JP2006085993A - Light emitting diode lighting device - Google Patents

Abstract

For example, in a light-emitting diode lighting device used for a backlight of a vehicle instrument, the current flowing in the light-emitting diode is controlled to be constant, and at the same time, the power consumption is reduced.
In the light emitting diode lighting device 100 of FIG. 1, a voltage across a resistor 51 is fed back to a switching regulator 30. The switching control circuit 34 controls the on / off operation of the transistor 34e in accordance with the difference between the feedback input voltage and the reference voltage. Accordingly, the charging voltage of the capacitor 33 applied to the light emitting diode circuit 40 changes so that the voltage across the resistor 51 is the same as the reference voltage. As a result, the current flowing through the series circuit 41 of the light emitting diodes can be controlled to be constant, and it is not necessary to use a transistor for controlling the current in the light emitting diode circuit 40. Therefore, power consumption can be reduced as compared with the conventional case. it can.
[Selection] Figure 1

Description

  The present invention relates to a light emitting diode lighting device that drives a plurality of light emitting diodes employed in a vehicle meter, for example.

Conventionally, as a lighting device for a plurality of light emitting diodes employed for a backlight of a vehicle meter, there is one as shown in Patent Document 1 (FIG. 6). In the circuit shown in the figure, the constant current circuit 340 forms a current mirror circuit with the bipolar transistor 364 of each light emitting diode circuit 360 by the bipolar transistor 341. Accordingly, the same current as that of the constant current circuit 340 flows through each light emitting diode circuit 360, and the light emitting diodes 362 and 363 of each light emitting diode circuit 360 are driven to emit light. Thereby, even if the forward voltage changes due to variations in the forward voltage of each light-emitting diode and the temperature, the same luminance can be maintained.
Japanese Patent Laid-Open No. 2003-1000047

  As described above, in the light emitting diode lighting device of Patent Document 1, even when the forward voltage Vf changes due to variations in each light emitting diode, a constant current is caused to flow to each light emitting diode by the transistor 364 or the like. Can do. However, in the circuit shown in the figure, the difference between the battery voltage 310 applied to the light emitting diode circuit 360 and the forward voltage of each of the light emitting diodes 362 and 363 and the voltage drop of the current limiting resistor 361 is applied to the transistor 364. Become. Therefore, power corresponding to the differential voltage is consumed by the transistor 364, which causes a large energy loss and causes a problem of heat generation.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a light-emitting diode lighting device capable of controlling the current flowing through the light-emitting diode to be constant and reducing the power consumption as compared with the prior art. .

  The light-emitting diode lighting device according to claim 1 is a light-emitting diode circuit in which a plurality of series circuits in which a plurality of light-emitting diodes and at least one resistor are connected in series are connected in parallel, and a reference voltage for generating a predetermined reference voltage A generation circuit, a comparison circuit that compares the reference voltage with a voltage drop caused by the resistor in one of the plurality of series circuits constituting the light emitting diode circuit, and based on the comparison result, And a voltage adjusting circuit that adjusts a voltage supplied to the light emitting diode circuit so that a voltage drop caused by a resistor is the same as the reference voltage.

  In this way, by controlling so that the voltage drop of the resistance of one series circuit in the light emitting diode circuit coincides with a predetermined reference voltage, the current flowing through the series circuit of light emitting diodes connected to the resistor is constant. Can be kept in. That is, regardless of the forward voltage light emitting diode, the flowing current can be controlled to be constant. Further, even when the forward voltage of the light emitting diode changes due to a change in ambient temperature, the flowing current can be controlled to be constant. Therefore, it is possible to realize a highly accurate light-emitting diode lighting device in which the lighting brightness does not change due to product variations, ambient temperature changes, and the like. Furthermore, since a transistor is not used in the light emitting diode circuit for controlling to a constant current, power consumption due to the transistor can be reduced.

  For other series circuits that do not monitor current, if a light emitting diode having a forward voltage similar to that of the series circuit that monitors the current and controls it to a predetermined current is used, this series circuit is used. Therefore, the current is controlled to be almost the same as the current flowing in the current. In addition, a light emitting diode having a similar forward voltage has a temperature dependency of a similar forward voltage. Therefore, even when the ambient temperature changes, a current that is substantially the same as the current that flows in the series circuit that monitors the current and controls it to a predetermined current flows in the series circuit that does not monitor the current. For example, the forward voltage of each light emitting diode can be made uniform by measuring the forward voltage of the light emitting diode in advance or by using the light emitting diodes produced at the same time.

