JP2005041309A - Electronic light emitting element driving circuit of lighting fixture for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic light emitting element driving circuit for a lighting fixture for a vehicle capable of enlarging the circuit when electronic light emitting elements of the same sort are allowed to emit light at two levels of lightness so as to generate a light-dark difference. <P>SOLUTION: The electronic light emitting element driving circuit 50 to drive the electronic light emitting elements 10 of the lighting fixture for the vehicle supplies the first constant current to the electronic light emitting elements in response to the first input signal, supplies the second constant current having different amperage from the first constant current to the electronic light emitting elements in response to the second input signal, and includes a bipolar transistor Tr connected with the fore-stage of the electronic light emitting elements for supplying the emitter current as the constant current source to the electronic light emitting elements. Further the electronic light emitting element driving circuit supplies either of the first and the second constant current to the electronic light emitting elements while the amperage of the emitter current is changed over on the basis of the first and the second input signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroluminescent element driving circuit for a vehicular lamp.
[0002]
[Prior art]
Conventionally, tail lamps (tail lights) and stop lamps (braking lights) having a signal function are known as examples of rear combination lamps provided at the rear of the vehicle. The tail lamp is used to prevent rear-end collisions by allowing the following vehicle to check the position and presence of the vehicle at night. The stop lamp is lit when the driver applies a brake throughout the day and night, and indicates the intention of stopping or decelerating to the following vehicle.
[0003]
In many cases, the stop lamp is combined with the tail lamp, and in that case, the stop lamp must have a brightness that is three to five times the brightness of the tail lamp. This is so that the driver can clearly see that the driver has applied the brakes.
[0004]
As described above, two functions of the tail lamp and the stop lamp are realized with the same lamp by causing the same lamp to emit light with a difference in brightness. Hereinafter, a description will be given with reference to FIG. Here, a light emitting diode (LED) is used as the electroluminescent element. The drive circuit 1 of the LED 10 is provided with two input units 2 and 3. The voltage V is applied to the first input unit 2 when the tail lamp switch 4 operated by the driver is in the ON state. When the brake pedal 5 is depressed, the same voltage V as the voltage V applied to the first input unit 2 is applied to the second input unit 3. The drive circuit 1 drives the LED 10 to emit light more brightly when the same voltage V is applied to the second input unit 3 than when the voltage V is applied to the first input unit 2.
[0005]
An LED is basically a current driving element, and the intensity of emitted light (radiant flux) is proportional to the current. FIG. 6 shows an example of a basic driving circuit of an LED. A current is supplied from the constant voltage power supply Vcc to the LED through the limiting resistor R. The forward voltage Vf of the LED has a dependency on the current If, but if it is considered almost constant in the use region, the current flowing through the LED is
If = (Vcc-Vf) / R
Given in. As described above, the radiant flux of the LED is proportional to the forward current If.
[0006]
Conventionally, when realizing the two functions of the tail lamp and the stop lamp with the same LED, a resistance driving circuit as shown in FIG. 7 is used. When used as a tail lamp, the tail lamp switch 4 is turned on and the power supply voltage Vcc is applied, whereby a current is supplied to the LED 10 through a series circuit of the resistors R1 and R2. When used as a stop lamp, when the brake pedal 5 is depressed and the power supply voltage Vcc is applied, a current is supplied to the LED 10 via the resistor R2. Thereby, when it is used as a stop lamp, a large current flows through the LED 10, and the LED 10 emits light brighter than when it is used as a tail lamp.
[0007]
By the way, since the forward voltage characteristics of LEDs have variations (individual differences) for each LED, even if the power supply voltage is kept constant, the current flowing through each LED does not follow the set current value. Therefore, a difference occurs in the light flux amount for each LED. Furthermore, since the value of the current flowing through each LED also changes when the power supply voltage changes, there is a difference in the amount of light flux for each LED.
[0008]
[Problems to be solved by the invention]
For example, when supplying a predetermined two-stage constant current to an electroluminescent device in order to make an electroluminescent device (LED) emit light with a difference in brightness according to each of two inputs, such as a vehicle rear combination lamp, It is desired to expand the circuit after the light emitting element. Conventionally, there has not been provided a driving circuit for an electroluminescent element for supplying a predetermined two-stage constant current as described above, which can be expanded as described above.
