JP2009199917A - Lighting control device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lighting control device for vehicles capable of performing on/off switching with high accuracy. <P>SOLUTION: The lighting control device has: an NMOS transistor 2 performing the on/off control of a drive current supplied to a semiconductor light source; and a control means controlling the NMOS transistor 2 according to a light adjustment control signal S2. The control means has: a triangular wave generating circuit 4 converting a voltage signal corresponding to the on/off state of the NMOS transistor 2 into a triangular wave voltage signal; and an operational amplifier unit including an operational amplifier 14 that compares the voltage value of the triangular wave voltage signal with a predetermined threshold on receiving the triangular wave voltage signal to move the triangular waveform voltage in the amplitude direction according to the comparison results maintaining the waveform of the triangular wave, and so controls the input value of the triangular wave generating circuit 4 as to constantly maintain the on-duty of the triangular wave for turning on the NMOS transistor 2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vehicle lighting control device, and more particularly to a vehicle lighting control device that controls lighting of a semiconductor light source composed of a semiconductor light emitting element.

  2. Description of the Related Art Conventionally, there is known a vehicle lighting control device that performs PWM (Pulse Width Modulation) dimming control on a part of a plurality of LEDs (Light Emitting Diodes) connected in series.

  The vehicle lighting control device described above is an NMOS (Negative Channel Metal Oxide Semiconductor) that functions as a switching element connected in parallel to some of the plurality of LEDs (hereinafter referred to as “bypass LEDs”). ) Including a transistor, a PWM signal generation circuit, and a dimming start signal generation circuit.

  In the above-described vehicle lighting control device, an NMOS transistor is connected in parallel to the bypass LED, and the bypass LED current supplied to the bypass LED is bypassed by turning on the NMOS transistor.

  Here, when the NMOS transistor receives the ON signal at the gate and changes from the OFF state to the ON state, or receives the OFF signal and changes from the ON state to the OFF state, the NMOS transistor supplies the bypass LED to the bypass LED. The bypass LED current to be changed fluctuates in synchronization with the on signal or the off signal.

  For example, since the bypass LED current is not supplied to the bypass LED when the NMOS transistor is turned on, the load corresponding to the drive voltage corresponding to the bypass LED current is reduced.

  Due to the decrease in the load, the charge (Q = CV) stored in the output smoothing capacitor constituting the switching regulator (DC-DC converter) that drives and controls the LED flows as an inrush current, and the LED current other than the bypass LED Overshoot will occur.

On the other hand, since the bypass LED functions as a load when the NMOS transistor is turned off, the control of the switching regulator cannot respond instantaneously to the off-switching control and an undershoot occurs. The occurrence of the overshoot and the undershoot is prevented by providing a CR circuit functioning as a delay circuit on the gate side of the NMOS transistor.

  In addition, please refer to the following patent document 1 as a prior art document relevant to the said prior art.

JP 2004-134147 A

  However, in the above-described prior art, when the threshold voltage of the gate signal of the NMOS transistor varies vertically (in the amplitude direction), the difference exceeds the range exceeding the threshold voltage of the gate signal, that is, the magnitude of the on-duty. For example, if the width of the on-duty is too large or too small, the probability that the on / off switching operation of the NMOS transistor receiving the high level signal becomes impossible increases, and the accuracy of the on / off switching operation decreases. To do.

  Then, this invention makes it a subject to provide the lighting control apparatus for vehicles which can perform on-off switching with high precision.

The vehicle lighting control device according to the first aspect of the present invention includes a switching means connected in parallel to a semiconductor light source for on / off control of a drive current supplied to the semiconductor light source, and the switching according to a dimming control signal. In a vehicle lighting control device having a control means for controlling the means,
The control means includes
A triangular wave generator for changing a voltage signal corresponding to ON / OFF of the switching means into a triangular wave voltage signal;
Compare the voltage signal corresponding to the on / off of the switching means with a predetermined threshold, and based on the comparison result, while moving the triangular wave voltage signal in the amplitude direction while maintaining the shape of the triangular wave voltage signal, A triangular wave control unit for controlling the on-duty of the triangular wave voltage signal for on-controlling the switching means so as to maintain a constant magnitude.

