JPH0878178A - Lighting circuit of discharge lamp - Google Patents

Abstract

PURPOSE: To improve the detecting sensitivity related to the load short-circuit detection of a discharge lamp. CONSTITUTION: A lighting circuit 1 has an igniter circuit 0 for generating a starting pulse to a metal halide lamp 11. A short-circuit detecting circuit 15 is provided, whereby the output voltage Vo of a DC booster circuit 7 is detected as the corresponding signal to the lamp voltage of the metal halide lamp 11. When the level of Vo does not reach a prescribed judgment level or more before a detecting period set during the period from the current-carrying start to the metal halide lamp 1 to the lighting of the metal halide lamp 1 passed, it is judged that the metal halide lamp 11 is laid in the load short-circuit state, a signal is transmitted from the short-circuit detecting circuit 15 to a power source interrupting relay circuit 6 through a hold circuit 17, and a relay contact 6a is opened to interrupt the power supply to the metal halide lamp 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to provide a novel discharge lamp lighting circuit for the purpose of improving the detection sensitivity in detecting a load short circuit of a discharge lamp.

[0002]

2. Description of the Related Art Recently, small metal halide lamps have been attracting attention as a light source to replace incandescent light bulbs. As a configuration of a lighting circuit for a vehicle metal halide lamp, for example,
It is known that a DC power supply is used as a power supply, a DC input voltage is boosted by a booster circuit, then converted into a sine wave or rectangular wave AC voltage by a DC-AC converter circuit, and then applied to a metal halide lamp. There is.

If the metal halide lamp falls into a load short-circuit state and the lighting operation is continued as it is, the possibility of causing heat generation or ignition of the short-circuited portion, heat generation or ignition of electronic components in the lighting circuit is increased. , Very dangerous. Further, when the short-circuited portion is caused by some damage, there is a possibility that a part of the human body may come into contact with the short-circuited portion, which increases the risk of causing an electric shock accident.

Therefore, safety measures have been taken such as detecting the short-circuit state of the metal halide lamp and stopping the operation of the lighting circuit.

FIG. 8 shows an example of such a lighting circuit a. The direct current voltage of the battery b is inputted to the direct current boosting circuit e through the lighting switch c and the protection circuit d, and then the latter stage. The AC is converted by the DC-AC conversion circuit f.

Reference numeral g denotes an igniter circuit, which is provided at a subsequent stage of the DC-AC conversion circuit f, generates a high voltage pulse when the metal halide lamp h is started, and superimposes the high-voltage pulse on the output voltage of the DC-AC conversion circuit f. And is applied to the metal halide lamp h. The metal halide lamp h is connected to the AC output terminals i and i '.

Reference numeral j denotes a short-circuit detection circuit, which detects the short-circuit state by monitoring the lamp voltage of the metal halide lamp h. By sending a detection signal to the protection circuit d, the operation of the lighting circuit is stopped. However, the power supply to the metal halide lamp h is cut off.

FIG. 9 shows a change over time in the output voltage of the lighting circuit a (which will be referred to as "V").
(A) shows the respective voltage changes when the metal halide lamp h normally lights up, and (b) shows the respective voltage changes when the metal halide lamp h falls into a load short-circuit state. The starting point of the time axis t is when the lighting switch c is turned on.

At the time of normal lighting, as shown by a graph curve k in FIG. 9 (a), the voltage V immediately rises from t = 0 and then becomes constant, and at time t1, a start pulse 1 by the igniter circuit g causes a metal halide lamp. When h is lit, the voltage V temporarily drops and then gradually approaches a steady value. The voltage level Vmin indicated by the broken line indicates the minimum value of the voltage V when the variation of the lamp voltage based on the individual difference of the metal halide lamp h is taken into consideration.

When the lamp is short-circuited, FIG.
As shown in the graph curve m of (b), from t = 0 to the voltage V
Rises immediately and reaches Vsat, then becomes constant, and does not exceed the voltage level Vsh indicated by the broken line in the figure.
This Vsat changes depending on the short impedance. That is, when the impedance is low, Vsa
When t is small (see the curve indicated by the one-dot chain line) and the impedance is high, Vsat also increases.

