Patent Application
20100066265
1. Technical Field
The present invention relates to a discharge lamp lighting device which lights a discharge lamp, and more particularly relates to a discharge lamp lighting device which reduces a rush current at start-up of lighting of the discharge lamp, and a projector provided with the discharge lamp lighting device.
2. Description of Related Art
A short arc type metal halide lamp or a high-pressure mercury lamp is used for a liquid crystal projector, an overhead projector, or general illumination, or the like. In order to light the metal halide lamp, a discharge lamp lighting device is used. The discharge lamp lighting device used for the projector etc. generates high voltage of about ten kV by an ignitor at start-up, and applies the high voltage to the discharge lamp, thereby causing dielectric breakdown. In this case, there is a problem that a rush current of high current flows through the discharge lamp at a moment of dielectric breakdown, thereby giving damage to an electrode of the discharge lamp. A charge source of the rush current is a capacitor which is inserted in parallel with the lamp in order to suppress a switching ripple current which flows through the lamp. A path of the rush current is a path which extends from the capacitor to the lamp and returns to the capacitor. Recently, there is a case where a choke coil etc. is not inserted in the path for reduction of a size of the discharge lamp lighting device. In this case, impedance of the path decreases and a rush current increases.
In order to solve this problem, conventionally a lighting device is proposed in which a plurality of capacitors having different capacitance are provided, and the capacitors are switched using a FET (Field-Effect Transistor) at start-up of lighting and after an arc discharge shift (for example, refer to Japanese Patent Application Laid-Open No. 2003-100487 or Japanese Patent Application Laid-Open No. 2005-203197). Also, a power supply apparatus is known in which a resistor for limiting a current is connected in series with the discharge lamp, a switch is turned on at start-up of lighting to connect the discharge lamp with the resistor, and after stabilization the switch is turned off to shut off connection with the resistor (for example, refer to Japanese Patent Application Laid-Open No. 2006-49061). Moreover, a method is known in which the capacitor, resistor, or switch etc. is switched based on a lamp current or lamp voltage which is detected, in addition to switching by a timer etc. (for example, refer to Japanese Patent Application Laid-Open No. 2000-182796).
However, the method disclosed in Japanese Patent Application Laid-Open No. 2003-100487 or Japanese Patent Application Laid-Open No. 2005-203197 in which the capacitors are switched has a problem that the FET generates heat. The respective lighting devices disclosed in Japanese Patent Application Laid-Open No. 2003-100487, Japanese Patent Application Laid-Open No. 2005-203197, Japanese Patent Application Laid-Open No. 2006-49061 and Japanese Patent Application Laid-Open No. 2000-182796 which use a timer etc. and adopt switching control have a problem that control by several μs unit cannot be realized, and a desired operation cannot follow the behavior of the lamp when an unexpected going-out of the lamp occurs, or the like.
The present invention has been made with the aim of solving the above problem, and it is an object of the present invention to provide a discharge lamp lighting device which reduce a rush current, reduce power consumption, has a high response speed, and follows a change of the lamp sufficiently, by using a thyristor and an auxiliary resistor which are connected in parallel with a resistor connected in series with a discharge lamp, and a projector provided with the discharge lamp lighting device.
Moreover, another object of the present invention is provide a discharge lamp lighting device capable of further reducing power consumption without reducing the response speed, by turning on a switching element connected in parallel after breakover of the thyristor, and a projector provided with the discharge lamp lighting device.
A discharge lamp lighting device according to the present invention is a discharge lamp lighting device which lights a discharge lamp, characterized by comprising: a resistor connected in series with said discharge lamp; a thyristor connected in parallel with said resistor; and an auxiliary resistor connected between an anode and a gate of said thyristor.
A discharge lamp lighting device according to the present invention is characterized in that said auxiliary resistor controls said thyristor from off to on, by passing a gate current through said thyristor with the use of voltage generated across said resistor as a power source.
A discharge lamp lighting device according to the present invention is characterized in that that said thyristor in an on-state shifts from on to off according to a state of a current which flows through said discharge lamp.
A discharge lamp lighting device according to the present invention is characterized in that said resistor, said thyristor and said auxiliary resistor are in floating states with respect to a ground.
A discharge lamp lighting device according to the present invention is characterized by further comprising: a switching element connected in parallel with said resistor, said thyristor, and said auxiliary resistor; and a switching controller which switches said switching element from off to on after breakover of said thyristor.