  The light-emitting diode lighting device according to claim 2, wherein the voltage adjustment circuit includes a switching element that performs an on / off operation, and controls the on / off operation of the switching element based on the comparison result, thereby controlling the light-emitting diode circuit. The voltage to be supplied is adjusted.

  Thus, by using the switching element, the target output voltage can be obtained efficiently with little energy loss.

  According to a third aspect of the present invention, in the light emitting diode lighting device, the voltage adjustment circuit is a booster circuit that outputs a voltage larger than an input voltage input to the voltage adjustment circuit.

  When a plurality of light emitting diodes are connected in series and a current is passed therethrough, a voltage larger than the sum of the forward voltages of the respective light emitting diodes must be applied to the series circuit of the light emitting diodes. In the light-emitting diode lighting device according to claim 3, even when the power supply voltage is lower than the voltage necessary for lighting the light-emitting diode, the power-supply voltage is a voltage necessary for lighting the light-emitting diode by the voltage adjusting circuit. The pressure can be increased to Therefore, many light emitting diodes can be connected in series, and a light emitting diode having a large forward voltage can also be used. For example, when used for a vehicle meter, a power supply voltage of DC 12V is generally used, and a light emitting diode having a forward voltage variation of 3.6V to 4.4V is used.

  The light-emitting diode lighting device according to claim 4 is characterized in that the light-emitting diode lighting device is for a backlight of a vehicle instrument.

  For example, it is used as a backlight of a vehicle meter. Even when used in a vehicular instrument with a drastic temperature change, the current flowing through the light emitting diode is controlled to be constant, and the light emitting diode can be lit stably. Therefore, it is particularly effective to use this apparatus as a backlight for a vehicle instrument.

  The light-emitting diode lighting device according to claim 5, wherein the voltage adjustment circuit generates a reference voltage for detecting an overvoltage with respect to a supply voltage to the light-emitting diode circuit; And a limiter circuit for limiting a supply voltage of the light emitting diode circuit to a reference voltage generated by the second reference voltage generation circuit.

  For example, when the current flowing in the series circuit of light emitting diodes controlled to a constant current stops flowing due to disconnection or the like, the voltage adjustment circuit outputs a very large voltage to try to flow the current through the series circuit . In this case, this very large voltage is applied to the light emitting diode circuit, and a very large current flows through the other series circuits that do not monitor the current. As a result, each light emitting diode may cause abnormal heat generation. In order to prevent such a problem, in the light-emitting diode lighting device according to claim 5, the voltage supplied to the light-emitting diode circuit is prevented from increasing beyond a predetermined threshold value. Therefore, the above problems can be prevented.

  Hereinafter, preferred embodiments of the present invention will be described with respect to an example realized as a backlight of a vehicle instrument.

(First embodiment)
FIG. 1 is a configuration diagram showing a schematic configuration of a light-emitting diode lighting device 100 according to the first embodiment. As shown in the figure, the light-emitting diode lighting device 100 includes a battery 10, a switching regulator 30, a light-emitting diode circuit 40, resistors 21, 22, 50, and a constant voltage power supply 11. Each component will be described below.

  The battery 10 supplies power for driving the light emitting diode lighting device 100. The voltage of the battery 10 is boosted to a predetermined voltage by a switching regulator 30 described later and supplied to the light emitting diode circuit 40. Moreover, as this battery 10, 12V DC power supply mounted in a vehicle is used, for example.

  The constant voltage power supply 11 is a power supply that generates a predetermined constant voltage. As will be described later, a voltage obtained by dividing the generated voltage by the resistors 21 and 22 is input to the switching regulator 30 as a reference voltage, and the voltage across the resistor 51 is controlled to the reference voltage.

  The switching regulator 30 is a circuit that boosts and outputs the voltage of the battery 10 to a predetermined voltage as described above. In the present embodiment, a voltage across the resistor 51, which will be described later, is fed back to the switching regulator 30, and the voltage across the resistor 51 becomes the same as a predetermined reference voltage (a voltage obtained by dividing the constant voltage 11 by the resistors 21 and 22). Adjust the output voltage as follows. By controlling the voltage across the resistor 51 to a predetermined reference voltage, the current flowing through the light emitting diode series circuit 41 can be kept constant. The switching regulator 30 includes a switching control circuit 34, a coil 31, a diode 32, and a capacitor 33.