Therefore, if the threshold value for short-circuit detection is set to Vsh, a short-circuit detection signal is obtained by providing a comparison circuit for detecting that Vsat <Vsh when the lamp is short-circuited, and this is sent to the protection circuit d. The operation of the lighting circuit can be stopped.

[0012]

By the way, the above circuit has a problem that only a short circuit having a low impedance can be detected at the time of short circuit.

That is, if the short-circuit detection threshold value Vsh is large, the voltage V becomes less than Vsh even during normal lighting, and the possibility of erroneous detection increases.
As shown in FIG. 9A, it is necessary to set the value of Vsh to a value lower than Vmin.

As described above, the value of Vsat is related to the short impedance, and if Vsh is lowered, only the short state with low impedance can be detected.

[0015]

In order to solve the above-mentioned problems, the present invention provides a lighting circuit for a discharge lamp, which comprises a starting means for generating a pulse or a high voltage for starting the discharge lamp. In addition to detecting the lamp voltage of the discharge lamp or its equivalent signal, the lamp voltage of the discharge lamp or the lamp voltage of the discharge lamp or its corresponding period from the start of energization of the discharge lamp to the lighting of the discharge lamp. A short-circuit detection circuit that determines that a load short-circuit condition of the discharge lamp has occurred when the level of the equivalent signal is below a predetermined determination level, and a signal indicating that the load short-circuit condition of the discharge lamp has been detected from the short-circuit detection circuit In this case, a protection circuit for stopping the operation of the lighting circuit or cutting off the power supply to the discharge lamp is provided.

[0016]

According to the present invention, the lamp voltage of the discharge lamp or its equivalent signal is detected, and the lamp voltage of the discharge lamp or its equivalent signal is detected from the start of energization of the discharge lamp to the elapse of a predetermined detection period. The short-circuit detection circuit determines that the discharge lamp has fallen into the load short-circuit state when the level of 1 does not exceed the predetermined determination level. That is, it is determined that the discharge lamp is normally lit when the lamp voltage is equal to or higher than the determination level during the detection period from the start of energization of the discharge lamp to the lighting of the discharge lamp, and the lamp is lit during the detection period. When the voltage is below the judgment level, it is judged that the discharge lamp has fallen into a load short-circuit state, so the judgment level is set to a level higher than the steady value of the lamp voltage that finally reaches when the discharge lamp normally lights up. Therefore, it is possible to detect a short-circuit state with high impedance.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the lighting circuit of the discharge lamp of the present invention will be described below with reference to the illustrated embodiments. In the illustrated embodiment, the present invention is applied to a lighting circuit of a vehicle discharge lamp.

1 to 4 show a first embodiment of the present invention.

FIG. 1 shows an outline of a lighting circuit 1, in which a battery 2 is connected between DC voltage input terminals 3 and 3 '.

4, 4'denotes DC power supply lines, and a lighting switch 5 is provided on one of the plus lines 4.

A relay contact 6a is provided on the plus line 4, and its opening / closing is controlled by the power cutoff relay circuit 6. That is, the power cutoff relay circuit 6 is a protection circuit provided to cut off the supply of the battery voltage to the circuit at the subsequent stage when an abnormality is detected in the circuit.

Reference numeral 7 is a DC boosting circuit, the plus side input terminal of which is connected to the output side terminal of the relay contact 6a, and the other ground side input terminal of which is connected to the DC voltage input terminal 3 '. The DC boosting circuit 7 is provided for boosting the battery voltage, and has a configuration of, for example, a flyback type DC-DC converter so that the boosting control is performed by a control circuit described later. Although the present embodiment is configured to only boost the battery voltage, it may be configured to perform the buck-boost control depending on the battery voltage value.

Reference numeral 8 denotes a DC-AC conversion circuit, which is provided in the subsequent stage of the DC boosting circuit 7 and converts the DC voltage sent from the DC boosting circuit 7 into a rectangular wave AC voltage. For the DC-AC conversion circuit 8, for example, a bridge-type drive circuit using two sets of semiconductor switch elements that are reciprocally switched is used.