A discharge lamp lighting device according to the present invention is characterized in that a resistance value of internal equivalent resistance between the anode and a cathode of said thyristor in an on-state is smaller than a resistance value of said resistor.
A discharge lamp lighting device according to the present invention is characterized in that a resistance value of on-resistance of said switching element in an on-state is smaller than a resistance value of internal equivalent resistance between the anode and the cathode of said thyristor in an on-state.
A projector according to the present invention is a projector, characterized by comprising one of the above-mentioned discharge lamp lighting devices.
In the present invention, the discharge lamp lighting device is constituted with the resistor connected in series with the discharge lamp, the thyristor, and the auxiliary resistor connected between the anode and gate of the thyristor.
A resistance value of internal equivalent resistance between the anode and cathode of the thyristor in an on-state is smaller than a resistance value of the resistor. A rush current after dielectric breakdown flows through the resistor since the thyristor is in an off-state. Then, the current flows through the gate of the thyristor via the auxiliary resistor with the rise of a pressure value of the resistor. Breakover of the thyristor occurs with the rise of a gate current, a current flows from the anode to the cathode of the thyristor and does not flow through the resistor and auxiliary resistor of a high resistance value.
In the present invention, the switching element is connected in parallel with the resistor and the thyristor. And the switching controller switches the switching element from off to on after elapse of a predetermined period of time after breakover of the thyristor. In this case, a resistance value of on-resistance of the switching element in an on-state is smaller than a resistance value of internal equivalent resistance between the anode and cathode of the thyristor in an on-state. Thereby, after the discharge lamp operates stably, a current which has flowed through the thyristor flows through the switching element connected in parallel.
According to the present invention, since the thyristor is connected in parallel with the resistor connected in series with the discharge lamp, a rush current after dielectric breakdown flows through the resistor since the thyristor is in an off-state. Thereby, a rush current can be absorbed by the resistor effectively and an improvement of the service life of the discharge lamp can be attained. Moreover, a current flows through a gate of the thyristor via the auxiliary resistor with the rise of a pressure value across the resistor. And breakover of the thyristor occurs with the rise of a gate current, a current flows from the anode to the cathode of the thyristor and does not flow through the resistor and auxiliary resistor of a high resistance value. As a result, the discharge lamp lighting device is constituted such that a flow of current can be switched in order of the resistor and the thyristor with a simple constitution, without using a switching element, a timer, etc. which require extremal control, thereby reducing a size thereof and obtaining a higher speed response. Moreover, the resistance value of internal equivalent resistance of the thyristor in an on-state is small enough as compared with the resistance value of the resistor, thereby reducing power consumption of the thyristor.
According to the present invention, the switching controller switches the switching element from off to on after elapse of a predetermined period of time after breakover of the thyristor. In this case, the resistance value of on-resistance of the switching element is smaller than the resistance value of internal equivalent resistance of the thyristor in an on-state. Thereby, after the discharge lamp operates stably, a current which has flowed through the thyristor flows through the switching element connected in parallel. Therefore, the present invention has an outstanding effect such as reducing more power consumption after the stable operation, without sacrificing a speed of response.
The above and further objects and features will more fully be apparent from the following detailed description with accompanying drawings.
The following description will explain Embodiments of the present invention, based on the drawings.
For actuating the lamp 15, converted voltage is generated at both ends of the capacitor 13 by the DC-DC converter 12, and the ignitor 14 operates in response to the voltage, and applies high voltage of several kV through tens of kV to the lamp 15. In the lamp 15, dielectric breakdown is caused by the high voltage, and a current begins to flow. At a moment when the dielectric breakdown occurs, a rush current flows through the lamp 15 in an instant (several microseconds). A source of a charge of the rush current is the capacitor 13, and the charge is proportional to the capacity of the capacitor 13 and voltage applied to both ends of the capacitor 13 before the dielectric breakdown. The rush current returns from the capacitor 13 via the ignitor 14 and lamp 15 to a low potential side of the capacitor 13. The rush current increases when the impedance of the path is low. For example, when the capacitor 13 has a capacity of 3 μF, applied voltage is 100V, and impedance is low because no choke coil etc. is inserted in the path through which a rush current flows, a current at its peak 100 A flows for a period of 6 μs (microsecond). When 100V is applied to 3 μF, a charge to be stored is 300 μq (microcoulomb) (=300 μF×100V), and when considering a current of 100 A which flows for 6 μs as a triangular wave and integrating a current waveform, about 300 μq (=6 μs×100 A/2) is obtained, and they coincide with each other. An initial lighting state of the lamp 15 after dielectric breakdown is a mode called glow discharge. When sufficient power is supplied to the lamp 15, the glow discharge is shifted to initial arc discharge. During the initial arc discharge, the lamp 15 generates heat, and lamp voltage increases. And eventually, the mode of the lamp 15 is shifted to steady arc discharge, and is lighted in the stabilized state.
