Discharge lamp lighting device

TECHNICAL FIELD

The present invention is directed to a discharge lamp driving device with an abnormality detection and protection function of detecting a lamp life end for circuit protection.

BACKGROUND ART

(First Prior Art)

FIG. 1

s a circuit diagram showing one example of a prior discharge lamp driving device which is identical in circuit configuration to that shown in

FIG. 36

of Japanese Patent Publication No. 8-251942. A rectifier DB composed of a diode bridge is connected to an AC power source AC through a surge absorption element ZNR and a filter circuit F. Connected across a pulsating output terminals are a high frequency bypassing capacitor C

2

, a series combination of switching elements Q

1

and Q

2

in the form of field effect transistors through a series circuit of diodes D

5

and D

6

, a series combination of a smoothing capacitor C

10

and a diode

13

, and a high frequency bypassing capacitor C

11

. A series circuit of an inductor L

2

and a diode D

12

is connected between a connection point of switching elements Q

1

and Q

2

and a connection point of smoothing capacitor C

10

and diode D

13

. A leakage transformer LT

1

has a primary winding N

1

that is connected in series with a DC blocking capacitor C

3

between the cathode of diode D

5

and the connection point of switching elements Q

1

and Q

2

. A secondary winding N

2

of the leakage transformer LT

1

has its one end connected through a DC blocking capacitor C

9

to one of filaments of one discharge lamp La

1

, and has its other end connected to one of filament of the other discharge lamp La

2

. The other filaments of the two discharge lamps La

1

and La

2

are connected at one ends thereof to each other through an auxiliary winding N

3

of the leakage transformer LT

1

and a DC blocking capacitor C

6

. The other ends of the filaments of the discharge lamps La

1

and La

2

are connected to each other through a resonant inducing capacitor C

7

. Further, a harmonic distortion improving capacitor C

4

is connected across diode D

6

.

The two switching elements Q

1

and Q

2

are driven by a control circuit CNT to turn on and off alternately. The leakage transformer LT

1

includes an auxiliary winding N

4

for detection of lamp voltage of the discharge lamps La

1

and La

2

. The detected voltage induced at the auxiliary winding N

4

is rectified by means of a diode D

8

and is fed to a detection circuit

20

for detection of the lamp voltage. Based upon thus detected lamp voltage, the control circuit CNT varies a switching frequency of the switching elements Q

1

and Q

2

. In short, the source AC voltage is rectified through rectifier DB of which pulsating output is partially smoothed out by a valley-filling power source in the form of a step-down chopper circuit composed of switching element Q

2

, diode D

12

, inductor L

2

, smoothing capacitor C

10

and a parasitic diode of switching element Q

1

. The partially smoothed DC output is converted into a high frequency output by means of an inverter circuit in the form of a half-bridge type including the switching elements Q

1

and Q

2

. The high frequency output is fed through the leakage transformer LT

1

to the discharge lamps La

1

and La

2

as a load for driving the same. Further, in this prior art, the harmonic distortion improving capacitor C

4

compensates for a voltage difference between the rectifier DB and the valley-filling power source, while an input voltage is switched on and off by utilization of a high frequency voltage appearing within the inverter circuit so as to draw in the input current from the rectifier DB through a resonant circuit composed of leakage transformer LT

1

, capacitor C

3

, discharge lamps La

1

and La

2

, and capacitor C

7

, and through capacitor C

4

for improving harmonic distortion of the input current. The operation of this prior art is known and therefore not discussed herein.

When the above prior art sees that the discharge lamps La

1

or La

2

reaches to the lamp life end, a protective action is made as follows. That is, when the lamp reaches its lamp life end as a result of the depletion of the negative thermion radiating material (emitter) coated on the filaments, the lamp voltage of the discharge lamps La

1

and La

2

increases than in a normal condition. With this result, the voltage induced at the auxiliary winding N

4

of the leakage transformer LT! increases so that the detection circuit

20

gives an abnormality detection signal to the control circuit CNT in response to the voltage induced at the auxiliary winding N

4

exceeds a threshold. The control circuit CNT responds to the abnormality detection signal for activating the inverter circuit to intermittently oscillate, thereby effecting a protective action of reducing the stress on the circuit.

(Second Prior Art)

FIG. 2

shows a circuit diagram of another prior art which is identical in configuration to the circuit disclosed in

FIG. 15

of a Japanese Patent Publication 2000-100587. The second prior art differs from the first prior art in that the inductor L

2

forming the step-down chopper circuit is omitted, that diode

12

has its anode connected to a connection point of smoothing capacitor C

10

and diode

13

and has its cathode connected to a connection point of the primary winding N

1

of the leakage transformer LT

1

and capacitor C

3

in order to share the leakage transformer LT

1

with the step-down chopper circuit, and that an output regulation circuit

21

is added in compensation for a large characteristic variation of a driving transformer T

2

. The output regulation circuit

21

includes a switching element Qb realized by a bipolar transistor connected across a control voltage source E through a variable resistor VR and a collector resistor Re. The switching element Qb has its base connected through a resistor Rd to a point between a resistor Rc and a capacitor Cb which are connected in series between the connection point of the switching elements Q

