JPH03153430A - Lightening circuit for electric discharge lamp on vehicle - Google Patents

Abstract

PURPOSE:To prevent the dielectric breakdown of an electric discharge lamp to which the output of a direct current step-up transforming circuit is applied through a converter circuit and a current limitting load by stopping the oscillating action of a converter circuit when the electric discharge lamp has been detected to be in an impossible lightening state. CONSTITUTION:A lightening circuit 1 of a metal highland lamp 8 for an automobile is provided with a DC step-up transforming circuit 4, a high-frequency step-up transforming circuit(inverter circuit) 6 which is provided on the rear of the circuit 4 and converts DC voltage into sine-wave AC voltage, and a current limitting load and igniter circuit 7, and a lamp 8 is connected between output terminals of the above circuit 7. In addition to that, whether the lamp has been lightened or not is detected on lamp current, and an igniter starting circuit 9 is provided to send a starting pulse generating signal to the current limitting load and igniter circuit 7 when the lamp has not been lightened. In the case of not lightening, sine-wave oscillation in the high frequency step-up transforming circuit 6 is stopped through a protecting circuit 14, and the generation of a control pulse sent from a control circuit 10 to the DC step-up transforming circuit 4 is also stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION The details of the lighting circuit for the vehicular discharge lamp of the present invention will be described in accordance with the following items.

A. Industrial field of application B0 Overview of the invention C9 Background technology 1 Problem to be solved by the invention E1 Means for solving the problem F. Embodiment a Overall circuit configuration [Fig. 1 J b. Circuit configuration [Fig. 2, Fig. 3] b -1,'
DC booster circuit b-2, high frequency booster circuit b-3, current limiting load and igniter circuit b-4. Igniter starting circuit b-5, control circuit [Figures 2 and 3] b-6. Protection circuit C9 operation C-1, normal time C-2, abnormal time c-2-a, lighting failure c-2-b, overvoltage 61 action G8 Effect of the invention (A, field of application in industry a) Book The present invention relates to a novel lighting circuit for a discharge lamp for a vehicle. Specifically, the present invention aims to provide a novel lighting circuit for a discharge lamp for a vehicle that can prevent dielectric breakdown of the discharge lamp due to abnormal lighting of the discharge lamp and electric shock accidents when replacing the discharge lamp. It is something.

(B. Summary of the Invention) A first lighting circuit for a vehicular discharge lamp of the present invention includes a DC booster circuit that boosts a DC voltage from a DC voltage input terminal;
A lighting circuit for a discharge lamp for a vehicle, comprising a converter circuit that converts the output voltage of the DC booster circuit into an AC voltage, and the output of the converter circuit is applied to the discharge lamp via a current limiting load. detection means for detecting lighting or non-lighting based on the current flowing through the lamp; and abnormal state detection for stopping the oscillation operation of the converter circuit when it is determined that the discharge lamp is in a state where it cannot be lit based on the signal from the detection means. The second one is further provided with a control circuit that controls the output voltage of the DC booster circuit by sending a control pulse to the DC booster circuit, and the control circuit is in an abnormal state. When a signal indicating that the discharge lamp cannot be lit is received from the detection means, the sending of control pulses to the DC booster circuit is stopped.Thus, when the discharge lamp is not lit, the converter circuit is activated. Stops the oscillation operation and the generation of control pulses output by the control circuit,
This makes it possible to prevent electric shock accidents and destruction of the discharge lamp and circuit elements when replacing the discharge lamp.

(C. Background Art) Incandescent light bulbs are currently widely used as light sources for automobile headlights, and lighting circuits for these incandescent light bulbs include, for example,
A circuit is used in which a relay coil is connected between one terminal of the battery via a lighting switch, and an incandescent light bulb is connected between one terminal of the battery via a relay contact.

In this kind of lighting circuit for incandescent light bulbs, even if an abnormality occurs due to the lifespan of the bulb or the battery becomes overvoltage, the worst case scenario would be a filament breakage, so it is a safety issue. There is no problem, and there is usually no special protection circuit for this purpose.

Metal halide lamps are attracting attention as a new light source to replace bulbs, but when using metal halide lamps as a light source for automobile headlights, it is necessary to turn on or relight the lamp instantly, and the starting voltage at that time is also low. Very high (about 10-20kV).