  The coil 31, the diode 32, and the capacitor 33 are a booster circuit that is connected to the battery 10 and converts the voltage into a voltage larger than the voltage of the battery 10 by an on / off operation of a switching element 34e described later and outputs the voltage. A light emitting diode circuit 40, which will be described later, is connected to the output terminal of the booster circuit including the coil 31, the diode 32, and the capacitor 33, and each light emitting diode is lit. The operations of the coil 31, the diode 32, and the capacitor 33 will be described later.

  The switching control circuit 34 includes an error amplifier 34a, a comparator 34b, a triangular wave oscillation circuit 34c, a driver 34d, and a transistor 34e. The transistor 34e is turned on / off according to a difference between a feedback voltage input to the error amplifier 34a and a predetermined reference voltage. It is a circuit that controls the operation. In this embodiment, the voltage across the resistor 51 is input as a feedback voltage input to the error amplifier 34a, and a voltage obtained by dividing the constant voltage 11 by the resistors 21 and 22 is input as a predetermined reference voltage.

  The error amplifier 34a has an inverting input terminal for inverting and outputting the input polarity and a non-inverting input terminal for outputting the inverting input without inverting the input polarity, and is input to both the inverting input terminal and the non-inverting input terminal. When a signal is given, it is an element that outputs a signal proportional to the difference. In the present embodiment, a voltage (reference voltage) obtained by dividing the constant voltage 11 by the resistors 21 and 22 is input to the non-inverting input terminal, and a voltage (resistor 51) corresponding to the current flowing through the series circuit 41 is input to the inverting input terminal. Is input). Therefore, a signal proportional to the difference between these voltages is output from the output terminal of the error amplifier 34a. The output terminal of the error amplifier 34a is connected to the inverting input terminal of the comparator 34b. This reference voltage is set based on the current value desired to flow through the series circuit 41, and the resistance values of the resistors 21 and 22 are determined accordingly.

  Similar to the error amplifier 34a, the comparator 34b has an inverting input terminal and a non-inverting input terminal, compares the magnitudes of signals input to the inverting input terminal and the non-inverting input terminal, and compares the signals input to the inverting input terminal. The element outputs an L level signal when the signal is larger, and outputs an H level signal when the signal input to the non-inverting input terminal is larger. The output terminal of the error amplifier 34a is connected to the inverting input terminal of the comparator 34b, and the output terminal of a triangular wave oscillation circuit 34c described later is connected to the non-inverting input terminal.

  The triangular wave oscillation circuit 34c is a circuit that outputs a triangular wave having a predetermined frequency. As described above, the output terminal of the triangular wave oscillation circuit 34c is connected to the non-inverting input terminal of the comparator 34b. The comparator 34b compares the triangular wave signal with the output signal of the error amplifier 34a, and outputs an H level signal or an L level signal. Therefore, pulse signals with different pulse widths are output from the comparator 34b depending on the magnitude of the output signal of the error amplifier 34a.

  The driver 34d is a circuit that converts an input signal into a predetermined magnitude and outputs it. The output terminal of the comparator 34b is connected to the input terminal of the driver 34d, and the output terminal is connected to the base terminal of a transistor 34e described later. Therefore, the driver 34d converts the pulse signal output from the comparator 34b to a voltage that can turn on the transistor 34e.

  The transistor 34e is a known bipolar transistor, and is a switching element that conducts / cuts off between the emitter and the collector by giving a signal to the base terminal. In this embodiment, since the transistor 34e uses a PNP transistor, the transistor 34e is turned on when the base voltage becomes L level, and turned off when the base voltage becomes H level. The base terminal of the transistor 34e is connected to the output terminal of the driver 34d as described above, and an on / off operation is performed by a signal from this driver. The collector terminal is connected to GND, and the emitter terminal is connected to the coil 31 so as to be in parallel with the diode 32. Therefore, when the transistor 34e is on, the current supplied from the battery 10 flows through the transistor 34e and flows into the GND. When the transistor 34e is off, the current supplied from the battery 10 is supplied to the capacitor 33 and the light emitting diode circuit 40 via the diode 32. Is done.