1

, Q

2

and the negative pole of the control voltage source E. Connected between the output terminal of the control circuit CNT and the negative pole of the control voltage source E is a series combination of a diode Da, a resistor Ra, and a switching element Qa of bipolar transistor. The switching element Qa has its base connected through a base resistor Rb to a connection point of collector resistor Re and variable resistor VR. Further, a capacitor Ca and a diode Db are connected in parallel across the series combination of the switching element Qb and the collector resistor Re, while a diode Dc is connected in a base-emitter path of the switching element Qb. While the one switching element Q

2

is off, capacitor Cb is charged through resistor Rc so that switching element Qb is caused to turn on in response to the voltage increase across capacitor Cb, thereby turning off the switching element Qa and giving no influence on the operation of the inverter circuit. When the switching element Q

2

turns on, the switching element Qb is turned off so that the control voltage source E acts to charge capacitor Ca through variable resistor VR. As the voltage across capacitor Ca increases, the switching element Qa responds to turn on, thereby causing the switching element Q

2

to turn off. Accordingly, it is made possible to regulate the on-period of switching element Q

2

by varying the resistance of the variable resistor VR to thereby maintain the output substantially at a constant level irrespective of the varying characteristic of the driving transformer T

2

. Also this prior art has the same protective action as is made in the first prior art when the lamp life end is reached.

In the second prior art, however, the inclusion of the output regulation circuit

21

brings about an asymmetry (unbalance) of the on-period of the switching elements Q

1

and Q

2

in the normal lamp operating condition, whereby a DC voltage will be applied to capacitor C

9

connected in series with the discharge lamps La

1

and La

2

. With this result, the DC voltage of the charged capacitor C

9

will be superimposed upon the high frequency output of the inverter circuit in the normal lamp operating, leading to a problem of causing a cataphoresis phenomenon particularly at a low temperature.

In order to solve the problem, it might be reasonable to remove capacitor C

9

connected to the secondary of the leakage transformer LT

1

. However, this would causes another problem. That is, as the discharge lamp reaches the lamp life end, capacitor C

9

accumulates an increased voltage so that the lamp voltage of the lamp of negative resistivity increases to make a great difference in the lamp voltage between the normal operating condition and the lamp life end condition. Such lamp voltage difference is utilized for detection of the lamp life end. However, in the absence of capacitor C

9

, the lamp voltage would make only a small difference between the normal operating condition and the lamp life end condition, making it difficult to detect the lamp life end particularly at a high temperature environment.

DISCLOSURE OF THE INVENTION

The present invention has been achieved in view of the above problem and has an object of providing a discharge lamp driving device which is capable of detecting the lamp life end reliably at either low or high temperature environment for circuit protection, yet preventing the cataphoresis phenomenon.

The discharge lamp driving device in accordance with the present invention includes a rectifier which rectifies an AC source voltage, a smoothing capacitor which smoothes out a pulsating output of the rectifier, an inverter circuit having one or more switching elements for conversion of the smoothed DC output made through the smoothing capacitor into a high frequency output, and a load circuit including a resonance circuit and a discharge lamp and being supplied with the high frequency output from the inverter circuit, an output transformer having a primary connected to an output end of the inverter circuit and having a secondary connected to one filament end of the discharge lamp, an impedance element inserted between the other filament end of the discharge lamp and a node having no high frequency amplitude, and an abnormality detection and protection means which detects an amplitude of the high frequency output flowing through the discharge lamp and the impedance element in order to make the circuit protection when the detected amplitude exceeds a predetermined threshold.

The abnormality detection and protection means judges the lamp life end of the discharge lamp when the amplitude of the high frequency output flowing through the discharge lamp and the impedance element exceeds the threshold. Since the impedance element is inserted between the other filament end of the discharge lamp and the node having no high frequency amplitude, reliable detection of the lamp life end can be made for the circuit protection at either low or high temperature environment. Further, since there is no need to connect a capacitor on the secondary of the output transformer, the cataphoresis phenomenon can be prevented.

In a preferred embodiment, the impedance element is inserted between the other filament end of the discharge lamp and a positive input terminal of the inverter circuit.

The impedance element may be inserted between the other filament end of the discharge lamp and a grounded input terminal or output terminal of the inverter circuit.

A plurality of the discharge lamps can be connected in series on the secondary side of the output transformer.

Each impedance element inserted between the filament of each of the individual discharge lamp and the node having no high frequency amplitude is preferred to have substantially the same impedance value.

In case where the plural discharge lamps are connected in series on the secondary side of the output transformer, the impedance element is inserted between the other filament end of at least one discharge lamp and the positive input terminal of the inverter circuit, while another impedance element is inserted between the other filament end of at least another discharge lamp and the grounded input terminal or output terminal of the inverter circuit.

In case where the plural discharge lamps are connected in series on the secondary side of the output transformer, the abnormality detection and protection means is set to make the circuit protective action when the amplitude of the high frequency output flowing through anyone of the discharge lamps and the impedance element exceeds a predetermined threshold.

Also in case where the plural discharge lamps are connected in series on the secondary side of the output transformer, the abnormality detection and protection means may be configured to detect the amplitude of a potential at a connection point of the filaments of the plural discharge lamps and also detect the amplitude of the high frequency output flowing through at least one discharge lamp and the impedance element such that it can make the circuit protective action when either or both of the amplitudes exceeds a predetermined threshold.

Further, in case where the plural discharge lamps are connected in series on the secondary side of the output transformer, the abnormality detection and protection means is configured to detect the amplitude of a potential at a connection point of the filaments of the plural discharge lamps such that it makes the circuit protective action when either of thus detected amplitude or the amplitude of the high frequency output flowing through at least one of the high-voltage and low-voltage side discharge lamps and the impedance element exceeds a predetermined threshold.

