JP2779558B2 - Lighting circuit for vehicle discharge lamps - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting circuit for a vehicular discharge lamp having a booster circuit for boosting a DC input voltage.
An object of the present invention is to provide a novel lighting circuit for a discharge lamp for a vehicle, which can maintain the lighting state of the lamp even when a sudden change occurs in the DC input voltage.

[0002]

2. Description of the Related Art In recent years, small metal halide lamps have attracted attention as light sources for automobiles, and a lighting circuit using a DC power supply has been designed so that a DC input voltage is boosted and then converted to AC and applied to the lamp. Are known.

One of the functions required for such a lighting circuit is to stabilize the circuit state against fluctuations in the power supply voltage and maintain the lighting of the lamp.

FIG. 6 shows an example of a lighting circuit a, in which a battery voltage is sent to a DC (DC) boosting circuit c via a lighting switch b, and DC boosting is performed. Thereafter, the voltage converted into AC in the inverter circuit d is supplied to the metal halide lamp f via the igniter circuit e.

[0005] The output voltage of the DC boosting circuit c is divided by a voltage dividing resistor g,
g ', and its output current is detected by a current detection resistor h, and these detection signals are sent to a PWM (pulse width modulation) control unit i. The output pulse of the PWM control unit i is fed back to the DC booster circuit c, and the output voltage of the DC booster circuit c is controlled by varying the duty cycle of the output pulse.

[0006]

However, in the conventional lighting circuit, there is a problem that it is difficult to maintain the lighting of the lamp with respect to the fluctuation of the DC power supply voltage.

FIG. 7 shows a power supply voltage (this is referred to as "B").
(This is referred to as "iL")
Is schematically shown.

FIG. 7A shows a sharp drop ΔB in the power supply voltage B.
Occurs, the lamp current waveform becomes as indicated by j, and the current value iL becomes smaller. However, after the delay time of .DELTA.t, the control of the voltage fluctuation starts to take effect, and the metal halide lamp f
Shows the state when the lighting state is maintained.

FIG. 7B shows how the metal halide lamp f disappears because the control for the fluctuation of the power supply voltage is too late, as shown by the lamp current waveform k.

[0010] The metal halide lamp f
Whether or not the lighting is maintained depends on the manufacturing conditions of the lamp. However, when conditions other than the lamp voltage are the same, there is a tendency that the higher the lamp voltage, the higher the probability of occurrence of extinguishing.

In order to cope with manufacturing variations in lamp performance, it is necessary to make the control response faster when the power supply voltage fluctuates. One method for this is to reduce the capacitance of the capacitor that is delaying the response. It is possible to do.

However, in this method, a sufficient phase margin in PWM control cannot be ensured, so that there is a disadvantage that oscillation occurs in a feedback loop of the DC booster circuit c and the PWM control unit i.

If the control response is fast, the PWM control section i responds quickly when the lamp is relighted and feedback is applied to the DC boosting circuit c, so that the output voltage is too low to maintain the lighting state of the lamp. However, there is an inconvenience that the disappearance occurs.

To summarize the above, if the response of the PWM control is slow, the control will not be able to follow the rapid change of the battery voltage B, so that the lamp will be easily extinguished. This causes an oscillation problem and an inconvenience that the lamp goes out when the lamp is turned on again.

[0015]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a DC input voltage from a DC power supply.
Output to detect the output voltage and output current of the booster circuit
Input to the input voltage detector, output current detector, and booster circuit.
Of the DC input voltage, and responds to the
Control signal by sending the same signal to the control circuit.
Response control means for variably controlling the speed;
Increase the control response speed of the control circuit by the output signal of the control means
To the output signal of the output current detector as a signal for
This is compared with a predetermined reference value, and the comparison result is obtained.
The output signal of the output voltage detection unit
Control circuit based on the control signal obtained by
Control the output voltage of the booster circuit.
You.

[0016]

According to the present invention, the control response is accelerated only when the DC input voltage is suddenly changed, whereby the lighting state of the lamp can be maintained. Is not accelerated, so that there is no inconvenience such as extinguishing or causing oscillation when the lamp is turned on again.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the lighting circuit for a vehicle discharge lamp according to the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 shows a main part of a lighting circuit 1 according to the present invention.

In FIG. 1, reference numeral 2 denotes a battery, which is connected between DC voltage input terminals 3, 3 '.

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

Reference numeral 6a denotes a relay contact provided on the plus line 4, which opens the relay contact 6a when the power cut-off relay circuit 6 receives a signal from an abnormality detection circuit (not shown), and connects the battery to a circuit at a subsequent stage. It is provided so as to cut off the supply of voltage.

