JP4553872B2 - Discharge lamp lighting circuit - Google Patents

Description

  The present invention relates to a lighting circuit for a discharge lamp such as a cold cathode tube such as an illumination fluorescent lamp or a backlight of a liquid crystal display device.

  Conventionally, a discharge lamp lighting circuit including a boost chopper circuit for power factor improvement and an inverter circuit is used (see Patent Document 1).

The configuration of the conventional discharge lamp lighting circuit shown in Patent Document 1 will be described with reference to FIG.
FIG. 1 is a circuit diagram showing the configuration of the entire discharge lamp lighting circuit. In FIG. 1, a diode bridge 34 full-wave rectifies a commercial AC power supply 32, and a chopper 35 and a smoothing capacitor 38 on the output side of the diode bridge 34 constitute a chopper circuit and outputs a boosted voltage. The inverter switch elements Q1 and Q2, the capacitor 40, and the induction reactor 41 are configured such that the resonant capacitor 42 forms an inverter circuit, and applies a high-frequency voltage generated by turning on and off the inverter switch elements Q1 and Q2 to the discharge lamp 37.

Thus, the power factor of the discharge lamp lighting circuit can be improved by directly inputting the rectified voltage of the commercial AC power supply to the boost chopper circuit.
JP 2001-110588 A

  The main loss of the chopper 35 is caused by the switching element, and it is necessary to adopt a heat dissipation structure in order to suppress the temperature rise of the switching element. This is inconvenient in terms of reduction in size and cost.

  On the other hand, in order to suppress the heat generation of this switching element, it is effective to configure a circuit so that a plurality of switching elements are connected in parallel and turned on / off simultaneously. However, when a plurality of switching elements are connected in parallel as described above, the following problems arise.

  That is, even if one switching element of the plurality of switching elements stops operating due to a failure or the like, the chopper circuit can be operated for a while, so there is almost no change in input / output characteristics of the entire discharge lamp lighting circuit. It is conceivable that the switching element continues to be used despite the failure. In this way, when any one of the plurality of switching elements fails, the loss in the remaining normal switching elements increases, so heat generation increases, and one of the plurality of switching elements stops operating. However, measures such as preliminarily providing a heat dissipation structure are necessary so that temperature rise does not become a problem.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a discharge lamp lighting circuit that solves the problem at the time of failure when a plurality of switching elements of a step-up chopper circuit are provided and that is reduced in size and cost.

(1) A discharge lamp lighting circuit according to the present invention includes a choke coil connected in series to an input power supply, a plurality of switching elements connected in parallel to each other to excite the choke coil with an input current when conducting, and a plurality of these And a capacitor that charges the discharge voltage from the choke coil when the switching element is turned off, and a boost chopper circuit that outputs a power supply voltage obtained by boosting the input power supply voltage, and inputs an output voltage of the boost chopper circuit and a high frequency Including an inverter switch element that performs switching, and an induction reactor provided between the inverter switch element and the discharge lamp, and an inverter circuit that outputs a drive voltage to the discharge lamp,
Among the plurality of switching elements, the non-inspection target switching element is kept in the off state, the inspection target switching element is controlled to be turned on / off, the output voltage of the boost chopper circuit is detected, and the inspection is performed based on the voltage It is characterized by comprising a failure detection means for detecting a failure of the target switching element.

  (2) Further, the discharge lamp lighting circuit according to the present invention is an inverter circuit stop means for stopping the operation of the inverter circuit when the failure detection means detects a failure of any one of the plurality of switching elements. Is provided.

  (3) Moreover, the said failure detection means shall operate | move at the time of the preheating of the filament of the said discharge lamp, for example.

  According to the present invention, an inspection is made among a plurality of switching elements of the boost chopper circuit by utilizing the fact that the output voltage is lowered without the boost chopper circuit operating normally by keeping the failed switching element off. Since a switching element failure is detected based on the output voltage when the step-up chopper circuit is operated with the switching elements other than the target switching element kept in the OFF state, the inverter is based on the failure detection result. The operation of the circuit can be stopped, and the problem that any one of the plurality of switching elements continues to be used with a failure can be avoided.

  Further, by configuring so that the operation of the inverter circuit is automatically stopped when a failure is detected, overheating of the switching element of the boost chopper circuit can be minimized.