Therefore, if the lamp does not light up after the lighting switch is turned on due to an abnormality caused by the lamp's lifespan, high voltage will continue to be generated between the output terminals of the lighting circuit, and the lamp will not turn on. There is a risk of ignition due to insulation breakdown between the contact terminals installed in the socket, or of electric shock if the user replaces the lamp without knowing that high voltage is being applied to the lamp. There's a problem. There is also a concern about electromagnetic interference caused by such high-voltage starting pulses.

(D. Problems to be Solved by the Invention) Incidentally, in recent years, incandescent lamps including halogen lamps (E. Means for Solving the Problems) Therefore, the vehicle lamp lighting circuit of the present invention aims to solve the above problems. The device is equipped with a DC booster circuit that boosts the DC voltage from the DC voltage input terminal, and a converter circuit that converts the output voltage of the DC booster circuit into an AC voltage, and the output of the converter circuit is connected to the discharge lamp via a current-limiting load. In the lighting circuit for a vehicle discharge lamp, the current is applied to the discharge lamp, a detection means for detecting lighting or non-lighting based on the current flowing through the discharge lamp;
An abnormal state detecting means is provided which stops the oscillation operation of the converter circuit when it is determined that the discharge lamp is in a non-lighting state based on the signal from the detecting means.

Therefore, according to the lighting circuit for a vehicle discharge lamp of the present invention, when the abnormal state detection means determines that the discharge lamp is in a state where it cannot be lit, the oscillation operation of the converter circuit is stopped.
No power is supplied to the circuits subsequent to the converter circuit, and it is possible to prevent dielectric breakdown of the discharge lamp and electric shock accidents during lamp replacement.

(F. Embodiment) Details of the lighting circuit for the vehicular discharge lamp of the present invention will be described below with reference to the illustrated embodiment. In the illustrated embodiment, the lighting circuit for a discharge lamp for a vehicle according to the present invention is applied to a lighting circuit for a metal halide lamp for an automobile.

(a, overall circuit configuration) [Figure 1] 1 is a lighting circuit for a metal halide lamp for an automobile.

A battery 2 has a voltage of approximately 12 V DC, and is connected between DC voltage input terminals 3 and 3'.

4 is a DC booster circuit, one of its input terminals is connected to the DC voltage input terminal 3 via the lighting switch 5, and the other input terminal is connected to the DC voltage input terminal 3'.

Reference numeral 6 denotes a high frequency booster circuit, which is provided at a subsequent stage of the DC booster circuit 4, and is provided to convert the DC voltage from the DC booster circuit 4 into a sine wave AC voltage. As the high frequency boost circuit 6, for example, a push-pull type inverter circuit is used.

Reference numeral 7 denotes a current limiting load and igniter circuit, which is arranged after the high frequency booster circuit 6, and a metal halide lamp 8 is connected between its output terminals.

Reference numeral 9 denotes an igniter starting circuit, which is provided to detect lighting or non-lighting of the lamp from the lamp current, and to send a signal for generating a starting pulse to the above-mentioned current limiting load and igniter circuit 7 when the lamp is not lit.

10 is a control circuit, and D detected via voltage dividing resistors 11 and 11' provided between the output terminals of the DC booster circuit 4
The voltage from the current detection resistor 12 provided on the ground line connecting the DC booster circuit 4 and the high frequency booster circuit 6 in order to convert the output voltage of the C booster circuit 4 and the output current of the DC booster circuit 4 into voltage. It is provided to generate a pulse signal with a duty cycle corresponding to the voltage, send this signal to the DC booster circuit 4 via the gate drive circuit 13, and control its output voltage. Note that the control circuit 10 and the battery 2 are connected to a common ground.

Reference numeral 14 is a protection circuit, which is used when the metal halide lamp 8 does not light up even when the lighting switch 5 is closed and this state continues for more than a predetermined time, or when a battery voltage higher than a predetermined voltage is applied to the DC input terminal. High frequency boost circuit 6
The control pulse is provided to stop the oscillation of the DC booster circuit 4 and to stop the oscillation of the control pulse sent from the control circuit 10 to the DC booster circuit 4 via the gate drive circuit 13.