Reference numeral 7 denotes a DC booster circuit, the positive input terminal of which is connected to the output terminal of the relay contact 6a, and the other input terminal (ground side) of which is connected to the DC voltage input terminal 3 '. The DC boosting circuit 7 is a circuit for boosting the battery voltage, and the boosting control is performed by a control circuit described later.

Reference numeral 8 denotes an inverter circuit, which is provided at the subsequent stage of the DC booster circuit 7 and converts a DC voltage from the DC booster circuit 7 into a sine wave AC voltage. For example, a push-pull self-excited inverter circuit is used.

Reference numeral 9 denotes an igniter circuit for controlling the starting of the lamp. The igniter circuit 9 is disposed downstream of the inverter circuit 8, and a metal halide lamp 11 having a rated power of 35 W is connected between its AC output terminals 10 and 10 '.

Reference numeral 12 denotes a PWM control circuit for controlling the output voltage of the DC booster circuit 7, which is detected by voltage dividing resistors 13 and 13 'provided between the output terminals of the DC booster circuit 7. (Hereinafter referred to as “V _O ”) is input. Also, D
A current detection signal corresponding to the output current of the DC booster circuit 7 (referred to as “I _O ”) is generated by a current detection resistor 14 provided on a ground line connecting the C booster circuit 7 and the inverter circuit 8. The voltage converted form is input to the PWM control circuit 12 via the amplifier 15.

Then, the PWM control circuit 12 generates a control signal whose duty cycle is varied in accordance with these detection signals (this signal is referred to as “P _S ”). The output voltage is controlled by feeding back to the booster circuit 7.

The output voltage V _O of the DC booster circuit 7 is input to the PWM control circuit 12 via the timer circuit 17 so that the transition point to the low power control is defined according to the lamp extinguishing time. It has become.

A response control circuit 18 detects a change in the battery voltage and sends a control signal to the PWM control circuit 12 to speed up the response of the control.

The detection point of the battery voltage is located after the relay contact 6a, and the response control circuit 18 detects the fluctuation of the battery voltage at the detection point.

FIG. 2 shows a main part of a power supply system for the lamp and a lighting control system in the lighting circuit 1.

The DC booster circuit 7 is a chopper type DC-D
It is configured as a C converter, and is provided between the plus line 4 and the ground line 4 ′ in the subsequent stage between the inductor 19 provided on the plus line 4 and the gate drive circuit 16 from the PWM control circuit 12. An N-channel FET 20 which is switched by a control pulse P _S sent through the
The rectifying diode 21 has an anode connected to the drain of the FET 20 and a smoothing capacitor 22 provided between the cathode of the diode 21 and the ground line 4 '.

Then, the DC boosting circuit 7 outputs the control pulse P _S
As a result, when the FET 20 is turned on, the inductor 19 stores energy, and when the FET 20 is turned off, the stored energy is released, and a voltage corresponding to this is superimposed on the input voltage to perform DC boosting. It has become.

A PWM control circuit 12 constituting a lighting control system
Converts the output voltage V _O of the DC booster circuit 7 to the voltage dividing resistors 13, 1
3 ′, an output current detection unit 24 that detects the output current I _O of the DC booster circuit 7 after voltage conversion by the current detection resistor 14, and an output voltage detection unit 23 and an output current and a PWM control unit 25 for receiving a signal from the detecting unit 24 controls the duty cycle of the control pulse P _S to the gate drive circuit 16.

The output voltage detector 23 detects the output voltage V _O of the DC booster 7, compares it with a predetermined reference voltage, and sends an error output to the PWM controller 25.

An error amplifier 26 uses an operational amplifier 28 to which a negative feedback is applied by a resistor 27. The output voltage V _O of the DC booster 7 is connected to a non-inverting input terminal of the resistor 13 and 13 '. It is input after the partial pressure by.

A predetermined reference voltage (referred to as “V ₁ ”) defined by the voltage dividing resistors 29 and 29 ′ is applied to the inverting input terminal of the operational amplifier 28. A predetermined voltage (referred to as “V _ref ”) from a reference voltage generator (not shown) is applied to one end of the voltage dividing resistor 29, and the V _ref is constant without being affected by the fluctuation of the battery voltage. Value.

Reference numeral 30 denotes a capacitor provided in parallel with the feedback resistor 27 of the operational amplifier 28.

The output current detector 24 detects the output current _IO of the DC booster circuit 7 after voltage conversion by the current detecting resistor 14, compares it with a predetermined reference value, and extracts a difference voltage as an error output. It is provided for receiving a detection signal from the response control circuit 18 at the time of a sudden change in the battery voltage to speed up the response of the PWM control.

