JPH065373A - Lighting circuit device for high brightness discharge lamp for car - Google Patents

Abstract

PURPOSE:To provide a lighting circuit device which is for a high brightness discharge lamp of a car, suppresses flow of a large current to the primary side through sensing the saturation phenomenon in a high voltage transformer when discharge lamp is to be lighted up, and can thereby protect a switching element against thermal destruction due to transient heat. CONSTITUTION:A lighting circuit for a discharge lamp 4 includes a transformer saturation sensing circuit 27 which senses saturation before a high voltage pulse transformer 24 is saturated when lighting-up of the lamp 4 is to be started. This allows suppressing a large current flowing in an FET 23, and the switching element of the lighting circuit is protected against thermal destruction due to transient heat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-intensity discharge lamp lighting circuit device for automobiles.

[0002]

2. Description of the Related Art In recent years, automobile designs tend to be more streamlined, and accordingly, compact headlights are required. However, when the headlight is made compact, the light collection efficiency of the lamp decreases, so a light source with higher efficiency and higher brightness than the conventional halogen bulb is required,
A system using a high-intensity discharge lamp has been developed as a next-generation headlight that satisfies these conditions. This high-intensity discharge lamp system is composed of an ultra-compact metal halide lamp in which a rare gas, mercury, and a metal halide as a luminescent substance are enclosed in an arc tube made of quartz glass, and a lighting circuit.

FIG. 3 shows a circuit block diagram of a conventional example, and its operation will be described. Reference numeral 1 denotes a DC power source provided in the automobile, which normally supplies a DC voltage of 9 to 16V. Two
Is a high-intensity discharge lamp lighting circuit device for an automobile (hereinafter referred to as a lighting circuit device), which is connected to a DC power source 1 through a lamp lighting switch 3 and controls lighting of a discharge lamp 4. The lighting circuit device 2 includes a DC / DC converter 21 that boosts the power supply voltage of the DC power supply 1 and outputs a boosted DC voltage, and
A polarity changeover switch circuit 22 for converting the boosted DC voltage boosted by the C / DC converter 21 into an alternating current, and a polarity changeover switch circuit 22 for generating a high voltage initially for lighting the discharge lamp 4 are provided. D on the primary side
A high-voltage pulse transformer 24 connected to the boosted direct-current voltage terminal of the C / DC converter 21 and the FET 23;
Starting circuit 25 for giving a switching signal to ET23 and D
It consists of a C / DC converter 21 and a control circuit 26 which controls the start-up circuit 25 and provides a suitable lighting for the vehicle headlights.

Next, a basic lighting operation will be described. The direct current power supply 1 for an automobile usually has an output voltage of 9 to 16 V and is used as a power supply for an electronic circuit device of an automobile. The lighting circuit device 2 also uses the DC power source 1 as a power source, and turns on / off the lighting switch 3 to turn on / off the discharge lamp 4. When the lighting switch 3 is turned on, a DC voltage is supplied to the control circuit 26 of the lighting circuit device 2, and the discharge lamp 4
The standby state of a series of control operations from the state where is turned off to the stable lighting is secured. In order for the discharge lamp 4 to light up, it is first necessary to apply a high voltage between the discharge terminals inside the discharge lamp 4 to shift to arc discharge. The DC / DC converter 21 starts operating to boost the input DC voltage 9 to 16 V to a high voltage.
Controlled by the DC / DC converter 21,
It is boosted to obtain C220V. Next, in order to obtain a high-voltage pulse voltage of about 15 kV between the discharge terminals of the discharge lamp 4, the voltage supply line connected from the boosted DC voltage side of the output end of the DC / DC converter 21 is connected to the high-voltage pulse transformer 24.
When the FET 23 is turned on, energy is stored in the inductance of the primary winding of the high voltage pulse transformer 24. When sufficient energy is stored, the FET 23 is turned off to store energy in the primary side inductance. Is discharged to the secondary side. With this, 15 kVP− is applied between the discharge terminals of the discharge lamp 4 connected in series between the two secondary windings of the high voltage pulse transformer 24.
A high voltage pulse voltage of P is generated.

The start-up circuit 25 controls ON / OFF of the FET 23. The control circuit 26 controls the generation of a series of high-voltage pulse voltages, and controls the step-up DC voltage of the DC / DC converter 21 and the start / stop of the operation of the starting circuit 25. The starter circuit 25 gives an ON signal having a pulse width of about 1.5 μs to the gate of the FET 23 at a cycle of about 40 kHz by receiving an operation start signal from the control circuit 26. With this signal, the FET 23 performs a switching operation, and the high voltage pulse transformer 24 transfers energy based on the principle described above.