In the lighting circuit 1, immediately after the lighting switch 5 is turned on, a starting pulse is generated by the signal sent from the igniter starting circuit 9 to the current limiting load and the igniter circuit 7, which triggers the metal halide lamp 8. is applied, and the control circuit 10 performs step-up control of the battery voltage as needed, and finally the lamp reaches a steady state in eight steps.

If the metal halide lamp 8 is not connected to the AC output terminal of the lighting circuit 1 or if the metal halide lamp 8 is malfunctioning and cannot be lit, the protection circuit 14 will control the lamp based on the signal from the igniter starting circuit 9. It is determined that the lighting is not possible, and the oscillation of the sine wave by the high frequency booster circuit 6 is stopped, and the generation of control pulses sent from the control circuit 10 to the DC booster circuit 4 via the gate drive circuit 13 is stopped. . This avoids the risk of electric shock when replacing the lamp, and prevents dielectric breakdown of the lamp and destruction of the control element.

The protection circuit 14 also detects overvoltage when the battery voltage becomes high and causes the high frequency boost circuit 6 to generate a sine wave alternating current or the control circuit 10 to generate a DC! 4. By stopping the generation of control pulses to the pressure circuit 4, the worst situation in which the control of the lamp power of the metal halide lamp 8 becomes unstable and the lamp is destroyed can be avoided.

(b. Circuit configuration of each part) [FIGS. 2 and 3] Next, each circuit part constituting the lighting circuit 1 will be described in detail.

(b-1, DC boost circuit) The DC boost circuit 4 is configured as a chopper type DC-DC converter, and includes an inductor 16 provided on the positive line 15 and a positive line 1 in the subsequent stage.
5 and the ground line 15' and is switched by a control pulse sent from the control circuit 10 via the gate drive circuit 13, and an N-channel FET 17 whose anode is connected to the positive line 15. It consists of a rectifying diode 18 connected to the drain of the FET 17, and a smoothing capacitor 19 provided between the cathode of the diode 18 and the ground line 15'.

Then, the DC booster circuit 4 receives a control pulse sent from the control circuit 10 via the gate drive circuit 13.
When T17 is turned on, the inductor 16 stores energy, and when the FET 17 is turned off, the stored energy is released, and the corresponding voltage is superimposed on the input voltage to perform DC boosting. It has become.

(b-2, High Frequency Boost Circuit) As the high frequency boost circuit 6, a self-excited push-pull inverter circuit that utilizes the reciprocal operation of two FETs is used.

20 is a choke coil, one end of which is connected to the positive output terminal of the DC booster circuit 4, and the other end connected to the transformer 21.
It is connected to the center tap of the primary winding 21a.

22 and 23 are N-channel FETs, the sources of which are both connected to the ground line 15'. The drain of one FET 22 is connected to one end of the primary winding 21a of the transformer 21, and the drain of the other FET 22 is connected to one end of the primary winding 21a of the transformer 21.
The drain of 23 is connected to the other end of the primary winding 21a.

24 is a feedback winding, one end of which is connected to F through a resistor 25.
It is connected to the gate of ET23 and also connected via a diode 26 to the collector of an NPN transistor 27 for stopping oscillation. Further, the other end of the feedback winding 24 is connected to the gate of the FET 22 via a resistor 28, and
It is also connected to the collector of transistor 27 via diode 29. Note that the transistor 27 forms part of the protection circuit 14.

30.30' is a capacitor, 31.31 and 31"
31' is a Zener diode, and the capacitor 30 and the opposing Zener diodes 31 and 31 are the FET 22.
The capacitor 30' and the opposing Zener diode 31'31' are inserted between the gate of the FET 23 and the ground line 15'.
5'. Note that the Zener diode is provided as a measure against surge voltage.

32.32' is a constant current diode, and FET22.32' is a constant current diode.
Discipline the switching timing in the switching operation of 23,
This is provided to reduce power loss, while 3
2 is inserted between the positive line 15 and the gate of FET 22, and the other 32' is inserted between the positive line 15 and the gate of FET 23.

33 is a resistor provided between the gate and source of FET 22, and 33' is a resistor provided between the gate and source of FET 23.

34 and 35 are each a capacitor, while 34
is provided between both terminals of the primary winding 21a of the transformer 21, and the other 35 is provided between both terminals of the secondary winding 21b.

