JP2008251276A - Failure detecting device of light emitting diode circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a failure detection device capable of detecting the failure even when only one unit of LEDs is short-circuited or disconnected. <P>SOLUTION: This failure detecting device is to detect the failure of an LED circuit formed by connecting a plurality of LEDs driven by the output voltage of a DC power supply 10 in series, and is equipped with a switching circuit 21 formed by parallel-connecting a plurality of switching elements 21a-e to respective LEDs, a switch control circuit 22 to short-circuit the LED parallel-connected to the switching element by turning on the respective switching elements of the switching circuit 21 in a fixed time (t1) within a prescribed period (T1) while going around the switching elements one by one in accordance with the period (T1), and an output voltage monitoring circuit 20 connected to the output end of the DC power supply to monitor fluctuation of the output voltage and output an abnormal signal when there is no fluctuation of the output voltage within the time (T1) of the period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for detecting a failure of an LED in a circuit for lighting a light emitting diode (LED).

  Since the LED is a substantially constant voltage element, a method of lighting the LED with a constant DC current is generally used.

FIGS. 7 and 8 show lighting circuits 2 and 3 for supplying power to a load circuit (lamp) 1 formed by connecting a plurality of (n) LEDs in series using a DC constant current power supply 10. The cause of failure in which some of the LEDs in the lamp 1 are not lit is generally a disconnection or a short circuit.
(1) As a method for detecting a failure due to disconnection, there are a method for detecting voltage and a method for detecting current.

  When detecting a disconnection failure with a voltage, if even one LED breaks, the output of the power supply becomes no load, so the output voltage of the lighting circuit rises to the output limit voltage (Vlim). When multiple (n) LEDs are connected in series as a load, the output limit voltage (Vlim) is the sum of the forward voltage (Vf) of each LED in consideration of manufacturing variations and temperature variations. By setting the detection voltage between the maximum value of the output limit voltage (Vlim) and the total voltage (Vf × n), the disconnection failure of the LED load circuit is detected. it can. However, with this method, the output limit voltage (Vlim) must be set to a value higher than necessary in order to provide a margin for the detection voltage, which increases the withstand voltage of the power supply components, resulting in performance degradation and cost increase. Bring.

  On the other hand, when a disconnection failure is detected by current, a current detection resistor 11 is connected in series with the load circuit in the lighting circuit 2 of FIG. 7, and a change in the voltage between terminals of this resistor is detected by the disconnection detection circuit 12. To do. If even one LED breaks, the output terminal of the DC constant current power supply 10 is unloaded, and the load circuit current becomes 0. Therefore, the voltage between the terminals of the current detection resistor 11 becomes 0V. This is used to detect a disconnection failure.

In this method, the current detection resistor 11 is required, and there is a problem that the efficiency is lowered due to the loss of the current detection resistor.
(2) As a method of detecting a failure due to a short circuit, there are a method of detecting a voltage drop of the total forward voltage (Vf × n) of n LEDs and a method of detecting an increase in output current.

  First, when a short circuit is detected by a voltage drop, a drop in output voltage is detected. Therefore, the lighting circuit 2 of FIG. 7 includes a short circuit detection circuit 13 that detects a short circuit from the output voltage Vout of the DC constant current power supply 10. The output voltage Vout is the total (Vf × n) of the forward voltage (Vf) of each LED. When one LED is short-circuited, the output voltage is Vf × (n−1). Therefore, in order to detect a short-circuit failure of one LED, the detection voltages are Vf × n and Vf × (n−1). It is necessary to set the voltage between. In general, a sufficiently low voltage is set as the detection voltage in consideration of manufacturing variations in the forward voltage and changes due to temperature. Therefore, there is a problem that a failure cannot be detected unless a plurality of LEDs are short-circuited.

  In the lighting circuit 2 of FIG. 7, since either the disconnection detection circuit 12 or the short circuit detection circuit 13 outputs an abnormal signal, the disconnection fault signal output from the disconnection detection circuit 12 and the short circuit detection circuit 13 are output. An OR circuit 14 for inputting the output short-circuit fault signal is provided.