The resistor 16 is connected in series with the latter part of the lamp 15, i.e., a cathode side of an electrode of the lamp 15. The thyristor 17, the auxiliary resistor 21 and the protective resistor 22 are connected in parallel with the resistor 16. The auxiliary resistor 21 is connected in series with the protective resistor 22, and the auxiliary resistor 21 has one end connected to a gate of the thyristor 17 and the other end connected to an anode of the thyristor 17. The protective resistor 22 has one end connected to the gate of the thyristor 17 and the other end connected to a cathode of the thyristor 17.
In the present embodiment, as an example, a resistance value of the resistor 16 is set to 10Ω, a resistance value of the auxiliary resistor 21 is set to 820Ω, and a resistance value of the protective resistor 22 is set to 1 kΩ. However, they are not restricted to these, and proper values thereof may be adopted according to rated voltage, specifications of the lamp 15, or the like. A resistance value of internal equivalent resistance between the anode and the cathode when the thyristor 17 is in an on-state is a value smaller enough than a resistance value of the resistor 16. For example, when a current of 2 A is flowing with a voltage drop of 0.8V, the resistance value of internal equivalent resistance is 0.4Ω. Note that hereinafter, voltage across the resistor 16 is represented by Vr, and a gate current of the thyristor 17 is represented by Ig.
In the circuit in
Next, the detailed circuit operation from start-up of the lighting device 1 to attainment of a steady operation time will be explained. Note that hereinafter, an example will be explained in which the lamp 15 goes out once because of an unstable operation mainly due to a large amount of enclosed mercury, when shifting from the initial arc discharge of the lamp 15 to rated arc discharge thereof.
The horizontal axes of
First, a switch of not-shown system power of the lighting device 1 is turned on, and the DC-DC converter 12 operates to generate voltage on the capacitor 13 (time a). This voltage is for example 400V. By the voltage, the ignitor 14 is activated, and high voltage is applied to the lamp 15. Period a-b is a period from voltage-output by the DC-DC converter 12 to high voltage-output by the ignitor 14. This period, which depends on the circuitry of the ignitor 14, is about several milliseconds. Period f-g mentioned later is also the same. Period b-c is a period from start-up of an operation of the ignitor 14 to dielectric breakdown of the lamp 15. This period, which depends on a state of the lamp 15, is approximately from tens of milliseconds to hundreds of milliseconds. In this period dielectric breakdown is caused by applied high voltage. At a moment when dielectric breakdown occurs, the voltage shown in
The glow discharge begins at time c or later, and lamp voltage VL decreases gradually toward time d, for example from 200V to 100V. For period c-d, the lamp current IL has little change, and is 0.5 A, for example. This period, which depends on a state, a type, etc. of the lamp 15, is about tens of milliseconds. Also for this period, the voltage Vr across the resistor 16 and the gate current Ig of the thyristor 17 also increase gradually. At time d, when the lamp voltage VL decreases to about 100V, the lamp 15 shifts from the glow discharge to the arc discharge. At time e, the lamp voltage falls to about 10V rapidly, and the lamp current IL tends to flow infinitely.
