JP2008041383A - Driving circuit for vehicle lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving circuit for vehicle lamp capable of preventing temperature rise of a light-emitting element of a vehicle lamp at the time of decrease of a vehicle speed with a simple structure. <P>SOLUTION: The driving circuit for vehicle lamp 10 is constituted by including a constant current circuit 11. A reference voltage which is generated on a cathode side of a Zenor diode 32 connected through a battery voltage input terminal 14 and a resistor 34 is inputted to a non-reverse input terminal of a differential amplifier 26 constituting the constant current circuit 11. However, since a resistor 30 is connected in parallel with the Zenor diode 32, when the battery voltage drops due to the ambient temperature rise or the like accompanying the decrease of vehicle speed, the reference voltage also drops accompanied with that. As the reference voltage drops, the current outputted from the constant current circuit 11 to an LED 20 also drops. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vehicular lamp driving circuit, and more particularly to a vehicular lamp driving circuit using a light emitting element such as an LED.

  Conventionally, there is a vehicle headlamp that uses a light emitting element such as an LED. When the vehicle speed decreases, the LED may become hot due to a decrease in wind pressure, but the LED may not emit light appropriately when the temperature becomes high. For this reason, Patent Document 1 discloses a vehicular lamp that suppresses heat generation and appropriately emits light by reducing the current supplied to the LED when the vehicle stops.

  Further, Patent Document 2 includes a first light emitting element that irradiates a distance in front of the vehicle, a second light emitting element that irradiates at least the vicinity of the vehicle, and a vehicle speed detecting unit that detects a vehicle speed. An apparatus for controlling a supply current based on a vehicle speed detected by a vehicle speed detection means is disclosed.

  Further, Patent Document 3 includes monitoring means for monitoring operating characteristics that change with a predetermined relationship with the junction temperature for at least one LED, and a comparison result between the operating characteristics obtained by the monitoring means and the reference characteristics. An apparatus for controlling the LED drive current based on the above is disclosed.

Further, as a technique related to the LED drive circuit, Patent Document 4 discloses a drive circuit that can prevent the battery from being consumed by continuously changing the current flowing through the LED in response to the fluctuation of the battery voltage. ing.
JP 2004-276740 A JP 2005-324657 A JP 2005-324656 A JP 2001-325824 A

  However, in the techniques described in Patent Documents 1 to 3, it is necessary to detect the vehicle speed or monitor the operation characteristics, and it is possible to easily reduce the current supplied to the LED and prevent the LED temperature from rising. Can not.

  Moreover, the technique described in Patent Document 4 is an LED drive circuit used for a portable terminal instead of a vehicle, and it is difficult to apply this to a lamp such as a headlamp for a vehicle as it is.

  The present invention has been made in consideration of the above facts, and provides a vehicle lamp drive circuit that can prevent a temperature rise of a light emitting element of a vehicle lamp when the vehicle speed is reduced with a simple configuration. Objective.

  In order to achieve the above object, the invention according to claim 1 is a light emitting means for emitting light toward the outside of a vehicle, a reference voltage generating means for generating a reference voltage based on a battery voltage of the vehicle, and the reference voltage. Constant current supply means for supplying a constant current to the light emitting means based on the comparison result with the voltage at the output terminal of the light emitting means, and fluctuation means for changing the reference voltage in the same fluctuation direction as the battery voltage fluctuation, It is provided with.

  According to this invention, the light emitting means that emits light toward the outside of the vehicle, that is, the light emitting means that constitutes a part of the vehicle lamp emits light when a constant current is supplied by the constant current supply means.

  The constant current supply means supplies a constant current to the light emitting means based on a comparison result between the reference voltage generated by the reference voltage generating means and the voltage at the output terminal of the light emitting means.

  Then, the fluctuation means varies the reference voltage in the same fluctuation direction as the battery voltage. That is, when the vehicle speed decreases and the battery voltage decreases, the reference voltage also decreases accordingly, and when the vehicle speed increases and the battery voltage increases, the reference voltage also increases accordingly. Therefore, even if the vehicle speed decreases, the reference voltage decreases and the drive current supplied to the light emitting means decreases, so that the temperature of the light emitting means can be prevented from rising.

  In addition, as described in Claim 2, the said light emission means can be set as the structure for the headlamps of the said vehicle.

  According to a third aspect of the present invention, the light emitting means may be an LED.

  According to a fourth aspect of the present invention, the reference voltage generating unit includes a Zener diode, and the changing unit includes a resistor connected in parallel to the Zener diode.

  By setting it as such a structure, the temperature rise of the light emitting element of the vehicle lamp at the time of the fall of a vehicle speed can be prevented with a simpler structure.

