuit comprising a capacitor C

11

and a resistor R

16

for dividing a voltage and removing an external high frequency noise is connected between the collector terminal and the negative electrode of the direct current power supply E, and a resistor R

15

for dividing a voltage is connected between the collector terminal and a positive electrode of the control power supply capacitor C

1

, so that a control signal output unit VOUT is constructed.

Incidentally, a diode D

3

connected between the non-inverting input terminal of the comparator IC

3

and the control power supply capacitor C

1

is a protective diode for clipping a voltage of the comparator IC

3

into a Zener voltage of the constant voltage diode DZ

1

.

Next, an operation of the circuit of the first embodiment shown in

FIG. 1

will be described below with reference to FIG.

1

and FIG.

2

. An operation of the circuit during a time between a start of the discharge lamp lighting apparatus and a start of discharge lamp LA is the same as the above conventional apparatus shown in FIG.

34

. Therefore, its description is omitted, and an operation of the protective circuit NP

2

is described below in particular.

When the discharge lamp lighting apparatus is started up and the IV control circuit IC

1

oscillates at a frequency f, the switching elements Q

1

and Q

2

are alternately turned on and off at the same frequency, and then, the discharge lamp LA is lighted. At this time, a terminal voltage of the switching element Q

2

, that is, an input voltage to the discharge lamp load circuit LAC

1

is a high frequency voltage as shown in

FIG. 2

(

a

), having a frequency f and a peak value of the voltage of the direct current power supply E (hereinafter, 440 V as one example). The high frequency voltage of

FIG. 2

(

a

) is expressed by a resultant (synthetic) voltage made of both a high frequency alternating voltage AC having a peak value of 220 V (440 V/2) and a frequency f as shown in

FIG. 2

(

b

) and a direct current voltage DC having a peak value of 220 V (440 V/2) as shown in FIG.

2

(

c

). Now, the voltage generated between both terminals of the coupling capacitor C

4

(i.e., negative electrode side of the direct current power supply E and discharge lamp LA side of the coupling capacitor C

4

) is examined. Since a capacity of the coupling capacitor C

4

is designed sufficiently larger, a high frequency voltage component shown in FIG.

2

(

b

) is offset by a charge and discharge of the coupling capacitor C

4

. As a result, in the coupling capacitor C

4

, a quasi-direct current voltage is generated which includes the direct current voltage shown in FIG.

2

(

c

), consisting of a direct current component, and a slight high frequency voltage.

In this manner, the quasi-direct current voltage is divided by the voltage detecting unit VIN of the protective circuit NP

2

, and then, a high frequency component is removed by the capacitor C

10

so as to be converted into a direct current voltage, and thereafter, is outputted to the comparator unit COMP. Then, the direct current voltage is compared with two reference voltages by the window type comparator composed of the comparator IC

2

and the comparator IC

3

. If the direct current voltage is out of the range between the reference voltages, the transistor Q

3

is turned off so that an oscillation stop signal is inputted to the terminal

5

of the IV control circuit IC

1

. Thus, the oscillation of the IV control circuit IC

1

is stopped, and also, each switching operation of the switching elements Q

1

and Q

2

is stopped. Although following is a description on the case where a control signal of the protective circuit NP

2

is inputted to the oscillation stop signal input terminal

5

of the IV control circuit IC

1

, these control signals may be inputted to, for example, a frequency control terminal

6

directly or via the frequency control circuit FC

1

so as to control the switching frequency of the switching elements Q

1

and Q

2

to reduce a high frequency output supplied to the discharge lamp LA.

Subsequently, an operation of the protective circuit NP

2

corresponding to each load state of the discharge lamp LA will be successively described below in detail.

FIG. 3

is a diagram showing an equivalent circuit of a discharge lamp load circuit LAC

1

and the voltage detecting unit VIN of the protective circuit NP

2

, in a fully normal lighting state based on the concept shown in FIG.

2

and shows one example of a practical frequency, circuit constant and impedance. In

FIG. 3

, “A” and “B” show a potential of the coupling capacitor C

4

on a positive electrode side and a potential of a detection resistor R

11

, respectively, on the basis of a negative electrode potential “G” of the direct current power supply E, respectively.

As shown in the equivalent circuit diagram of

FIG. 3

, for the discharge lamp LA is lighting at a high frequency of 45 kHz in this case, it is equivalently regarded as a resistance. Here, the resistance is set as 280Ω considering an FHF32 (Hf) lamp of JIS standard to be used. In this equivalent circuit, a voltage generated between both terminals of the coupling capacitor C

4

is considered as follows. The total of resistance values of the detection resistors R

10

and R

11

is a high resistance of about 1000 times as much as the discharge lamp LA. For this reason, the coupling capacitor C

4

is charged to about 220 V by the direct current power supply DC via the ballast chock T

1

and the discharge lamp LA while the same charge is alternately charged and discharged by the high frequency power supply AC via the ballast chock T

1

, the discharge lamp LA and the starting capacitor C

3

. As a result, a potential “A” of the coupling capacitor C

4

becomes a direct current voltage of about 220 V with which a slight high frequency component is overlapped. Moreover, a potential “B” of the detection resistor R

11

becomes a direct current voltage of about 7 V because the potential “A” is divided by the detection resistor R

10

(300 kΩ) and the detection resistor R

11

(10 kΩ), and a high frequency component is removed by the capacitor C

10

. As described in the conventional example, in the discharge lamp LA, a lamp voltage generally varies according to a variation of environmental temperature, an aged deterioration or a difference between individual product even if a lamp current is fixed; namely its equivalent resistance value greatly varies. However, according to the first embodiment described above, the detection resistors R

10

and R

11

have a high resistance value; therefore, for example, even if the equivalent resistance value of the discharge lamp LA varies by about 30% to 50%, the potentials “A” and “B” of the coupling capacitor C

4

and the detection resistor R

11

hardly change.

Next, the following is a description on an operation of rectification lighting 1 (a state where electrons are hardly emitted from the electrode F

1

in the end of life) and rectification lighting 2 (a state where electrons are hardly emitted from the electrode F

2

in the end of life) of fault states of the discharge lamp LA.

FIG. 4

shows a high frequency lamp current waveform of the discharge lamp LA in each case of full lighting, rectification lighting 1 and rectification lighting 2 (directions for charging and discharging the coupling capacitor C

4

are shown as positive and negative, respectively). As seen from

FIG. 4

, in the full lighting state, a waveform is symmetrical; on the contrary, in the rectification lighting 1 state and the rectification lighting 2 state, a waveform is asymmetrical. A characteristic change of the discharge lamp LA by a difference in the above lighting states is shown in FIG.

5

and FIG.

6

.

FIG.

5

and

FIG. 6

are equivalent circuit diagrams of the discharge lamp load circuit LAC

1

and the voltage detecting unit VIN in the protective circuit NP

2

with respect to rectification lighting 1 and rectification lighting 2, wherein a characteristic change of the discharge lamp LA is expressed by a connective direction of an equivalent circuit comprising an anti-parallel circuit of both a series circuit of a resistor (low) (tens of ohms(Ω) to hundreds of ohms(Ω)) and a diode, and a series circuit of a resistor (high) (hundreds of ohms(Ω) to several kilo-ohms (KΩ)) and a diode. In regard to FIG.

5

and

FIG. 6

, a potential of the coupling capacitor C

4

in the rectification lighting states

1

and

2

is considered as follows. The coupling capacitor C

4

is charged to about 220 V by the direct current power supply DC via the ballast chock T

1

and the discharge lamp LA (the resistor (low) and the diode in the rectification lighting 1 state, and the resistor (high) and the diode in the rectification lighting 2 state), like the normal lighting state of FIG.

3

. Moreover, the same charge is charged and discharged from the high frequency power supply AC via the ballast chock T

1

and the starting capacitor C

3

. By the above characteristic change of the discharge lamp LA, in the rectification lighting 1 state, a charging current becomes much via the discharge lamp LA in comparison to a discharging current; conversely, in the rectification lighting 2 state, a discharging current becomes much in comparison to a charging current. For this reason, the potentials “A” and “B” are individually changed to a high value in the rectification lighting 1 state (in this equivalent circuit, “A” is 290 V, and “B” is 9.4 V), and to a low value in the rectification lighting 2 state (in this equivalent circuit, “A” is 150 V, and “B” is 4.8 V) in comparison to the normal full lighting state.

