JP2004051014A - Led headlamp device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED headlamp device for a vehicle capable of suppressing heat generation in a circuit to a minimum extent, reducing the number of wires, making the brightness of a light emitting diode uniform, and preventing the fluctuation of brightness. <P>SOLUTION: Eight LEDs 9 are connected in series in an LED unit 10. Since a voltage is insufficent when a 12V-voltage of a power supply 3, namely, a battery of the vehicle is supplied, a boosting circuit 4 is provided in a control unit 2 to apply a voltage boosted up to about 16V to eight LEDs 9. The tip of the LED unit 10 is connected with a constant current circuit 8. A voltage detection circuit 7 detecting a voltage applied to the constant current circuit 8 is connected with the vicinity of the constant current circuit 8. The detected voltage is compared with a reference voltage 5 taken in from the power supply 3, is amplified by an amplifier 6, and is inputted into the boosting circuit 4 as a boosting control signal. This boosting control signal is outputted to control a boosted current so that the voltage detected by the voltage detection circuit 7 is reduced as much as possible. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a vehicle LED headlamp device for controlling a vehicle LED headlamp using a light emitting diode as a light source.
[0002]
In the present specification, the LED chip itself, or the entirety thereof including an optical device such as a package resin or a lens system on which the LED chip is mounted is referred to as a “light emitting diode” or “LED”.
[0003]
[Prior art]
With the increase in brightness of light emitting elements, vehicle LED lamps using LEDs as light sources have been increasingly used as stop lamps of automobiles and the like. The LED has a sharp spectrum and good visibility. In addition, since the response speed is high, the signal transmission speed to the following vehicle is high, and a remarkable effect in reducing the stationary distance during high-speed running has been recognized. Furthermore, since the LED itself is a monochromatic light source, there is no need to filter light other than the required color as in an incandescent light bulb, so that the monochromatic light source is highly efficient and leads to energy saving.
[0004]
FIG. 4 shows an example of such a vehicle LED headlamp device. FIG. 4 is a circuit diagram showing an example of a conventional vehicle LED headlamp device. As shown in FIG. 4, the vehicle LED headlamp device 50 includes a control unit 51 and a light emitting diode unit 52. The eight light emitting diodes 54 of the light emitting diode unit 52 are connected in parallel with each other. I have.
[0005]
[Problems to be solved by the invention]
Therefore, a current limiting circuit (resistor or transistor) 55 is required for each light emitting diode 54. When the number of light emitting diodes 54 increases, the number of current limiting circuits 55 also increases, and the amount of heat generated by itself cannot be ignored. . Further, since the number of wirings connecting the control unit 51 and the light emitting diode unit 52 is increased to the number of power supply lines + the number of parallel wirings, wiring is troublesome and cost is increased. Also, if there is a variation in the forward voltage of each light emitting diode 54, the flowing current will vary, and eventually the brightness of the light emitting diodes 54 will vary. Furthermore, when the current limiting circuit 55 is a resistor, if the power supply voltage fluctuates, the current flowing through the light emitting diode 54 also fluctuates, causing a problem that the brightness fluctuates.
[0006]
Accordingly, an object of the present invention is to provide a vehicle LED headlamp device capable of minimizing heat generation of a circuit, reducing the number of wirings, making the brightness of a light emitting diode uniform, and preventing a change in brightness. Things.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an LED headlamp device for a vehicle, wherein a plurality of light emitting diodes are connected in series using a light emitting diode as a light source, and a voltage boosted from a power supply voltage is applied to light the light emitting diode.
[0008]
Typically, the voltage of a vehicle battery is about 12V and the forward voltage of a light emitting diode is about 2V. Therefore, when arranging LEDs in series and lighting them, the limit is six. In view of this, the LEDs are rearranged in series from the conventional parallel, and a booster circuit is provided between the LEDs arranged in series with the battery to increase the voltage so that the number of LEDs can be increased. As a result, the number of wires between the power supply and the LED unit becomes two, and workability can be improved and cost can be reduced. Also, since the LEDs are arranged in series, a current of the same magnitude flows through all the LEDs, so that variations in brightness between the LEDs are suppressed, and even when the power supply voltage fluctuates, the voltage applied to the LEDs by the booster circuit is constant. Since the brightness is controlled so that the brightness does not fluctuate.