  As described above, according to the present invention, it is possible to prevent an increase in the temperature of the light emitting element when the vehicle speed is reduced with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the vehicle lamp driving circuit according to the present invention is applied to a headlamp of an automobile will be described.

  FIG. 1 shows a circuit diagram of a vehicular lamp driving circuit 10. As shown in the figure, the vehicular lamp driving circuit 10 includes a constant current circuit 11 and is a direct current obtained by boosting a battery voltage (for example, about 12 to 14 V) of a vehicle (not shown) by a DC-DC converter described later. A DC voltage input terminal 12 to which a voltage is input, a battery voltage input terminal 14 to which the battery voltage is input, and a ground terminal 16 for grounding are provided.

  The DC voltage input terminal 12 is connected to the drain of the N-channel MOS-FET 18, and the source of the MOS-FET 18 is connected to the anode side of the LED 20 constituting the vehicle headlamp. The cathode side of the LED 20 is connected to one end of the resistor 22 connected to the ground terminal 16 at the other end and to one end of the resistor 24. The other end of the resistor 24 is connected to the inverting input terminal of the differential amplifier 26.

  A resistor 28 is connected between the inverting input terminal and the output terminal of the differential amplifier 26. The output terminal of the differential amplifier 26 is connected to the gate of the MOS-FET 18, and the non-inverting input terminal of the differential amplifier 26 is connected to one end of a resistor 30 whose other end is connected to the ground terminal 16. .

  One end of the resistor 30 is connected to the cathode of a Zener diode 32 whose other end is connected to the ground terminal 16 and one end of a resistor 34 whose other end is connected to the battery voltage input terminal 14. Zener diode 32 acts as a constant voltage circuit.

  The DC voltage input terminal 12 receives a voltage output from a DC-DC converter 40 having a general configuration as shown in FIG.

  As shown in the figure, the DC-DC converter 40 includes a battery voltage input terminal 42 to which a vehicle battery voltage (not shown) is input and a ground terminal 44 for grounding, and a capacitor 46 is connected between both terminals. Has been. The battery voltage input terminal 42 is connected to one end of the coil 48. The other end of the coil 48 is connected to the anode side of the diode 50 and the drain of the N-channel MOS-FET 52.

  The cathode side of the diode 50 is connected to one end of a capacitor 54 whose other end is connected to the ground terminal 44, one end of a resistor 56, and an output terminal 58. The other end of the resistor 56 is connected to one end of a resistor 60 connected to the ground terminal 44 and one end of a resistor 62.

  The other end of the resistor 62 is connected to the inverting input terminal of the differential amplifier 64. The non-inverting input terminal of the differential amplifier 64 is connected to the ground terminal 44 via the resistor 66. A resistor 68 is connected between the output terminal and the inverting input terminal of the differential amplifier 64. The output terminal of the differential amplifier 64 is connected to the PWM modulator 72 via the resistor 70. The output side of the PWM modulator 72 is connected to the gate of the MOS-FET 52.

  In the DC-DC converter 40 configured as described above, the battery voltage input to the battery voltage input terminal 42 is boosted by the coil 48, smoothed by the diode 50 and the capacitor 54, and output to the output terminal 58. .

  The output voltage is detected by the resistors 56 and 60, and the detected voltage is input to the inverting input terminal of the differential amplifier 64. For this reason, a voltage corresponding to the detected voltage is output from the differential amplifier 64.

  The PWM modulator 72 includes a triangular wave generating circuit (not shown). The triangular wave output from the triangular wave generating circuit is compared with the output voltage of the differential amplifier 64, and a pulse signal having a pulse width corresponding to the comparison result, That is, a pulse signal is output to the gate of the MOS-FET 52 such that the pulse width decreases as the detection voltage increases and the pulse width increases as the detection voltage decreases. Thus, the PWM modulator 72 outputs a pulse signal PWM-modulated according to the detected voltage to the gate of the MOS-FET 52. As a result, a DC voltage obtained by boosting the input battery voltage is stably output.

  Note that how much the battery voltage is boosted by the DC-DC converter 40 is determined according to the number of LEDs 20, but may be about 50 V as an example.

  In the vehicle lamp drive circuit 10, when lighting of the headlamp is instructed, the output voltage of the DC-DC converter 40 is input to the DC voltage input terminal 12 and the battery voltage is supplied to supply power to the LED 20. Input to the battery voltage input terminal 14.

  The reference voltage based on the battery voltage, that is, the reference voltage at point A in FIG. 1 is input to the non-inverting input terminal of the differential amplifier 26, and the output voltage of the LED 20 is input to the inverting input terminal of the differential amplifier 26. . Accordingly, a voltage corresponding to the difference between the two terminals is output from the differential amplifier 26, whereby the gate of the MOS-FET 18 is driven and current is supplied to the LED 20.