Reference numeral 9 denotes an igniter circuit, which is arranged in the latter stage of the DC-AC conversion circuit 8 and has an AC output terminal 1
A metal halide lamp 11 having a rated power of 35 W is connected between 0 and 10 '.

Reference numeral 12 is a control circuit for controlling the output voltage of the DC boosting circuit 7, which is detected by the voltage dividing resistors 13 and 13 'provided between the output terminals of the DC boosting circuit 7. Output voltage (this is referred to as "Vo")
The voltage detection signal corresponding to is input. In addition, the current detection signal corresponding to the output current of the DC booster circuit 7 is converted into a voltage by the current detection resistor 14 provided on the ground line connecting the DC booster circuit 7 and the DC-AC converter circuit 8. It is adapted to be input to the control circuit 12.

Then, the control circuit 12 generates control signals according to these detection signals and sends them to the DC boosting circuit 7,
By controlling the output voltage, electric power control is performed according to the state of the metal halide lamp 11 at the time of starting, and the starting time and the restart time of the lamp can be shortened.

Reference numeral 15 is a short-circuit detection circuit, which is provided to detect the load short-circuit state of the metal halide lamp 11 by monitoring the output voltage Vo of the DC booster circuit 7.

Continuing to supply electric power to the metal halide lamp 11 under the short-circuit condition may cause a risk of ignition due to heat generation in the circuit and its surroundings, or may cause an electric shock accident. Circuit 15
The short-circuit detection signal due to is sent to the hold circuit 17 through the diode 16, and the signal sent from the hold circuit 17 to the power cutoff relay circuit 6 opens the relay contact 6a to stop the operation of the lighting circuit 1. The power supply to the metal halide lamp 11 is cut off. Note that the hold circuit 17 is provided to hold this cutoff state until the lighting switch 5 is turned on again.

FIG. 2 shows an example of the configuration of the short detection circuit 15, which is composed of a timer section 18 and a voltage comparison section 19.

A capacitor 20 is used in the timer section 18, and one end of the capacitor 20 is connected to a power supply terminal 22 via a resistor 21 and the other end is grounded. The power supply terminal 22 is supplied with a predetermined power supply voltage generated based on the battery voltage by a constant voltage power supply circuit (not shown).

Reference numeral 23 is a diode connected in parallel with the resistor 21, and the lighting switch 5 is turned off to turn on the power supply terminal 2
It is provided to form a discharge path for the capacitor 20 and reset it when the power supply to 2 is cut off.

Reference numeral 24 is an emitter-grounded NPN transistor, the base of which is connected via a resistor 25 to the capacitor 20.
Is connected between the resistor 21 and the resistor 21. The collector of the transistor 24 is connected between the resistors 26 and 26 'for dividing the predetermined voltage (Vref) to obtain the reference voltage. A resistor 27 is inserted between the base and the emitter of the transistor 24.

The voltage comparison section 19 is composed of a comparator 28, and the negative input terminal of the comparator 28 is connected between the voltage dividing resistors 13 and 13 '.
Its positive input terminal is connected between the resistor 26 and S26 '. The output terminal of the comparator 28 is connected to the anode of the diode 16 and a pull-up resistor 29 is attached.

In the short-circuit detection circuit 15, however, a period until the capacitor 20 of the timer section 18 is charged by turning on the lighting switch 5 and its terminal voltage reaches a predetermined value (hereinafter referred to as "detection period", " Since the transistor 24 is off, the voltage comparison unit 19 divides the output voltage Vo of the DC boosting circuit 7 and the reference voltage by the resistors 26 and 26 '(this is referred to as "E2").
6 ”. ) Is compared with.

That is, the divided value of the output voltage Vo by the resistors 13 and 13 '(referred to as "V13") is the reference value E.
When it is 26 or more, the comparator 28 outputs an L (low) signal, and conversely, the divided voltage value V13 of the output voltage Vo is the reference value E.
When it is less than 26, the comparator 28 outputs an H (high) signal.