The impedance element may include a resistor, capacitor, and a series combination of a resistor and a capacitor.

When the inverter circuit is of a self-excited type, at least a portion of a driving circuit for driving the inverter circuit can be shared with components of the abnormality detection and protection means, enabling to reduce the number of the circuit components.

Still further, the impedance element can be shared with the resonance circuit included in the load circuit for reducing the number of the circuit components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic circuit diagram showing the first prior art;

FIG. 2

is a schematic circuit diagram showing the second prior art;

FIG. 3

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a first embodiment of the present invention;

FIG. 4

is a circuit diagram of a principal portion of the above device;

FIGS. 5A-5F

are waveform charts for explaining the circuit operation at a normal condition;

FIGS. 6A-6F

are waveform charts for explaining the circuit operation at an emitter depletion condition;

FIG. 7

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a second embodiment of the present invention;

FIG. 8

is a circuit diagram of a principal portion of the above device;

FIG. 9

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a third embodiment of the present invention;

FIG. 10

is a circuit diagram of a principal portion of the above device;

FIG. 11

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a fourth embodiment of the present invention;

FIG. 12

is a circuit diagram of a principal portion of the above device;

FIG. 13

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a fifth embodiment of the present invention;

FIG. 14

is a circuit diagram of a principal portion of the above device;

FIG. 15

is a partly omitted schematic circuit diagram showing a discharge lamp driving device in accordance with a sixth embodiment of the present invention;

FIG. 16

is a partly omitted schematic circuit diagram showing a discharge lamp driving device in accordance with a seventh embodiment of the present invention;

FIG. 17

is a partly omitted schematic circuit diagram showing a discharge lamp driving device in accordance with an eighth embodiment of the present invention;

FIG. 18

is a circuit diagram of a principal portion of the above device;

FIG. 19

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a ninth embodiment of the present invention;

FIG. 20

is a schematic circuit diagram showing a modification of the above device;

FIG. 21

is a schematic circuit diagram showing another modification of the above device;

FIG. 22

is a schematic circuit diagram showing a further modification of the above device; and

FIG. 23

is a schematic circuit diagram showing a discharge lamp driving device in accordance with a tenth embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

(First Embodiment)

FIG. 3

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment. A series connected pair of switching elements Q

1

and Q

2

and a smoothing capacitor C

0

are connected in parallel across pulsating output terminals of a rectifier DB that is composed of a diode bridge to rectify an AC source voltage AC. A leakage transformer LT

1

has a primary winding N

1

which is connected between the high-side output terminal of the rectifier DB and a connection point of the switching elements Q

1

and Q

2

, and has a secondary winding N

2

connected to filaments (a) and (d) of discharge lamps La

1

and La

2

of the same rating. For supplying a pre-heating current, the leakage transformer LT

1

has an auxiliary winding N

3

which is connected through a DC blocking capacitor C

3

to the other filaments (b) and (c) of the discharge lamps La

1

and La

2

. A capacitor C

2

is connected to the ends of the filaments (a) and (d) away from the voltage source such that a resonant load circuit is constituted by the leakage transformer LT

1

, capacitor C

2

and the discharge lamps La

1

and La

2

.

In the present embodiment, the switching elements Q

1

and Q

2

is cooperative with the resonant load circuit to realize an inverter circuit INV of a half-bridge type which receives, as an input voltage, the DC voltage smoothed by the smoothing capacitor C

0

. The half-bridge type inverter circuit INV is known and is driven by a driver circuit (not shown but including a self-excited type using a driving transformer) to turn on and off the switching elements Q

1

and Q

2

alternately at a high frequency, applying a square wave high frequency voltage to the resonant load circuit so as to make the use of the resonance by a leakage inductance of the leakage transformer LT

1

and the resonant-inducing capacitor C

2

of the resonant load circuit to supply a high frequency voltage of substantially the sinusoidal waveform for operating the discharge lamps La

1

and La

2

.

Next, the characterizing features of the present embodiment will be explained. Impedance elements Z

1

, Z

1

are inserted respectively between the filament (a) of the discharge lamp La

1

and a node (ground) having no high frequency amplitude and between the filament (d) of the discharge lamp La

2

and the node, while an impedance element Z

2

is inserted between the filament (b) and the capacitor C

3

that is connected between the high-side terminal of the rectifier DB and the auxiliary winding N

3

of the leakage transformer LT

1

. Further, a series circuit of impedance elements Z

3

and Z

4

is connected between the ground and a connection point of the auxiliary winding N

3

and the filament (c).

FIG. 4

is a circuit diagram showing the resonant load circuit extracted as a principal portion. The lamp voltages VLa

1

and VLa

2

supplied to the two discharge lamps La

1

and La

2

are each applied to each closed loop composed of the impedance elements Z

1

, Z

3

, and Z

4

. Also, the pulsating output Vdc from the rectifier DB divided by the impedance element Z

2

is applied as a DC voltage to the series circuit of the impedance elements Z

3

and Z

4

. A detected voltage Vk derived from the connection point of the impedance elements Z

3

and Z

4

is a voltage corresponding to a combination of an AC component which is a difference between the lamp voltages VLa

1

and VLa

2

of the two discharge lamps La

1

and La

2

respectively divided by the impedance elements Z

1

, Z

3

and Z

4

, and a DC component which is the pulsating output Vdc from the rectifier DB divided by the impedance elements Z

2

, Z

3

, and Z

4

.