Next, the following is a description on the case where the discharge lamp is in a non-lighting state or no-load state of fault states of the discharge lamp LA. In the case where the discharge lamp LA is in a non-lighting state or no-load state, an equivalent resistance value of the discharge lamp LA becomes infinite. Consequently, the equivalent circuit becomes as shown in

FIG. 7

where a circuit of the discharge lamp LA is deleted. In

FIG. 7

, a potential of the coupling capacitor C

4

is considered as follows. Since, there is no path for charging the coupling capacitor C

4

from the direct current power supply DC and the same charge is alternately charged and discharged to the coupling capacitor C

4

from the high frequency power supply AC via the ballast chock T

1

and the starting capacitor C

3

, both the potentials “A” and “B” become 0 V.

FIG. 8

shows the potential “A” of the coupling capacitor C

4

and the potential “B” of the detection resistor R

11

corresponding to each load state of the discharge lamp in this first embodiment.

Thus, the resistors R

12

, R

13

and R

14

are previously designed so that a reference voltage of a high threshold value of the comparator unit COMP composed of the comparator IC

2

and IC

3

in

FIG. 1

is set 8 V, and a reference voltage of a low threshold value is set to 6 V. Then, the above potential “B” shown in

FIG. 8

is inputted to the comparator unit, and thereby, in the normal full lighting state, the outputs of the comparator IC

2

and IC

3

are both HIGH, and the transistor Q

3

of the control signal output unit VOUT is in an on state. Therefore, no oscillation stop signal is outputted to the terminal

5

of the IV control circuit IC

1

; as a result, it is possible to continue the normal full lighting state. On the other hand, in the rectification lighting 1 state, the output of the comparator IC

2

becomes LOW, and in the rectification lighting 2 state and no-lighting or no-load state, the output of the comparator IC

3

becomes LOW, and the transistor Q

3

is in an off state. Therefore, an oscillation stop signal is outputted to the terminal

5

of the IV control circuit IC

1

so as to stop an oscillation of the inverter circuit IV. As a result, an over current to the ballast chock T

1

and the starting capacitor C

3

is shut out in the rectification lighting state or no-lighting state to prevent a breakdown of the circuit, and a high frequency voltage generated in a socket of the discharge lamp LA is turned off in a no-load state.

As described above, according to this first embodiment, a voltage between both terminals of the coupling capacitor C

4

is detected to detect a fault of the discharge lamp circuit LC

1

, as a variation of lamp voltage due to a difference between individual products of discharge lamp LA and a variation of environmental temperature hardly influence the voltage between the both terminals in the normal lighting state, and moreover, the voltage between both terminals greatly varies in accordance with each load state of the discharge lamp in the fault states. Therefore, a margin for making no operation of the protective circuit in the normal lighting state of the discharge lamp LA is sufficiently secured, and the protective circuit is securely operated in a fault state of the discharge lamp LA so as to stop an oscillation of the inverter circuit IV. Thereby, it is possible to obtain a discharge lamp lighting apparatus having a high reliability. As a result, there is an effect that a continued operation of rectification lighting generated with a discharge lamp LA which is in the end of life or is defective, a failure of the discharge lamp lighting apparatus and a breakdown of the discharge lamp LA, caused by no-lighting of lamp or accidents such as ground fault in a lamp replacement can be effectively prevented.

Further, according to this first embodiment, as described above, there is an effect that a sufficient margin is secured in an operation of the protective circuit NP

2

, and a design of the protective circuit NP

2

such as setting of reference voltage or the like can be easily made.

Furthermore, according to this first embodiment, the protective circuit NP

2

is composed of the voltage detecting unit VIN, the comparator unit COMP and the control signal output unit VOUT, and the comparator unit COMP is constructed as a window type comparator having two reference voltages. Therefore, there is an effect to detect the rectification lighting 1 state in which a detection voltage rises up as compared with the normal full lighting state, and both faults of the rectification lighting 2 state and no-lighting state, in which a detection voltage rises up as compared with the fully normal lighting state.

The above

FIG. 1

shows the case where only one discharge lamp LA is connected. Even in the case where a plurality of discharge lamps LA are connected in series, the protective circuit NP

2

detects the fault state at the point of time when one of the plural discharge lamps is in a fault state, according to the same circuit operation as above, and then, outputs an oscillation stop signal to the IV control circuit IC

1

. Therefore, the same effect as above can be obtained.

In addition, the above

FIG. 1

shows the case where the resistors R

12

, R

13

and R

14

for setting reference voltages of the comparator unit are composed of fixed resistors. However, if some of these resistors are composed of variable resistors so as to vary the reference voltages, there is an effect that for discharge lamps having different rated values, a reference value can be precisely set in accordance with a characteristic of the discharge lamps LA, for example.

SECOND EMBODIMENT

FIG. 9

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a second embodiment of the present invention. This second embodiment is different from the above first embodiment in only construction of the voltage detecting unit VIN of the protective circuit. More specifically, in the above first embodiment, the voltage detecting unit VIN is composed of the detection resistors R

10

and R

11

; on the contrary, according to this second embodiment, in a protective circuit NP

3

, a voltage is divided by detection resistors R

20

and R

21

and a constant voltage diode DZ

4

. In this case, a resistor R

22

connected in parallel with the voltage regulation diode DZ

4

has a high resistance of several times or more as much as these detection resistors R

20

and R

21

, and further, discharges a charge of the coupling capacitor C

4

after the inverter circuit IV stops its oscillation. Even if no resistor R

22

is provided, there is no influence in an operation of the protective circuit NP

3

. Like reference numerals are used to designate the same portion as the first embodiment shown in

FIG. 1

or portion corresponding thereto, and the details are omitted.

FIG. 10

to

FIG. 13

exemplify equivalent circuit diagrams of a discharge lamp load circuit LAC

1

and a voltage detecting unit VIN of the protective circuit NP

3

in each load state of a normal full lighting state (FIG.

10

), a rectification lighting 1 state (an electrode F

1

is in the end of life) (FIG.

11

), a rectification lighting 2 state (an electrode F

2

is in the end of life) (FIG.

12

), and a no-lighting state or no-load state (FIG.

13

), of the discharge lamp lighting apparatus in the second embodiment. In these

FIG. 10

to

FIG. 13

, symbols “A” and “B” express a potential of the coupling capacitor C

4

and a potential of the detection resistor R

21

, respectively, like FIG.

3

.

In the same manner as the first embodiment, direct current potentials “A” and “B” in each load state of the discharge lamp LA are calculated from these equivalent circuit diagrams, and the calculated result is as shown in FIG.

14

. In

FIG. 14

, potentials in the case of the above first embodiment and potentials in a case of a reduced lumen output operation described later in the fourth embodiment are set forth together, in order to make a comparison.

As is evident from

FIG. 14

, the potential “A” of the coupling capacitor C

4

becomes the same value in the above first embodiment and this second embodiment. On the other hand, it can be seen in this second embodiment as compared with the first embodiment, that the potential “B” changes more clearly between the normal full lighting state and fault states (rectification lighting 1 state, rectification lighting 2 state, no-lighting state and no-load state) because of a threshold value characteristic of the voltage regulation diode DZ

4

. Therefore, according to this second embodiment, a voltage on a high threshold value side of the window type comparator composed of the comparator IC

2

and IC

3

can be set to, for example, 10 V, and a voltage on a low threshold value side thereof can be set to, for example, 4 V. That is, a difference of threshold values of the potential “B” in a normal state and an abnormal state can be set greater than the first embodiment, so that there is another effect that a reliability of the protective circuit can be further improved. Incidentally, a voltage of the voltage regulation diode DZ

4

of the protective circuit NP

3

is set to the vicinity of the voltage generated in the coupling capacitor C

4

during normal lighting of the discharge lamp, the aforesaid operation can be performed more effectively.

As described above, in this second embodiment, the voltage detecting unit VIN of the protective circuit NP

3

is composed of the detection resistors R

20

and R

21

and the voltage regulation diode DZ

4

. Therefore, the potential “B” can be changed greatly, and even if there is a dispersion in a characteristic value of parts and a lamp characteristic, the protective circuit NP

3

continues an oscillation of the inverter circuit IV (without stopping it) during normal lighting of the discharge lamp, and surely stops the oscillation of the inverter circuit IV during abnormal lighting of the discharge lamp. As a result, there is another effect that a reliability is further improved as compared with the first embodiment.

In this second embodiment (FIG.