  In general, the switching element has a high probability of failure at the time of transition such as when driving is started. However, the failure detection can be efficiently performed by performing the failure detection at the time of preheating the filament of the discharge lamp. Moreover, when the filament is preheated, even if the output voltage of the step-up chopper circuit fluctuates due to stopping the operation of the switching element for failure detection, it does not appear as a change in the amount of light. Does not occur.

<< First Embodiment >>
A discharge lamp lighting circuit according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is an overall block diagram of the discharge lamp lighting circuit. As shown in FIG. 2, a diode bridge DB for full-wave rectifying the commercial AC power supply AC is provided at the input of the commercial AC power supply AC. On the output side of the diode bridge DB, a boost chopper circuit 20 including a choke coil L1 connected in series, two switching elements Tr1 and Tr2, each connected to a shunt, a rectifier diode D5, and a smoothing capacitor C4 is configured. The step-up chopper circuit 20 outputs 360V under normal conditions.

  A switching element drive circuit 13 for driving the switching elements Tr1 and Tr2 is provided at the gates of the switching elements Tr1 and Tr2. The microcomputer 10 normally turns on and off the switching elements Tr1 and Tr2 by providing a rectangular wave signal to the switching element drive circuit 13.

  An AC input detection circuit 11 is provided between the commercial AC power line and ground, and the microcomputer 10 detects the presence or absence of AC input based on this detection signal.

  A choke coil output detection circuit 12 is provided on the secondary side of the choke coil L1, and the microcomputer 10 controls the ON timing of the switching elements Tr1 and Tr2 based on the detection signal of the detection circuit 12.

  The control circuit power supply circuit 14 receives the output voltage (360 V) of the step-up chopper circuit, and outputs the power supply voltages (14 V and 5 V) for control circuits such as the microcomputer 10 and the half bridge drive circuit 17.

  The connector of the discharge lamp FL is provided with an inverter circuit 21 including inverter switch elements Tr3 and Tr4, an induction reactor L2, and capacitors C18 and C19.

  A half bridge drive circuit 17 is connected to the inverter switch elements Tr3 and Tr4 of the inverter circuit 21. The half bridge drive circuit 17 alternately turns on and off the inverter switch elements Tr3 and Tr4 based on a control signal from the microcomputer 10.

  The life / end-of-life detection circuit 18 detects the current flowing through the filament of the discharge lamp FL and the voltage between the electrodes (tube voltage). The microcomputer 10 detects the life and end of the discharge lamp FL based on the signal from the life / end detection circuit 18.

  The power supply voltage detection circuit 15 detects the output voltage (360 V) of the boost chopper circuit 20. The microcomputer 10 detects the output voltage of the boost chopper circuit 20 based on the detection signal from the power supply voltage detection circuit 15.

  The remote control light receiving circuit 16 is a circuit that receives a transmission signal from the infrared remote control, and the microcomputer 10 performs dimming control and lighting / extinguishing control according to the detection signal from the remote control light receiving circuit 16.

  In this way, a plurality (two in the example of FIG. 2) of switching elements of the step-up chopper circuit are connected in parallel and simultaneously turned on / off to reduce the current flowing through each switching element. Temperature rise can be suppressed.

  FIG. 3 is a circuit diagram of the switching element drive circuit 13 and the first and second switching elements Tr1 and Tr2 shown in FIG. In FIG. 3, a switching element drive signal output circuit 13a is connected to the gates of the first switching element Tr1 and the second switching element Tr2. The switching element drive signal output circuit 13a is connected to a first switching element stop circuit 13b and a second switching element stop circuit 13c, respectively.

First, consider the case where both the Tr1 stop signal Sg1 and the Tr2 stop signal Sg2 are at a low level.
When the switching control signal Ss output from the microcomputer 10 shown in FIG. 2 is at a low level, the Tr11 is turned off, and the Tr10 is turned on accordingly. When Tr10 is turned on, the base potential of Tr6 is lowered and Tr6 is turned off. At the same time, Tr7 is turned on when the base potential of Tr7 is lowered. As a result, the gate potential of the first switching element Tr1 is lowered and the Tr1 is turned off. When Tr10 is turned on, the base potential of Tr9 is lowered and Tr9 is turned on. As a result, the gate potential of the second switching element Tr2 is lowered and Tr2 is also turned off. That is, when the switching control signal Ss is at a low level, both Tr1 and Tr2 are turned off.