The length of the detection period ΔTm is defined by the time constant related to the resistance value of the resistor 21 and the electrostatic capacitance of the capacitor 20, but in order to guarantee the stable operation of the lighting circuit 1, this is determined by the igniter circuit. It is preferable to set it to be equal to or less than one cycle of the start pulse generated by 9. When the length of the detection period ΔTm is set to be longer than one cycle of the start pulse by the igniter circuit 9, for example, when the metal halide lamp 11 is normally turned on by one start pulse, the lamp is detected within the detection period ΔTm. Since the voltage may drop and the comparator 28 may output the H signal and erroneous short circuit detection may be performed, it is necessary to provide a delay circuit or the like to avoid such an inconvenience.

When the detection period ΔTm elapses, the transistor 24 is turned on and the potential of the plus input terminal of the comparator 28 becomes substantially zero, so that the output signal of the comparator 28 becomes the L signal.

FIG. 4 schematically shows an example of a temporal change in the output voltage Vo. (A) shows a case where the metal halide lamp 11 is normally lit, and (b) shows a load short circuit occurring in the metal halide lamp 11. The change in voltage is shown when the voltage is changed.

When the metal halide lamp 11 is normally turned on, as indicated by the solid curve curve 30 in FIG.
Immediately rises and then becomes constant, and when the metal halide lamp 11 is turned on by the start-up pulse 31 generated by the igniter circuit 9, Vo drops sharply and then rises and gradually approaches a steady value. In the figure, ΔTm indicates the detection period, the voltage level Vsh indicated by the broken line indicates the determination level related to the short circuit detection, and the value of Vsh is the variation in the steady value of Vo due to the individual difference of the metal halide lamp 11. In consideration of the above, the level is set to a level slightly higher than the maximum value of the steady value of Vo (this is the voltage E26 above).
It is done by setting. ).

Until the detection period ΔTm elapses, V
Since o ≧ Vsh, the comparator 28 of the short-circuit detection circuit 15 determines that V13 ≧ E26 and outputs the L signal. After the detection period ΔTm has passed, the metal halide lamp 1
When 1 is lit, Vo <Vsh, but at this time, the timer unit 18 is up and the transistor 24
Is ON, the comparator 28 outputs the L signal.

When the load of the metal halide lamp 11 is short-circuited, the graph curve 32 shown by the solid line in FIG.
As described above, Vo rises and reaches a steady value indicated by Vsat and becomes constant. As described above, the value of Vsat is defined by the short impedance.

In this case, Vo <Vsh is always satisfied, and the comparator 28 of the short circuit detection circuit 15 outputs the H signal. Incidentally, after the detection period ΔTm has elapsed, the comparator 28 is set to L by the time-up of the timer unit 18.
A signal is output, but since the H signal output to the hold circuit 17 before that is held, the subsequent L signal is ignored.

As described above, the judgment level Vsh is Vo.
Since the level is set to be slightly higher than the maximum value related to the steady value of, it is possible to detect a short circuit with high impedance.

FIG. 3 shows a configuration example of the power cutoff relay circuit 6 and the hold circuit 17.

Reference numeral 33 is a power supply terminal, which is connected between the lighting switch 5 and the relay contact 6a via a reverse voltage preventing diode 34.

Reference numeral 35 is a relay, one end of the coil 35a of which is connected to the power supply terminal 33 and the other end of which is connected to the collector of the NPN transistor 36. This coil 35
The relay contact 6a is opened / closed according to the presence or absence of the exciting operation of a.

The hold circuit 17 has its input terminal 37.
The output signal of the short-circuit detection circuit 15 is sent to the input terminal 37. When the input terminal 37 goes high, this state is held and the transistor 36 is turned off.

That is, as shown in FIG.
The collector of the NP transistor 38 is grounded via the resistor 39 and the capacitor 40, and the resistor 39,
It is connected to the base of the NPN transistor 42 via 41. The input terminal 37 is connected to the collector of the transistor 38. Incidentally, 41 'is a resistor provided between the base and collector of the transistor 42.