Here, the lamp current IL is controlled by an operation of a current limiter of the DC-DC converter 12, and in this example 2 A is considered as an upper limit. Period d-e is a momentary period of 100 microseconds, for example. For period d-e, the gate current Ig of the thyristor 17 rises with the rise of the voltage Vr across the resistor 16. And the breakover of the thyristor 17 occurs at the operating point which is set by the voltage Vak between the anode and the cathode and a gate current Ig of the thyristor 17. Here, the auxiliary resistor 21 is assumed to be 820Ω. At time d, the gate current Ig is 6 mA (=10Ω×0.5 A/820Ω), and at time e the gate current Ig is 24 mA (=10Ω×2 A/820Ω). When the thyristor 17 is a thyristor which has breakover at 20 mA, the breakover occurs when the lamp current is about 1.6 A. That is, in the course of period d-e, the thyristor 17 is turned on by the breakover, and a current begins to flow between the anode and the cathode of the thyristor 17. As mentioned above, the resistor 16 suppresses a rush current and the thyristor 17 is turned on automatically by the lamp current. Therefore, it is not necessary to carry out complicated control from the outside. Although the resistor 16 and the thyristor 17 are inserted on a low potential side (side on which the potential is near a ground) of the lamp 15 in
After the thyristor 17 is turned on, the voltage Vak between the anode and the cathode of the thyristor 17 is 0.8V, for example. As shown in
For period e-f, the initial arc discharge is maintained, the lamp current is in a controlled state at 2 A by current limiting of the DC-DC converter 12. Usually lamp voltage rises gradually like in a below-mentioned period k-l, the DC-DC converter 12 starts constant power operation, and the lamp current decreases. However, depending on circumstances, discharge may go out at the initial arc discharge time. In
For example, when a gate current Ig required for the breakover of the thyristor 17 is 40 mA, a resistance value of the auxiliary resistor 21 may be set to 390Ω (40 mA =10Ω×1.6 A/390Ω). That is, a timing of the breakover can be adjusted by a resistance value of the auxiliary resistor 21, and parameters are not linked to each other complicatedly. In the above-mentioned operations, a lamp current flows through the resistor 16 during glow discharge (period c-d and period h-i). The loss is 5 W in a case of 10Ω and 0.5 A. Since this period is tens of milliseconds, a resistance may be selected which has a rating capable of losing 5 W in an instant.
Moreover, although in the above-mentioned constitution, a timing when the thyristor 17 is turned on during period d-e is explained, the thyristor 17 may be designed so as to turn on during period c-d. For example, it is assumed, as the conditions for causing the thyristor 17 to shift from off to on, when the lamp current during the glow discharge time is 0.5 A, that the voltage Vak between the anode and the cathode is 15 V, and the gate current Ig is 20 mA. A resistance value of the resistor 16 is selected to 30Ω. At time c, while a rush current is suppressed by the resistor 16, a voltage drop of 15V (=0.5 A×30Ω) occurs across the resistor 16 with a glow current of 0.5 A. When a resistance value of the auxiliary resistor 21 is selected at 750Ω, the gate current Ig flows by 20 mA (=15V/750Ω) with this voltage. Therefore, the voltage Vak between the anode and the cathode becomes 15V, the gate current Ig becomes 20 mA, and the thyristor 17 is turned on during period c-d. A loss in a case of a current of 0.5 A flowing through the resistor 16 is 7.5 W (=0.5 A×0.5 A×30Ω). As mentioned above, a constitution may be designed in which the thyristor 17 is turned on during the glow discharge. When a current of 2 A of initial arc discharge flows through the resistor 16, a loss of the resistor 16 increases, thereby increasing a size of the resistor 16 considering a permissible loss. In order to avoid such a situation, the resistance values of the resistor 16 and the auxiliary resistor 21 may be selected so that the thyristor 17 is turned on during period c-e. Moreover, since the resistor 16 and the auxiliary resistor 21 do not act on temporary going-out of light during the lighting time, a constitution may be designed so as to turn on the thyristor 17. A main purpose of the protective resistor 22 is protection against overvoltage of the gate of thyristor 17, and the protective resistor 22 does not act on the operations of the present embodiment. Therefore, according to the specifications of the thyristor 17, a resistance value of the protective resistor 22 may be set to 1 kΩ to 10 kΩ, for example. When protection for the gate is not required, the protective resistor 22 may be omitted.
After time j, the voltage Vak between the anode and the cathode of the thyristor 17 is 0.8V, for example. When a current of 2 A flows, internal equivalent resistance between the anode and the cathode of the thyristor 17 in an on-state is 0.4Ω (=0.8V/2 A). As shown in
Embodiment 2 relates to an embodiment in which reduces more power consumption by additionally connecting a switching element in parallel and turning on the switching element after elapse of a predetermined time.