When both of the two discharge lamps La

1

and La

2

are normal, the lamp voltages VLa

1

and VLa

2

of the lamps La

1

and La

2

are sinusoidal of the same amplitude but in out of phase relation to each other by about one-half cycle, as shown in

FIGS. 5A and 5B

, such that the lamp voltages are cancelled at the connection point of the impedance elements Z

3

and Z

4

, causing the detected voltage Vk to have substantially zero AC component Vk(AC), as shown in FIG.

5

C. In this condition, since the connection point of the Impedance elements Z

3

and Z

4

sees the DC component Vk(DC) depending upon the dividing ratio of the impendance elements Z

2

to Z

4

, as seen in

FIG. 5

, the detected voltage Vk is eventually equal to the DC component Vk(DC).

When, on the other hand, the filament of the discharge lamp La

1

becomes depleted (emitter depletion condition), for example, the filament radiates only a reduced amount of thermion, whereby the lamp voltage VLa

1

of the discharge lamp La

1

be comes asymmetric with respect to the zero voltage with a larger amplitude than in the normal condition. With this result, no cancellation of the voltages is made at the connection point of the impedance elements Z

3

and Z

4

, whereby an oscillation voltage appears as the AC component Vk(AC) of the detected voltage Vk, as shown in FIG.

6

C. It is noted that the DC component Vk(DC) is kept unvaried, as shown in FIG.

6

D. That is, the detected voltage Vk will be the voltage corresponding to the high frequency AC component Vk(AC) superimposed on the DC component Vk(DC), as shown in FIG.

6

E. Therefore, the detected voltage Vk, which is the high frequency AC component Vk(AC) superimposed on the DC component Vk(DC), can be processed such as by a peak detection in order to obtain a purely DC detected voltage Vk′, as shown in

FIG. 6F

, depending on the lamp voltage VLa

1

of the discharge lamp La

1

suffering from the depletion of the emitter. Thus obtained detected voltage Vk′ is compared with a predetermined threshold Vth such that the discharge lamp can be judged to reach the lamp life end when the detected voltage Vk′ exceeds the threshold Vth. This judgment is made at an abnormality detection circuit (not shown) which transmits an abnormality detection signal to a control circuit (not shown) when the abnormality (the lamp life end due to the emitter depletion condition) is detected. In response to the abnormality signal, the control circuit responds to control the switching elements Q

1

and Q

2

in such a manner as to intermittently oscillate the inverter circuit for making the circuit protection.

The present embodiment is contemplated to insert the impedance elements Z

1

, Z

1

respectively between the one filament of the discharge lamp La

1

and the node having no high frequency amplitude (the ground) and between the one filament of the discharge lamp La

2

and the node, and to detect the AC component difference between the lamp voltages VLa

1

and VLa

2

of the discharge lamps La

1

and La

2

in the respective closed loops each including the impedance element Z

1

and each of the discharge lamps La

1

and La

2

in order to judge whether or not there is the abnormality due to the depletion of the emitter. Therefore, it is made possible to detect the occurrence of the abnormality reliably irrespective of the fact that the discharge lamps La

1

and La

2

give the lamp voltages VLa

1

and VLa

2

of varying amplitudes depending on the temperature, i.e., irrespective of the low and high temperature environments. Also, since there is no need to include a DC blocking capacitor on the side of the secondary winding N

2

of the leakage transformer LT

1

, no DC component is applied to the discharge lamps La

1

and La

2

so as to prevent the cataphoresis phenomenon. Further, since the present embodiment is configured such that the pulsating output Vdc of the rectifier DB has an effect on the detected voltage Vk′, it is possible to reliably detect the occurrence of the abnormality even with the use of the inverter circuit of which output varies with the varying AC source voltage, that is, increases with the raised AC source voltage and decreases with the lowered AC source voltage.

(Second Embodiment)

FIG. 7

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment, while

FIG. 8

shows a circuit diagram about a principal portion of the above. A basic configuration of the present embodiment is identical to the first embodiment and therefore no duplicate explanation is made herein. The like parts are designated by the like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

The present embodiment is contemplated to insert series combinations of impedance elements Z

1

and Z

5

respectively between the filament (a) of the discharge lamp La

1

and the ground, and between the filament (d) of the discharge lamp La

2

, and also insert a impedance element Z

3

alone between the filament (c) of the discharge lamp La

2

and the ground. The like abnormality detection circuit (not shown) is included to judge the presence of the abnormality with regard to the one discharge lamp La

1

based upon the detected voltage Vk

1

derived from the connection point of the impedance elements Z

1

and Z

5

, and to judge the presence of the abnormality with regard to the other discharge lamp La

2

based upon the detected voltage Vk

2

derived from the connection point of the impedance elements Z

1

and Z

6

. When the abnormality is judged fro anyone of the discharge lamps La

1

and La

2

, the like control circuit (now shown) operates to give the protective action such as by making the intermittent oscillation.