[0009]
FIG. 8 shows a circuit example in which the circuit cannot be expanded although it is a drive circuit for an electroluminescent element that supplies a predetermined two-stage constant current according to each of the two inputs as described above. As shown in FIG. 8, in a constant current circuit using a bipolar transistor, an electroluminescent element (LED 10) is connected between a power supply (input terminals 1 and 2) and a collector of the transistor. With this configuration, it is possible to switch the constant current flowing in the LED 10 in two stages depending on whether the terminal to which the power supply voltage Vcc is applied is the input terminal 1 or the input terminal 2. However, as shown in FIG. 8, the load (including the LED 10) cannot be connected unless it is “between the power source and the collector” described above. The extension circuit could not be connected.
[0010]
An object of the present invention is to drive an electroluminescent element of a vehicular lamp capable of expanding a circuit when the same electroluminescent element is made to emit light at two different brightness levels so as to produce a difference in brightness as a vehicular lamp. To provide a circuit.
Another object of the present invention is to extend the circuit when the same electroluminescent element is made to emit light at two different brightness levels so as to produce a difference in brightness as a vehicular lamp. To provide an electroluminescent element driving circuit for a vehicular lamp that can supply a predetermined two-stage constant current even if it changes.
[0011]
[Means for Solving the Problems]
An electroluminescent element driving circuit for driving an electroluminescent element of a vehicle lamp according to the present invention, wherein a first constant current is supplied to the electroluminescent element in response to a first input signal, and a second input In response to the signal, a second constant current having a current value different from that of the first constant current is supplied to the electroluminescent element, and the electroluminescent element is connected to the preceding stage of the electroluminescent element.
The electroluminescent element is connected between the electroluminescent element driving circuit of the vehicular lamp of the present invention and the ground. According to the present invention, the electroluminescent device driving circuit of the vehicle lamp emits the electroluminescent device with two kinds of brightness, and the circuit is expanded between the electroluminescent device and the ground (after the electroluminescent device). It can be carried out.
[0012]
The electroluminescent device driving circuit for a vehicle lamp according to the present invention includes a bipolar transistor for supplying an emitter current to the electroluminescent device as a constant current source, and the emitter current is controlled based on the first and second input signals. One of the first and second constant currents is supplied to the electroluminescent element by switching the current value.
[0013]
In the electroluminescent element driving circuit of the vehicular lamp of the present invention, the first constant current source that generates a third constant current based on the first input signal, and the second input signal. And a second constant current source that generates a fourth constant current, and each of the first and second constant currents includes at least one of the third and fourth constant currents. It is characterized by. Thereby, even if the power supply voltage changes, it is possible to supply a predetermined two-stage constant current.
[0014]
In the electroluminescent device driving circuit for a vehicle lamp of the present invention, first and second Zener diodes each having the electroluminescent device connected to the anode side and an emitter current as a constant current source are supplied to the electroluminescent device. A bipolar transistor, a series circuit comprising a first resistor and a second resistor connected in series between the emitter of the bipolar transistor and the electroluminescent device, and a control electrode on the cathode side of the first Zener diode And a switching transistor having a first electrode connected to a connection node of the first resistor and the second resistor, and a second electrode connected to the electroluminescent element.
[0015]
In the electroluminescent element driving circuit of the present invention, a third constant current is generated based on the first input signal, and the first constant current source is connected to the control electrode of the switching transistor; A fourth constant current is generated based on a second input signal, and a second constant current source connected to the cathode side of the second Zener diode and the base of the bipolar transistor is provided. And
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Constituent elements that are the same as those in the above-described drawings are given the same reference numerals, and detailed descriptions thereof are omitted.
[0017]
(First embodiment)
The present embodiment is a circuit for driving an LED used as a rear combination lamp for a vehicle. By using the same power supply voltage to cause the LED to emit light with a difference in brightness, the same LED can be used for two functions, a tail lamp and a stop lamp. It is an LED drive circuit that realizes and enables an extension circuit to be connected to the subsequent stage of the LED.
[0018]
FIG. 3 shows the above-described characteristics and circuit configuration necessary for this embodiment. As shown in FIG. 3, the LED driving circuit 50 is a constant current circuit that supplies a predetermined constant current to the LED 10, and needs to have a current value switching function to cause the LED 10 to emit light with a difference in brightness. is there. In other words, as shown in the table in FIG. 3, the current value switching function means that when the input terminal 1 (input (1)) is ON, the LED is turned on regardless of the state of the input terminal 2 (input (2)). This is a function for switching the output current to be small when the output current from the drive circuit 50 is large and the input terminal 1 is OFF and the input terminal 2 is ON.