9

), the coupling capacitor C

4

is arranged on a negative electrode side of the switching element Q

2

. The coupling capacitor C

4

may be arranged on a positive electrode side of the switching element Q

1

so as to detect each voltage of both terminals. Moreover, in

FIG. 9

, a voltage between both terminals of the coupling capacitor C

4

(negative electrode side of direct current power supply E and discharge lamp LA side of coupling capacitor C

4

) is used as a voltage inputted to the protective circuit NP

3

. However, the voltage between a positive electrode side of the direct current power supply E and the discharge lamp LA side of coupling capacitor C

4

may be detected, for example. In this case, the detection voltage is a resultant voltage of the voltage of the direct current power supply E and the voltage of the coupling capacitor C

4

, and the voltage of the coupling capacitor C

4

is readily detected from the resultant voltage. Substantially, a quasi-direct current voltage between both terminals of the coupling capacitor C

4

is detected, so that to obtain the same effect as the above second embodiment can be obtained. Moreover, the coupling capacitor C

4

may be composed of a plurality of coupling capacitors to detect a voltage of any of these capacitors. In addition, a capacitor for detection may be provided independently of the coupling capacitor C

4

. In this manner, various modification examples can be considered as a method of detecting a quasi-direct current voltage generated in the coupling capacitor C

4

while maintaining the substantial construction of the above second embodiment.

THIRD EMBODIMENT

FIG. 15

shows a circuit diagram of a discharge lamp lighting apparatus according to a third embodiment of the present invention as one of modification example. In the above second embodiment (FIG.

9

), the discharge lamp load circuit LAC

1

is connected to both terminals of the switching element Q

2

of the inverter circuit IV. On the contrary, in this third embodiment, a discharge lamp load circuit LAC

4

is connected to both terminals of the switching element Q

1

, that is, to a positive electrode side of the direct current power supply E, and a voltage detected by the protective circuit NP

3

is set to a voltage between the negative electrode side of the direct current power supply E and the discharge lamp LA side of the coupling capacitor C

4

. In this case, a detected voltage is a voltage subtracting a voltage of both terminals of the coupling capacitor C

4

from a voltage of the direct current power supply E. Even if the above voltage value is used, it is possible to construct a protective circuit in the same manner as the above second embodiment, and further, even if a connecting position of the coupling capacitor C

4

and a position of voltage to be detected are variously changed, the same effect as the above second embodiment can be obtained.

FOURTH EMBODIMENT

FIG. 16

shows a circuit diagram of a discharge lamp lighting apparatus according to a fourth embodiment of the present invention. In this fourth embodiment, a function of continuously dimming a discharge lamp LA is added to the above second embodiment. For this purpose, a main oscillation resistor R

99

of the frequency control circuit FC

2

for determining an oscillation frequency of the IV control circuit IC

1

is composed of a variable resistor. In

FIG. 16

, like reference numerals are used to designate the same portion as

FIG. 9

or the portion corresponding thereto, and the details are omitted.

The following is a description on an operation of this fourth embodiment. In

FIG. 16

, when the IV control circuit IC

1

is oscillating, the terminal

6

of the IV control circuit IC

1

has a constant direct current voltage. The IV control circuit IC

1

has a characteristic such that an oscillation frequency becomes higher in the case when a current flowing to a negative electrode of the direct current power supply E from the terminal

6

increases. Therefore, when the variable resistor R

99

gradually decreases from a state that the discharge lamp LA is fully lighting, a current flowing to a negative electrode of the direct current power supply E from the terminal

6

increases. As a result, an oscillation frequency of the IV control circuit IC

1

becomes gradually high, and then, an impedance of the ballast chock T

1

becomes large, so that a current of the discharge lamp LA decreases, and then, a light is reduced.

FIG. 17

shows an equivalent practical circuit of the discharge lamp load circuit LAC

1

and the voltage detecting unit VIN of the protective circuit NP

3

in a reduced lumen output normal lighting state. As shown in the equivalent circuit diagram of

FIG. 17

, in this case, a switching frequency is increased to 70 kHz by a reduced lumen output operation, and an equivalent resistance value of the discharge lamp LA is consequently increased

27

times as much as the normal full lighting state, that is, to 7.5 KΩ. As the resistance value of the detection resistors R

20

and R

21

is set to a sufficient by high value with respect to the resistance 7.5 KΩ, the potentials “A” and “B” of the coupling capacitor C

4

and the detection resistor R

11

in the reduced lumen output lighting state are 218 V and 7 V, that is, they hardly change from 220 V and 7 V in the normal full lighting state as shown in FIG.

14

. Thus, these potentials become the substantially same voltage as the normal full lighting state.

As described above, even if the equivalent resistance value of the discharge lamp LA changes from hundreds of Ω to several KΩ or tens of KΩ by a dimming operation during the normal lighting of the discharge lamp LA, the potential “B” to be detected has almost no change. Therefore, the protective circuit NP

3

is applicable to the discharge lamp lighting apparatus having a dimming function. Further, the potential “B” has a great change with normal and abnormal states of the discharge lamp LA so that there is an effect that a protective circuit and a discharge lamp lighting apparatus having a high reliability can be obtained in the same way as the above first and second embodiments. Furthermore, a circuit constant of the protective circuit NP

3

can be set to the same, regardless of a kind of the discharge lamp LA and the presence of dimming function, so that there is an advantage that components can be standardized in various discharge lamp lighting apparatuses.

FIG. 18

shows an equivalent circuit diagram in the case where the resistor R

2

is replaced with a variable resistor to carry out a reduced lumen output operation in the first embodiment. In this case, the potentials “A” and “B” are 215 V and 7 V, that is, they hardly change from 220 V and 7 V in the normal full lighting state as shown in FIG.

14

. Therefore, the same effect as the above fourth embodiment can be obtained.

FIFTH EMBODIMENT

FIG. 19

is a circuit diagram of a discharge lamp lighting apparatus according to a fifth embodiment of the present invention. In this fifth embodiment, to form a discharge lamp load circuit LAC

3

, a discharge lamp load circuit comprising a discharge lamp LAY (parallel with a starting capacitor C

3

Y), a coupling capacitor C

4

Y and a ballast chock T

1

Y is connected in parallel to a discharge lamp load circuit of the above second embodiment comprising the discharge lamp LA (parallel with the starting capacitor C

3

), the coupling capacitor C

4

and the ballast chock T

1

. In accordance with this construction, a protective circuit NP

4

includes two detecting units consisting of a voltage detecting unit VIN (detection resistor R

21

, voltage regulation diode DZ

4

, detection resistor R

21

) and a voltage detecting unit VIN

2

(detection resistor R

21

Y, voltage regulation diode DZ

4

Y, detection resistor R

21

Y), and two comparator units consisting of a comparator unit COMP (comparators IC

2

and IC

3

and reference resistors R

12

, R

13

and R

14

) and a comparator unit COMP

2

(comparators IC

2

Y and IC

3

Y and reference resistors R

12

Y, R

13

Y and R

14

Y). Outputs from these two comparator units are inputted to a single control signal output unit VOUT, and then, the control signal output unit VOUT puts them together to output one control signal to the terminal

5

of the IV control circuit IC

1

. Like reference numerals are used to designate the same portion as the above second embodiment or a portion corresponding thereto, and the details are omitted.

The following is a description on an operation of the fifth embodiment. In

FIG. 19

, when both discharge lamps LA and LAY are normally lighting, outputs of the comparators IC

2

, IC

3

, IC

2

Y and IC

3

Y all become HIGH in the same manner as the second embodiment. Consequently, the transistor Q

3

is turned on so that the protective circuit NP

4

outputs no oscillation stop signal to let the discharge lamps LA and LAY continue normal lighting. On the other hand, when any of discharge lamps LA and LAY is in a fault state, a detection voltage outputted from the voltage detecting unit connected to each discharge lamp load circuit is compared with reference voltages by the comparators IC

2

and IC

3

or IC

2

Y and IC

3

Y, and then, any of these outputs becomes LOW. Consequently, the transistor Q

3

is turned off so that the protective circuit NP

4

outputs an oscillation stop signal to the IV control circuit IC

1

to stop an oscillation of the inverter circuit IV.

As described above, according to this fifth embodiment, the voltage detecting units VIN and VIN

2

are connected to respective one of the plurality of discharge lamp load circuits. Therefore, the oscillation of the inverter circuit IV is stopped at the point of time when any of discharge lamps is in a fault state, so that there is an effect that the above protective circuit is applicable to a two-lamp parallel lighting circuit of the discharge lamps LA and LAY.

Further, since the comparator units COMP and COMP

2

are connected to the voltage detecting units VIN and VIN

2

, respectively, reference voltages of the comparator units COMP and COMP

2

can be set in accordance with the characteristic of each discharge lamp load circuit. Thus, there is an effect to perform precise setting.

Furthermore, a single control signal output unit VOUT is provided with respect to a plurality of the voltage detecting units VIN and VIN

2

and the comparator units COMP and COMP

2

, and the outputs from the plurality of the comparator units COMP and COMP

2

are put together to output a control signal. Therefore, there is an effect to reduce the number of the control signal output units VOUT.