  When the switching control signal Ss is at a high level, contrary to the above operation, Tr11 is turned on, and accordingly Tr10 is turned off. When Tr10 is turned off, the base potential of Tr6 is increased and Tr6 is turned on. At the same time, Tr7 is turned off by increasing the base potential of Tr7. As a result, the gate potential of the first switching element Tr1 rises and Tr1 is turned on. Further, when Tr10 is turned off, the base potential of Tr9 is increased and Tr9 is turned off. Along with this, the gate potential of the second switching element Tr2 becomes high and Tr2 is also turned on. That is, Tr1 and Tr2 are both turned on when the switching control signal Ss is at a high level.

  Thus, when both the Tr1 stop signal Sg1 and the Tr2 stop signal Sg2 are at the low level, the Tr1 and Tr2 are simultaneously turned on / off based on the switching control signal Ss.

Next, consider a case where the Tr1 stop signal Sg1 is at a high level.
When the Tr1 stop signal Sg1 becomes a high level, the Tr24 is turned on and the base potential of the Tr7 is lowered, whereby the Tr7 is turned on, and accordingly, the first switching element Tr1 is turned off. In this state, even if the switching control signal Ss becomes high level, Tr1 remains off, so that the first switching element Tr1 remains off.

  Further, when the Tr2 stop signal Sg2 becomes a high level, Tr23 is turned on and the base potential of Tr9 is lowered, whereby Tr9 is turned on, and accordingly, the second switching element Tr2 is turned off. In this state, even if the switching control signal Ss becomes high level, Tr2 remains off, so that the second switching element Tr2 remains off.

  Therefore, when the Tr1 stop signal Sg1 is at a high level and the Tr2 stop signal Sg2 is at a low level, only Tr2 is turned on / off based on the switching control signal Ss. Further, when the Tr1 stop signal Sg1 is at a low level and the Tr2 stop signal Sg2 is at a high level, only Tr1 is turned on / off based on the switching control signal Ss.

  FIG. 4 is a waveform diagram showing the relationship between the current of the choke coil L1 shown in FIG. 2, the switching control signal Ss, and the choke coil voltage detection signal Sc.

  The microcomputer 10 has a programmable one-shot pulse generation mode, and outputs a one-shot pulse for a predetermined time by an internal trigger and an external trigger.

  When the microcomputer 10 starts up the step-up chopper circuit, as shown at t0 in FIG. 4, the microcomputer 10 generates a one-shot pulse that lasts for a predetermined time (Ton) as the switching control signal Ss. As a result, the switching elements Tr1 and Tr2 are turned on, and the current flowing through the choke coil L1 increases. When the switching control signal Ss becomes a low level at t1 after the lapse of a certain time (Ton), the current of the choke coil L1 falls. Thereafter, the current of the choke coil L1 changes (turns back) at t2, thereby inverting the level of the choke coil voltage detection signal Sc. The microcomputer 10 generates, as the switching control signal Ss, a one-shot pulse that lasts for a predetermined time (Ton) with the rising of the choke coil voltage detection signal Sc as an external trigger. Thereafter, the boost chopper circuit 20 shown in FIG. 2 is operated by repeating the same processing.

  The microcomputer 10 controls the high-level period Ton of the switching control signal Ss based on the detection signal from the power supply voltage detection circuit 15, and stabilizes the output voltage (360V) of the boost chopper circuit 20.

Next, specific processing contents of the microcomputer 10 will be described based on the flowcharts shown in FIGS.
FIG. 5 is a flowchart showing a processing procedure for stabilizing the output voltage of the boost chopper circuit. This operation is performed by a timer interrupt every 1 ms, for example. Here, PFC_OPERATE is a flag set by the main program, and is in a stopped state when PFC_OPERATE = 0 and in an operating state when PFC_OPERATE = 1.

  As shown in FIG. 5, first, if PFC_OPERATE = 1, that is, the mode in which the boost chopper circuit is operated, the state of the flag F_PFC_OP is determined (S11 → S12). This flag F_PFC_OP indicates a state in which a one-shot pulse is generated by an external trigger, and is initially in a reset state. Therefore, first, the timer Z is started (a one-shot pulse is generated) and the flag F_PFC_OP is set (S11 → S12 → S13 → S14). This timing corresponds to t0 shown in FIG.