[0009]
In this manner, a plurality of light emitting diodes are connected to provide a sufficient amount of light as a headlamp, the number of wirings is reduced, the brightness of the light emitting diodes is made uniform, and the fluctuation of the brightness can be prevented. It becomes a headlamp device.
[0010]
According to a second aspect of the present invention, in the vehicle LED headlamp apparatus according to the first aspect, the light emitting diodes connected in series are driven at a constant current and a variable voltage is applied.
[0011]
In this vehicle LED headlamp apparatus, in addition to arranging LEDs in series and applying a boosted power supply voltage, a constant current drive is performed by adding a constant current circuit or the like. Then, a variable voltage is applied so that the constant current matches the forward current of the LED. As a result, the voltage applied to the constant current circuit or the like decreases, and the amount of heat generated in this portion decreases. Since heat is generated almost only in this portion, the amount of heat generated in the entire apparatus is reduced and the efficiency is improved.
[0012]
In this way, a vehicle LED headlamp device capable of minimizing the heat generation of the circuit, reducing the number of wirings, making the brightness of the light emitting diodes uniform, and preventing the brightness from fluctuating.
[0013]
According to a third aspect of the present invention, in the vehicle LED headlamp device according to the second aspect, the circuit for increasing the voltage from the power supply voltage includes a constant current circuit and a voltage detection circuit of the constant current circuit. The voltage boosted from the power supply voltage is such that the variable voltage is applied to the plurality of light emitting diodes as the voltage detected by the voltage detection circuit is as low as possible enough to cause the plurality of light emitting diodes to emit light. is there.
[0014]
This LED headlamp device for a vehicle has a constant current circuit for driving the LED at a constant current, and a voltage detection circuit for detecting a voltage applied to the constant current circuit. Then, the voltage is applied by changing the magnitude of the variable voltage so that the voltage detected by the voltage detection circuit is as low as possible to cause the plurality of light emitting diodes to emit light. As a result, the amount of heat generated in the constant current circuit is reduced, and heat is generated almost only in this portion. Therefore, the amount of heat generated in the entire apparatus is also reduced, and the efficiency is improved.
[0015]
In this way, the vehicle LED headlamp device can more reliably minimize the heat generation of the circuit, reduce the number of wirings, make the brightness of the light emitting diodes uniform, and prevent the brightness from fluctuating.
[0016]
According to a fourth aspect of the present invention, there is provided an LED headlamp device for a vehicle, wherein a light emitting diode connected in series is provided with a current alternative circuit.
[0017]
In this vehicle LED headlamp device, even if one of the LEDs connected in series is disconnected and turned off, the current flows through the alternative circuit, and the other LEDs continue to light.
[0018]
In this way, the LED headlamp device for a vehicle can make the brightness of the light emitting diode uniform, prevent the brightness from fluctuating, and avoid simultaneous turning off at the time of disconnection.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram schematically showing a circuit of a vehicle LED headlamp device according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a more detailed circuit of the LED headlamp device for a vehicle according to the embodiment of the present invention.
[0020]
As shown in FIG. 1, a vehicle LED headlamp device 1 according to the present embodiment includes a control unit 2 and a light emitting diode unit 10. In the LED unit 10, all eight LEDs 9 are connected in series, and each of the LEDs 9 has an alternative circuit for disconnection to constitute an LED headlamp. Since the voltage of the power supply 3, that is, the battery of the vehicle is about 12V, the voltage of the LED unit 10 requiring about 2V × 8 = about 16V is insufficient. Therefore, a booster circuit 4 is provided in the control unit 2 to apply a voltage boosted to about 16 V to the eight LEDs 9. The tip of the LED unit 10 is connected to the constant current circuit 8 and grounded. A voltage detection circuit 7 for detecting a voltage applied to the constant current circuit 8 is connected near the constant current circuit 8, and is compared with a reference voltage 5 taken from the power supply 3 and amplified by an amplifier 6. It is input to the booster circuit 4 as a booster control signal. This boost control signal is output so as to control the boost voltage so that the voltage detected by the voltage detection circuit 7 is as low as possible.