[0019]
Further, as a circuit configuration desired in the present embodiment, the LED drive circuit 50 is installed at the front stage of the LED 10 so that the expansion circuit 40 can be connected to the rear stage of the LED 10, that is, between the LED 10 and the ground (GND). Must be possible configuration.
[0020]
Here, the expansion circuit 40 includes, for example, a resistor (not shown) connected between the LED 10 and the ground, and detects the voltage of the resistor, thereby detecting the constant current supply function of the LED drive circuit 50. This is a circuit that detects that an overcurrent flows through the LED 10 due to a failure or the like, and outputs the detection result (abnormal signal) to another circuit (not shown). As shown in FIG. 8, in a configuration in which a circuit having a constant current supply function and a current value switching function is connected to the subsequent stage of the LED 10, an extension circuit cannot be provided in the subsequent stage of the LED 10.
[0021]
The specific circuit configuration of this embodiment will be described below.
As shown in FIG. 1, the vehicle LED drive circuit 50 according to the present embodiment has a function of switching a current value of a current flowing through an LED (electroluminescent device) 10 and a constant current for supplying a constant current to the LED 10. Circuit. An input terminal 1 and an input terminal 2 are provided on the input side of the LED drive circuit 50. The LED 10 serving as a load is connected to the output side of the LED drive circuit 50 between the LED drive circuit 50 and the ground (GND).
[0022]
The vehicle power supply voltage Vcc (first input signal) is applied to the input terminal 1 when a brake pedal (not shown) is depressed. When the tail lamp switch (not shown) is in the ON state, the same power supply voltage Vcc (second input signal) as that described above is applied to the input terminal 2.
[0023]
With reference to FIG. 2, the relationship between the input and output current of the LED drive circuit 50 will be described. When the power supply voltage Vcc is applied to the input terminal 1, the LED drive circuit 50 supplies a relatively large current to the LED 10 regardless of whether or not the power supply voltage Vcc is applied to the input terminal 2. That is, the LED 10 always emits light relatively brightly when the brake pedal is depressed.
[0024]
When the power supply voltage Vcc is not applied to the input terminal 1 and the power supply voltage Vcc is applied to the input terminal 2, the LED drive circuit 50 supplies a relatively small current to the LED 10. That is, when the tail lamp switch is in the ON state and the brake pedal is not depressed, the LED 10 emits light relatively darkly.
[0025]
When the power supply voltage Vcc is not applied to the input terminal 1 and the input terminal 2, the LED drive circuit 50 does not supply current to the LED 10. That is, when the tail lamp switch is OFF and the brake pedal is not depressed, the LED 10 does not emit light.
[0026]
As shown in FIG. 1, the LED drive circuit 50 includes an FET 1, a junction FET (JFET) 2, a junction FET 3, resistors R1, R2, R3, R4, Zener diodes ZD1, ZD2, and a bipolar transistor Tr. And.
[0027]
Zener diode ZD1 is used to ensure the ON voltage of FET1. The FET 1 is used as a switching element that switches a current value supplied to the LED 10. The junction type FET2 is a junction type FET (n-type) for limiting the base current of the transistor Tr and the current of the Zener diode ZD2. The junction type FET 3 is a junction type FET (n-type) for limiting the current of the Zener diode ZD1.
[0028]
The resistors R1 and R2 are resistors for switching the current supplied to the LED 10. The resistor R3 is a resistor that adjusts the base current of the transistor Tr and the current of the Zener diode ZD2. The resistor R4 is a resistor for limiting the current of the Zener diode ZD1. RON is the ON resistance of FET1. The transistor Tr is an n-type transistor for limiting the current supplied to the LED 10.
[0029]
A diode D 1 is connected between the LED drive circuit 50 and the input terminal 1, and a diode D 2 is connected between the LED drive circuit 50 and the input terminal 2.
The input terminal 1 is connected to the anode side of the diode D1. The cathode side of the diode D1 is connected to the drain terminal of the junction FET 3. The input terminal 2 is connected to the anode side of the diode D3. The cathode side of the diode D2 is connected to the drain terminal of the junction FET2. The anode side of the diode D2 is connected to the cathode side of the diode D1. The cathode side of the diode D3 is connected to the cathode side of the diode D2. The diodes D1, D2, and D3 are rectifier diodes.