  The light emitting diode circuit 40 is a circuit in which a plurality of series circuits in which a plurality of light emitting diodes are connected in series are connected in parallel. This light-emitting diode has an anode terminal and a cathode terminal. When a predetermined forward voltage is applied from the anode side to the cathode side, a current flows, and accordingly, light of a predetermined color is emitted. When used as a backlight of a vehicle meter, for example, a light emitting diode having a forward voltage variation of 3.6 V to 4.4 V and a forward voltage temperature dependency of ± 0.3 V is used. For example, the forward voltage of each light emitting diode of the light emitting diode circuit 40 can be made uniform by measuring the forward voltage of the light emitting diode in advance or by using the light emitting diode produced at the same time. The upper stage of the light emitting diode circuit 40 is connected to the diode 32 so as to be parallel to the capacitor 33. On the other hand, the lower stage is connected to a resistor 50 described later. Therefore, the charging voltage of the capacitor 33 is applied to the light emitting diode circuit 40, and each light emitting diode is turned on.

  The resistor 50 is a resistor for adjusting the current flowing through the light emitting diode circuit 40. Further, the resistor 51, which is one of the resistors 50, is also a current detection resistor that converts the current value into a voltage and feeds it back to the switching control circuit 34 in order to control the current flowing therethrough constant.

  Next, the operation of the light-emitting diode lighting device 100 having the above-described configuration will be described based on the waveform diagrams of FIGS. Here, FIG. 2 shows the switching control circuit 34 when the current flowing through the series circuit 41 that monitors the current and controls it to a predetermined current (current flowing through the current detection resistor 51) is smaller than the reference current. The operation of each component is shown. On the other hand, FIG. 3 shows each of the switching control circuits 34 when the current flowing through the series circuit 41 that monitors the current and controls it to a predetermined current (current flowing through the current detection resistor 51) is larger than the reference current. The operation of the component is shown.

  First, it is assumed that the current flowing through the series circuit 41 (current flowing through the resistor 51) decreases as shown in FIG. 2A with respect to the target reference current. Note that such current fluctuation occurs when the forward voltage of each light emitting diode fluctuates due to, for example, a change in the temperature of the vehicle. For convenience of explanation, it is assumed that the current waveform of the resistor 51 shown in FIG.

  The voltage across the resistor 51 corresponding to this current is fed back to the inverting input terminal of the error amplifier 34a of the switching control circuit 34. In the error amplifier 34a, the difference between the feedback input voltage and the reference voltage obtained by dividing the constant voltage 11 input to the non-inverting input terminal by the resistors 21 and 22 (voltage corresponding to the reference current to be passed through the series circuit 41). A signal proportional to is output (FIG. 2B). At this time, the error amplifier 34a outputs a negative signal when the inverting input signal is larger than the non-inverting input signal, and outputs a positive signal when the non-inverting input is larger. Therefore, a predetermined plus signal is output from the error amplifier 34a. This output signal is input to the inverting input terminal of the comparator 34b.

  The comparator 34b compares the output signal from the error amplifier 34a with the output signal of the triangular wave oscillation circuit 34c input to the non-inverting input terminal (FIG. 2B), and the signal from the error amplifier 34a is larger. Sometimes an L level signal is output, and when the signal from the error amplifier 34a is smaller, an H level signal is output. Note that the triangular wave oscillation circuit 34c generates a triangular wave that fluctuates in a positive region as shown in FIG. Therefore, a pulse signal in which an L level signal having a predetermined time width and an H level signal having a predetermined time width are repeated is output to the output terminal of the comparator 34b (FIG. 2C). This output signal is input to the driver 34d and converted into a signal having a predetermined magnitude in order to operate the transistor 34e. The signal converted by the driver 34d is input to the base terminal of the transistor 34e.

  As shown in FIG. 1, since the transistor 34e uses a PNP transistor, it is turned on when the base voltage becomes L level and turned off when it becomes H level. Therefore, the transistor 34e is turned off when the output of the comparator 34b is at the H level, and is turned on when the output is at the L level. Therefore, the on / off operation is repeated as shown in FIG.