The collector of the NPN transistor 42 whose emitter is grounded is connected to the base of the above transistor 36 via the diode 43 and the resistor 44, and the collector is connected to the power supply terminal 3 via the resistors 45 and 45 '.
3 and the base of the PNP transistor 38 is connected between the resistors 45 and 45 '. Incidentally, 44 'is a resistor provided between the base and emitter of the transistor 36.

Therefore, the input terminal 37 of the hold circuit 17
When the H signal is applied from the short detection circuit 15 to the transistors 42 and 38, the transistors 42 and 38 are turned on, this state is held, and the transistor 36 is turned off.

Therefore, the relay 35 is turned off and its contact 6
a is opened, and the supply of the battery voltage to the DC booster circuit 7 is cut off. This state is maintained until the lighting switch 5 is turned off and then turned on again.

5 to 7 show a second embodiment 1A of the lighting circuit of the discharge lamp according to the present invention.

The discharge lamp lighting circuit according to the second embodiment 1A differs from the discharge lamp lighting circuit according to the first embodiment 1 described above in that the short-circuit detection circuit is configured and control is performed when a short-circuit is detected. The operation of the lighting circuit is stopped by stopping the power supply to the circuits and the like. Therefore, regarding the constituent parts of the second embodiment 1A, the parts having the same functions as those of the constituent parts of the first embodiment 1 are given the same reference numerals as those used in the first embodiment. The description is omitted.

FIG. 5 shows the structure of the lighting circuit 1A, in which a constant voltage power supply unit 46 for generating a predetermined power supply voltage based on the voltage supplied from the battery 2 (this is referred to as "+ B") is provided. It is provided. This constant voltage power supply unit 46
The power supply voltage (+ Vcc) obtained by
2 and the control unit in the DC-AC conversion circuit 8 and the like. The constant voltage power supply unit 46 has a function as a protection circuit, and is configured not to generate a power supply voltage when receiving a short circuit detection signal sent from the short circuit detection circuit 15A through the hold circuit 17. There is.

FIG. 6 shows an example of the configuration of the short circuit detection circuit 15A, which is composed of a voltage comparison section 47, a signal holding section 48, and a timer section 49.

Comparator 5 which constitutes the voltage comparison unit 47
The output voltage Vo of the DC boost circuit 7 is applied to the positive input terminal of 0.
Is supplied with the voltage V13 divided by the resistors 13 and 13 ', and the reference voltage (referred to as "E51") from the constant voltage source 51 is supplied to the negative input terminal of the comparator 50. The output of the comparator 50 is sent to the signal holding unit 48 via the diode and a pull-up resistor 52 is attached to the output terminal of the comparator 50.

The signal holding section 48 is the hold circuit 1 described above.
7 has the same configuration as that of the PNP transistor 53.
Is grounded via a resistor 54 and a capacitor 55, and is connected to the output terminal of the comparator 50 via a diode. The emitter of the transistor 53 is connected to the power supply terminal 56, and the power supply terminal 5
A predetermined power supply voltage is supplied to 6.

The base of the NPN transistor 57 having a grounded emitter is connected between the resistor 54 and the capacitor 55 via the resistor 58, and the collector thereof is connected to the base of the transistor 53 via the resistor 59.
It is connected to the power supply terminal 56 via the resistors 59 and 59 '. A resistor 60 is inserted between the base and the emitter of the transistor 57.

A capacitor 61 is used in the timer section 49. One end of the capacitor 61 is connected to the power supply terminal 56 via the resistor 62 and the diode 63 is also connected.
Is connected to the collector of the transistor 57 via, and the other end is grounded. A diode 64 connected in parallel with the resistor 62 is provided to form a discharge path for the capacitor 20 and reset when the lighting switch 5 is turned off and the power supply to the power supply terminal 56 is cut off. .

Reference numeral 65 denotes a comparator, the plus input terminal of which is connected between the capacitor 61 and the resistor 62, and the minus input terminal thereof is supplied with the reference voltage from the constant voltage source 66. Then, the output of the comparator 65 passes through the diode 16 and the hold circuit 17
Sent to A pull-up resistor 67 is attached to the output terminal of the comparator 65.