[0021]
Thus, the amount of heat generated by the constant current circuit 8 itself can be suppressed as low as possible, and the efficiency of the circuit can be increased. In addition, since all the eight LEDs 9 are connected in series, the same current flows through all the LEDs 9, thereby suppressing variations in brightness. Further, since the voltage applied to the LED 9 (boosted voltage) is also controlled, the brightness of the LED 9 does not change even if the power supply voltage changes. Furthermore, only two wires are required between the control unit 2 and the LED unit 10, so that the workability is improved and the cost can be reduced.
[0022]
Next, a more detailed operation of the circuit will be described with reference to FIG. In the present embodiment, the booster circuit 4 for generating a boosted voltage V2 to be boosted and applied to the LED 9 is of a chopper type using a coil L and a transistor Tr. Further, a rectifying diode D and a smoothing capacitor C are used. Here, the transistor Tr repeatedly turns ON and OFF at high speed, and the boosted voltage V2 can be changed by controlling the duty ratio of the ON and OFF of the transistor Tr. Duty ratio = ON time of transistor Tr / (ON time + OFF time). When the duty ratio is increased, the boosted voltage V2 increases, and when the duty ratio is decreased, the boosted voltage V2 decreases. The current I flowing through the eight LEDs 9 flows to the resistor R1. This resistor R1 corresponds to the constant current circuit 8 in FIG.
[0023]
The voltage V1 of the resistor R1 is detected by the operational amplifier Q1, amplified to a voltage V3, and input to the boost control IC. The resistors R2, R3, and R4 determine the amplification factor of the operational amplifier Q1. Therefore, the operational amplifier Q1 and the resistors R2, R3, and R4 constitute the voltage detection circuit 7 in FIG. In the step-up control IC, the input V3 is compared with the internal reference voltage 5, and the duty ratio of the transistor Tr of the step-up circuit 4 is controlled so that both are constantly equal. The oscillator 12 in the step-up control IC determines a cycle in which the transistor Tr is repeatedly turned ON and OFF, and the PWM amplifier 13 plays a role in determining the duty ratio and driving the transistor Tr.
[0024]
For example, when the voltage of the battery 3 decreases for some reason, the voltage V2 first decreases, and at the same time, the current I flowing through the LED 9 decreases, and the voltage V1 of the resistor R1 also decreases. Then, since the voltage V3 also decreases, a difference from the reference voltage 5 in the boost control IC occurs. In the boost control IC, in order to eliminate this difference, control is performed in the direction of increasing the duty ratio of the transistor Tr, and the voltage V2 eventually stabilizes at the value before the rise and change.
[0025]
In this circuit, since the value of the voltage V1 is controlled to be constant, the current I flowing through the LED 9 is I = V1 / R1, and is constant. That is, a constant current circuit is formed by the resistor R1.
[0026]
Unless the value of the voltage V1 is made unnecessarily large, the heat generated in the resistor R1 is suppressed, and unnecessary heat generation is reduced. For example, when all eight LEDs are connected in parallel as in a conventional circuit, and resistors are used for limiting the current of each of the LEDs, when the power as a source of heat generated in the resistors is obtained, the power supply voltage is 12 V Assuming that the forward voltage Vf is 2 V and the current flowing through the LED is 0.02 A, the voltage applied to each resistor is 12 V−2 V = 10 V.
10V x 0.02A x 8 (pieces) = 1.6W
It becomes. On the other hand, in the circuit of FIG. 2, the power applied to the resistor R1 is controlled such that the voltage V1 is 1 V and the current flowing through the LED is also 0.02 A.
1V × 0.02A = 0.02W
Therefore, the number is extremely reduced as compared with the conventional circuit.
[0027]
Further, even if the forward voltage Vf changes due to variations in the characteristics of the LED 9, the voltage V1 is constant and the variation is absorbed by the change in the boosted voltage V2. This means that even if the forward voltage Vf of the LED 9 fluctuates to a smaller value, the heat generated by the resistor R1 does not increase.
[0028]
Furthermore, comparing the overall efficiency, when the former eight LEDs are connected in parallel, the power consumed by the LEDs is:
2V x 0.02A x 8 (pieces) = 0.32W
If the input power from the power supply is ignored because the control circuit is small,
12V x 0.02A x 8 (parallel) = 1.92W
Therefore, the efficiency is
0.32 / 1.92 × 100 = 16.7 (%)
It becomes. On the other hand, in the circuit of FIG.