  After the flag F_PFC_OP is set, as shown at t2 in FIG. 4, a one-shot pulse is generated triggered by the rise of the choke coil voltage detection signal Sc. When this flag F_PFC_OP is in a set state, the detection voltage by the power supply voltage detection circuit 15 shown in FIG. S12 → S15). If this value does not reach the value corresponding to 360 V, the timer set value TZPR is increased by a predetermined amount (S16 → S17). If the value exceeds 360 V, the timer setting value TZPR is decreased by a predetermined amount (S18 → S19). Since the set value TZPR of the timer is a value that determines the width of the one-shot pulse, the output voltage of the boost chopper circuit 20 is stabilized by repeating the above processing.

  If the flag PFC_OPERATE is set to 0 by the main program, the timer Z is stopped and the flag F_PFC_OP is reset (S20 → S21). As a result, the operation of the boost chopper circuit is stopped.

FIG. 6 is a flowchart showing a processing procedure of inverter control executed every 1 ms by the timer interruption.
Here, INV_OPERATE is a flag set by the main program. When INV_OPERATE = 0, the inverter is stopped (discharge lamp is turned off), and when INV_OPERATE = 1, the inverter is operated (discharge lamp is turned on). INV_OP_MODE is a status indicating the mode of the inverter. In this inverter control, the time from the start is counted, and the mode is switched in the order of “preheating” → “startup” → “lighting”. First, if INV_OP_MODE = “stop”, INV_OP_MODE = “preheating”, the inverter output frequency is set to the preheating frequency, the inverter is operated, and the timer INV_TMC is reset (S31 → S32 → S33 → S34). . Here, the output frequency is set by an output frequency setting signal Sf from the microcomputer 10 to the half bridge drive circuit 17. Further, the inverter circuit is operated by outputting the inverter control signal Si from the microcomputer 10 to the half bridge drive circuit 17.

  If INV_OP_MODE = “preheat”, the analog voltage signal from the life / end detection circuit 18 is read, the lamp life (filament breakage) and end are determined according to the A / D conversion value, and if necessary The inverter operation is stopped (S35 → S36).

  After that, if the timer INV_TMC is 0.4 seconds or less, the first switching element Tr1 of the step-up chopper circuit 20 is stopped and only the second switching element Tr2 is operated (only Tr2 is turned on / off) (S37 → S38). This is performed by setting the Tr1 stop signal Sg1 to the high level and the Tr2 stop signal Sg2 to the low level from the microcomputer 10 to the switching element drive circuit 13.

  Subsequently, if the output voltage PFC_OUT_LV of the boost chopper circuit 20 is 301 V or higher, the timer INV_TMC is counted (S39 → S40 → S41).

  If Tr2 fails and does not turn on / off normally, the output voltage PFC_OUT_LV of the step-up chopper circuit 20 decreases to less than 301V. If the output voltage PFC_OUT_LV of the step-up chopper circuit 20 becomes less than 301V, INV_OP_MODE is set to “abnormal stop” (S39 → S46). If INV_OP_MODE = “abnormal stop”, the inverter control signal Si from the microcomputer 10 to the half-bridge drive circuit 17 is set to high level to stop the operation of the inverter circuit (S32 → S47). Thus, it is possible to avoid an abnormal state in which the boost chopper circuit is operated only with Tr1 and proceeds after the start.

  When the timer INV_TMC exceeds 0.4 seconds, both Tr1 and Tr2 are operated (S42 → S43). This is done by setting both the Tr1 stop signal Sg1 and the Tr2 stop signal Sg2 to a low level. By this processing, both Tr1 and Tr2 are not stopped due to a delay in circuit operation or the like, and a stable operation is performed.

  Thereafter, when the timer INV_TMC becomes 0.5 seconds or longer, the second switching element Tr2 of the boost chopper circuit 20 is stopped, and only the first switching element Tr1 is operated (only Tr1 is turned on / off) (S42 → S44). This is performed by setting the Tr2 stop signal Sg2 to the high level and the Tr1 stop signal Sg1 to the low level from the microcomputer 10 to the switching element drive circuit 13.

  Subsequently, if the output voltage PFC_OUT_LV of the boost chopper circuit 20 is 301 V or higher, the timer INV_TMC is counted (S39 → S40 → S41).

  If Tr1 fails and does not turn on / off normally, the output voltage PFC_OUT_LV of the step-up chopper circuit 20 drops to less than 301V. If the output voltage PFC_OUT_LV of the step-up chopper circuit 20 becomes less than 301V, INV_OP_MODE is set to “abnormal stop” (S39 → S46). If INV_OP_MODE = “abnormal stop”, the inverter operation is stopped by setting the inverter control signal Si from the microcomputer 10 to the half-bridge drive circuit 17 to a high level (S32 → S47). As a result, it is possible to avoid an abnormal state in which the operation proceeds after the start while the boost chopper circuit is operated only by Tr2.