In the present embodiment, the detected voltage Vk

1

reflecting the lamp voltage VLa

1

of the discharge lamp La

1

is used to detect the abnormality (depletion of the emitter), and the detected voltage Vk

2

reflecting the lamp voltage VLa

2

of the discharge lamp La

2

is used to detect the abnormality (depletion of the emitter). Also in the present embodiment, it is equally possible to reliably judge the abnormality irrespective of the varying amplitudes of the lamp voltage VLa

1

and VLa

2

from low to high temperature environments as is made in the first embodiment. Also, since the detected voltages Vk

1

and Vk

2

are made reflective of the DC component of the pulsating output Vdc from the rectifier DB as is made in the first embodiment, it is possible to reliably detect the occurrence of the abnormality even with the use of the inverter circuit of which output varies with the varying AC source voltage, that is, increases with the raised AC source voltage and decreases with the lowered AC source voltage.

(Third Embodiment)

FIG. 9

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment, while

FIG. 10

shows a circuit diagram about a principal portion of the above. A basic configuration of the present embodiment is identical to the first embodiment and therefore no duplicate explanation is made herein. The like parts are designated by the like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

The present embodiment is characterized to insert a series combination of impedance elements Z

1

and Z

5

between the filament (a) of the discharge lamp La

1

and the ground in order to obtain a detected voltage Vk

1

derived from the connection point between the impedance elements Z

1

and Z

5

, and to obtain a detected voltage Vk

2

derived from the connection point between impedance elements Z

3

and Z

4

such that the like abnormality detection circuit (not shown) can judge the occurrence of the abnormality for the discharge lamps La

1

and La

2

based upon the detected voltages Vk

1

and Vk

2

. When the abnormality is judged to occur in the discharge lamps La

1

and La

2

, the like control circuit (not shown) operates to give the protective action such as by making the intermittent oscillation. In the first embodiment, either when there occurs the depletion of the emitter in the filament (a) of the discharge lamp La

1

connected to the secondary winding N

2

and also in the filament (c) of the discharge lamp La

2

connected to the auxiliary winding, or when there occurs the depletion of the emitter in the filament (b) of the discharge lamp La

1

connected to the auxiliary winding N

3

and also in the filament (d) of the discharge lamp La

2

connected to the secondary winding N

2

, the detected voltage Vk has only a small AC component Vk(DC) which makes it difficult to judge the presence of the abnormality.

However, in the present embodiment, the detected voltage Vk

2

derived from the connection point of the impedance elements Z

3

and Z

4

is relied upon to judge whether anyone of the discharge lamps La

1

and La

2

reaches the lamp life end due to the depletion of the emitter, while the detected voltage Vk

1

, which is derived from the connection point of the impedance elements Z

1

and Z

5

as corresponding to the lamp voltage VLa

1

of the discharge lamp La

1

, is relied upon to judge whether both of the discharge lamps La

1

and La

2

reach the lamp life end due to the depletion of the emitter. That is, the lamp life end can be judged even in a condition which satisfies both of the events, one in which the depletion of the emitter occurs in the filament (a) of the discharge lamp La

1

connected to the secondary winding N

2

or in the filament (c) of the discharge lamp La

2

connected to the auxiliary winding, and the other in which the depletion of the emitter occurs in the filament (b) of the discharge lamp La

1

connected to the auxiliary winding N

3

, or in the filament (d) of the discharge lamp La

2

connected to the secondary winding N

2

.

(Fourth Embodiment)

FIG. 11

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment, while

FIG. 12

shows a circuit diagram about a principal portion of the above. A basic configuration of the present embodiment is identical to the first embodiment and therefore no duplicate explanation is made herein. The like parts are designated by the like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

The present embodiment, which combines the features of the first embodiment and the second embodiment, is characterized to insert a series circuit of impedance elements Z

1

and Z

5

between the filament (a) of the discharge lamp La

1

and the ground, and another series circuit of impedance elements Z

1

and Z

6

between the filament (d) of the discharge lamp La

2

and the ground, and to utilize the like abnormality detection circuit (not shown) which judges the abnormality in either or both of the discharge lamps La

1

and La

2

based upon a detected voltage Vk

1

derived from the point to the impedance elements Z

2

and Z

5

as corresponding the lamp voltage VLa

1

of the discharge lamp La

1

, upon a detected voltage Vk

2

derived from the connection point of the impedance elements Z

3

and Z

4

, and upon a detected voltage Vk

3

derived from the connection point of the impedance elements Z

1

and Z

6

as corresponding to the lamp voltage VLa

2

of the discharge lamp La

2

.

With the present embodiment, it is possible to judge the abnormality in all events including the depletion of the emitter in anyone of the discharge lamps but also in both of the discharge lamps La

1

and La

2

.

(Fifth Embodiment)

FIG. 13

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment, while

FIG. 14

shows a circuit diagram about a principal portion of the above. A basic configuration of the present embodiment is identical to the first embodiment and therefore no duplicate explanation is made herein. The like parts are designated by the like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

The present embodiment utilizes capacitors C

101

and C

102

as the individual impedance elements Z

1

and Z

1

, and a resistor

109

connected between the capacitors C

101

, C

102

and the ground. The resistor

109

limits a high frequency signal flowing through capacitors C

101

and C

012

to the ground in the normal operating condition of the discharge lamps La

1

and La

2

, reducing circuit noises. An inductor may be utilized instead of resistor

109

.