Though,

FIG. 19

shows the case where the discharge lamp load circuit is two, the protective circuit is, of course, applicable to a plural parallel lighting circuit for three or more discharge lamps.

SIXTH EMBODIMENT

FIG. 20

is a circuit diagram of a discharge lamp lighting apparatus according to a sixth embodiment of the present invention. In this sixth embodiment, the protective circuit of the above second embodiment is provided with a mask circuit MSK which masks a function of the protective circuit for a predetermined time after the discharge lamp lighting apparatus is turned on. For example, the above protective circuit is applicable to a discharge lamp lighting apparatus which preheats an electrode of the discharge lamp LA for a predetermined time, and thereafter, lights the discharge lamp LA. The mask circuit MSK and a frequency control circuit FC

3

which are constituent components characterizing this sixth embodiment will be mainly described below. Like reference numerals are used to designate the same portion as the above second embodiment (

FIG. 9

) or the portion corresponding thereto, and the details are omitted.

As shown in

FIG. 20

, in this sixth embodiment, the frequency control circuit FC

3

includes a series circuit comprising a preheat oscillation resistor R

3

and a preheat oscillation capacitor

30

between the terminal

6

of the IV control circuit IC

1

and the negative electrode of the direct current power supply E, in addition to a main oscillation resistor R

2

and an oscillation capacitor C

2

. Moreover, a protective circuit NP

5

includes a mask circuit MSK having a timer circuit TM composed of resistors R

18

and R

19

, a capacitor C

12

and a voltage regulation diode DZ

3

. The mask circuit MSK includes a transistor Q

4

which is connected between the oscillation stop terminal

5

of the IV control circuit IC

1

and the negative electrode of the direct current power supply E. An input terminal of the transistor Q

4

is connected with an output terminal of a transistor Q

5

which is driven by an output of the timer circuit TM. When the discharge lamp lighting apparatus is turned on, the capacitor C

12

is charged via the resistors R

1

and R

18

, and at the point of time when a voltage of the capacitor C

12

exceeds a Zener voltage of the constant voltage diode DZ

3

after a predetermined time, the transistor Q

5

is turned on to turn off the transistor Q

4

. In order to drive the timer circuit TM, a positive electrode side of the resistor R

18

is connected to the control power supply capacitor C

1

, and further, in order to drive the transistor Q

4

, the resistor R

17

is connected between the control power supply capacitor C

1

and a base of the transistor Q

4

.

Next, with reference to

FIG. 20

to

FIG. 23

, an operation of the mask circuit MSK and the frequency control circuit FC

3

in this sixth embodiment will be described below.

FIG. 21

is a diagram showing an LC series resonance curve of the ballast chock T

1

and the starting capacitor C

3

in the discharge lamp load circuit LAC

1

. In

FIG. 21

, (1) is a resonance curve at the time when the discharge lamp LA is lighting, and (2) is a resonance curve at the time when the discharge lamp LA is no-lighting. FIG.

22

and

FIG. 23

show a time change of voltage between both electrodes of the discharge lamp LA after turning on the direct current power supply E, in the cases where the discharge lamp LA is normally lighting and no-lighting, and each operation of transistors Q

3

and Q

4

, respectively.

First, in

FIG. 20

, when the inverter circuit IV is connected to the direct current power supply E and a charged voltage of the control power supply capacitor C

1

reaches an oscillation starting voltage of the IV control circuit IC

1

, the IV control circuit IC

1

starts its oscillation. At this time, the terminal

6

of the IV control circuit IC has a constant direct current voltage, and a current flows out from the terminal

6

via the main oscillation resistor R

2

and the preheat oscillation resistor R

3

. However, a current via the preheat oscillation resistor R

3

charges a preheat oscillation capacitor C

30

, and then, the charge decreases with an elapsed time, and becomes zero after about 3 seconds, for example. By the way, the IV control circuit IC

1

has a characteristic such that the more the flowing out current from the terminal

6

is, the higher an oscillation frequency becomes. Thus, with a decrease of the flowing out current from the terminal

6

, the IV control circuit IC

1

first starts an oscillation at a high frequency, and then, is controlled so that the oscillation frequency is gradually lowered to a predetermined frequency.

A change of oscillation frequency of the IV control circuit IC

1

and a change of resonance voltage between both electrodes of the discharge lamp LA will be described below with reference to FIG.

21

and FIG.

22

. The direct current power supply E is turned on, and thereafter, an oscillation frequency at the time when the IV control circuit IC

1

first oscillates after turning on the direct current power supply is designed so as to be controlled to a frequency range higher than a resonance frequency f

0

of the ballast chock T

1

and the starting capacitor C

3

. Therefore, the direct current power supply E is turned on, and thereby, the discharge lamp lighting apparatus starts an oscillation at a time t

0

, at a frequency fH, and at an operating point H

2

. On the other hand, a voltage between both electrodes of the discharge lamp LA at this time is designed so as to become a voltage VH

2

lower than a starting voltage VS

2

of the discharge lamp LA. Therefore, the discharge lamp LA is no lighting, and the electrodes F

1

and F

2

are preheated by a resonance current flowing through electrodes F

1

and F

2

of the discharge lamp LA.

Thereafter, when the oscillation frequency of the IV control circuit IC

1

, that is, a switching frequency of the switching elements Q

1

and Q

2

gradually becomes low, a voltage between both electrodes of the discharge lamp LA gradually rises up along a resonance curve for no lighting of the discharge lamp LA. When the voltage between both electrodes of the discharge lamp LA reaches VS

2

at the time t

1

, and at an operating point S

2

of the frequency fS, the discharge lamp LA starts (thus, a time from t

0

to t

1

is a preheat time). When the discharge lamp LA starts lighting, an impedance of the discharge lamp LA changes, and at the same time with the start, the operating point is shifted from S

2

to S

1

on the resonance curve for lighting of the discharge lamp, so that the voltage between both electrodes of the discharge lamp LA is lowered to VS

1

. Thereafter, the frequency is lowered to an fL which is a steady state, in response to lowering of the oscillation frequency of the IV control circuit IC

1

, and then, the discharge lamp LA continues lighting by a predetermined lamp current determined by an impedance of the ballast chock T

1

.

On the other hand, the entire operation of the protective circuit NP

5

is as shown in FIG.

22

. More specifically, a duration from the time t

0

when the direct current power supply E is turned on to the starting time t

1

of the discharge lamp LA is subject to a no-lighting state as described in the above second embodiment so that the transistor Q

3

is turned off. Until the capacitor C

12

of the timer circuit TM is charged to a predetermined voltage, the transistor Q

5

is in an off state, and the transistor Q

4

is in an on state so that a potential of the terminal

5

is kept at a low potential. In the case where there is no mask circuit MSK, the transistor Q

3

is turned off during preheat, and the protective circuit NP

5

outputs an oscillation stop signal to the IV control circuit IC

1

so as to prevent the discharge lamp LA from lighting. However, according to this sixth embodiment, as the potential of the terminal

5

is kept at a low potential by the mask circuit MSK even during preheat, no oscillation stop signal is outputted to the terminal

5

of the IV control circuit IC

1

from the protective circuit NP

5

, so that the discharge lamp LA can be lit at the time t

1

without hindrance.

The capacitor C

12

is charged by a current of closed loop consisting of the control power supply capacitor C

1

→the resistor R

18

→the capacitor C

12

→the control power supply capacitor C

1

. When a charged voltage of the capacitor C

12

reaches a Zener voltage of the voltage regulation diode DZ

3

at the time t

3

, the transistor Q

5

is turned on and the transistor Q

4

is turned off (therefore, the time from t

0

to t

3

is a mask time of the protective circuit NP

5

by the mask circuit MSK, and the mask time is set longer than the above preheat time). However, the discharge lamp LA is already lighting at the time t

3

, and this state corresponds to the normal full lighting state as described in the above second embodiment. Therefore, the transistor Q

3

is turned on, and no oscillation stop signal is outputted from the protective circuit NP

5

; as a result, a lighting state is continued.

Meanwhile, in the case where the discharge lamp LA is not lighting because of being in the end of life or being defective, in

FIG. 21

, the oscillation frequency of the IV control circuit IC

1

lowers from an initial oscillation frequency to a steady state frequency as fH→fS→fL, and the operating point is shifted as H

2

→S

2

→L

2

in accordance with lowering of the frequency. The voltage between both electrodes of the discharge lamp LA rises from VH

2

to VL

2

during the time from t

0

to t

2

, and thereafter, becomes constant as shown in FIG.