  If both Tr1 and Tr2 operate normally, the output voltage of the step-up chopper circuit maintains 301V or higher. Thereafter, when the timer INV_TMC has passed for 1 second or more, the timer INV_TMC is reset and the operation mode is shifted to the start mode (S41 → S45).

If INV_OP_MODE is “start”, start processing is performed (S48 → start processing). In this starting process, the output frequency of the inverter circuit 21 is set to the starting frequency, and the inverter circuit 21 is operated.
If it is determined in the start-up process that the start is successful, INV_OP_MODE is switched to “lighting”. Thus, the process proceeds to the lighting process (S49 → lighting process). In this lighting process, the output frequency of the inverter circuit 21 is set so that the discharge lamp is lit with the light intensity at the stage where the light control is set.

Step S50 is a process in a mode in which INV_OP_MODE is other than “abnormal stop”, “stop”, “preheat”, “start”, and “lighting”.
If INV_OPERATE = 0 is set in the main program, INV_OP_MODE is set to “stop” and the inverter circuit 21 is stopped (S31 → S51 → S52).

  As described above, failure detection of the first and second switching elements Tr1 and Tr2 of the step-up chopper circuit 20 is performed when the filament is preheated. The operation of the inverter circuit 21 is stopped. Thereby, the problem of overheating of the switching element Tr1 or Tr2 can be avoided.

  In addition, when the filament is preheated, even if the output voltage of the boost chopper circuit fluctuates due to the operation of the switching element being stopped to detect a failure, it does not appear as a change in the amount of light. Does not occur.

  Further, since the operation of the inverter circuit 21 is stopped instead of stopping the operation of the boost chopper circuit at the time of an abnormal stop, the power supply voltage to the microcomputer 10 and the half bridge drive circuit 17 can be continuously supplied. Necessary processing can be continued. Thus, in the state where the operation of the inverter circuit 21 is stopped, the average value of the current flowing through the switching elements Tr1 and Tr2 is low, so that the problem of overheating of the switching elements Tr1 and Tr2 does not occur.

  However, when the operation of the microcomputer may be stopped immediately at the time of abnormal stop, the operation of not only the boost chopper circuit but also the inverter circuit 21 may be stopped at the time of abnormal stop.

<< Second Embodiment >>
In the example shown in FIG. 6, the presence / absence of failure of the switching elements Tr1 and Tr2 of the boost chopper circuit 20 is detected during preheating of the filament. However, in the second embodiment, the failure detection of the switching element is performed other than the preheating operation. For example, it is performed during lighting. FIG. 7 is a flowchart showing the processing contents.

  This process is repeated at a predetermined cycle during the lighting process. First, the analog voltage signal from the life / end detection circuit 18 is read, the end of the lamp is determined according to the A / D conversion value (lamp voltage), and the inverter circuit 21 is stopped if necessary (S61).

  Thereafter, if the timer INV_TMC is 0.4 seconds or less, the first switching element Tr1 of the step-up chopper circuit 20 is stopped and only the second switching element Tr2 is operated (S62 → S63).

  Subsequently, if the output voltage PFC_OUT_LV of the boost chopper circuit 20 is 301 V or higher, the timer INV_TMC is counted (S64 → S65).

  If Tr2 fails and does not turn on / off normally, the output voltage PFC_OUT_LV of the step-up chopper circuit 20 decreases to less than 301V. When the output voltage PFC_OUT_LV of the step-up chopper circuit 20 becomes less than 301V, INV_OP_MODE is set to “abnormal stop” (S64 → S66). If INV_OP_MODE = “abnormal stop”, the inverter control signal Si from the microcomputer 10 to the half bridge drive circuit 17 becomes high level, and the operation of the inverter circuit 21 is stopped. As a result, it is possible to avoid an abnormal state in which the step-up chopper circuit is continuously operated only by Tr1.

  When the timer INV_TMC exceeds 0.4 seconds, both Tr1 and Tr2 are operated (S68 → S69). This is done by setting both the Tr1 stop signal Sg1 and the Tr2 stop signal Sg2 to a low level. By this processing, both Tr1 and Tr2 are not stopped due to a delay in circuit operation or the like, and a stable operation is performed.