  Here, when the transistor 34e is on, the current supplied from the battery 10 flows through the transistor 34e. At this time, energy is stored in the coil 31. Here, when the transistor 34 e is turned off, the energy stored in the coil 31 becomes a high voltage and is generated at both ends of the coil 31. This voltage is charged to the capacitor 33 via the diode 32. Thus, by repeating the on / off operation of the transistor 34e, the voltage charged in the capacitor 33 increases. Since the charging voltage of the capacitor 33 is applied to the series circuit 41, the current flowing through the series circuit 41 increases as the charging voltage of the capacitor 33 increases. Thereafter, this operation is continued until the voltage across the resistor 51 becomes the same as the reference voltage generated by the resistors 21 and 22.

  As described above, when the current flowing through the resistor 51 decreases with respect to the reference current, the voltage charged to the capacitor 33, that is, the voltage applied to the series circuit 41 is increased, so that the current becomes the same as the reference current. So that it is controlled.

  On the other hand, it is assumed that the current flowing through the series circuit 41 (current flowing through the resistor 51) increases as shown in FIG. 3A with respect to the target reference current. As described above, the voltage across the resistor 51 corresponding to this current is fed back to the inverting input terminal of the error amplifier 34a of the switching control circuit 34 and compared with the reference voltage generated at the resistors 21 and 22. In this case, a predetermined negative signal is output from the error amplifier 34a as shown in FIG.

  In the same manner as described above, the output signal of the error amplifier 34a is compared with the magnitude of the triangular wave generated by the triangular wave oscillation circuit 34c by the comparator 34b (FIG. 3B). As shown in FIG. 3, since the triangular wave is larger than the output signal of the error amplifier 34a, an H level signal is output from the comparator 34b (FIG. 3C). Therefore, the transistor 34e is always off (FIG. 3 (d)). At this time, the voltage charged in the capacitor 33 is gradually reduced as the light emitting diode circuit 40 is discharged.

  As described above, when the current flowing through the resistor 51 increases with respect to the reference current, the voltage charged to the capacitor 33, that is, the voltage applied to the series circuit 41 of the light emitting diodes is decreased, so that the current becomes the reference current. Controls to be the same.

  As described above, in the light emitting diode lighting device 100 according to the present embodiment, the current flowing through the arbitrarily selected series circuit of the light emitting diode circuit 40 is fed back to the switching regulator 30 to control the current to a predetermined reference value. be able to. That is, it is possible to realize stable lighting of the light emitting diodes without being affected by variations in the forward voltage of each light emitting diode. Further, since the transistor is not used in the light emitting diode circuit 40 in order to control the current flowing through the light emitting diode to be constant as in the prior art, the power consumption can be reduced compared to the conventional case. Further, even when the device is used in an environment where the temperature change is severe as in a vehicle and the forward voltage of the light emitting diode changes due to the temperature change, stable lighting of the light emitting diode can be realized.

  In the present embodiment, the voltage of the battery 10 is boosted by the switching regulator 30 in order to drive a series circuit of light emitting diodes. If a battery with a large voltage is used, the switching regulator may be configured so that the battery voltage drops to a predetermined voltage and is output. In addition, when the number of light emitting diodes connected in series is small or when a light emitting diode having a small forward voltage is used, a switching regulator that drops the voltage may be used as necessary.

  In addition, although the example using a PNP transistor as a switching element of the switching control circuit 34 in the above-described embodiment has been described, it may be configured by other types of switching elements such as an NPN transistor or a MOSFET.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described. FIG. 4 is a configuration diagram showing a schematic configuration of the light-emitting diode lighting device 200 in the present embodiment. Hereinafter, each component will be described with a focus on differences from the first embodiment. The battery 10, coil 31, diode 32, capacitor 33, resistors 21, 22, 50, constant voltage 11, error amplifier 34a, comparator 34b, triangular wave oscillation circuit 34c, driver 34d, transistor 34e, and light emitting diode circuit 40 are the first The detailed description will be omitted because it works the same as the embodiment.

  In the switching control circuit 34 of the present embodiment, a limiter circuit 34f that limits the voltage applied to the light emitting diode circuit 40 to a predetermined reference voltage or less is provided. As shown in FIG. 3, a voltage obtained by dividing the voltage applied to the light emitting diode circuit 40 (voltage at the terminal 1) by resistors 25 and 26 is input to the limiter circuit 34f, and the voltage of the battery 10 is input by resistors 23 and 24. The divided reference voltage is input. The output terminal of the limiter circuit 34f is connected to the inverting input terminal (terminal 2 in FIG. 4) of the comparator 34b in parallel with the error amplifier 34a.