Also, a peak detection circuit P is provided to convert the detected voltage Vk at the connection point of the impedance elements Z

3

and Z

4

respectively in the form of resistors R

101

and R

102

into a detected DC voltage Vk′. The peak detection circuit P includes a series circuit of a DC blocking capacitor C

401

and a diode D

402

connected to the point between the resistors R

101

and R

102

, a diode D

401

inserted between the ground and the connection point of capacitor C

401

and diode D

401

, and a smoothing capacitor C

402

connected between the cathode of diode D

402

and the ground. Thus, the capacitor C

401

DC cuts out the DC component Vk(DC) of the detected voltage Vk so as to charge C

402

with energy corresponding to the peak value of the AC component Vk(AC) of the detected voltage Vk, thereby effectively obtaining the detected voltage Vk′ having only the DC component corresponding to the difference in the lamp voltages VLa

1

and VLa

2

of the discharge lamps La

1

and La

2

. As is explained with reference to the first embodiment, the detected voltage Vk′ is compared with the predetermined threshold Vth such that the discharge lamps La

1

and La

2

can be judged to reach the lamp life end when the detected voltage exceeds the threshold Vth.

(Sixth Embodiment)

FIG. 15

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment. A basic configuration of the present embodiment is identical to the fifth embodiment and therefore no duplicate explanation is made herein. The like parts are designated by the like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

The present embodiment is characterized in that capacitors C

501

and C

502

are utilized respectively as impedance elements Z

1

and Z

1

, and also act as the resonant inducing capacitor C

2

to dispense with capacitor C

2

. The circuit operation such as for detecting the depletion of the emitter is identical to the fifth embodiment and therefore its explanation is not made herein.

Thus, the present embodiment has an advantage of reducing the number of the components as the capacitors C

501

and C

502

are utilized as the impedance elements Z

1

and also as the resonant inducing capacitor C

2

.

(Seventh Embodiment)

FIG. 16

is a partially omitted schematic circuit diagram showing the present embodiment which is basically similar to the second prior art of FIG.

2

. Therefore, like configuration common to the second prior art is not shown and no duplicate explanation is made herein. Like parts are designated by like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

As shown in

FIG. 16

, a resistor R

1

is inserted between the high-side output terminal of the rectifier DB and a connection point of capacitor C

6

connected to the auxiliary winding N

3

of the leakage transformer LT

1

and one filament (b) of the discharge lamp La

1

. A parallel circuit of a capacitor C

8

and a resistor R

5

is connected in series with resistors R

3

and R

4

between the ground and the connection point of the auxiliary winding N

3

and the filament (c) of the discharge lamp La

2

. Further, the switching element Q

2

has its gate connected through a triggering element TD such as Diac to the connection point of resistor R

4

and capacitor C

8

, while a series circuit of a diode D

11

and a resistor R

10

is inserted between the drain of the switching element Q

2

and the connection point of resistor R

4

and capacitor C

8

. A series combination of the triggering element TD, diode D

11

and resistor R

10

constitutes a starting circuit for turning on the switching element Q

2

when the AC source voltage AC is applied so as to start the inverter. The like peak detection circuit P as explained with reference to the fifth embodiment is connected to the point between resistors R

3

and R

4

to derive a detected voltage Vk from the connection point.

When the AC source voltage is applied, the rectifier DB charge capacitor C

8

through resistor R

1

, filament (b) of discharge lamp La

1

, filament (c) of discharge lamp La

2

, and resistors R

3

and R

4

. When voltage across capacitor C

8

increases to the break voltage of the triggering element TD, the triggering element responds to break-down for supplying the charge of capacitor C

8

to the gate of switching element Q

2

, thereby turning on switching element Q

2

and therefore starting the inverter circuit. When the switching element Q

2

is turned on, capacitor C

8

is discharged through diode D

11

, resistor R

10

and switching element Q

2

so that the inverter circuit continues to oscillate. If the filament (b) of the discharge lamp La

1

or the filament (c) of the discharge lamp La

2

is broken, or if anyone of the discharge lamps La

1

and La

2

is disconnected (in no-load condition) at the time of emerging the device, no charging path is established for capacitor C

8

. Consequently, in view of that capacitor C

8

is shunt by resistor R

5

, the triggering element TD would not break-down and therefore the inverter circuit would not start. Thus, the inverter circuit is prevented from starting at the no-load condition for protection of the circuit at the no-load condition.

As explained in the above, since the starting circuit for the inverter circuit of the present embodiment includes the no-load detecting and circuit protective function of dealing with the broken filaments and the disconnection of the discharge lamps La

1

and La

2

, in addition to the abnormality detection and protection function of dealing with the depletion of the emitter, the circuit components can be reduced significantly in number.

(Eighth Embodiment)

FIG. 17

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment, while

FIG. 18

shows a circuit diagram about a principal portion of the above. A basic configuration of the present embodiment is identical to the second prior art of

FIG. 2

as well as to the seventh embodiment. Therefore no duplicate explanation is made herein but the like parts are designated by the like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

The present embodiment is configure to insert impedance elements Z

1

and Z

1

respectively between the filament (a) of the discharge lamp La

1

and the ground and between the filament (c) of the discharge lamp La

2

, and insert a series combination of impedance elements Z

3

and Z

4

between the ground and the connection point of the auxiliary winding N

3

and the filament (c) of the discharge lamp La

2

. Also, the like peak detection circuit P as explained with reference to the fifth embodiment is connected to a connection point of the impedance elements Z

3

and Z

4

so that the detected voltage Vk derived from the connection point of the impedance elements Z

3

and Z

4

is converted into a DC detected voltage Vk′,

The control circuit CNT compares the detected voltage Vk′ from the peak detection circuit P with a predetermined threshold Vth so as to judge that the discharge lamp La

1

or La

2

reaches the lamp life end when the threshold Vth is exceeded, and makes the protective action of intermittently oscillating the inverter circuit.