[0030]
The junction type FETs 2 and 3 each have a gate terminal connected to a source terminal and function as a constant current source. A resistor R4 is connected between the gate terminal and the source terminal of the junction FET 3. A resistor R3 is connected between the gate terminal and the source terminal of the junction FET2.
[0031]
The source terminal of the junction FET 3 is connected to the gate terminal of the FET 1 via the resistor R4, and the cathode side of the Zener diode ZD1 is connected. The gate terminal of the junction FET 3 is connected to the gate terminal of the FET 1 and the cathode side of the Zener diode ZD 1. The LED 10 is connected to the anode side of the Zener diode ZD1.
[0032]
The cathode side of the Zener diode ZD2 is connected to the source terminal of the junction FET 2 through the resistor R3. The cathode side of the Zener diode ZD2 is connected to the gate terminal of the junction FET2. The LED 10 is connected to the anode side of the Zener diode ZD2.
[0033]
Both the cathode side of the diode D2 and the cathode side of the diode D3 are connected to the collector of the bipolar transistor Tr. The source terminal of the junction FET 2 is connected to the base of the transistor Tr via the resistor R3, and the gate terminal of the junction FET 2 is connected to the base of the transistor Tr. The cathode side of the Zener diode ZD2 is connected to the base of the transistor Tr.
[0034]
A resistor R1 is connected to the emitter of the transistor Tr, and a resistor R2 is connected in series to the resistor R1. A drain terminal of the FET 1 is connected to a connection node between the resistors R1 and R2. The source terminal of the FET 1 is connected to the LED 10.
[0035]
Since the Zener diode ZD1 is driven at a constant current by the junction FET 3, the voltage drop of the Zener diode ZD1 becomes a constant value, always generates a constant Zener voltage, and functions as a constant voltage source. Similarly, since the Zener diode ZD2 is driven with a constant current by the junction type FET2, the voltage drop of the Zener diode ZD2 becomes a constant value, always generates a constant Zener voltage, and functions as a constant voltage source.
[0036]
The resistor R4 is a resistor for limiting the current flowing through the Zener diode ZD1. There is an individual difference in each junction type FET 3, which may cause a constant current not to be supplied from each junction type FET 3 with high accuracy. Therefore, the resistor R4, which is set to a resistance value that absorbs individual differences between the junction FETs 3, is used for each junction FET 3, and a constant current is supplied with high accuracy by the combination of the junction FET 3 and the resistor R4. To do.
The resistor R3 is a resistor that adjusts the current flowing through the Zener diode ZD2 and the base current of the transistor Tr. Similarly, the resistance R3 that is set to a resistance value that absorbs individual differences of each junction type FET2 is used for each junction type FET2, and a constant current is supplied with high accuracy by the combination of the junction type FET2 and the resistance R3. To do.
[0037]
The transistor Tr is a constant current source. The base potential of the transistor Tr is always fixed to a constant voltage (zener voltage) by the Zener diode ZD2. The Zener voltage of the Zener diode ZD2 is equal to the sum of the emitter-base voltage of the transistor Tr and the combined resistance of the resistor R1 and the resistor R2 when the FET 1 is OFF. The Zener voltage of the Zener diode ZD2 is equal to the sum of the resistance value of the combined resistance of the resistor R1 and the ON resistance RON of the FET 1 when the FET 1 is ON.
[0038]
The Zener diode ZD1 generates a predetermined Zener voltage when current is supplied. This Zener voltage is applied to the base of the FET 1 to turn on the FET 1. The FET 1 functions as a switching element. That is, when FET1 is OFF, the emitter resistance of the transistor Tr is a combined resistance of the resistance R1 and the resistance R2. When the FET 1 is turned on, the emitter resistance of the transistor Tr becomes a combined resistance of the resistor R1 and the ON resistance RON of the FET 1.
[0039]
The current supplied to the LED 10 via the Zener diode ZD1 is i1, the current supplied from the FET 1 to the LED 10 is i2, the current supplied to the LED 10 via the resistor R2 is i3, and the current supplied to the LED 10 via the Zener diode ZD2 is supplied to the LED 10. Assuming that the current to be i4 is, the total current of the currents i1 to i4 is supplied to the LED 10.
[0040]
Next, the operation of this embodiment will be described.