Next, when a signal for stopping the operation is given from the control circuit 26, the starting circuit 25 stops the operation and the FET 2
3 also stops operating. Therefore, the high voltage pulse transformer 2
There is no energy transfer at 4. Next, discharge lamp 4
When a high-voltage pulse voltage starts the discharge phenomenon and a path for electrons to flow is formed inside the discharge lamp 4, the impedance of the discharge lamp 4 sharply decreases and a current easily flows.

In this process, the polarity changeover switch circuit 2 connected to the output terminal of the DC / DC converter 21.
An alternating current is supplied to the discharge lamp 4 via 2. However, an alternating current is applied to the discharge lamp 4 as a bias from the polarity switching switch circuit 22 before the high voltage pulse voltage is applied.

Next, in a state where the discharge lamp 4 reaches arc discharge, the temperature of the discharge tube of the discharge lamp 4 gradually rises with time, and the impedance of the discharge lamp 4 is increased by the emission of the gas enclosed in the discharge lamp 4. Although rising, the electric power of the discharge lamp 4 is controlled in order to control the stable luminous flux in the control circuit 26.

In the automobile headlight system, since it is required to shorten the time required to reach a stable luminous flux as much as possible, about twice as much electric power as that at the time of stable lighting is supplied at the time of lighting start until the discharge lamp 4 becomes stable. A large amount of current will flow through the discharge lamp 4. When the discharge lamp 4 is stable in temperature, the discharge lamp is controlled with a constant power of about 35 W as power control. When the discharge lamp 4 that has been turned on is turned off and turned on again for a short time (about 1 to 30 seconds), a means for changing the control at the time of lighting start depending on the time when the discharge lamp 4 is turned off is used.

Next, a specific circuit of a part of the lighting circuit device 2, the high voltage pulse transformer 24, the discharge lamp 4, and the FE.
The lighting mechanism of the discharge lamp 4 will be described in more detail with reference to T23 and the drawings of the voltage-current waveforms of the respective parts. FIG. 4 is a specific circuit diagram of a part of the polarity changeover switch circuit 22, the high voltage pulse transformer 24, the FET 23, and the discharge lamp 4. Reference numeral 211 is a flyback transformer, 212 is a diode, and 213 is a capacitor, which is a secondary circuit of the flyback system of the DC / DC converter 21. The AC voltage that is switched on the primary side of the flyback transformer 211 and boosted to the secondary side is
V _DC1 is output to the cathode side of the diode 212 as a boosted DC voltage that is rectified by the diode 212 and the capacitor 213. A diode 221 applies a voltage V _DC2 to the cathode side. 222 to 225 are FETs, which are configured as a full bridge circuit.
The drain of 24 is V _DC2 and the source of FET 222 is F
The drain of the ET 223 and the secondary winding terminal 241 of the high-voltage pulse transformer 24 are connected, and the source of the FET 224 is similarly connected to the drain of the FET 225 and the secondary winding terminal 244 of the high-voltage pulse transformer 24. FET2
The sources of 23 and 225 are both connected to GND.
An ON / OFF signal as shown in FIG. 5 is input to the gates of the FETs 222 to 225, and the FETs 222 and FET2
25, and FET223 and FET224 are the same ON / O
FF operation, FET222,225 and FET223,
The ON / OFF operations of 224 are reversed. Thereby, the secondary side terminal 2 of the high voltage pulse transformer 24
An AC voltage is applied to the discharge lamp 4 connected to 42 and 243.

FIG. 6 shows a voltage V _DC1 and a current I flowing through the discharge lamp 4 in a series of states from the extinguished state of the discharge lamp 4 to the stable lighting (lighting start, lighting start, stable lighting). It shows the relationship of. Before the lighting is started, the output voltage V _DC1 of the DC / DC converter is boosted toward about _DC 220 V, and the DC / DC converter operates under constant voltage control during this period.

When V _DC1 exceeds this voltage at the boundary of about 180 V, the control circuit 26 causes the FET 2 to operate via the starting circuit 25.
A pulse signal is sent from the starting circuit 25 so as to apply a voltage exceeding the threshold value to the gate of 3. As a result, the drain and source of the FET 23 become conductive, and a current starts to flow from the V _DC1 line through the primary winding of the high voltage pulse transformer 24 to accumulate energy in the high voltage pulse transformer 24. As a result, a high-voltage pulse voltage of 15 kVP-P is applied to the discharge terminals of the discharge lamp 4 by about 40 k through the process of energy transfer by the high-voltage pulse transformer 24 described above.
It is generated in Hz cycle. This state is when lighting is started.