Thus, in the like manner as in the first embodiment, the present embodiment includes the impedance elements Z

1

and Z

2

which are inserted respectively between the one filament of the one discharge lamp La

1

and the node having no high frequency amplitude (the ground), and between the one filament of the other discharge lamp La

2

and the ground, in order to detect a difference in the AC component of the lamp voltages VLa

1

and VLa

2

of the discharge lamps La

1

and La

2

within the closed loops each including the impedance element Z

1

and each of the discharge lamps La

1

and La

2

, for the purpose of judging the abnormality due to the depletion of the emitter. Accordingly, it can be made to reliably judge the abnormality irrespective of the varying amplitudes of the lamp voltage VLa

1

and VLa

2

from low to high temperature environments. Also, since there is no need to include a DC blocking capacitor on the side of the secondary winding N

2

of the leakage transformer LT

1

, no DC component is applied to the discharge lamps La

1

and La

2

so as to prevent the cataphoresis phenomenon.

(Ninth Embodiment)

FIG. 19

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment. The present embodiment includes a rectifier DB in the form of a diode bridge responsible for a full-wave rectification of an AC source voltage AC to provide a pulsating output that is smoothed by a smoothing capacitor C

1

to give a voltage source for an inverter circuit. The inverter circuit is of a so-called half-bridge configuration and includes a series combination of switching elements Q

1

and Q

2

respectively in the form of bipolar transistors connected across the smoothing capacitor C

1

, diodes D

1

and D

2

each connected in anti-parallel relation across each of the switching elements Q

1

and Q

2

, and a series circuit of capacitors C

3

and C

4

connected across the smoothing capacitor C

1

. Connected to a point between capacitors C

3

and C

4

is a series circuit of a primary winding N

1

of a leakage transformer LT

1

and a primary winding of a driving transformer T

1

which is provided for driving the switching elements Q

1

and Q

2

. The leakage transformer LT

1

has a secondary winding N

2

connected to filaments (a) and (d) of the discharge lamps La

1

and La

2

, and an auxiliary winding N

3

connected to filaments (b) and (c) of the discharge lamps La

1

and La

2

. A resonant inducing capacitor C

5

is connected to filaments (a) and (d) of the discharge lamps La

1

and La

2

on the non-energized side thereof. Instead of using the combination of the bipolar transistors and the diodes D

1

and D

2

, the switching elements Q

1

and Q

2

may be realized by field effect transistors having parasitic diodes.

The switching elements Q

1

and Q

2

are activated by the driving transformer T

1

to turn on and off alternately with the switching elements Q

1

and Q

2

being responsible for flowing currents in opposite directions through the leakage transformer LT

1

to the discharge lamps La

1

and La

2

respectively from capacitors C

3

and C

4

, thereby applying a high frequency voltage developed across capacitor C

5

resulting from a series resonant circuit of a leakage inductance and capacitor C

5

for starting and operating the lamps.

Also in the present embodiment, a capacitor C

8

is inserted as the impedance element between the filament (a) of the discharge lamp La

1

and a node (the ground) having no high frequency amplitude, while a capacitor C

9

is inserted as the impedance element between the filament (b) of the discharge lamp La

2

and the node (the high-side output terminal of rectifier DB). Further, an emitter depletion detection and protection circuit

10

is connected between a connection of a base resistor R

2

of the switching element Q

2

with the secondary winding of the driving transformer T

1

and the auxiliary winding N

3

in order to detect the depletion of emitter in anyone of the filaments (a) to (d) of the discharge lamps La

1

and La

2

for protection of the circuit.

The emitter depletion detection and protection circuit

10

includes a series circuit of a DC blocking capacitor C

7

and a diode D

6

connected between the filament (c) of the discharge lamp La

2

and the ground, a diode D

5

having an anode connected to a cathode of diode D

6

connected to the capacitor C

7

, a zener diode ZD

1

having a cathode connected to the cathode of diode D

5

, and a parallel combination of a smoothing capacitor C

6

and a discharging resistor R

5

connected between the cathode of zener diode ZD

1

and the ground. A capacitor C

10

is connected in parallel with a biasing resistor R

4

between the anode of zener diode ZD

1

and the ground, while a switching element Q

3

of PNP-type bipolar transistor is connected in series with a diode D

7

between the base resistor R

2

of the switching element Q

2

and the resistor R

4

. Further, a biasing resistor R

3

is connected in an emitter-base path of the switching element Q

3

, while a switching element Q

4

of NPN-type bipolar transistor is connected between resistor R

3

and the switching element Q

4

.

As the capacitor C

8

is inserted between the filament (a) of the discharge lamp La

1

and the ground and the capacitor C

9

is inserted between the filament (d) of the discharge lamp La

2

and the high-side output terminal of the rectifier DB, the high frequency currents respectively flowing through the discharge lamps La

1

and La

2

becomes asymmetrical with each other if anyone of the filaments (a) to (d) of the discharge lamps La

1

and La

2

sees the depletion of the emitter. The resulting asymmetrical high frequency currents are responsible for charging the capacitor C

7

and the capacitor C

6

through diode D

5

. When the voltage across capacitor C

6

exceeds the zener voltage of zener diode ZD

1

, capacitor C

6

is discharged to turn on the switching element Q

4

, which in turn causes the switching element Q

3

to turn on, thereby connecting the secondary winding of the driving transformer T

1

for driving the switching element Q

2

to the ground through diode D

7

. With this result, the switching element Q

2

becomes not capable of turning on to stop the inverter circuit. Thus, the emitter depletion detection and protection circuit

10

can detect the depletion of the emitter of the discharge lamps La

1

and La

2

, and stops the inverter circuit for protection of the circuit upon detection of the depletion of the emitter.