  Thereafter, when the timer INV_TMC becomes 0.5 seconds or more, the second switching element Tr2 of the boost chopper circuit 20 is stopped, and only the first switching element Tr1 is operated (only Tr1 is turned on / off) (S68 → S70).

  Subsequently, if the output voltage of the boost chopper circuit 20 is 301 V or higher, the timer INV_TMC is counted (S64 → S65).

  If Tr1 fails and does not turn on / off normally, the output voltage PFC_OUT_LV of the step-up chopper circuit 20 drops to less than 301V. When the output voltage PFC_OUT_LV of the step-up chopper circuit 20 becomes less than 301V, INV_OP_MODE is set to “abnormal stop” (S64 → S67). If INV_OP_MODE = “abnormal stop”, the inverter control signal Si from the microcomputer 10 to the half bridge drive circuit 17 becomes high level, and the operation of the inverter circuit 21 is stopped. As a result, it is possible to avoid an abnormal state in which the step-up chopper circuit is continuously operated only by Tr2.

  Thereafter, if the timer INV_TMC exceeds 0.9 seconds, both the first switching element Tr1 and the second switching element Tr2 of the boost chopper circuit 20 are operated (S68 → S69). This shifts to normal operation.

  When the timer INV_TMC reaches 600000 (10 minutes), the value of the timer INV_TMC is reset to 0.

  In this way, the failure detection of the switching elements Tr1 and Tr2 of the step-up chopper circuit 20 can be detected even during lighting, and the inverter circuit 21 can be stopped when one of them fails.

  In the first and second embodiments described above, the boost chopper circuit including the two switching elements Tr1 and Tr2 is configured. However, the boost chopper circuit is configured by connecting three or more switching elements in parallel. It can be applied to the same as above. That is, it is possible to detect a failure similarly by operating only the switching element to be inspected and detecting whether or not the output voltage of the step-up chopper circuit is lowered with the other switching elements stopped.

It is a circuit diagram which shows the structure of the discharge lamp lighting circuit shown by patent document 1. FIG. It is a block diagram of the discharge lamp lighting circuit which concerns on 1st Embodiment. FIG. 3 is a circuit diagram of a boost chopper circuit portion in FIG. 2. 4 is a waveform showing the operation of the boost chopper circuit. It is a flowchart which shows the processing content of the microcomputer of the discharge lamp lighting circuit. It is a flowchart which shows the processing content of the microcomputer of the discharge lamp lighting circuit. It is a figure which shows the content regarding the failure detection of the switching element in the pressure | voltage rise chopper circuit which the microcomputer of the discharge lamp lighting circuit which concerns on 2nd Embodiment processes.

Explanation of symbols

10-microcomputer 11-AC input detection circuit 12-choke coil output detection circuit 13-switching element drive circuit 14-control circuit power supply circuit 15-power supply voltage detection circuit 16-remote control light receiving circuit 17-half bridge drive circuit 18-life Terminal detection circuit AC-commercial AC power supply DB-diode bridge L1-choke coil Tr1-first switching element Tr2-second switching element Tr3, Tr4-inverter switching element L2-inductive reactor C19-resonance capacitor FL-discharge lamp Ss- Switching control signal Sg1-Tr1 stop signal Sg2-Tr2 stop signal Si-inverter control signal Sf-inverter frequency control signal

Claims (3)

A choke coil connected in series to the input power source, a plurality of switching elements connected in parallel to excite the choke coil with an input current when conducting, and a discharge from the choke coil when these switching elements are off A boost chopper circuit that outputs a power supply voltage obtained by boosting an input power supply voltage, an inverter switch element that inputs an output voltage of the boost chopper circuit and performs high-frequency switching, and the inverter switch element. A discharge lamp lighting circuit including an induction reactor provided between the discharge lamp and an inverter circuit that outputs a driving voltage to the discharge lamp;
Among the plurality of switching elements, the non-inspection target switching element is kept in the off state, the inspection target switching element is controlled to be turned on / off, the output voltage of the boost chopper circuit is detected, and the inspection is performed based on the voltage A discharge lamp lighting circuit comprising a failure detection means for detecting a failure of a target switching element.   2. The discharge lamp lighting circuit according to claim 1, further comprising an inverter circuit stop unit that stops the operation of the inverter circuit when the failure detection unit detects a failure of any one of the plurality of switching elements.   The discharge lamp lighting circuit according to claim 1 or 2, wherein the failure detection means operates during preheating of the filament of the discharge lamp.

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