Therefore, in the high frequency booster circuit 6, the transistor 2
When FET 7 is off, diodes 26 and 29 are off, and feedback winding 24 performs opposite switching control of FETs 22 and 23, so that a sine wave output is obtained through transformer 21.

(b-3, current limiting load and igniter circuit) 36.36'
is an AC line, one of which 36 connects one end of the secondary winding 21b of the transformer 21 and one of the AC output terminals 37, 37'; A line 38b is provided. Also, the line 36' connects the other end of the secondary winding 21b to the AC output terminal 37.
A capacitor 39 for lamp current detection is provided on the line 36'.

The secondary winding 38b of the trigger transformer 38 and the capacitor 39 constitute a current-limiting load, and the capacitor 3
9 also plays the role of detecting the lamp current of the metal halide lamp 8. When the capacitor 39 also serves to detect the lamp current, the circuit becomes simpler and costs can be reduced compared to the case where a current transformer is used to detect the lamp current.

Note that a metal halide lamp 8 is connected between the AC output terminal 37 and '37''.

One end of the primary winding 38a of the trigger transformer 38 is connected to the AC line 36 near the high frequency booster circuit 6, and the other end is connected to the anode of the thyristor 41 via a resistor 40. In addition, when a thyristor is used as a switching element, the rated value for the current is high, so reliability is higher than when using a thyristor (SSS).

A capacitor 42 is provided between the AC line 36 near the transformer 21 and the cathode of the thyristor 41, and a resistor 43 is connected in parallel to the capacitor 42.

44 is a Zener diode whose cathode is connected to the AC line 36 near the transformer 21, and whose anode is connected to the cathode of the thyristor 41 via resistors 45 and 46. The gate of thyristor 41 is connected between resistors 45 and 46.

47 is a capacitor provided in parallel with the resistor 46.

48 and 48' are resistors connected in parallel, one end of which is connected to the cathode of the thyristor 41, and the other end connected to the anode of the diode 49.

50 is a thyristor whose anode is a diode 4
9, and that cathode is connected to AC line 3.
6'. A voltage from the igniter starting circuit 9 is applied between the gate and cathode of the thyristor 50, thereby controlling the thyristor 50 on and off.

In the igniter circuit, the thyristor 50 is turned on by a signal from the igniter starting circuit 9, which will be described later, at the time of starting lighting or temporarily turning off the light after lighting, and the capacitor 42 turns on half of the AC output output from the high frequency booster circuit 6. It is gradually charged during the wave period (this is due to the switching operation of the diode 49).

A circuit consisting of a Zener diode 44 and resistors 45 and 46 detects the terminal voltage of the capacitor 42, and when the terminal voltage of the capacitor 42 rises and the Zener diode 44 becomes conductive, the thyristor 41 is turned on and the capacitor 42 is discharged. .

The voltage generated at this time is stepped up by the trigger transformer 3B to become a high-voltage starting pulse, which is superimposed on the sine wave alternating current and applied to the metal halide lamp 8 to start the lamp.

(b-4, igniter starting circuit) 51 is a rectifier diode, the anode of which is connected to the AC pressure terminal 37', and the cathode connected to the NPN through an integral circuit consisting of a resistor 52 and a capacitor 53 and a base resistor 54. Connected to the base of transistor 55.

The NPN transistor 55 has its emitter grounded, its collector connected to a power supply terminal 57 via a resistor 56, and a resistor 58 interposed between its base and emitter. The power supply terminal 57 is connected to the positive line 15 through a diode, and a predetermined voltage (this is assumed to be 10 B (V)) is applied when the lighting switch 5 is closed.

Reference numeral 59 designates an NPN transistor as an emitter follower, the base of which is connected to the collector of the transistor 55, and the emitter of which is connected to the gate of the thyristor 50 described above via a resistor 60. A resistor 61 and a capacitor 62 are provided in parallel between the gate and cathode of the thyristor 50.

Reference numeral 63 denotes an NPN transistor whose emitter is grounded, the base of which is connected to the emitter of the transistor 59 via a resistor 64, the collector of which is connected to the power supply terminal 57 via a resistor 65, and the protective circuit 14. is connected to the input terminal of

66 is a resistor inserted between the base and emitter of the transistor 63.