First, an operation when the brake pedal is depressed and the power supply voltage Vcc is applied to the input terminal 1 will be described.
[0041]
A current flows from the input terminal 1 to the junction FET 3 through the diode D1. A constant current is supplied to the Zener diode ZD1 by the junction FET 3 and the resistor R4. In this case, for example, even if there is a change in the power supply voltage Vcc applied to the input terminal 1 according to the charge amount of the battery mounted on the vehicle, a constant constant current is always maintained by the junction FET 3 and the resistor R4. The zener diode ZD1 is supplied. Thereby, a constant current is supplied to the LED 10 as the current i1. Further, when a current is supplied to the Zener diode ZD1, the Zener diode ZD1 generates a predetermined Zener voltage, whereby the FET 1 is turned on.
[0042]
The current flowing from the input terminal 1 via the diode D1 is also supplied to the collector of the transistor Tr and the junction FET 2 via the diode D2. A constant current is supplied to the Zener diode ZD2 and the base of the transistor Tr by the junction FET2 and the resistor R3. In this case, even if the power supply voltage Vcc applied to the input terminal 1 changes, a constant constant current is always supplied to the Zener diode ZD1 and the base of the transistor Tr by the junction FET 2 and the resistor R3. Thereby, a constant current is supplied to the LED 10 as the current i4.
[0043]
As described above, when the base current is supplied to the transistor Tr through the junction FET 2 and the resistor R3, the transistor Tr is turned on, and the transistor Tr functions as a constant current source. Here, since the FET 1 is in the ON state, the constant current output from the transistor Tr is supplied to the LED 10 as the current i2 through the resistor R1 and the ON resistor RON of the FET1. In this case, even if the power supply voltage Vcc applied to the input terminal 1 is changed, a constant constant current is always output to the resistor R1 and the FET1 by the transistor Tr. Therefore, the constant current is supplied to the LED 10 as the current i2. Is done.
[0044]
As described above, when the brake pedal is depressed and the power supply voltage Vcc is applied to the input terminal 1, the currents i1, i2, and i4, which are all constant currents, are supplied to the LED 10.
[0045]
Next, the operation when the tail lamp switch is turned on and the power supply voltage Vcc is applied to the input terminal 2 will be described.
[0046]
Since the cathode side of the diode D2 is connected to the cathode side of the diode D3, when the power supply voltage Vcc is applied to the input terminal 2, the current flowing through the diode D3 does not flow to the diode D2. Therefore, since a predetermined voltage is not applied to the gate of FET1, FET1 is not turned on and is in an OFF state. Therefore, the current i2 is zero. Further, since no current is supplied to the junction type FET 3, the current i1 is also zero.
[0047]
A current is supplied from the input terminal 2 to the collector of the transistor Tr and the junction FET 2 via the diode D3. A constant current is supplied to the Zener diode ZD2 and the base of the transistor Tr by the junction FET2 and the resistor R3. In this case, even if there is a change in the power supply voltage Vcc applied to the input terminal 2, a constant current is always supplied to the Zener diode ZD1 and the transistor Tr by the junction FET 2 and the resistor R3. Thereby, a constant current is supplied to the LED 10 as the current i4. The value of the current i4 that flows when the tail lamp switch is turned on and the power supply voltage Vcc is applied to the input terminal 2 is the same as that when the brake pedal is depressed and the power supply voltage Vcc is applied to the input terminal 1. It is the same as the current value of the flowing current i4.
[0048]
As described above, when the base current is supplied to the transistor Tr through the junction FET 2 and the resistor R3, the transistor Tr is turned on, and the transistor Tr functions as a constant current source. Here, since the FET 1 is in the OFF state, the constant current output from the emitter of the transistor Tr is supplied to the LED 10 as the current i3 through the resistor R1 and the resistor R2. In this case, even if there is a change in the power supply voltage Vcc applied to the input terminal 2, a constant current is always output to the resistors R1 and R2 by the transistor Tr, so that a constant current is supplied to the LED 10 as the current i3. The In the present embodiment, the resistance value of the resistor R2 is larger than the ON resistance RON of the FET1. Therefore, the current i3 that flows when the tail lamp switch is turned on and the power supply voltage Vcc is applied to the input terminal 2 is the current that flows when the power supply voltage Vcc is applied to the input terminal 1 when the brake pedal is depressed. The current is smaller than i2.