23

. For the duration, a state of the discharge lamp load circuit LAC

1

corresponds to the no-lighting state as described in the above second embodiment; therefore, the transistor Q

3

of the protective circuit NP

5

is in an off state. However, in the case of no-lighting state, the transistor Q

3

keeps an off state even after the time t

2

. Therefore, at the time t

3

when a mask time of the mask circuit MSK is completed, the transistor Q

4

is turned off, and, at the same time, the protective circuit NP

5

outputs an oscillation stop signal to the terminal

5

of the IV control circuit IC

1

. As a result, an oscillation of the inverter circuit IV is stopped so as to shut off an over resonance current from continuously flowing through the ballast chock T

1

and the starting capacitor C

3

.

As described above, in this sixth embodiment, the protective circuit NP

5

is additionally provided with the mask circuit which masks the protective circuit NP

5

so as to output no oscillation stop signal for a predetermined time from the time when the direct current power supply E is turned on. Therefore, there are effects that the protective circuit NP

5

is applicable to a discharge lamp lighting apparatus having a function of lighting the discharge lamp LA after preheating of the electrodes F

1

and F

2

, and lighting of a non-defective discharge lamp can be secured, and a discharge lamp lighting apparatus which can securely stop an oscillation in a fault state can be obtained.

The mask time is set by the above-mentioned timer circuit, or by another method in which, for example, the lighting state of the discharge lamp LA is detected by an output state of the comparator IC

2

and IC

3

, and then, a mask function is released in synchronous with the detection result.

SEVENTH EMBODIMENT

FIG. 24

is a circuit diagram of a discharge lamp lighting apparatus according to a seventh embodiment of the present invention. In this seventh embodiment, the discharge lamp lighting apparatus of the above sixth embodiment is further provided with an over resonance detection circuit AP which detects a high frequency current flowing through the discharge lamp load circuit LAC

1

so as to detect faults. By doing so, for example, even in a discharge lamp lighting apparatus which is so constructed that a control range of oscillation frequency of the inverter circuit IV passes a resonance frequency f

0

of the ballast chock T

1

and the starting capacitor C

3

, or approaches the resonance frequency f

0

, the discharge lamp lighting apparatus can securely light the discharge lamp LA and detect the faults more precisely. Like reference numerals are used to designate the same portion as the above sixth embodiment (

FIG. 20

) or the portion corresponding thereto, and the details are omitted.

As shown in

FIG. 24

, in this seventh embodiment, an over resonance detection circuit AP is additionally interposed between the terminal

5

of the IV control circuit IC

1

and the negative electrode of the direct current power supply E. The over resonance detection circuit AP is composed of a detection resistor R

5

of about 1Ω connected between the coupling capacitor C

4

and the negative electrode of the direct current power supply E, and a series circuit comprising a voltage regulation diode DZ

5

, a resistor

26

and a diode D

5

which are connected between a connecting portion of the detection resistor R

5

and the coupling capacitor C

4

and the terminal

5

of the IV control circuit IC

1

. Moreover, in a protective circuit NP

6

, a diode D

6

for separating the protective circuit NP

6

from the over resonance detection circuit AP is connected between the terminal

5

of the IV control circuit IC

1

and a collector of the transistor Q

3

.

An operation of the protective circuit NP

6

and the over resonance detection circuit AP will be described below with reference to FIG.

24

and

FIG. 25

showing a LC series resonance curve of this seventh embodiment. In FIG.

24

and

FIG. 25

, the inverter circuit IV is connected to the direct current power supply E, and when a charged voltage of the control power supply capacitor C

1

reaches an oscillation starting voltage of the IV control circuit IC

1

, like the above sixth embodiment, the IV control circuit IC

1

starts its oscillation at a frequency fH and at the operating point H

2

. When the frequency gradually lowers in accordance with decrease of a flowing out current from the terminal

6

, a voltage between both electrodes of the discharge lamp LA rises along an LC series resonance curve for no-lighting of the discharge lamp, and for the duration, the electrodes F

1

and F

2

of the discharge lamp LA are preheated. Then, when the voltage between both electrodes of the discharge lamp LA reaches the starting voltage at a frequency fS, the discharge lamp LA starts up, and simultaneously, the operating point is shifted from S

2

to S

1

on the resonance curve for lighting of the discharge lamp. Thereafter, the frequency further passes through f

0

which is a resonance frequency, and then, gradually lowers to fL which is an operating point, and thus, at the operating point L

1

, the discharge lamp LA is continuously lit by a predetermined lamp current determined by an impedance of the ballast chock T

1

. In the above operation, the protective circuit NP

6

of this seventh embodiment includes a mask circuit as the sixth embodiment, so that no oscillation stop signal is outputted until the discharge lamp LA starts lighting.

The above is a description on the case where the discharge lamp is lighting. In the discharge lamp lighting apparatus which is so constructed that a control range of oscillation frequency of the inverter circuit IV passes a resonance frequency f

0

of the ballast chock T

1

and the starting capacitor C

3

, or approaches the resonance frequency f

0

, for example, in the case where the discharge lamp LA is no lighting because of being in the end of life or being defective, the operating point rises along a resonance curve for no-lighting of the discharge lamp, and a resonance voltage and a resonance current between the electrodes F

1

and F

2

of the discharge lamp LA becomes excessive around the resonance frequency f

0

, so that there is a problem that the discharge lamp LA and parts of the discharge lamp load circuit are broken down.

The following is a description how to solve the above problem by the over resonance detection circuit AP of this seventh embodiment. An operation of the over resonance detection circuit AP will be described below with reference to FIG.

25

and FIG.

26

. In

FIG. 25

, when an oscillation frequency of the IV control circuit IC

1

lowers from fH→fS (the operating point is shifted from H

2

→S

2

), a resonance current flowing through the detection resistor R

5

of the over resonance detection circuit AP increases, and then, a positive peak value VP of high frequency voltage waveform of both terminals of the detection resistor R

5

rises up as shown in FIG.

26

. If the discharge lamp LA does not start lighting during the time when the frequency lowers from fS to f

0

, a positive voltage peak value VP of the detection resistor R

5

exceeds a Zener voltage of the voltage regulation diode DZ

5

at the point of time when the voltage reaches the maximum voltage VP

2

set for protecting a circuit (operating point P

2

, frequency fp); for this reason, an oscillation stop signal is outputted to the terminal

5

of the IV control circuit IC

1

so as to stop an oscillation of the inverter circuit IV.

As described above, in this seventh embodiment, independently of the protective circuit NP

6

, there is provided the over resonance detection circuit AP which detects a high frequency current flowing through the discharge lamp load circuit LAC

1

to output an oscillation stop signal to the IV control circuit IC

1

in a fault state. Therefore, the above protective circuit is applicable to the discharge lamp lighting apparatus which is so constructed that an oscillation frequency of the inverter circuit IV approaches the resonance frequency f

0

, and the same effect as the above sixth embodiment can be obtained.

Moreover, in the above description, the operation of the over resonance detection circuit AP is explained as a means for avoiding an over resonance state generated in the discharge lamp lighting apparatus which is so constructed that an oscillation frequency of the inverter circuit IV approaches the resonance frequency f

0

. However, the over resonance detection circuit AP may be additionally provided in all of the above embodiments to detect a fault state of the discharge lamp LA in cooperation with the protective circuit. In this case, a high frequency current waveform supplied from the switching element is detected in addition to a voltage generated in the coupling capacitor C

4

, to make a fault detection, so that there effects that a fault can be detected more precisely, and a reliability of the protective circuit can be further improved.

EIGHTH EMBODIMENT

FIG. 27

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to an eighth embodiment of the present invention. In this eighth embodiment, a power supply rectifying and smoothing a commercial alternating power supply is used as the direct current power supply E of the above seventh embodiment. In service interruption (in particular, instantaneous blackout) of the commercial alternating power supply, in order to prevent the discharge lamp LA from being turned off after service interruption is returned, an instantaneous blackout restoring circuit SH is provided so that a mask function of the protective circuit NP

6

again becomes effective. Like reference numerals are used to designate the same portion as

FIG. 24

or the portion corresponding thereto, and the details are omitted.