2V x 0.02A x 8 (pieces) = 0.32W
The power consumed by the resistor R1 is
1V × 0.02A = 0.02W
Assuming that the efficiency of the booster circuit 4 is 70%, the input voltage from the power supply also ignores the control circuit,
(0.32W + 0.02W) /0.7=0.48W
Therefore, the efficiency is
0.32 / 0.48 × 100 = 66.7 (%)
It can be seen that the efficiency is much higher than that of the conventional circuit.
[0029]
As described above, in the vehicle LED headlamp apparatus according to the present embodiment, it is possible to prevent unnecessary heat generation, and even if the forward voltage Vf of the LED varies, it is absorbed by the change in the boosted voltage V2 and is fixed. The heat generation of the current circuit can be prevented from increasing, and the efficiency is much higher than that of the conventional parallel circuit.
[0030]
In the present embodiment, the chopper method is used as a method of boosting the power supply voltage, but there are various methods of boosting, and any method such as a charge pump method and a transformer method may be used. .
[0031]
The configuration, shape, quantity, material, size, connection relationship, and the like of other portions of the vehicle LED headlamp device are not limited to the present embodiment.
[0032]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram showing a circuit of each LED 9 in the vehicle LED headlamp device according to the second embodiment of the present invention.
[0033]
As shown in FIG. 3, in each LED 9 of the vehicle LED headlamp device 1 of the present embodiment, resistors R5 and R6 for dividing the voltage between both ends of the LED 9 are arranged in parallel with the LED 9. Further, a transistor Tr2 for a current substitute circuit and a shunt regulator Q2 for driving the transistor Tr2 are connected in parallel with the resistors R5 and R6 and the LED 9 as shown in the figure. Here, R5 = 27 kΩ, R6 = 68 kΩ, and the reference voltage of Q2 = 2.5V.
[0034]
When the light emitting diode 9 is normally lit, the current is flowing through the LED 9 along the path (1). The forward voltage Vf of the LED is 2.0 V, and the voltage applied to R5 is V5 = 2.0 × 68 / (27 + 68) = 1.43V
It has become. At this time, Q2 acts to set Vf to the reference voltage of 2.5 V, and raises V4 so that V4 becomes substantially equal to the value of Vf. Accordingly, the base current for turning on Tr2 does not flow as in the path of (3), and Tr2 remains OFF, and no current flows in the path of (2) of the alternative path.
[0035]
On the other hand, when the light emitting diode 9 is disconnected, the current stops flowing through the path (1), and the current tries to flow through the path (4). Since R5 and R6 have large resistance values, the value of Vf suddenly increases and tends to increase to near the power supply voltage value. At the same time, V5 also rises. At this time, Q2 acts to suppress V5 to the reference voltage of 2.5 V and lowers V4. Then, the base current of Tr2 flows through the path of (3), and Tr2 is turned ON. Therefore, a current alternative path is formed by Tr2.
[0036]
Thus, even if the path of (1) is cut off due to the disconnection of the light emitting diode 9, the current continues to flow instantaneously through the path of (2), and the other light emitting diodes continue to light. After that, Vf is stabilized around 3.5 V by Q2.
[0037]
In this embodiment, the shunt regulator and the transistor are used for disconnection detection and the formation of an alternative path for current. However, a circuit using a thyristor or a circuit combining transistors may be used, and similar effects can be obtained.
[0038]
【The invention's effect】
As described above, the LED headlamp device for a vehicle according to the first aspect of the present invention uses a light emitting diode as a light source, connects a plurality of the light emitting diodes in series, and applies a voltage boosted from a power supply voltage. It is to light up.
[0039]
Typically, the voltage of a vehicle battery is about 12V and the forward voltage of a light emitting diode is about 2V. Therefore, when arranging LEDs in series and lighting them, the limit is six. In view of this, the LEDs are rearranged in series from the conventional parallel, and a booster circuit is provided between the LEDs arranged in series with the battery to increase the voltage so that the number of LEDs can be increased. As a result, the number of wires between the power supply and the LED unit becomes two, and workability can be improved and cost can be reduced. In addition, since LEDs are arranged in series, the same amount of current flows through all LEDs, which reduces variations in brightness between LEDs and controls the voltage applied to LEDs by a booster circuit even if the power supply voltage fluctuates. Therefore, the brightness does not fluctuate.