An operational amplifier 32 to which a negative feedback is applied by a resistor 31 is used as the amplifier 15, and a non-inverting input terminal of the operational amplifier 32 receives a terminal voltage of a capacitor 33 connected in series to the current detecting resistor 14. Is to be entered via The inverting input terminal of the operational amplifier 32 is grounded via a resistor 35.

An error amplifier 36 uses an operational amplifier 38 to which negative feedback is applied by a resistor 37. The output of the amplifier 15 is input to a non-inverting input terminal of the operational amplifier 38 via a resistor 39. 18 output voltages are applied.

The voltage V _ref is applied to the inverting input terminal.
Is divided by the resistors 40 and 40 ′, and a reference voltage (this is referred to as “V ₂ ”) is applied via the voltage buffer 41. Note that a capacitor 42 is provided in parallel with the feedback resistor 37.

In the response control circuit 18, the power supply voltage after the relay contact 16 a is applied to the capacitor 44 via the diode 43, and the terminal voltage is divided by the resistors 45 and 46, and the voltage is divided via the coupling capacitors 47 and 48. To be applied to the non-inverting input terminal of the operational amplifier 38.

That is, the fluctuation of the battery voltage is sent to the error amplifier 36.

The timer circuit 17 is a circuit provided for defining the timing of transition to the constant power control in accordance with the time required from the previous lamp extinguishing time to the relighting starting time.

The timer circuit 17 includes a time constant circuit 49,
The NPN transistor 50 is controlled by the switching operation.
The emitter is connected to the non-inverting input terminal of the operational amplifier 38 via a resistor 51.

The PWM control unit 25 is provided with the comparator 5
The sum output of the operational amplifier 28 and 38 in 2 compared with a triangular wave from the oscillator 53, is intended to generate a control pulse P _S duty cycle corresponding to the input voltage.

That is, the minus input terminal of the comparator 52 is connected to the output terminals of the operational amplifiers 28 and 38, and the plus input terminal is connected to the output terminal of the oscillator 53.

The output signal of the comparator 52 is
4 to the gate drive circuit 16.

In the lighting circuit 1 described above, when the fluctuation of the battery voltage is small, the output voltage of the response control circuit 18 is small.
Or PWM control is performed based on a detection signal of the output current detecting unit 24, the output voltage of the DC booster circuit 7 is controlled by a variable control of the duty cycle of the control pulse P _S.

At this time, the physical state of the metal halide lamp 11 (tube temperature and restart voltage) differs depending on how much time has elapsed since the last lighting.
The timer circuit 17 indirectly monitors the state of the lamp, and defines the time from the start of lighting of the lamp to the transition to the constant power control.

For example, when the lighting is started from a cold state of the lamp, PWM control is initially performed mainly based on the output of the output voltage detecting section 23, and the output voltage of the DC booster circuit 7 is controlled. After that, however, the control by the output current detection unit 24 becomes mainstream. When the transistor 50 of the timer circuit 17 is turned on, the addition output of the detection signal relating to the output voltage V _O and the output current I _O of the DC boosting circuit 7 is controlled to be constant, and V _O · I _O = constant Finally, a transition is made to constant power control that realizes the constant power curve in the form of linear approximation.

When the lamp is turned off and re-lighting is to be performed shortly, the lamp is turned on after the time specified by the time constant circuit 49 via the PWM control under the control of the output current detecting unit 24 from the time when the lighting switch 5 is turned on. Shift to power control.

Next, when a sudden change in the battery voltage occurs, the response control circuit 18 detects the amount of the change in the battery voltage, and sends the detected voltage to the error amplifier 38 of the output current detecting section 24. PWM control is forcibly performed so that the difference between the detection voltage and the reference voltage V ₂ becomes zero,
As a result, the response speed of the control is increased.

This makes it difficult for the lamp to extinguish due to the voltage fluctuation.

FIG. 3 shows a sharp drop ΔB in the battery voltage B.
The output voltage V (18: OUT) of the response control circuit 18, the input voltage V (38: + IN) of the non-inverting input terminal of the operational amplifier 38, and the output voltage V
(38: OUT), and schematically shows a temporal change of the output voltage V _O of the DC boosting circuit 7.

In the figure, the waveform indicated by the solid line indicates the waveform according to the present invention, and the waveform indicated by the broken line indicates the case where the response control circuit 18 is not provided, that is, the PWM control is performed without considering any change in the battery voltage. The waveform in the case is shown.

According to the present invention, V (38: + IN), V (3
8: OUT), the influence of the fluctuation of the battery voltage is clearly recognized, the slope of the rise is large, and the responsiveness is improved through the correction of the error voltage.