Next, the discharge lamp 4 starts arc discharge,
The resistance component between the discharge terminals drops sharply, and FET222-
225 drain-source, high voltage pulse transformer 24
At the same time as the lamp current starts to flow in the secondary winding of the discharge lamp 4 and the discharge lamp 4, the DC / DC converter shifts to the constant current control,
As a result, V _DC1 drops sharply. When V _DC1 falls below approximately 150 V, the control circuit 26 detects that the discharge lamp 4 has arced, and the starting circuit 25 stops and the drain-source state of the FET 23 becomes open. .

During the process in which the discharge lamp 4 starts lighting and reaches stable lighting (at the time of lighting start), the resistance component of the discharge lamp 4 gradually rises and the control circuit 26 is power-controlled, and accordingly, V _DC1 and I _DC. Transition to. Finally, the discharge lamp 4 operates as a lamp having a resistance component of about 206Ω,
Settle down to V _DC1 and I, which is determined by the balance with other circuit constants. This state is stable lighting.

[0015]

However, as described in the conventional example, since the control of the operation stop of the starting circuit 25 at the time of lighting starting is performed by detecting the value of V _DC1 , the discharge lamp 4 is discharged. Start high voltage pulse transformer 2
Even if a current starts to flow to the secondary side of No. 4, the starting circuit 25 does not stop, and therefore the FET 23 does not stop operating, and a current flows to the primary side of the high voltage pulse transformer 24. At this time,
Since the current flowing through the secondary side of the high-voltage pulse transformer 24 is higher than the saturation current of the high-voltage pulse transformer 24, the high-voltage pulse transformer 24 is saturated and the inductance on the primary side is minimized. Then, a large current flows between the drain and the source of the FET 23. Therefore, it is desirable to use it in a non-saturated state,
For that purpose, it is necessary to take measures to increase the core of the high-voltage pulse transformer 24, but if this is done, the system becomes large and it cannot be mounted on an automobile. Therefore, there is no choice but to use the high-voltage pulse transformer 24 in a saturated state. From the above, even if the high-voltage pulse transformer 24 is saturated at the time of lighting start, F
There is a problem that a large current flows because the ET 23 performs a switching operation and thermal destruction occurs due to the transient heat of the FET 23.

The present invention solves the above-mentioned conventional problems, and it is possible to operate the control circuit so as to detect the saturation of the high-voltage pulse transformer at the start of lighting and protect the FET from thermal destruction due to transient heat. A lighting circuit device is provided.

[0017]

In order to achieve this object, a high-intensity discharge lamp lighting circuit device for an automobile according to the present invention comprises:
A power supply circuit having an input terminal to which a direct current power supply is connected and having a power supply terminal for boosting a voltage input from the direct current power supply to obtain a boosted voltage and a power supply terminal for supplying power to a discharge lamp; A high-voltage pulse transformer having a secondary winding, one end of which is connected to a power supply terminal of the power supply circuit and the other end of which is connected to a switching element; a starting circuit for starting the discharge lamp; A control circuit for controlling the electric power of the lamp, and a transformer saturation detection circuit for detecting the saturation of the high-voltage pulse transformer at the time of starting the lighting of the discharge lamp.

[0018]

With this configuration, the switching element connected in series to the primary winding of the high voltage pulse transformer can be turned off before the high voltage pulse transformer is saturated, and a large current can be prevented from flowing through the switching element. Therefore, the switching element can be protected from thermal destruction due to transient heat.

[0019]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a specific circuit around a discharge lamp 4 of a high-intensity discharge lamp lighting circuit device for an automobile of the present invention. Flyback transformer 211, diode 212,
Capacitor 213, diode 221, FET 222-
225, capacitor 226, FET 23, high voltage pulse transformer 24, secondary winding terminal 2 of high voltage pulse transformer 24
41 to 244, the starting circuit 25, the control circuit 26, and the discharge lamp 4 have the same configurations as those of the conventional example shown in FIG.

A high voltage pulse voltage is applied to both ends of the discharge lamp 4 by the DC voltage V _DC1 boosted by the flyback transformer 211 and rectified by the diode 212 and the capacitor 213 and the switching operation of the FET 23. The applied high voltage pulse voltage causes the discharge lamp 4
Lighting start control is started until the process of discharging the LED and reaching stable lighting. The resistor 5 is connected between the sources of the FETs 223 and 225 and the ground as a means for detecting the saturation of the high voltage pulse transformer 24. At the start of lighting, when the discharge lamp 4 causes arc discharge and the lamp current starts to flow, the DC / DC converter 21 shifts from the constant voltage control until then to the constant current control. Therefore, V _DC1 sharply decreases and at the same time, the lamp current increases. At this time, before the lamp current reaches the saturation current of the high-voltage pulse transformer 24, the transformer saturation detection circuit 27 that detects the increase of the lamp current by the increase of the voltage appearing across the resistor 5,
The switching operation of the FET 23 can be stopped before the high voltage pulse transformer 24 is saturated. Therefore, even if the high-voltage pulse transformer 24 is saturated and the inductance on the primary side becomes extremely small, the FET 23 stops operating.
It does not flow to 23 and can protect FET 23 from thermal damage due to transient heat.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to FIG. FIG. 2 shows a specific circuit around the discharge lamp 4 of the high-intensity discharge lamp lighting circuit device for an automobile of the present invention. Flyback transformer 211, diode 212, capacitor 213, diode 221,
FET 222 to 225, capacitor 226, FET 2
3, high voltage pulse transformer 24, high voltage pulse transformer 24
Since the secondary winding terminals 241-244, the starting circuit 25, the control circuit 26, and the discharge lamp 4 have the same configurations as those of the conventional example shown in FIG.