[0040]
In this way, a sufficient amount of light can be obtained as a headlamp by connecting a plurality of light emitting diodes, the number of wirings can be reduced, the brightness of the light emitting diodes can be made uniform, and fluctuations in brightness can be prevented. It becomes an LED headlamp device.
[0041]
According to a second aspect of the present invention, in the vehicle LED headlamp apparatus according to the first aspect, the light emitting diodes connected in series are driven at a constant current and a variable voltage is applied.
[0042]
In this vehicle LED headlamp apparatus, in addition to arranging LEDs in series and applying a boosted power supply voltage, a constant current drive is performed by adding a constant current circuit or the like. Then, a variable voltage is applied so that the constant current matches the forward current of the LED. As a result, in addition to the effect of the first aspect, the voltage applied to the constant current circuit and the like is reduced, and the amount of heat generated in this portion is reduced. Since heat is generated almost only in this portion, the amount of heat generated in the entire apparatus is reduced and the efficiency is improved.
[0043]
In this way, a vehicle LED headlamp device capable of minimizing the heat generation of the circuit, reducing the number of wirings, making the brightness of the light emitting diodes uniform, and preventing the brightness from fluctuating.
[0044]
According to a third aspect of the present invention, in the vehicle LED headlamp device according to the second aspect, the circuit for increasing the voltage from the power supply voltage includes a constant current circuit and a voltage detection circuit of the constant current circuit. The voltage boosted from the power supply voltage is such that the variable voltage is applied to the plurality of light emitting diodes as the voltage detected by the voltage detection circuit is as low as possible enough to cause the plurality of light emitting diodes to emit light. is there.
[0045]
In addition to the effects described in claim 2, the vehicle LED headlamp device includes a constant current circuit for driving the LED with a constant current, and a voltage detection circuit for detecting a voltage applied to the constant current circuit. I have. Then, the voltage is applied by changing the magnitude of the variable voltage so that the voltage detected by the voltage detection circuit is as low as possible to cause the plurality of light emitting diodes to emit light. As a result, the amount of heat generated in the constant current circuit is reduced, and heat is generated almost only in this portion. Therefore, the amount of heat generated in the entire apparatus is also reduced, and the efficiency is improved.
[0046]
In this way, the vehicle LED headlamp device can more reliably minimize the heat generation of the circuit, reduce the number of wirings, make the brightness of the light emitting diodes uniform, and prevent the brightness from fluctuating.
[0047]
According to a fourth aspect of the present invention, there is provided an LED headlamp device for a vehicle according to the first to third aspects, wherein a current replacement circuit is formed in the light emitting diodes connected in series.
[0048]
In addition to the effects described in claims 1 to 3, in this vehicle LED headlamp device, even if one of the LEDs connected in series is disconnected and turned off, the current is passed through the alternative circuit, so that the remaining LED is supplied. Other LEDs continue to light.
[0049]
In this way, the LED headlamp device for a vehicle can make the brightness of the light emitting diode uniform, prevent the brightness from fluctuating, and avoid simultaneous turning off at the time of disconnection.
[Brief description of the drawings]
FIG. 1 is a circuit diagram schematically showing a circuit of a vehicle LED headlamp device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a more detailed circuit of the LED headlamp device for a vehicle according to the embodiment of the present invention.
FIG. 3 is a circuit diagram showing an alternative route when an LED is disconnected.
FIG. 4 is a circuit diagram showing an example of a conventional vehicle LED headlamp device.
[Explanation of symbols]
1 LED headlamp device for vehicle 9 Light emitting diode (LED)
20 Current replacement circuit

Claims (4)

An LED headlamp device for a vehicle, wherein a plurality of light emitting diodes are connected in series using a light emitting diode as a light source, and a voltage boosted from a power supply voltage is applied to the plurality of light emitting diodes to light them. The LED headlamp device for a vehicle according to claim 1, wherein the light-emitting diodes connected in series are driven at a constant current and a variable voltage is applied. The circuit for boosting the voltage from the power supply voltage includes a constant current circuit and a voltage detection circuit of the constant current circuit, and the voltage detected by the voltage detection circuit is sufficient to cause the plurality of light emitting diodes to emit light. The vehicular LED headlamp device according to claim 2, wherein the variable voltage is applied to the plurality of light emitting diodes as a voltage as low as possible. 4. The LED headlamp device for a vehicle according to claim 1, wherein a current substitute circuit is formed in the light emitting diodes connected in series.

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