  The operation of the limiter circuit 34f will be described with reference to the waveform diagram of FIG. For example, it is assumed that no current flows through the resistor 51 as shown in FIG. At this time, the maximum plus signal is output from the error amplifier 34a as shown in FIG. If the limiter circuit 34f is not provided, as described in the first embodiment, the transistor 34e repeats the on / off operation based on the output signal of the error amplifier 34a, and the charging voltage of the capacitor 33 increases. This step-up operation is continued until the current flowing through the resistor 51 becomes the same as the reference current. However, when the disconnection occurs as described above, the charging voltage of the capacitor 33 increases without limitation. Therefore, it is expected that an overvoltage is applied to the light emitting diode circuit 40, and accordingly, an overcurrent flows through the series circuit other than the series circuit 41 to cause problems such as heat generation. In order to prevent such a problem, when the charging voltage of the capacitor 33 (the voltage at the terminal 1) reaches the reference voltage generated by the resistors 23 and 24, the limiter circuit 34f is activated to force the signal at the terminal 2 to zero. Below the level (FIGS. 3C and 3D). That is, since the signal input to the inverting input terminal of the comparator 34b is equal to or lower than the zero level, the on / off operation of the transistor 34e is stopped and always turned off. As a result, the boosting operation is stopped, and thus problems such as heat generation due to overvoltage as described above can be prevented.

  In addition to the above, the operation of the limiter circuit 34f is such that the voltage at the terminal 1 is set so that the voltage divided by the resistors 25 and 26 is equal to the voltage determined by the reference voltage generated by the resistors 23 and 24. There is also a method that prevents the voltage from rising without limit and prevents overcurrent.

It is a schematic structure figure showing the whole light emitting diode lighting device 100 in a 1st embodiment. It is a wave form diagram for demonstrating the effect | action of the switching control circuit 34 when the electric current which flows into the resistance 51 (series circuit 40) in 1st Embodiment reduces with respect to a reference current. It is a wave form chart for explaining an operation of switching control circuit when the current which flows into resistance 51 (series circuit 40) in a 1st embodiment increases with respect to a reference current. It is a schematic block diagram which shows the whole light emitting diode lighting device 200 in 2nd Embodiment. It is a wave form diagram for demonstrating the effect | action of the limiter circuit 34f in 2nd Embodiment. It is a schematic block diagram which shows the whole light emitting diode lighting device 300 of patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Battery 11 Constant voltage power supply 30 Switching regulator 31 Coil 32 Diode 33 Capacitor 21-26, 80 Resistance 34 Switching control circuit 34a Error amplifier 34b Comparator 34c Triangular wave oscillation circuit 34d Driver 34e PNP transistor 34f Limiter circuit 40 Light emitting diode circuit 41, 42 Light emission Diode series circuit

Claims (5)

A light emitting diode circuit in which a plurality of series circuits in which a plurality of light emitting diodes and at least one resistor are connected in series are connected in parallel;
A reference voltage generating circuit for generating a predetermined reference voltage;
A comparison circuit for comparing the reference voltage with a voltage drop caused by the resistor in one of the plurality of series circuits constituting the light emitting diode circuit;
A light-emitting diode lighting device comprising: a voltage adjustment circuit that adjusts a voltage supplied to the light-emitting diode circuit so that a voltage drop due to the resistor is equal to the reference voltage based on the comparison result.   The voltage adjustment circuit includes a switching element that performs an on / off operation, and adjusts a voltage supplied to the light emitting diode circuit by controlling an on / off operation of the switching element based on the comparison result. Item 4. The light-emitting diode lighting device according to item 1.   The light emitting diode lighting device according to claim 1, wherein the voltage adjustment circuit is a booster circuit that outputs a voltage larger than an input voltage input to the voltage adjustment circuit.   The light emitting diode lighting device according to any one of claims 1 to 3, wherein the light emitting diode lighting device is for a backlight of a vehicle instrument. The voltage adjustment circuit includes:
A second reference voltage generation circuit for generating a reference voltage for detecting an overvoltage with respect to a supply voltage to the light emitting diode circuit;
5. The light-emitting diode lighting device according to claim 1, further comprising: a limiter circuit that limits a supply voltage of the light-emitting diode circuit to a reference voltage generated by the second reference voltage generation circuit.

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