  Therefore, the voltage signal corresponding to ON / OFF of the drive current supplied to the semiconductor light source is changed to a triangular wave voltage signal, the triangular wave voltage signal is received, and the voltage value of the triangular wave voltage signal is compared with a predetermined threshold value. Then, the triangular wave voltage signal is translated in the amplitude direction while maintaining the shape of the triangular wave voltage signal based on the comparison result. The input value of the generating unit that generates the triangular wave voltage signal is controlled so that the on duty of the triangular wave voltage signal for on-control is maintained at a constant level.

The vehicle lighting control device according to the present invention includes a switching unit that is connected in parallel to a semiconductor light source and controls on / off of a drive current supplied to the semiconductor light source, and a control unit that controls the switching unit according to a dimming control signal In a vehicle lighting control device having:
The control means includes
A triangular wave generator for changing a voltage signal corresponding to ON / OFF of the switching means into a triangular wave voltage signal;
Compare the voltage signal corresponding to the on / off of the switching means with a predetermined threshold, and based on the comparison result, while moving the triangular wave voltage signal in the amplitude direction while maintaining the shape of the triangular wave voltage signal, And a triangular wave control unit that controls the on-duty of the triangular wave voltage signal for on-controlling the switching means so as to maintain a constant magnitude.

  Therefore, even when the threshold voltage of the switching means for controlling on / off of a part of the semiconductor light source varies, the on-duty width can be kept constant, and highly accurate on / off switching can be performed. it can.

  According to a second aspect of the present invention, the triangular wave generator includes a differential amplifying unit that holds a power supply at a predetermined voltage value, and the triangular wave voltage signal is output while holding the predetermined voltage value. Since the input voltage value of the differential amplifier is controlled so as to translate in the amplitude direction, the input voltage of the differential amplifier can be varied, and the power supply voltage of the differential amplifier can be kept constant. However, the triangular voltage signal can be translated in the amplitude direction.

  In the invention described in claim 3, since the power supply voltage value of the triangular wave generator is higher than the on / off threshold voltage value of the switching means, the triangular wave voltage signal is translated in the amplitude direction. As a result, until the output of the triangular wave control section is saturated, the switching means can be turned on when the input voltage of the switching means exceeds the threshold gate threshold voltage. Therefore, highly accurate on / off switching can be performed even when the threshold voltage of the high-level signal of the switching means varies.

  In the invention described in claim 4, since the triangular wave control unit has a digital-analog conversion unit for converting the output signal voltage of the switching means into an analog voltage, an analog necessary for parallel movement of the triangular wave voltage signal is provided. A signal can be generated.

  Below, the lighting control apparatus for vehicles which concerns on embodiment of this invention is demonstrated with reference to FIGS. 1-3.

  The vehicle lighting control device 1 includes an NMOS transistor 2 that functions as a switching means, a PWM-analog voltage conversion circuit 3 that functions as a digital-analog conversion unit, an operational amplifier unit that functions as a triangular wave control unit, and a triangular wave generation that functions as a triangular wave generation unit A circuit 4 is provided.

  The NMOS transistor 2 is connected in parallel to the LED 6-N which is a part of the LEDs 6-1 to 6-N as semiconductor light sources. Driving current is supplied from the switching regulator 10 to the LEDs 6-1 to 6-N via the output terminals 7 and 9.

  The PWM-analog voltage conversion circuit 3 includes an NPN transistor 12 and a PNP transistor 13. The emitter of the NPN transistor 12 is connected to the collector of the NPN transistor 11, the base is connected to the drain of the NMOS transistor 2 via the resistor R4, and the collector is connected to the base of the PNP transistor 13 via the resistor R5. The emitter of the PNP transistor 13 is connected to the first power supply voltage Vcc.