In the igniter starting circuit 9, since no voltage is generated across the capacitor 39 immediately after the lamp starts lighting, the transistor 55 is turned off, the transistor 59 is turned on, and the thyristor of the igniter circuit is turned off. 50 turns on. This generates the activation pulse as described above.

Further, at this time, the transistor 63 is also in an on state, and its collector output is sent to a protection circuit 14, which will be described later, as a signal indicating that the metal halide lamp 8 is not yet lit.

After that, when the lamp is turned on, a voltage higher than a predetermined value is applied to the capacitor 39, so the transistor 55 is turned on.
Transistors 59 and 63 are turned off. Therefore, the thyristor 50 is turned off and the generation of the starting pulse is stopped.
Furthermore, the protection circuit 14 is informed that the lamp has been turned on.

(b-5, control circuit) [Fig. 2, Fig. 3 1 control circuit 10
is a voltage dividing resistor 11 provided at the output stage of the DC booster circuit 4.
the output voltage of the DC booster circuit 4 detected by 11';
A duty cycle control pulse is generated in accordance with a signal indicating the output current of the DC booster circuit 4 detected by the current detection resistor 12, and the DC voltage is increased via the gate drive circuit 13.
This signal is sent to the gate of FET 17 of booster circuit 4.

Reference numeral 67 denotes a PWM control IC, and for example, as shown in FIG.
A predetermined reference voltage is applied to the inverting input terminal.

Further, the terminal voltage of the current detection resistor 12 is sent to the non-inverting input terminal 69a of the error amplifier 69 after passing through the amplifier circuit 70 and the low-pass filter 71. A reference voltage of is applied. The output terminals of these error amplifiers 68 and 69 are OR-connected to the minus input terminal of the PWM comparator 72, and the sawtooth wave from the oscillator 73 is input to the plus input terminal of the PWM comparator 72.

Reference numeral 74 denotes a rest period adjustment comparator, whose negative input terminal is connected to the control terminal 74a, and whose positive input terminal is connected to the output terminal of the oscillator 73.

Reference numeral 75 denotes a constant voltage generator, which generates a predetermined power supply voltage (referred to as VCC (v)) from the battery voltage, and this voltage VCC is obtained from the power supply terminal 75a.

76 and 77 are voltage dividing resistors provided between the power supply terminal 75a and the ground line, 78 is a capacitor provided in parallel with the resistor 76, and a comparator 7 for adjusting the idle period.
A control terminal 74a of No. 4 is connected between voltage dividing resistors 76 and 77, and is also connected to the emitter of a transistor provided at the output stage of a protection circuit 14, which will be described later.

79 is an AND circuit, where PWM comparator 7
An AND operation is performed on the output of output mode switching circuit 80. It is sent to the control output terminal 82 via the buffer 81.

Then, the output signal of the PWM control IC 67 is sent to the gate of the FET 17 of the DC booster circuit 4 via the gate drive circuit 13.

(b-6, protection circuit) 83 is an NPN transistor whose base is resistor 8
4 to the collector of the transistor 63 of the igniter starting circuit 9. And transistor 83
A collector resistor 85 is connected to the power supply terminal 57 via a diode 86, and a resistor 87 and a capacitor 8 are connected in series between the power supply terminal 57 and the ground line.
8.

89 is a diode whose anode is connected between the resistor 87 and the capacitor 88 via a resistor 90, and whose cathode is an NPN transistor 9 whose emitter is grounded.
It is connected to the base of 1.

A Zener diode 92 has a cathode connected to the power supply terminal 57 and an anode connected to the base of the transistor 910 via a resistor 93.

94 is a resistor provided between the base and emitter of the transistor 91.

95.96 are PNP) transistors, their emitters are connected to the power supply terminal 75a of the PWM control IC 67, and their bases are connected to their respective base resistors 97.9
8 to the collector of a transistor 91.

The collector of the transistor 95 is connected to the base of the transistor 27 described above via a resistor 99.

100 is a resistor provided between the base and emitter of the transistor 27.

In addition, the collector of the transistor 96 is connected to a PWM control IC.
67, and is also grounded via a capacitor 101.

102 and 103 are resistors provided between the base and emitter of transistors 95 and 96, respectively.