The following is a description on a power supply and an instantaneous blackout restoring circuit SH which are constituent features of this eighth embodiment. In

FIG. 27

, an AC is a commercial alternating power supply, and the commercial alternating power supply AC is connected to a diode bridge DB, and further, an output terminal of the diode bridge DB is connected to a smoothing capacitor C

7

and an input terminal of the inverter circuit IV via a separate diode D

7

. Moreover, the output terminal of the diode bridge DB is connected with the instantaneous blackout restoring circuit SH which is constructed as follows. More specifically, a ripple current voltage inputted to the instantaneous blackout restoring circuit SH from the diode bridge DB is divided by resistors R

90

and R

91

, and then, a voltage of the resistor R

91

is connected to an input terminal of a transistor Q

90

via a resistor R

92

, and further, both terminals of the resistor R

91

are connected in parallel with a capacitor C

90

. An output of a comparator IC

4

is connected to a contact point of the resistors R

18

and R

19

of the protective circuit NP

6

, and a connecting portion of resistors R

23

and R

24

connected in series to both terminals of the control power supply capacitor C

1

and a connecting portion of resistors R

25

and R

26

are connected to a non-inverting terminal which is a reference voltage input terminal of the comparator IC

4

, and to an inverting terminal which is a detection voltage input terminal thereof, respectively. Further, a collector of the transistor Q

90

is connected to the inverting terminal of the comparator IC

4

.

The following is a description on an operation of the instantaneous blackout restoring circuit SH. First, in the case where the commercial alternating power supply AC stably supplies a power, in

FIG. 27

, an alternating current inputted to the diode bridge DB from the commercial alternating power supply AC is rectified into a direct current by the diode bridge DB, and further, is smoothened by the smoothing capacitor C

7

, and thereafter, is inputted to the inverter circuit IV so as to function as a direct current power supply. On the other hand, a base current is always supplied from the commercial alternating power supply AC to the transistor Q

90

via the diode bridge DB, the resistors R

90

and R

92

; for this reason, the transistor Q

90

is always in an on state. As a result, the output of the comparator IC

4

becomes an off state, and then, the mask circuit MSK functions, and further, by the same circuit operation as the seventh embodiment of

FIG. 24

, the commercial alternating power supply AC is turned on, and thereafter, the discharge lamp LA is stably lighting.

Next, the following is a description on an operation of the instantaneous blackout restoring circuit SH in the case where an instantaneous blackout is generated in the commercial alternating power supply AC such that during lighting of the discharge lamp LA, the discharge lamp LA is instantaneously turned off First, during normal lighting of the discharge lamp LA, like the seventh embodiment, the transistor Q

3

of the protective circuit NP

6

is in an on state; on the other hand, the transistor Q

4

is in an off state. In this state, an instantaneous blackout is generated in the commercial alternating power supply AC, and when the discharge lamp LA is instantaneously turned off, this is equivalent to a no-lighting state as described in the above second embodiment; for this reason, the transistor Q

3

of the protective circuit NP

6

becomes an off state. However, at this time, a ripple current voltage output of the diode bridge DB becomes zero; for this reason, a base current supplied to the transistor Q

90

from the ripple current voltage output via the resistors R

90

and R

92

is instantaneously shut off. As a result, the transistor Q

90

is instantaneously turned off.

In this case, each resistance value of resistors R

23

, R

24

, R

25

and R

26

is set so that an inverting input terminal voltage of the comparator IC

4

becomes higher than a non-inverting input terminal thereof; therefore, the output terminal of the comparator IC

4

is instantaneously inverted together with an off of the transistor Q

90

, that is, becomes L

0

. In this manner, a charge stored in the capacitor C

12

of the timer circuit TM is instantaneously discharged; for this reason, the transistor Q

5

is in an off state; on the other hand, the transistor Q

4

is in an on state. As a result, the mask circuit MSK is automatically reset. When the service interruption is restored, the transistor Q

90

becomes in an on state while the mask circuit MSK starting to function, and then, the capacitor C

12

is again charged, and until the voltage is charged up to a Zener voltage of the constant voltage diode DZ

3

, an on-state of the transistor Q

4

is continued. Therefore, after the service interruption is restored, the mask circuit MSK functions for a predetermined time; as a result, even if the discharge lamp LA is instantaneously turned off by the instantaneous blackout and the transistor Q

3

of the protective circuit NP

6

once becomes an off state, after restart, the protective circuit NP

6

outputs no oscillation stop signal to the IV control circuit IC

1

; therefore, the discharge lamp is securely lighting.

As described above, in this eighth embodiment, there is additionally provided the instantaneous blackout restoring circuit SH which automatically resets the mask circuit MSK in response to a blackout. For example, in the case of using a power supply rectifying and smoothening a commercial alternating power supply AC as the direct current power supply of the inverter circuit IV, even if an instantaneous blackout is generated in a commercial alternating power supply AC, after the blackout is restored, the mask circuit again functions effectively, and thereby, it is possible to securely again light the discharge lamp LA after the power supply is restored, and to apply a protective function of the protective circuit NP

6

as it is.

In particular, in this eighth embodiment, the instantaneous blackout restoring circuit SH is constructed so that a charge of the capacitor C

12

is rapidly discharged; therefore, it is possible to reset the mask circuit MSK at a high speed as compared with the case where a charge of the capacitor C

12

is discharged via the resistor R

19

, and to take a suitably step with respect to a fast phenomenon such as an instantaneous blackout or the like.

The above eighth embodiment has described the operation and effect of the instantaneous blackout restoring circuit SH for an instantaneous blackout. It is evident from the operation principle that the instantaneous blackout restoring circuit SH effectively functions with respect to a general service interruption other than the instantaneous blackout. Moreover, it is evident that the instantaneous blackout restoring circuit SH is effective not only to a service interruption such that a voltage fully becomes zero, but also to a so-called sag such that a voltage drops down.

NINTH EMBODIMENT

FIG. 28

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a ninth embodiment of the present invention. In this ninth embodiment, a voltage resonance type one stone circuit is applied as a inverter circuit IV

2

. In place of the switching element Q

1

, a parallel resonance circuit comprising an oscillation transformer T

2

and a resonance capacitor C

31

is connected, and an oscillation terminal of an IV control circuit IC

2

is connected to only switching element Q

2

. Like reference numerals are used to designate the same portion as the second embodiment (

FIG. 9

) or the portion corresponding thereto, and the details are omitted.

The following is a description on a difference in the operation between this ninth embodiment and the second embodiment. In this ninth embodiment,

FIG. 29

shows a voltage waveform applied to the discharge lamp load circuit LAC

1

when the discharge lamp LA is normally lighting, that is, a high frequency voltage waveform between terminals of the switching element Q

2

. By a resonance operation of a resonance capacitor C

31

, the ballast chock T

1

and an oscillation transformer T

2

, the high frequency voltage waveform becomes a sine half wave (rectangular wave as shown in FIG.

2

(

a

) in the second embodiment). However, the high frequency voltage waveform becomes the substantially same as the second embodiment in an equivalent circuit; for this reason, a change of voltage of the coupling capacitor C

4

in normal and fault states of the discharge lamp LA is the same as the second embodiment. Therefore, the protective circuit NP

3

is applicable to a discharge lamp lighting apparatus which employs the above voltage resonance type one stone circuit like the above second embodiment, and the same protective operation is performed.

TENTH EMBODIMENT

FIG. 30

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a tenth embodiment of the present invention. In this tenth embodiment, in order to reduce an electrode loss during discharge lamp LA lighting, the starting capacitor C

3

of the above second embodiment (

FIG. 9

) is divided into two separate starting capacitors C

8

and C

9

(resultant capacity of the C

8

and C

9

is the substantially same as C

3

). One of two, that is, the separate starting capacitor C

9

is arranged on the switching element Q

2

with respect to the discharge lamp LA. Like reference numerals are used to designate the same portion as

FIG. 9

or the portion corresponding thereto, and the details are omitted.

As described above, according to this tenth embodiment, the starting capacitor C

3

is divided into a plurality of separate starting capacitors C

8

and C

9

, and at least one of two, that is, the separate starting capacitor C

9

is arranged on the switching element Q

2

with respect to the discharge lamp LA. Therefore, when the discharge lamp LA is normally lighting, a high frequency current flowing through the ballast chock T

1

dispersively flows through both the separate starting capacitor C

8

(equal to an electrode current flowing through the electrodes F

1

and F

2

) and the separate starting capacitor C

9

, and then, a current flowing through the separate starting capacitor C

9

bypasses the electrodes F

1

and F

2

. As a result, an electric power (electrode loss) consumed in the electrodes of the discharge lamp LA becomes small, and an energy efficiency can be improved as compared with the second embodiment.

Moreover, according to this tenth embodiment, it is possible to realize the operation and effect of the protective circuit NP

3

by the same equivalent circuit as the second embodiment, and to obtain the same effect as the above embodiments described thus far.

As shown in the fourth embodiment (FIG.