The operational amplifier unit includes an operational amplifier 14 and a buffer 15. The non-inverting input terminal (positive input terminal) of the operational amplifier 14 is connected to the emitter of the PNP transistor 13 via the resistor R7, and the inverting input terminal (negative input terminal) is connected to the reference voltage V _REF via the resistor R10. . The power supply terminal of the operational amplifier 14 is connected to a second power supply voltage Vcc that functions as an operational amplifier power supply. The output terminal of the operational amplifier 14 is connected to the positive input terminal of the buffer 15 via the resistor R11.

  The triangular wave generation circuit 4 includes an operational amplifier 16. The positive input terminal of the operational amplifier 16 is connected to the output terminal of the buffer 15 via R15 and is connected to the output terminal of the operational amplifier 16 via R16, and the negative input terminal is the output of the operational amplifier 16 via the capacitor C3 and the resistor R17. Connected to the terminal. The power supply positive input terminal and the power supply negative input terminal of the operational amplifier 16 are connected via a Zener diode ZD. The output terminal of the operational amplifier 16 is connected to the gate of the NMOS transistor 2 through the resistor R17.

  Below, operation | movement of the lighting control apparatus 1 for vehicles is demonstrated with reference to the timing chart of FIG.2 and FIG.3.

  First, operations of the PWM-analog voltage conversion circuit 3 and the operational amplifier unit will be described. Note that the PWM-analog voltage conversion circuit 3 functions as a digital-analog conversion unit, but the digital means that the drain voltage high (H) / low (L) due to on / off of the switching means is digital. Means that the positive input voltage to the operational amplifier 14 is analog.

  When the dimming start signal S1 is input to the input terminal 5, the low level signal changes to a high level signal (see FIG. 2A), and the high level signal is input to the base of the NPN transistor 11. The NPN transistor 11 is turned on by inputting a high level signal to the base. Note that after the NPN transistor 11 is once turned on, the on state is maintained until the supply of the dimming start signal S1 is stopped.

  Since the drain voltage of the NMOS transistor 2 (the voltage between the anode and the cathode of the LED 6-N) is detected when the dimming start signal S1 is supplied to the NPN transistor 11, the NPN transistor 12 is in the on state.

  The PNP transistor 13 is turned on when a low level signal is supplied to the base. When the PNP transistor 13 is turned on, the voltage from the first power supply voltage Vcc is supplied to the positive input terminal of the operational amplifier 14 via the collector, and the positive input voltage of the operational amplifier 14 increases according to the time constant of the resistor R7 and the capacitor C1. (See FIG. 2 (b)). As the positive input voltage of the operational amplifier 14 increases, the output voltage of the operational amplifier 14 also increases, and the output voltage is supplied to the positive input terminal of the buffer 15.

  When the positive input voltage of the operational amplifier 14 increases, the NMOS transistor 2 is controlled to be turned on / off by a triangular wave voltage signal (hereinafter referred to as “triangular wave”) output from the triangular wave generating circuit 4. When the NMOS transistor 2 is turned on by the on-control by the triangular wave, the drain voltage of the NMOS transistor 2 is supplied to the base of the NPN transistor 12, the NPN transistor 12 is turned on, the PNP transistor 13 is also turned on, and the operational amplifier 14 A positive input voltage is supplied to the positive input terminal. Thereafter, when the NMOS transistor 2 is turned off by the turn-off control using the triangular wave, the drain voltage is not detected, so that the NPN transistor 12 is turned off. Therefore, the PNP transistor 13 is turned off. Thereafter, the PNP transistor 13 is turned on again, and the voltage output from the first power supply voltage Vcc is supplied to the positive input terminal of the operational amplifier 14. Thereafter, this operation is repeated. Since the voltage output from the first power supply voltage Vcc is charged by the capacitor C1, the input waveform at the positive input terminal of the operational amplifier 14 is as shown in FIG.