A high voltage pulse voltage is applied across the discharge lamp 4 by the DC voltage V _DC1 boosted by the flyback transformer 211 and rectified by the diode 212 and the capacitor 213 and the switching operation of the FET 23. The applied high voltage pulse voltage causes the discharge lamp 4
Lighting start control is started until the process of discharging the LED and reaching stable lighting. The coil 6 is connected to the V _DC2 line capable of detecting the current flowing through the FETs 222 and 224 as a means for detecting the saturation of the high voltage pulse transformer 24. At the start of lighting, when the discharge lamp 4 causes arc discharge and the lamp current starts to flow, the DC / DC converter 21 shifts from the constant voltage control until then to the constant current control. Therefore, V _DC1 sharply decreases and at the same time, the lamp current increases. At this time, the lamp current is high voltage pulse transformer 24.
The switching operation of the FET 23 can be stopped before the high-voltage pulse transformer 24 is saturated by the transformer saturation detection circuit 27 that detects the increase in the lamp current by the induced electromotive voltage appearing across the coil 6 before reaching the saturation current. . Therefore, even if the high-voltage pulse transformer 24 is saturated and the inductance on the primary side becomes extremely small, the FET 23 stops operating. Therefore, a large current due to the saturation of the high-voltage pulse transformer 24 does not flow to the FET 23, and the FET 23 is caused by transient heat. Can be protected from thermal destruction.

[0023]

As described above, the lighting circuit device for a high-intensity discharge lamp for automobiles according to the present invention detects an increase in the current flowing through the discharge lamp and forcibly turns off the switching element.
By connecting the transformer saturation detection circuit to the switching element, the switching element can be turned off before the high voltage pulse transformer is saturated, and the switching element can be protected from thermal destruction due to transient heat.

[Brief description of drawings]

FIG. 1 is a specific circuit diagram of a lighting circuit device for an automobile high-intensity discharge lamp according to an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of a lighting circuit device for an automobile high-intensity discharge lamp according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional lighting circuit device for a high-intensity discharge lamp for automobiles.

FIG. 4 is a specific circuit diagram of a conventional lighting circuit device for an automobile high-intensity discharge lamp.

FIG. 5 is a gate signal waveform diagram of the FET in FIG.

FIG. 6 is a waveform diagram of voltage V _DC1 and current I in a series of processes from lighting start-up to stable lighting after lighting start-up.

[Explanation of symbols]

 1 DC power supply 2 Lighting circuit device 3 Lighting switch 4 Discharge lamp 5 Resistance 21 DC / DC converter 22 Polarity changeover switch circuit 23 FET 24 High voltage pulse transformer 25 Starting circuit 26 Control circuit 27 Transformer saturation detection circuit

Front page continuation (72) Inventor Masanori Hatanaka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A power supply circuit having a power supply terminal for boosting a voltage input from a DC power supply to obtain a boosted voltage and a power terminal for supplying power to a discharge lamp, a primary winding and a secondary winding, and A high-voltage pulse transformer in which one end of the primary winding is connected to the power supply terminal of the power supply circuit and the other end is connected to a switching element, a starting circuit for starting the discharge lamp, and control for controlling the electric power of the discharge lamp. And a circuit, and a high-intensity discharge lamp lighting circuit device for an automobile, comprising a transformer saturation detection circuit for detecting saturation of the high-voltage pulse transformer at the time of starting lighting of the discharge lamp. 2. The high-intensity discharge lamp lighting for an automobile according to claim 1, wherein the transformer saturation detection circuit detects the saturation of the high-voltage pulse transformer by the voltage across a resistor arranged in series with the secondary winding of the high-voltage pulse transformer. Circuit device. 3. The high brightness for automobile according to claim 1, wherein in the transformer saturation detection circuit, the saturation of the high voltage pulse transformer is detected by a coil inductance-coupled to a current supply line connected to the secondary winding of the high voltage pulse transformer. Discharge lamp lighting circuit device.