  Although the battery voltage depends on the adjustment voltage of an alternator (not shown) of the vehicle, the battery voltage has a temperature characteristic that decreases when the ambient temperature increases and increases when the ambient temperature decreases. Further, as shown in FIG. 3, the battery voltage has a characteristic that it becomes constant as the engine speed increases and decreases as the engine speed decreases. This is because when the vehicle is traveling at a relatively high speed, the wind entering the engine room becomes stronger, so the ambient temperature decreases, and when the vehicle is traveling at a relatively low speed, the engine room is entered. This is because the ambient temperature rises because the wind weakens.

  Therefore, it can be said that the fluctuation of the battery voltage is related to the fluctuation of the vehicle speed, the temperature of the engine room, the outside air temperature and the like. For this reason, the temperature rise of LED20 can be prevented by reducing the electric current supplied to LED20 in conjunction with the fall of a battery voltage.

  For this reason, in this embodiment, a resistor 30 is provided in parallel with the Zener diode 32 acting as a constant voltage circuit, and this resistor is connected to the battery voltage input terminal 14 via the resistor 34. Further, the resistance value of the resistor 30 is set to such a value that the reference voltage input to the non-inverting input terminal of the differential amplifier 26 decreases as the battery voltage decreases.

  Conventionally, since it is usual that the resistor 30 is not provided, there is basically no change in the reference voltage due to the change in the battery voltage. However, in this embodiment, the resistor 30 is provided in parallel with the Zener diode 32. Therefore, when the vehicle speed decreases and the battery voltage decreases, the reference voltage input to the non-inverting input terminal of the differential amplifier 26 decreases. As a result, the output voltage of the differential amplifier 26 varies according to the difference in input voltage between the input terminals of the differential amplifier 26. Thereby, the electric current supplied to LED20 falls. In other words, the current supplied to the LED 20 decreases as the reference voltage decreases. For example, as shown in FIG. 3, when the engine speed becomes lower than a predetermined speed N, or when the vehicle speed becomes lower than a predetermined speed VA (for example, 20 km) as shown in FIG. 4, the engine room is entered. Although the temperature of the engine room increases due to the weak wind, the current supplied to the LED 20 decreases, so that the temperature increase of the LED 20 can be prevented.

  As described above, in this embodiment, the constant current characteristic of the constant current circuit is a characteristic that depends on the battery voltage, and is supplied to the LED 20 in conjunction with a decrease in the vehicle speed, that is, a decrease in the battery voltage without detecting the vehicle speed. The current is reduced. For this reason, the temperature rise of LED20 can be prevented with a simple structure, and it becomes possible to extend the lifetime of LED20.

  In the present embodiment, the case where the present invention is applied to a headlamp of an automobile has been described. However, the present invention is not limited to this, and the present invention can also be applied to other lamps such as a blinker lamp and a brake lamp.

  Further, in the present embodiment, the case where the light source of the automobile headlamp is an LED has been described. However, the present invention is not limited thereto, and the present invention can be applied to other light sources as long as the light source has the same temperature characteristics as the LED. It is.

It is a circuit diagram of a vehicle lamp drive circuit. It is a circuit diagram of a DC-DC converter. It is a diagram which shows the relationship between an engine speed and a battery voltage. It is a diagram which shows the relationship between a vehicle speed and LED current.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle lamp drive circuit 11 Constant current circuit (constant current supply means)
12 DC voltage input terminal 14 Battery voltage input terminal 16 Ground terminal 18 MOS-FET
20 LED (light emitting means)
22, 24, 28 Resistance 26 Differential amplifier 30 Resistance (fluctuation means)
32 Zener diode (reference voltage generating means)
34 resistor 40 DC-DC converter 42 battery voltage input terminal 44 ground terminal 46, 54 capacitor 48 coil 50 diode 56, 60, 62, 66, 68, 70 resistor 58 output terminal 64 differential amplifier 72 PWM modulator

Claims (4)

A light emitting means for emitting light toward the outside of the vehicle;
A reference voltage generating means for generating a reference voltage based on the battery voltage of the vehicle;
Constant current supply means for supplying a constant current to the light emitting means based on a comparison result between the reference voltage and the voltage at the output terminal of the light emitting means;
Fluctuating means for fluctuating the reference voltage in the same fluctuation direction as the fluctuation of the battery voltage;
A vehicle lamp driving circuit comprising:   2. The vehicle lamp drive circuit according to claim 1, wherein the light emitting means is for a headlamp of the vehicle.   3. The vehicle lamp driving circuit according to claim 1, wherein the light emitting means is an LED.   4. The vehicle according to claim 1, wherein the reference voltage generation unit includes a Zener diode, and the variation unit includes a resistor connected in parallel to the Zener diode. 5. Lamp drive circuit.

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