Until the positive input voltage supplied to the positive input terminal of the operational amplifier 14 exceeds the resistance voltage division of the reference voltage V _REF supplied to the negative input terminal of the operational amplifier 14 (voltage division determined by the resistors R10 and R9), The output voltage continues to rise. When the voltage supplied to the positive input terminal exceeds the resistance voltage division, the output voltage of the operational amplifier 14 becomes constant. Although the output waveform of the operational amplifier 14 is not shown, the waveform is similar to the input waveform of the operational amplifier 14.

  Next, the operation of the triangular wave generation circuit 4 will be described.

  The output voltage output from the buffer 15 is supplied to the positive input terminal of the operational amplifier 16 via the resistor R15 and to the power supply positive input terminal and the power supply negative input terminal. The triangular wave generation circuit 4 generates a triangular wave by feeding back (positive feedback) the output voltage of the operational amplifier 16 and supplying it to the positive input terminal of the operational amplifier 16.

  Here, the magnitude of the triangular wave voltage (hereinafter referred to as “triangular wave voltage”) is proportional to the magnitude of the voltage supplied to the positive input terminal of the operational amplifier 16. Therefore, when the output voltage of the operational amplifier 14 output from the output terminal of the operational amplifier 14 via the buffer 15 increases, the maximum value of the triangular wave voltage increases as the output voltage increases, and the triangular wave has an amplitude direction. Translate upwards.

  Here, since the power supply positive input terminal and the power supply negative input terminal are connected via the Zener diode ZD, the power supply positive input voltage and the power supply negative input voltage of the operational amplifier 16 are always kept constant. Since the amplitude of the triangular wave voltage is determined by the power supply positive input voltage and the power supply negative input voltage, the amplitude of the triangular wave voltage is maintained while maintaining the shape of the triangular wave substantially the same even when the triangular wave is translated upward. Is kept constant (see FIG. 2C). Note that the shape of the triangular wave described above is determined by the inclination of the triangular wave, the magnitude of the amplitude (the magnitude of the voltage), and the duty ratio. For example, the fact that the two triangular waves to be compared have the same shape means that the slopes, amplitudes, and duty ratios of the two triangular waves are substantially the same.

  The triangular wave output from the triangular wave generating circuit 4 is supplied to the gate of the NMOS transistor 2 as the dimming control signal S2. The image of the duty of the triangular wave supplied to the gate of the NMOS transistor 2 is as shown in FIG. As is apparent from FIG. 2D, the duty ratio of the triangular wave changes from the time of rising to the steady state, but becomes constant after the steady state is reached.

  Note that the triangular wave shown in FIG. 2C continues to be output unless the dimming start signal S1 is stopped.

  Hereinafter, the control of the parallel movement of the triangular wave will be described.

The threshold value of the gate voltage (gate threshold voltage V _GTH ) for operating the NMOS transistor 2 at a high level has a predetermined value as shown in FIG. 2C immediately after the start of the dimming control. Thereafter, when the gate threshold voltage V _GTH varies in the amplitude direction, for example, when the gate threshold voltage V _GTH increases, the waveform of the triangular wave with respect to the gate threshold voltage V _GTH is the triangular wave (b in FIG. )become that way. That is, in order to perform highly accurate PWM dimming control, a waveform (solid line) as shown by the triangular wave (a) in FIG. 3 is necessary, but in the state of the triangular wave (b), the duty is too small (FIG. 3 ( Refer to b)) High-precision PWM dimming control cannot be performed.

  At this time, as shown in FIG. 2 (c), parallel movement is performed so as to increase the maximum value of the triangular wave voltage without changing the amplitude of the triangular wave. As a result, the triangular wave (b) in FIG. 3 changes to a triangular wave (a), and the magnitude of the on-duty returns to the state immediately after the start of the PWM dimming control.

In order to perform the above-described PWM dimming control, the condition is that the value of the power supply voltage of the operational amplifier 16 is higher than the value of the gate threshold voltage V _GTH (threshold voltage) of the NMOS transistor 2. When such a condition is satisfied, when the triangular wave is translated in the amplitude direction, the gate voltage of the NMOS transistor 2 always exceeds the gate threshold voltage V _GTH until the output of the operational amplifier 14 is saturated. It becomes. Therefore, even when the gate threshold voltage V _{GTH of} the NMOS transistor 2 varies in the amplitude direction, highly accurate dimming control can be performed.