In the present embodiment, the impedance elements C

8

and C

9

are inserted respectively between the filaments of the discharge lamps La

1

, La

2

and the nodes having no high frequency amplitude (the ground or the high-side output terminal of rectifier DB) in order to detect the asymmetric high frequency currents at the connection between the discharge lamps La

1

and La

2

for judging whether there occurs the depletion of emitter. Therefore, it is possible to reliably judge the occurrence of the depletion of the emitter irrespective of whether it is operating in the low or high temperature environment. Further, since there is no need to connect a DC blocking capacitor to the secondary winding N

2

of the leakage transformer LT

1

, the discharge lamps La

1

and La

2

can be free from the DC component so as to be prevented from causing the cataphoresis phenomenon.

It may be equally possible to insert capacitors C

8

and C

9

respectively between the filament (a) of the discharge lamp La

1

and the high-side output terminal of the rectifier DB, and between the filament (d) of the discharge lamp La

2

and the high-side output terminal, as shown in

FIG. 20

; to insert capacitors C

8

and C

9

respectively between the filament (a) of the discharge lamp La

1

and the ground, and between the filament (d) of the discharge lamp La

2

and the ground, as shown in

FIG. 21

; to insert resistors Ra and Rd instead of capacitors C

8

and C

8

between the respective filaments (a) and (d) of the discharge lamps La

1

and La

2

and the respective one of the high-side output terminal of rectifier DB and the ground, as shown in

FIG. 22

; or even to use a series combination of resistor and capacitor as the impedance element. In any case, the high frequency currents flowing through the discharge lamps La

1

and La

2

becomes asymmetrical with each other when there occurs the depletion of the emitter in anyone of the filaments (a) to (d) of the discharge lamps La

1

and La

2

so that the emitter depletion detection and protection circuit

10

can responds to detect the asymmetrical high frequency currents for judging whether or not there occurs the depletion of the emitter.

(Tenth Embodiment)

FIG. 23

shows a schematic circuit diagram of the discharge lamp driving device in accordance with the present embodiment which is basically similar to the second prior art of FIG.

2

. Therefore, like configuration common to the second prior art is not shown and no duplicate explanation is made herein. Like parts are designated by like reference numerals. Here, only the characterizing features of the present embodiment will be now explained.

In the present embodiment, capacitor C

8

is inserted as the impedance element between the filament (a) of the discharge lamp La

1

and the node (the high-side output terminal of rectifier DB) having no high frequency amplitude, while capacitor C

9

is inserted as the impedance element between the filament (d) of the discharge lamp La

2

and the node (ground). Also, connected between the gate of the switching element Q

2

and the auxiliary winding N

3

is the like emitter depletion detection and protection circuit

10

which detects the depletion of the emitter in anyone of the filaments (a) to (d) of the discharge lamps La

1

and La

2

for protection of the circuit. The emitter depletion detection and protection circuit is identical in configuration and operation to that of the ninth embodiment, and therefore no duplication explanation is made.

Similar to the ninth embodiment, the present embodiment is configured to insert capacitor C

8

between the filament (a) of the discharge lamp La

1

and the high-side output terminal of rectifier DB, to insert capacitor C

9

between the filament (d) of the discharge lamp La

2

and the ground, and to provide the emitter depletion detection and protection circuit

10

which detects the asymmetric high frequency currents at the connection between the discharge lamps La

1

and La

2

for judging whether there occurs the depletion of the emitter. Therefore, it is possible to reliably judge the occurrence of the depletion of the emitter irrespective of whether it is operating in the low or high temperature environment. Further, since there is no need to connect a DC blocking capacitor to the secondary winding N

2

of the leakage transformer LT

1

, the discharge lamps La

1

and La

2

can be free from the DC component so as to be prevented from causing the cataphoresis phenomenon.

The inverter circuit may be of different circuit configurations including, for example, one in which the resonant load circuit is connected between the connection point of the switching elements Q

1

and Q

2

and the low-side output terminal of the rectifier DB, and one in which a valley-filling power source composed of a voltage doubler is utilized instead of the valley-filling power source composed of the step-down chopper circuit. The concept of the present invention can be applied

It is noted that the concept of the present invention can be applied to various circuit configurations of the inverter circuit. For example, the inverter circuit may be of different configurations including one in which the resonant load circuit is connected between the connection point of the switching elements Q

1

and Q

2

and the low-side output terminal of the rectifier DB, and one in which a valley-filling power source composed of a voltage doubler is utilized instead of the valley-filling power source composed of the step-down chopper circuit.

Number	Name	Date	Kind
4498031	Stupp et al.	Feb 1985	A
6057652	Chen et al.	May 2000	A
6075715	Maehara et al.	Jun 2000	A
6118224	Murakami et al.	Sep 2000	A

Number	Date	Country
8-167484	Jun 1996	JP
8-251942	Sep 1996	JP
8-264293	Oct 1996	JP
2000-100587	Apr 2000	JP

Discharge lamp lighting device

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

PCT Information

US Referenced Citations (4)

Foreign Referenced Citations (4)