16

), in the discharge lamp lighting apparatus which has a dimming function by the frequency control circuit FC

2

, with the reduce lumen output operation of the discharge lamp LA, a voltage and frequency between both electrodes of the discharge lamp LA rise, and thereby, the discharge lamp lighting apparatus has a characteristic such that a current of the starting capacitor increases as compared with the fully lighting state. Thus, the above construction such that the starting capacitor is dispersively arranged is applied to the discharge lamp lighting apparatus, and thereby, the current of the starting capacitor increases by the reduced lumen output operation, and it is possible to prevent an electrode loss from rapidly increasing.

This tenth embodiment (

FIG. 30

) has described a circuit to which the protective circuit NP

3

or the like is added. The effect of the above separate starting capacitors C

8

and C

9

is evident from the operating principle, and is common to the discharge lamp lighting apparatus applying the inverter circuit IV. Thus, the same effect can be obtained regardless of the presence of the protective circuit and the instantaneous blackout restoring circuit SH.

ELEVENTH EMBODIMENT

FIG. 31

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to an eleventh embodiment of the present invention. In this eleventh embodiment, as a discharge lamp load circuit LAC

5

, like the above fifth embodiment, in addition to the discharge lamp load circuit comprising the discharge lamp LA (connected parallel with the starting capacitor C

3

), the coupling capacitor C

4

and the ballast chock T

1

, a discharge lamp load circuit comprising two discharge lamps LAY and LAZ (parallel with a starting capacitor C

3

Y and C

3

Z), two coupling capacitors C

4

Y and C

4

Z and two ballast chocks T

1

Y and T

1

Z, is connected in parallel.

Moreover, in the case where a plurality of discharge lamp load circuits are provided, in the above fifth embodiment, in accordance with an increase of the discharge lamp load circuits, a comparator unit and a voltage detecting unit have been provided independently from those. In this eleventh embodiment, the voltage detecting unit for one comparator unit is divided into two, that is, a first voltage detecting unit for detecting a stepped-up voltage of the coupling capacitor and a second voltage detecting unit for detecting a dropped voltage of the coupling capacitor. By doing so, the number of the divided resistors and reverse current blocking diodes is increased in accordance with an increase of the discharge lamp load circuit, and thereby, it is possible to make a coupling voltage detection of one inverter parallel lighting. Like reference numerals are used to designate the same portion as the above fifth embodiment or the portion corresponding thereto, and the details are omitted.

The following is a description on a detailed construction of a voltage detecting unit VIN.

The voltage detecting unit VIN of this eleventh embodiment is composed of a first voltage detecting unit VA and a second voltage detecting unit VB. More specifically, the first voltage detecting unit VA detects each step-up voltage of the coupling capacitors C

4

, C

4

Y and C

4

Z, and then, converts it into a direct current voltage, and further, inputs the detection voltage to an inverting input terminal of the first comparator IC

2

, and the second voltage detecting unit VB detects each drop voltage of the coupling capacitors C

4

, C

4

Y and C

4

Z, and then, converts it into a direct current voltage, and further, inputs the detection voltage to a non-inverting input terminal of the second comparator IC

3

.

The first voltage detecting unit VA has diodes D

31

, D

31

Y and D

31

Z whose each anode is connected to each of coupling capacitors C

4

, C

4

Y and C

4

Z, a divided resistor R

30

connected to each cathode of diodes D

31

, D

31

Y and D

31

Z, a constant voltage diode DZ

4

whose cathode is connected to the divided resistor R

30

, and a divided resistor R

31

which has one end connected to the anode of the constant voltage diode DZ

4

and the other end grounded. A connecting point of the constant voltage diode DZ

4

and the divided resistor R

31

is connected to the inverting input terminal of the first comparator IC

2

.

On the other hand, the second voltage detecting unit VB has diodes D

32

, D

32

Y and D

32

Z whose each cathode is connected to each of coupling capacitors C

4

, C

4

Y and C

4

Z, a constant voltage diode DZ

5

whose cathode is connected to the anode of each of diodes D

32

, D

32

Y and D

32

Z, and a divided resistor R

33

which has one end connected to the anode of the constant voltage diode DZ

5

and the other end grounded. A connecting point of the constant voltage diode DZ

5

and the divided resistor R

33

is connected to the non-inverting input terminal of the comparator IC

3

, and further, the cathode of the constant voltage diode DZ

5

is connected to a plus side of the direct current power supply E via a divided resistor R

32

.

The following is a description on an operation of this eleventh embodiment.

In

FIG. 31

, when the discharge lamps LA, LAY and LAZ are all normally lighting, each direct current voltage of the coupling capacitors C

4

, C

4

Y and C

4

Z is detected by the first voltage detecting unit VA, and a detection voltage outputted to the first comparator IC

2

from the first voltage detecting unit VA is set so as to become less than a reference voltage of the first comparator IC

2

. Thus, an output of the first comparator IC

2

becomes HIHG.

Moreover, in the second voltage detecting unit VB, a direct current voltage of the direct current power supply E is divided by the divided resistors R

32

and R

33

, and the constant voltage diode DZ

5

, and a voltage thus divided is outputted to the second comparator IC

3

, and further, the voltage is set so as to become high than a reference voltage of the second comparator IC

3

. Thus, an output of the second comparator IC

3

also becomes HIGH. Therefore, the transistor Q

3

is in an on state; for this reason, the protective circuit NP

5

outputs no oscillation stop signal, and thereby, the discharge lamps LA, LAY and LAZ continue a normal lighting state.

As described above, when the discharge lamps LA, LAY and LAZ are all normally lighting, the voltage detected by the second voltage detecting unit VB is a voltage obtained by dividing a voltage of the direct current power supply E by the divided resistor R

32

, the constant voltage diode DZ

5

and the resistor R

33

.

Moreover, in the case where any of the discharge lamps LA, LAY and LAZ is in a fault state, in other words, for example, in the case where the discharge lamp LA is in a rectification lighting 1 state and a direct current voltage of the coupling capacitor C

4

of the discharge lamp LA rises up as compared with the fully normal lighting state, the highest direct current voltage among the coupling capacitors is applied to the divided resistor R

30

on the side of the D

31

of the first voltage detecting unit VA, through diodes D

31

, D

31

Y and D

31

Z connected in parallel. Thus, the direct current voltage (a stepped-up voltage) of the coupling capacitor C

4

is reduced by a voltage drop in the diode D

31

and a voltage of the constant voltage diode DZ

4

, and further, divided by the resistors R

30

and R

31

. The devide

4

d direct current voltage is inputted to a minus pin which is an inverting input terminal of the first comparator IC

2

. Then, the direct current voltage exceeds a reference voltage inputted to a plus pin which is a non-inverting input terminal of the first comparator IC

2

; for this reason, the output of the first comparator IC

2

is inverted. Whereupon the transistor Q

3

becomes an off state, the oscillation stop signal is outputted to the terminal

5

of the IC

1

so as to stop an oscillation of the inverter circuit IV.

In addition, in the case where any of the discharge lamps LA, LAY and LAZ is in a fault state, in other words, for example, in the case where the discharge lamp LA is in a rectification lighting 2 state or no-lighting state and a direct current voltage of the coupling capacitor C

4

of the discharge lamp LA drops down as compared with the fully normal lighting state, or in the case where the direct current voltage of the coupling capacitor C

4

of the discharge lamp LA becomes 0 V in a no-load state such that the discharge lamp LA is dismounted, a direct current voltage detected by the second voltage detecting unit VB becomes 0 V. The direct current voltage is inputted as a dropped voltage to a plus pin which is a non-inverting input terminal of the second comparator IC

3

, and then, is less than a reference voltage inputted to a minus pin which is an inverting input terminal of the second comparator IC

3

; for this reason, the output of the comparator IC

3

is inverted. Whereupon the transistor Q

3

becomes an off state, the oscillation stop signal is outputted to the terminal

5

of the IC

1

so as to stop an oscillation of the inverter circuit IV.

As described above, the reason why the direct current voltage detected by the second voltage detecting unit VB becomes 0 V, is as follows. When the direct current voltage of the coupling capacitor C

4

of the discharge lamp LA drops down or becomes 0 V, a voltage on the anode side of the reverse current blocking diode D

32

among the diodes D

32

, D

32

Y and D

32

Z connected to the divided resistor R

32

for diving a direct current voltage of the direct current power supply E, becomes high; for this reason, the reverse current blocking diode D

32

becomes an on state, and then, the direct current voltage of the direct current power supply E is applied to the coupling capacitor C

4

via the divided resistor R

32

.