In the short detection circuit 15A, however, when the metal halide lamp 11 is normally turned on, the output signal of the voltage comparison section 47 is sent to the timer section 49 via the signal holding section 48 and its operation is suspended. Further, when the load of the metal halide lamp 11 is short-circuited, the output signal of the voltage comparison unit 47 must hold the operation of the timer unit 49 through the signal holding unit 48 until the timer unit 49 times up, and the comparator 65 holds the signal. The H signal is sent to the circuit 17.

That is, when the metal halide lamp 11 is normally turned on, the detection voltage V13 and the reference voltage E51 (Vo above) are detected by the comparator 50 of the voltage comparison section 47 during the detection period ΔTm until the timer section 49 times out.
And Vsh correspond to Vsh. ) And V13 ≧ E51, the comparator 50 sends an H signal to the signal holding unit 48 and holds the H signal. As a result, the diode 63 and the transistor 5
Since the discharge path of the capacitor 61 is formed by 7 and 7, the comparator 65 of the timer unit 49 always outputs the L signal.

When the load of the metal halide lamp 11 is short-circuited, the detection voltage V13 is compared with the reference voltage E51 by the comparator 50 of the voltage comparison unit 47 in the detection period ΔTm until the timer unit 49 times out, and V13 <E51. Therefore, the L signal is sent from the comparator 50 to the signal holding unit 48. Therefore, the transistors 53 and 57 of the signal holding unit 48 are both turned off, the capacitor 61 of the timer unit 49 is charged, and its terminal voltage rises even after the detection period ΔTm elapses, and the reference by the constant voltage source 66 is maintained. When the voltage exceeds the voltage, the comparator 65 outputs the H signal. That is, unless the H signal is sent from the voltage comparison unit 47 via the signal holding unit 48 to the timer unit 49 within the detection period ΔTm, the timer unit 49 performs the time counting operation, and the H signal is output from the comparator 65 at the time-up. It

FIG. 7 shows an example of the configuration of the constant voltage power source unit 46, which is a flyback type DC-DC converter.

That is, the battery voltage (+ B) is supplied to one end of the primary winding 68a of the transformer 68, and the NPN transistor 69 connected to the other end of the primary winding 68a.
Is grounded through a resistor 70. The battery voltage is supplied to the power supply terminal (Vc) of the control IC 71 that controls the switching of the transistor 69, and the control signal from the control IC 71 is supplied to the base of the transistor 69.

The control IC 71 is a hold circuit 17
The oscillating operation can be controlled in accordance with the signal from S. (this is referred to as "S17"), and the oscillating operation is performed when S17 is the H signal (that is, when a short circuit is detected). It is about to be stopped. The emitter current of the transistor 69 is detected by the resistor 70 and input to the current detection terminal (Is) of the control IC 71, whereby the current is limited.

The terminal voltage of the secondary winding 68b of the transformer 68 is output as a power supply voltage (+ Vcc) via a rectifying / smoothing circuit 74 composed of a diode 72 and a capacitor 73.

However, when the metal halide lamp 11 is normally turned on, the control IC 71 controls the switching of the transistor 69 to generate a predetermined power supply voltage (+ Vcc), which is supplied to the control circuit 12 and the like. However, when a short circuit is detected, the control circuit I is controlled by the short circuit detection circuit 15A through the hold circuit 17.
Since the signal S17 sent to C71 is the H signal, the oscillation of the control IC 71 is stopped, the power supply voltage is not generated, the power supply to the control circuit 12 and the like is stopped, and the operation of the lighting circuit 1A is stopped. .

[0069]

As is apparent from the above description, according to the first aspect of the invention, the lamp voltage is judged within the detection period from the start of energization of the discharge lamp to the lighting of the discharge lamp. If it is above the level, it is judged that the discharge lamp has normally lighted, and if the lamp voltage is below the judgment level within the detection period, it is judged that the discharge lamp has fallen into the load short-circuit state and it is lit by the protection circuit. Since the circuit operation is controlled so as to stop or cut off the power supply to the discharge lamp, it is better to set the judgment level to a level higher than the steady value of the lamp voltage that finally reaches when the discharge lamp normally lights up. It is possible to detect a short-circuit state with high impedance.