(c. Operation) Next, the operation of the lighting circuit 1 of the above-mentioned vehicular discharge lamp is performed when there is no abnormality in the metal halide lamp 8 or the battery voltage and the lamp lights up normally after the lighting switch 5 is turned on (hereinafter,
The explanation will be divided into two cases: "normal time") and a lamp abnormality due to the lifespan of the metal halide lamp 8 or battery overvoltage (hereinafter referred to as "r abnormality").

(c-1, normal state) Immediately after closing the lighting switch 5, the lamp voltage is not lit and the output current of the DC booster circuit 4 is small, so the PW
The duty cycle of the control pulse sent from the M control IC 87 to the gate of the FET 17 of the DC booster circuit has a value corresponding to the value detected by the voltage dividing resistor 11.11'. Therefore, the output voltage of the DC booster circuit 4 is increased, and this is converted into a sinusoidal alternating current by the high frequency booster circuit 6 and applied to the metal halide lamp 8.

Further, since no voltage is generated in the lamp current detection capacitor 39, the igniter starting circuit 9 is activated, and in order to turn on the thyristor 50 of the igniter circuit, the capacitor 42 is charged, and the thyristor 41 is activated at regular intervals. It turns on and a high voltage pulse is generated. This is superimposed on the AC output of the high frequency booster circuit 6 as a lamp starting pulse, and the metal halide lamp 8 is triggered.

Until the metal halide lamp 8 lights up, the transistor 63 of the igniter starting circuit 9 is on, so the transistor 83 of the protection circuit 14 is off.
Capacitor 88 is gradually charged, however, since metal halide lamp 8 lights up before transistor 91 turns on, this is detected by capacitor 39 and igniter starting circuit 9, transistor 63 turns off, and protection circuit No. 14 transistor 83 is turned on and capacitor 88 is discharged.

Therefore, under normal conditions, the transistor 91.9 of the protection circuit 14
5,96,27 remains off, and the high frequency booster circuit 6 performs DC-AC conversion and the PWM control IC 67 generates control pulses as scheduled.

Then, a control pulse with a duty cycle corresponding to the output voltage and output current of the DC booster circuit 4 is used for PWM control.
C67 and is fed back to the FET 17 of the DC booster circuit 4 via the gate drive circuit 13, so that the output voltage of the DC booster circuit 4 is controlled.

As the luminous flux of the metal halide lamp 8 increases after lamp lighting, the lamp voltage rises, and the output current of the DC booster circuit 4 increases.
The duty cycle of the control pulse output by C67 decreases, and the output voltage of the DC booster circuit 4 decreases accordingly. Finally, the output current of the DC booster circuit 4 is saturated to a steady level, and the metal halide lamp 8
The luminous flux of will settle down to the rated luminous flux.

(c-2, Abnormality) Next, the operation of the lighting circuit 1 in an abnormality will be explained separately when the lamp cannot be lit and when the battery is overvolted.

(c-2-a, when lighting is not possible) In this case, immediately after the lighting switch 50 is turned on, a starting pulse is generated by the igniter starting circuit 9 and applied to the metal halide lamp 8, which is the same as in normal times, but when the lamp is It doesn't light up like this.

Therefore, the transistor 63 of the igniter starting circuit 9 remains on, the transistor 83 of the protection circuit 14 turns off, and the rise in the terminal voltage of the capacitor 88 turns on all the transistors 91, 95, 96, and 27.

When the transistor 27 is turned on, the diodes 26 and 29 of the high-frequency booster circuit 6 are turned on, and the feedback winding 24 is short-circuited, thereby stopping the oscillation of the high-frequency booster circuit 6.

Also, by turning on the transistor 96, the PWM control IC
The potential of the control terminal 74a of the control pulse 67 increases, and the duty cycle of the control pulse becomes determined by the potential of the control terminal 74a, regardless of the output voltage of the error amplifier 68, 69 (duty cycle =
0%), the generation of control pulses stops.

In this way, the output of the high frequency booster circuit 6 becomes Ov, and the boosting operation of the DC booster circuit 4 is also no longer performed.

(c-2-b, at A voltage) The voltage applied to the DC voltage input terminal 3.3' is excessive (17
above), the Zener diode 9 of the protection circuit 14
Since transistor 2 is conductive, transistor 91 is turned on, and therefore transistors 95, 96, and 27 are turned on.