The FET 18 has a drain connected to the lamp 15, a source connected between the ignitor 14 and resistor 16, and a gate connected to the switching controller 181. The switching controller 181 alternatively outputs to the FET 18 a low signal of 0V or a high signal of 5V, for example. When a low signal is outputted, the FET 18 is turned off, and when a high signal is outputted, the FET 18 is turned on. The current detecting circuit 183 is a circuit which detects a lamp current, and outputs a detected current signal to the timer 182. Note that although the present embodiment is an embodiment in which a current which flows through the thyristor 17 is detected by the current detecting circuit 183 and current detecting resistor 184, the constitution is not restricted to this, and a signal related to voltage applied to the thyristor 17, voltage applied to the resistor 16, or a current which flows through the resistor 16 may be outputted to the timer 182. Detection results of the voltage and current of the respective parts may not be linked with the timer 182, and the detection results may be linked with a switch of system power. The DC-DC converter 12 contains a circuit which detects a lamp current in order to control power to be supplied to the lamp 15. The current detecting circuit 183 shown in
The timer 182 stores a threshold value in an internal memory (not shown), and starts clocking when a signal related to a current outputted from the current detecting circuit 183 is smaller than the threshold value. In the examples of
A resistance value of an internal resistance of the FET 18 is about 0.2Ω, and is smaller than a resistance value of 0.8Ω of internal resistance of the thyristor 17. In this case, a current which has flowed through the thyristor 17 flows through the FET 18 mostly, and the thyristor 17 is turned off, thereby decreasing power consumption to 0.2 W when a lamp current IL of 1 A flows. Moreover, the voltage Vr across the resistor 16 changes from 0.8V to 0.2V by turning on the FET 18. When a not-shown system power of the lighting device 1 is turned off, clocking of the timer 182 is reset to 0, a signal outputted from the switching controller 181 is also reset to a low signal, and the FET 18 is turned off. Note that in the present embodiment, although the FET 18 is turned on after elapse of a predetermined time after breakover of the thyristor 17, the FET 18 may be turned on after the lamp 15 starts a stable rated operation and then a sufficient time has passed. In this case, the FET 18 is turned on after turning on the not-shown system power, for example, after 30 seconds. A resistance value of the current detecting resistor 184 is for example 50 milliΩ, and does not affect the on/off operation of the thyristor 17.
Embodiment 2 is constituted like the above, since other constitutions and operations are the same as those of Embodiment 1, the same reference numbers are given to the corresponding portions, and the detailed explanation is omitted.
The above mentioned lighting device 1 is applied to a projector.
The main control section 39 controls the above mentioned respective parts of hardware according to a program stored in a not-shown memory. A video signal is inputted to the video signal processing section 391. The video signal processing section 391 performs processing on the video signal, such as synchronizing separation and scaling, etc. and outputs a processed video signal to the image forming device control circuit 37. In the projector 30, white light emitted from the lamp 15 is condensed, and is emitted to the color wheel 32. The color wheel 32 is constituted as a disk on which a red light filter, a blue light filter and a green light filter are arranged in a circumferential direction thereof, and is rotated at a high speed by a not-shown drive motor.
The color filters are inserted one by one in an optical path of light emitted from the lamp 15 with rotation of the color wheel 32, and the white light irradiating the color wheel 32 is separated to each homogeneous light of red light, green light and blue light by time sharing. And each separated homogeneous light is sent to the reflecting mirror 321, and irradiates the DMD 36. Note that instead of the DMD, a liquid crystal panel may be used. Drive of the DMD 36 is controlled by the image forming device control circuit 37. The image forming device control circuit 37 drives the DMD 36 according to the inputted video signal. Specifically, by turning on or turning off each cell and minute mirror of the DMD 36 according to the inputted video signal, the irradiating homogeneous light is reflected pixel by pixel, and is light-modulated, thereby forming an image light. The formed image light is incident on the projector lens 38, and is enlarged and projected to a not-shown screen etc. by the projector lens 38.
The lighting device 1 controls turning on and off of the lamp 15. The fan 33 is a component for cooling the inside of the lamp 15 or the projector 30, and driven by a not-shown motor. Note that although in the present embodiment the configuration is explained in which the lighting device 1 is applied to the projector 30, the configuration is not restricted to this, and may be applied to general illumination, a head lamp of a car, etc.
Embodiment 3 is constituted like the above, and since other constitutions and operations are the same as those of Embodiments 1 and 2, the same reference numbers are given to the corresponding portions, and the detailed explanation is omitted.
Embodiment 4 is constituted like the above, and since other constitutions and operations are the same as those of Embodiments 1 and 3, the same reference numbers are given to the corresponding portions, and the detailed explanation thereof is omitted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-321653 | Nov 2006 | JP | national |
(US only) This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP2007/71129 which has an International filing date of Oct. 30, 2007 and designated the United States of America.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/071129 | 10/30/2007 | WO | 00 | 5/28/2009 |