As described above, according to this eleventh embodiment, in the discharge lamp lighting apparatus having plurality of discharge lamp load circuits, the voltage detecting unit VIN is divided into two, that is, the first voltage detecting unit VA for detecting a stepped-up voltage (a maximum voltage in this embodiment) of each coupling capacitor connected to each of a plurality of discharge lamps, and the second voltage detecting unit VB for detecting a dropped voltage (in this embodiment, 0 volt is outputted after detecting a minimum voltage). By doing so, the number of divided resistors and reverse current blocking diodes is increased in accordance with an increase of the discharge lamp load circuit, and thereby, it is possible to make a coupling voltage detection of one inverter parallel lighting, and to reduce the number of components as compared with the case where the comparator unit and the voltage detecting unit are independently provided in response to the number of increased discharge lamp load circuits like the fifth embodiment. Therefore, in this eleventh embodiment, in accordance with an increase of the number of discharge lamp load circuits, the number of components can be reduced.

Moreover, even if the number of discharge lamp load circuits is increased, it is possible to detect the presence of discharge lamp which is in the following states; more specifically, in a state such that any of the plurality of discharge lamps is in a fault state, that is, in a rectification lighting 1 state such that a detection voltage steps up as compared with the fully normal lighting state, in a rectification lighting 2 state such that a detection voltage drops as compared with the fully normal lighting state, and a detection voltage becomes 0 V by the removal of the discharge lamp. In this case, the presence of discharge lamp can be detected; however, it is impossible to make a distinction between the presence of discharge lamp and the presence of fault.

The first voltage detecting unit VA outputs a voltage divided by the divided resistors R

30

and R

31

and the constant voltage diode DZ

4

to the first comparator IC

2

, and the second voltage detecting unit VB outputs a voltage divided by the divided resistors R

32

and R

33

and the constant voltage diode DZS to the second comparator IC

3

in the case where any voltage of the coupling capacitors C

4

, C

4

Y and C

4

Z is higher than a predetermined voltage. Therefore, it is possible to largely set a difference in a reference voltage between normal and abnormal lighting states in the first and second comparator IC

2

and IC

3

, and thus, to further improve a reliability of the protective circuit.

In

FIG. 31

, there is shown the case where the discharge lamp load circuit is three. Of course, this eleventh embodiment is applicable to three or more plural parallel lighting circuits.

TWELFTH EMBODIMENT

FIG. 32

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a twelfth embodiment of the present invention. This twelfth embodiment is a modification example of the eleventh embodiment, and is different from the above eleventh embodiment in a position of detecting a voltage of the coupling capacitor of the second voltage detecting unit VB.

More specifically, in this twelfth embodiment, one terminal of reverse current blocking diodes D

32

, D

32

Y and D

32

Z of the second voltage detecting unit VB is connected a starting capacitor side of the discharge lamps LA, LAY and LAZ.

Therefore, in the case where any of the discharge lamps LA, LAY and LAZ is in a fault state, for example, in the case where the direct current voltage of the coupling capacitor C

4

of the discharge lamp LA drops down because the discharge lamp LA is in a rectifying 2 state or no-lighting state as compared with the fully normal lighting state, a direct current voltage detected by the second voltage detecting unit VB becomes 0 V, and the direct current voltage is inputted to a plus pin which is a non-inverting input terminal of the comparator IC

3

, and is less than a reference voltage inputted to a minus pin which is an inverting input terminal of the comparator IC

2

. As a result, an output of the comparator IC

3

is inverted. Whereupon the transistor Q

3

becomes an off state, and then, an oscillation stop signal is outputted to the terminal

5

of the IC

1

so as to stop an oscillation of the inverter circuit IV.

For example, in the case where a discharge lamp F

1

Z is removed, in the second voltage detecting unit VB, a circuit of the coupling capacitor C

4

Z of the discharge lamp LAZ and the reverse current blocking diode D

32

Z is shut off; for this reason, the discharge lamps LA, LAY and LAZ all becomes a normal state. A voltage detected by the second voltage detecting unit VB becomes a voltage obtained by dividing a direct current voltage of the direct current power supply E by the divided resistor R

32

, the constant voltage diode DZ

5

and the divided resistor R

33

. The voltage is inputted to the second comparator IC

3

; therefore, an output of the second comparator IC

3

becomes HIGH as it is, and then, the transistor Q

3

is in an on state. As a result, the protective circuit NP

5

outputs no oscillation stop signal. As seen from the above description, when the number of discharge lamp load circuits is increased, in the case of no-load removing any of the discharge lamps is removed, the presence of discharge lamp is not detected.

THIRTEENTH EMBODIMENT

FIG. 33

is a circuit diagram showing a construction of a discharge lamp lighting apparatus according to a thirteenth embodiment of the present invention. This thirteenth embodiment is another modification example of the eleventh embodiment, and is different from the above eleventh embodiment in a position of providing a reverse current blocking diode constituting an OR circuit of the first voltage detecting unit VA and the second voltage detecting unit VB.

In this thirteenth embodiment, the first voltage detecting unit VA is composed of: divided resistors R

40

, R

42

and R

44

connected to coupling capacitors C

4

, C

4

Y and C

4

Z; constant voltage diodes DZ

4

, DZ

4

Y and DZ

4

Z whose cathodes are connected to divided resistors R

40

, R

42

and R

44

; divided resistors R

41

, R

43

and R

45

having one end connected to each anode of constant voltage diodes DZ

4

, DZ

4

Y and DZ

4

Z, and the other end grounded; reverse current blocking diodes D

31

, D

31

Y and D

31

Z whose anodes are connected to connecting point of constant voltage diodes DZ

4

, DZ

4

Y and DZ

4

Z and divided resistors R

41

, R

43

and R

45

, and whose cathode is connected to the inverting input terminals of the first comparator IC

2

.

The second voltage detecting unit VB has divided resistors R

40

, R

42

and R

44

, constant voltage diodes DZ

4

, DZ

4

Y and DZ

4

Z, divided resistors R

41

, R

43

and R

45

which are common to the first voltage detecting unit VA. Further, the second voltage detecting unit VB includes reverse current blocking diodes D

32

, D

32

Y and D

32

Z whose anodes are connected to connecting point of constant voltage diodes DZ

4

, DZ

4

Y and DZ

4

Z and divided resistors R

41

, R

43

and R

45

, another constant voltage diode DZ

5

connected to the anode and cathode of the reverse current blocking diodes D

32

, D

32

Y and D

32

Z, and a divided resistor R

46

which has one end connected to the anode of the constant voltage diode DZ

5

, and the other end grounded. A connecting point of the constant voltage diode DZ

5

and the divided resistor R

46

is connected to the non-inverting input terminal of the second comparator IC

3

, and further, the cathode of the constant voltage diode DZ

5

is connected to a plus side of the direct current power supply E via the divided resistor R

32

.

According to this thirteenth embodiment, each direct current voltage of the coupling capacitors C

4

, C

4

Y and C

4

Z is divided by a divided circuit comprising the divided resistor R

40

, the constant voltage diode DZ

4

and the divided resistor R

41

, a divided circuit comprising the divided resistor R

42

, the constant voltage diode DZ

4

Y and the divided resistor R

43

, and a divided circuit comprising the divided resistor R

44

, the constant voltage diode DZ

4

Z and the divided resistor R

45

. Then, the divided voltage is inputted to the first comparator unit IC

2

via the reverse current blocking diodes D

31

, D

31

Y and D

31

Z, and a direct current voltage of the direct current power supply E is divided by a divided circuit comprising the divided resistor R

32

, the constant voltage diode DZ

5

and the divided resistor R

46

. Further, the divided voltage is inputted to the coupling capacitors C

4

, C

4

Y and C

4

Z via the reverse current blocking diodes D

32

, D

32

Y and D

32

Z. Therefore, it is possible to use the reverse current blocking diodes D

31

, D

31

Y, D

31

Z, D

32

, D

32

Y and D

32

Z, which have a withstand voltage lower than the eleventh embodiment.

Other operation and effect are the same as the eleventh embodiment, and therefore, the explanation of the operation and effect is omitted.

Number	Date	Country	Kind
11-120888	Apr 1999	JP
12-093070	Mar 2000	JP

Number	Name	Date	Kind
5355055	Tary	Oct 1994	A
5410221	Mattas et al.	Apr 1995	A
5589742	Ueda	Dec 1996	A
5850127	Zhu et al.	Dec 1998	A
5883473	Li et al.	Mar 1999	A
5910713	Nishi et al.	Jun 1999	A
6008590	Giannopoulos et al.	Dec 1999	A
6011358	Knobloch et al.	Jan 2000	A

Discharge lamp lighting apparatus

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (2)

US Referenced Citations (8)

Foreign Referenced Citations (1)