Therefore, the generation of sine wave alternating current by the high frequency booster circuit 6 and P
Generation of control pulses by the WM control IC 67 is stopped.

(d. Effect) However, in the lighting circuit 1 of a vehicle discharge lamp, there are cases where the metal halide lamp 8 is not connected between the AC output terminals 37 and 37', or when it cannot be lit due to lamp life, etc. At the time of overvoltage, the protection circuit 14 stops the oscillation of the high frequency booster circuit 6, so the starting pulse does not continue to be generated, preventing electric shock and lamp insulation breakdown when replacing the lamp, and also serves as the center of the control circuit 10. P
Since the transmission of control pulses from the WM control IC 67 to the DC booster circuit 4 is stopped by the protection circuit 14, it! of the control element (FET etc.) It is also possible to prevent accidents such as those around Ii, requiring double safety measures.

(G. Effects of the Invention) As is clear from the above description, the first lighting circuit for a vehicle discharge lamp of the present invention includes a DC booster circuit that boosts the DC voltage from the DC voltage input terminal; A lighting circuit for a discharge lamp for a vehicle, comprising a converter circuit that converts the output voltage of the DC R voltage circuit into an AC voltage, and the output of the converter circuit is applied to the discharge lamp via a current limiting load, A detection means that detects lighting or non-lighting based on the current flowing through the discharge lamp, and an abnormality that stops the oscillation operation of the converter circuit when it is determined that the discharge lamp is in a state where it cannot be lit based on the signal from the detection means. The second one is characterized in that it further includes a control circuit that controls the output voltage of the DC booster circuit by sending a control pulse to the DC booster circuit; The present invention is characterized in that when the circuit receives a signal from the abnormal state detection means indicating that the discharge lamp cannot be lit, the control pulses are stopped from being sent to the DC booster circuit.

Therefore, according to these, when the abnormal state detection means determines that the discharge lamp is in a state where it cannot be lit, the oscillation operation of the converter circuit is stopped, so that power is not supplied to the circuits subsequent to the converter circuit. Therefore, it is possible to prevent dielectric breakdown of the discharge lamp and electric shock accidents when replacing the lamp.

Note that the above-described embodiment has higher operational reliability because it does not have a mechanical contact, compared to an embodiment that is provided with a relay or the like to cut off the supply of battery voltage when the lamp is turned on abnormally.

9.39...detection means, 10... control circuit, 14... Abnormal state detection means, 38b, 39... Current limiting load Application Man Koito Manufacturing Co., Ltd.

[Brief explanation of the drawing]

1 to 3 show an example of the implementation of a lighting circuit for a discharge lamp for a vehicle according to the present invention. FIG. 1 is a circuit block diagram showing the overall configuration, and FIG. 2 is a circuit showing the main parts in detail. 3 are circuit block diagrams showing the configuration of the PWM control IC. Explanation of symbols 1...Lighting circuit for vehicle discharge lamp, 3.3'...DC voltage input terminal, 4...DC booster circuit, 6...Converter circuit, 8...Discharge lamp, / Circuit block whistle diagram of PVM field IC

Claims (2)

[Claims] (1) Equipped with a DC booster circuit that boosts the DC voltage from the DC voltage input terminal and a converter circuit that converts the output voltage of the DC booster circuit into an AC voltage, the output of the converter circuit is released via a current limiting load. A lighting circuit for a vehicular discharge lamp in which an electric current is applied to the electric lamp includes a detection means for detecting lighting or non-lighting based on a current flowing through the discharge lamp, and a detection means for detecting lighting or non-lighting of the discharge lamp based on a signal from the detection means. A lighting circuit for a discharge lamp for a vehicle, characterized in that it is provided with an abnormal state detection means that stops the oscillation operation of a converter circuit when it is determined that the lighting is impossible. (2) A control circuit is provided that controls the output voltage of the DC booster circuit by sending control pulses to the DC booster circuit, and the control circuit receives a signal from the abnormal state detection means indicating that the discharge lamp cannot be lit. A lighting circuit for a discharge lamp for a vehicle according to claim 1, characterized in that the sending of control pulses to the DC booster circuit is stopped when