[0049]
As described above, when the tail lamp switch is turned on and the power supply voltage Vcc is applied to the input terminal 2, the currents i3 and i4, which are constant currents, are supplied to the LED 10. In this case, the sum of the current values i3 and i4 supplied to the LED 10 is smaller than the sum of the currents i1, i2 and i4 that flow when the brake pedal is depressed and the power supply voltage Vcc is applied to the input terminal 1. The LED 10 emits light darker than when the brake pedal is depressed.
[0050]
As described above, the LED drive circuit 50 is provided in the preceding stage of the LED 10 and drives the LED 10 with a constant current and has a function of switching current values in two stages. That is, unlike the constant current circuit shown in FIG. 8, the LED driving circuit 50 is not directly connected to the ground (GND) but is connected to the ground via the LED 10 as a load.
[0051]
The base current supplied to the transistor Tr and the Zener current to the Zener diode ZD2 are limited by a current limiting circuit formed by a combination of the junction FET 2 and the resistor R3. Thus, by using the resistor R3 whose resistance value is adjusted in advance so that the potential difference of the Zener diode ZD2 does not change greatly even if the power supply voltage Vcc changes, a current is supplied to the LED 10 even if the power supply voltage Vcc varies. A change in the current value supplied as i4 can be reduced.
[0052]
When only the input terminal 2 is in the ON state, the FET 1 is OFF, and in the constant current circuit of the transistor Tr, the current is limited when the current limiting resistance is (R1 + R2).
When only the input terminal 1 is in the ON state, a current is supplied to the transistor Tr via the diode D1 and the diode D2. When the Zener diode ZD1 is turned ON and the FET 1 is turned ON, the current limiting resistance becomes (R1 + RON), and a larger current is supplied to the LED 10 than when only the input terminal 2 is in the ON state.
[0053]
When both the input terminal 1 and the input terminal 2 are in the ON state, the FET 1 is in the ON state. Therefore, as in the case where only the input terminal 1 is in the ON state, the current limiting resistance becomes (R1 + RON), and only the input terminal 2 A larger current is supplied to the LED 10 than when the is in the ON state.
With the above current switching function, the current value shows the result as shown in FIG.
[0054]
The LED drive circuit 50 of this embodiment inputs the power supply voltage Vcc to its input part (the drain terminals of the junction type FET2 and the junction type FET3), passes through a constant current circuit, and its output part (the anode side of the Zener diodes ZD1 and ZD2). The output current is limited on the source terminal side of FET1. Since the current is constant between the output terminal n1 and the ground, to which the LED 10 as a load is connected, a resistor is connected between the output terminal n1 and the ground, and the expansion circuit 40 including the resistance is connected. (See FIG. 3) can be added.
[0055]
According to this embodiment, the following effects can be achieved.
When an LED is connected to the load, the current value does not vary due to the forward voltage characteristics of the LED, and the current value is kept constant even when the power supply voltage changes greatly. . Thereby, the lamp | ramp of the stable light beam quantity can be comprised.
Moreover, since a difference can be provided in the magnitude | size of an electric current value, two patterns can be provided in the light beam quantity of LED, and it can apply to a rear combination lamp.
Furthermore, it is possible to connect a load such as an LED from the output terminal, connect a resistor or the like between the cathode and ground of the LED, read the potential, and expand to other systems.
[0056]
Next, a modification of the present embodiment will be described with reference to FIG.
In this modification, only differences from the present embodiment will be described. About the same structure as this embodiment, the same code | symbol is attached | subjected and the detailed description is abbreviate | omitted.
[0057]
In the LED drive circuit 51 of this modification, a Zener diode ZD3 having a Zener voltage different from that of the Zener diode ZD2 is provided in parallel with the Zener diode ZD2, and the Zener diode ZD2 and the Zener diode ZD3 are switched by the switch SW1. The switch SW1 is switched depending on whether or not the power supply voltage Vcc is applied to the input terminal 1. Thereby, since the voltage applied to resistance R1 can be switched, the electric current of two steps of magnitude | size can be supplied with respect to LED10.
[0058]
Also with the LED drive circuit 51 of this modification, the extension circuit 40 (FIG. 3) can be connected to the subsequent stage of the LED drive circuit 51. If the configuration is such that the Zener diodes ZD2 and ZD3 having different Zener voltages are switched as in the present modification, the resistor R2 and the FET 1 are unnecessary.