According to the second aspect of the invention, when the short circuit detection circuit receives the signal indicating that the load short-circuit state of the discharge lamp is detected, the hold circuit holds the signal, and the hold circuit holds the protection circuit. Through this, the operation of the lighting circuit is stopped or the power supply to the discharge lamp is cut off, and this state is maintained until the power is reapplied to the lighting circuit, ensuring complete circuit protection. it can.

According to the third aspect of the invention, the frequency of erroneous detection is reduced by setting the detection period in the short-circuit detection circuit to be less than or equal to the generation cycle of the pulse for starting the discharge lamp or the high voltage. be able to.

[Brief description of drawings]

1 shows a first embodiment of a lighting circuit for a discharge lamp according to the present invention, together with FIGS. 2 to 4, and is a block diagram showing an outline thereof.

FIG. 2 is a circuit diagram showing a configuration example of a short circuit detection circuit.

FIG. 3 is a circuit diagram showing a configuration example of a power cutoff relay circuit and a hold circuit.

4A and 4B show an example of a temporal change of an output voltage Vo of a DC booster circuit, in which FIG. 4A is a voltage change when a metal halide lamp is normally lit, and FIG. 4B is a voltage change when a load of the metal halide lamp is short-circuited. Are shown respectively.

5 shows an outline of a second embodiment relating to the lighting circuit of the discharge lamp of the present invention together with FIG. 6 and FIG. 7, and this figure is a block diagram showing the outline.

FIG. 6 is a circuit diagram showing a configuration example of a short circuit detection circuit.

FIG. 7 is a circuit diagram showing a configuration example of a constant voltage power supply circuit.

FIG. 8 is a circuit block diagram showing a configuration example of a conventional lighting circuit.

9A and 9B show an example of temporal changes in the output voltage V of the DC booster circuit shown in FIG. 8, in which FIG. 9A shows voltage changes during normal lighting of the metal halide lamp, and FIG. 9B shows load short circuit of the metal halide lamp. The voltage changes over time are shown.

[Explanation of symbols]

 1 Discharge Lamp Lighting Circuit 6, 6a Protection Circuit 9 Igniter Circuit (Starting Means) 11 Metal Halide Lamp (Discharge Lamp) 15 Short Circuit Detection Circuit 17 Hold Circuit 1A Discharge Lamp Lighting Circuit 15A Short Circuit Detection Circuit 46 Constant Voltage Power Supply Section (Protection Circuit) )

Claims (3)

[Claims] 1. A discharge lamp lighting circuit comprising a starting means for generating a pulse or a high voltage for starting the discharge lamp and detecting the lamp voltage of the discharge lamp or a signal corresponding thereto and energizing the discharge lamp. When the lamp voltage of the discharge lamp or the level of its equivalent signal is lower than the predetermined judgment level during the period from the start to the time when the discharge lamp lights up, the load short circuit of the discharge lamp A short circuit detection circuit that determines that a state has occurred, and to stop the operation of the lighting circuit or cut off the power supply to the discharge lamp when a signal indicating that the load short circuit state of the discharge lamp is detected from the short circuit detection circuit And a protection circuit provided for the discharge lamp lighting circuit. 2. The discharge lamp lighting circuit according to claim 1, further comprising a hold circuit for holding the signal when a signal indicating that a load short-circuit state of the discharge lamp is detected is received from the short-circuit detection circuit, and the hold circuit holds the signal. The operation of the lighting circuit is stopped by the signal sent from the circuit to the protection circuit or the power supply to the discharge lamp is cut off, and this state is maintained until the power is turned on again to the lighting circuit. The lighting circuit for the discharge lamp. 3. The lighting circuit for a discharge lamp according to claim 1 or 2, wherein a detection period by the short-circuit detection circuit is set to be equal to or shorter than a pulse for starting the discharge lamp or a generation period of a high voltage. Discharge lamp lighting circuit characterized by.