On the other hand, when the gate threshold voltage V _GTH decreases, the waveform of the triangular wave with respect to the gate threshold voltage V _GTH is as shown by the triangular wave (c) in FIG. That is, in order to perform highly accurate PWM dimming control, a waveform (solid line) as shown by the triangular wave (a) in FIG. 3 is necessary. However, in the state of the triangular wave (c), the duty is too large (FIG. 3 ( See c)) Highly accurate PWM dimming control cannot be performed.

  At this time, it is moved in parallel so as to reduce the maximum value of the triangular wave voltage without changing the amplitude of the triangular wave (not shown). As a result, the triangular wave (c) in FIG. 3 changes to a triangular wave (a), and the magnitude of the on-duty returns to the state immediately after the start of the PWM dimming control.

  Note that the triangular wave shown in FIG. 3 has a curved shape compared to the triangular wave shown in FIG. 2C because of the influence of the capacitors and resistors constituting the triangular wave generating circuit 4. is there.

According to the configuration of the vehicle lighting control device 1 according to the above-described embodiment, desired switching control is performed with high accuracy even when the gate threshold voltage V _{GTH of} the NMOS transistor 2 varies in the amplitude direction. By shifting the triangular wave in the amplitude direction until an appropriate on-duty level that can be reduced, it is possible to prevent a decrease in switching control accuracy due to variations in the on-duty size.

  It is to be noted that a sine wave generation circuit may be provided instead of the triangular wave generation circuit 4 so that the sine wave signal output from the sine wave generation circuit is supplied to the gate of the NMOS transistor 2 as the dimming control signal S2. Action and effect are obtained.

  The above-described embodiment is merely an example of a preferred embodiment of the present invention, and the present invention can be implemented with various modifications without departing from the gist thereof.

It is the figure which showed the structure of the lighting control apparatus for vehicles which concerns on embodiment of this invention. It is a timing chart for demonstrating operation | movement of the lighting control apparatus for vehicles. It is a timing chart for demonstrating control which translates a triangular wave to an amplitude direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lighting control apparatus for vehicles, 2 ... NMOS transistor, 3 ... PWM-analog voltage conversion circuit, 4 ... Triangular wave generation circuit, 5 ... Input terminal, 6-1-6-N ... LED, 7, 8, 9 ... Output Terminals, 10 ... switching regulators, 11, 12 ... NPN transistors, 13 ... PNP transistors, 14, 16 ... operational amplifiers, 15 ... buffers, 16 ... PNP transistors

Claims (4)

In a vehicular lighting control device comprising switching means connected in parallel to a semiconductor light source for on / off control of a drive current supplied to the semiconductor light source, and control means for controlling the switching means in response to a dimming control signal ,
The control means includes
A triangular wave generator for changing a voltage signal corresponding to ON / OFF of the switching means into a triangular wave voltage signal;
Compare the voltage signal corresponding to the on / off of the switching means with a predetermined threshold, and based on the comparison result, while moving the triangular wave voltage signal in the amplitude direction while maintaining the shape of the triangular wave voltage signal, A lighting control device for a vehicle, comprising: a triangular wave control unit that controls the on-duty of the triangular wave voltage signal for on-controlling the switching means so as to maintain a constant magnitude. The triangular wave generator is
A differential amplifier that holds the power supply at a predetermined voltage value,
2. The vehicle lighting control according to claim 1, wherein an input voltage value of the differential amplifying unit is controlled so that the triangular wave voltage signal is translated in an amplitude direction while maintaining the predetermined voltage value. apparatus. The vehicle lighting control device according to claim 1 or 2, wherein a value of a power supply voltage of the triangular wave generating unit is higher than a value of an on / off threshold voltage of the switching means. The vehicle lighting control device according to claim 1, wherein the triangular wave control unit includes a digital-analog conversion unit that converts an output signal voltage of the switching means into an analog voltage. .

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