[0059]
In the above embodiment, the LED has been described as a vehicular lamp that realizes two functions of a tail lamp and a stop lamp, but the present invention is not limited thereto. The LED of each of the above embodiments can be applied to a vehicular lamp that provides two types of brightness as a room lamp of a vehicle. In that case, the input terminals 1 and 2 of the embodiment correspond to the first contact and the second contact of the room lamp changeover switch.
[0060]
【The invention's effect】
According to the present invention, it is possible to expand the circuit when the same electroluminescent element is made to emit light with two kinds of brightness so as to produce a difference in brightness as a vehicular lamp.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an embodiment of an electroluminescent element driving circuit for a vehicular lamp according to the present invention.
FIG. 2 is a diagram showing a relationship between an input current and an output current in an embodiment of an electroluminescent element driving circuit for a vehicle lamp according to the present invention.
FIG. 3 is a diagram showing characteristics and a circuit configuration of an embodiment of an electroluminescent element driving circuit for a vehicular lamp according to the present invention.
FIG. 4 is a circuit diagram showing a modified example of the embodiment of the electroluminescent element driving circuit of the vehicular lamp of the present invention.
FIG. 5 is a diagram for explaining a configuration in which two functions of a tail lamp and a stop lamp are realized by the same lamp by causing the same lamp to emit light with a difference in brightness.
FIG. 6 is a diagram illustrating an example of an LED drive circuit;
FIG. 7 is a circuit diagram for causing the same LED to emit light with a difference in brightness by a resistance driving method.
FIG. 8 is a circuit diagram for supplying two types of constant currents so that the same LED emits light with a difference in brightness.
[Explanation of symbols]
1 Drive circuit
2 First input section
3 Second input section
4 Tail lamp switch
5 Brake pedal
10 LED (electroluminescent device)
40 Expansion circuit
50 LED drive circuit (electroluminescent device drive circuit)
51 LED drive circuit (electroluminescent device drive circuit)
D1-D3 diode
FET1 FET
FET2 Junction FET
FET3 Junction FET
i1-i4 current
If current
R1-R4 resistance
SW1 switch
Tr bipolar transistor
V voltage
Vf forward voltage
Vcc supply voltage
ZD1-ZD3 Zener diode

Claims (5)

An electroluminescent element driving circuit for driving an electroluminescent element of a vehicle lamp,
In response to a first input signal, a first constant current is supplied to the electroluminescent element, and in response to a second input signal, the first constant current is a current value of the electroluminescent element. An electroluminescent element driving circuit for a vehicular lamp characterized by supplying a different second constant current and connected to the preceding stage of the electroluminescent element. In the electroluminescent element drive circuit of the vehicular lamp according to claim 1,
Including a bipolar transistor for supplying an emitter current to the electroluminescent device as a constant current source;
One of the first and second constant currents is supplied to the electroluminescent element by switching a current value of the emitter current based on the first and second input signals. An electroluminescent element driving circuit for a vehicular lamp. In the electroluminescent element drive circuit of the vehicular lamp according to claim 1 or 2,
In addition,
A first constant current source for generating a third constant current based on the first input signal;
A second constant current source for generating a fourth constant current based on the second input signal,
Each of the first and second constant currents includes at least one of the third and fourth constant currents. An electroluminescent element drive circuit for a vehicular lamp, wherein: In the electroluminescent element drive circuit of the vehicular lamp according to claim 1 or 2,
First and second Zener diodes each having the electroluminescent element connected to the anode side;
A bipolar transistor for supplying an emitter current to the electroluminescent device as a constant current source;
A series circuit comprising a first resistor and a second resistor connected in series between the emitter of the bipolar transistor and the electroluminescent device;
A switching transistor in which a control electrode is connected to a cathode side of the first Zener diode, a first electrode is connected to a connection node between the first resistor and the second resistor, and a second electrode is connected to the electroluminescent element. An electroluminescent element driving circuit for a vehicular lamp characterized by comprising: In the electroluminescent element drive circuit of the vehicular lamp according to claim 4,
In addition,
A first constant current source configured to generate a third constant current based on the first input signal and connected to the control electrode of the switching transistor;
A fourth constant current is generated based on the second input signal, and a second constant current source connected to a cathode side of the second Zener diode and a base of the bipolar transistor is provided. An electroluminescent element driving circuit for a vehicular lamp.

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