FIG. 4 shows a situation where the battery voltage B sharply rises. The meanings of the symbols and the lines are the same as those described with reference to FIG.

In this case, the rise of the input / output voltage of the operational amplifier 38 is fast, and the output voltage V
It can be seen from the figure that the overshoot of _O is suppressed.

FIG. 5 shows the change in the lamp current accompanying the rise and fall of the battery voltage B. In the figure, "iL" indicates the lamp current when the response control circuit 18 is not provided.
“IL” indicates a lamp current according to the present invention.
It is needless to say that the same lamp is used for comparison between the two.

As shown, when the response control circuit 18 is not provided, the amplitude level of the lamp current iL becomes smaller as shown by the arrow m when the battery voltage drops, and is smaller than the amplitude level of the lamp current IL shown by the arrow M. And quite small,
It appears that it is difficult to maintain lighting of the lamp when the voltage fluctuates.

In the lighting circuit 1, the response control circuit 18 detects a change in the battery voltage, and controls the response speed for the PWM control according to the amount of the change. Is a problem caused by suppressing the occurrence of the lamp extinguishing due to the above, and uniformly increasing the responsiveness of the PWM control, that is, the feedback control composed of the DC booster circuit 7, the PWM control circuit 12, and the gate drive circuit 16. It is possible to prevent the problem of the oscillation described above and the occurrence of the extinguishing when the lamp is turned on again.

[0063]

As is apparent from the above description, according to the present invention, the response of the lighting control can be optimized in accordance with the fluctuation of the DC input voltage. In addition to reducing the frequency of lamp extinguishment due to sudden changes, it is difficult to address the problem simply by improving responsiveness by simply selecting circuit constants. Occurrence) can be solved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a lighting circuit according to the present invention.

FIG. 2 is a circuit diagram showing a main part of a lighting circuit according to the present invention.

FIG. 3 is a schematic waveform diagram for describing control when the battery voltage is lowered.

FIG. 4 is a schematic waveform diagram for describing control when the battery voltage rises.

FIG. 5 is a schematic waveform diagram showing a relationship between a battery voltage and a lamp current.

FIG. 6 is a block diagram illustrating a configuration of a conventional lighting circuit.

FIG. 7 is a waveform diagram for explaining a problem, and FIG.
FIG. 4 is a diagram showing a lamp current waveform when the lighting state of the lamp is maintained when the battery voltage fluctuates, and FIG. 4B is a diagram showing a lamp current waveform when the lamp extinguishes when the battery voltage fluctuates.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 lighting circuit for vehicle discharge lamp 2 DC power supply 7 booster circuit 11 discharge lamp 12 control circuit 13, 13 ′ output voltage detector 14, 15 output current detector 18 response control means

Continuation of the front page (72) Inventor Masatoshi Sugasawa 500 Kitawaki, Shimizu-shi, Shizuoka Pref. Koito Manufacturing Co., Ltd. Shizuoka Plant (56) References JP-A-62-259391 (JP, A) JP-A 60-207294 (JP) JP-A-60-207293 (JP, A) JP-A-3-153430 (JP, A) JP-A-52-54278 (JP, A) JP-A-2-177298 (JP, A) 3-11595 (JP, A) JP-A-3-171596 (JP, A) JP-A-4-163887 (JP, A) JP-A-5-121187 (JP, A) Japanese Utility Model Laid-Open No. 59-146899 (JP, A) U) Japanese Utility Model Hei 3-130198 (JP, U) Japanese Utility Model Utility Model Hei 3-118594 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 41/16-41/29 B60Q 1 / 04

Claims (1)

(57) [Claims] 1. A step-up circuit for boosting a DC input voltage from the DC power source, an output voltage detection unit for detecting an output voltage of the booster circuit, and an output current detector for detecting an output current of the booster circuit, the output Based on signals from the voltage detector and output current detector
In a lighting circuit for a vehicle discharge lamp having a control circuit for controlling the lighting of the discharge lamp by varying the output voltage of the booster circuit, while detecting the amount of change in the DC input voltage input to the booster circuit , Response control means for variably controlling the speed of the control response by sending a signal corresponding to the variation to the control circuit is provided , and the output signal of the response control means is used to control the control response speed of the control circuit.
As a signal for speeding up, the output signal of the output current detection unit is used.
And compare it with a predetermined reference value.
The signal indicating the comparison result and the output signal of the output voltage detection unit
Control based on the control signal obtained by adding
A lighting circuit for a vehicular discharge lamp, wherein a control circuit controls an output voltage of the booster circuit.