  Further, when the power supply 10 is a non-stabilized DC power supply, the LED current changes due to the fluctuation of the power supply voltage, so that the fluctuation of Vf becomes large. For this reason, since it is necessary to set a detection voltage with a margin in consideration of fluctuations in the power supply, an abnormality cannot be detected unless more LEDs are short-circuited.

  For example, the forward voltage of a white power LED is about 3.5V. The forward voltage varies from 2.8V to 4.2V because there are about ± 20% variation due to manufacturing variations and temperature. When 20 LEDs are connected in series, the total forward voltage varies from 56V to 84V. For this reason, if the detection voltage is not set to 56 V or less, the normal operation state is determined to be abnormal, so the set voltage is set to 56 V or less. This voltage value is a voltage for about 13 LEDs when the forward voltage is a maximum of 4.2V. Therefore, a short circuit failure cannot be detected unless the seven LEDs have a short circuit failure.

  Therefore, in this method, a short circuit failure of one LED cannot be detected, and a short circuit failure cannot be detected unless a plurality of LEDs have a short circuit failure. When the number of LEDs increases, the lower limit of variation due to manufacturing variations and temperature of the forward voltage (Vf) falls below Vf × (n−1), and the detection voltage cannot be set.

  An in-vehicle lamp such as a vehicle headlamp has a light distribution standard, which must be satisfied. However, when seven of the 20 LEDs are not lit, the light distribution standard cannot be satisfied. Moreover, if the light intensity decreases by one third, the vehicle will run in a dark state in front of the vehicle, which is dangerous.

  On the other hand, when a short circuit failure of one LED is detected due to an increase in output current, a current limiting resistor or a new current detecting resistor is inserted in series with the LED, and the voltage change is detected. Also in this method, the current change due to one LED short-circuit is very small, the variation in forward voltage manufacturing and the current change due to temperature are larger, and the detection voltage cannot be set. Moreover, a short circuit failure cannot be detected unless a plurality of LEDs have a short circuit failure. Furthermore, in the case of a DC power supply that is not stabilized, a short-circuit failure cannot be detected unless more LEDs are short-circuited. Further, when the current detection resistor is used, there is a problem that the efficiency is lowered due to the loss of the current detection resistor.

  On the other hand, in the lighting circuit 3 of FIG. 8, a current limiting (current limiting) circuit 15 is connected in series between the power supply and the load circuit. As the current limiting circuit, a resistance element or a constant current circuit is generally used, and the current of the load circuit is held almost constant. The value of the resistance element is determined by the difference between the voltage of the DC power supply 10 and the total forward voltage (Vf × n) of the LED and the value of the current flowing through the LED.

  In the lighting circuit 3 of FIG. 8, in order to detect a disconnection failure by a voltage change, the input end of the disconnection detection circuit 12 is connected to the output end of the DC constant current power supply 10, and a short-circuit failure is detected by a current change. The input terminals of the short circuit detection circuit 13 are connected to both ends of the current detection resistor 11. As with the lighting circuit 2 of FIG. 7, an OR circuit 14 is provided for inputting a disconnection fault signal output from the disconnection detection circuit 12 and a short-circuit fault signal output from the short-circuit detection circuit 13.

  The method for detecting the non-lighting due to the disconnection is the same as that in the case of the DC constant current power source when the connection point between the current limiting resistor or the constant current source and the load is regarded as the output voltage (Vout) of the power source.

  In the above-described conventional techniques, Patent Documents 1 and 2 have proposed techniques for avoiding the case where even one LED is disconnected when the LEDs are disconnected.

  Patent Document 1 proposes a disconnection monitoring circuit connected in parallel with each LED, and a circuit that maintains a short circuit of the disconnected LED by the output of the disconnection monitoring circuit when the LED is disconnected, and maintains the lighting of the other LEDs. Yes.

  Patent Document 2 proposes a circuit that outputs a disconnection detection signal when at least one LED is disconnected in addition to the above-described function.

However, neither technique can detect a short circuit failure of the LED. Further, when the wiring between the LEDs or the wiring connecting the power source and the LED is disconnected and becomes unlit, the disconnection detection signal cannot be output. When outputting a disconnection detection signal, it is necessary to provide at least one wiring from the lamp.
JP 2002-025784 A JP 2003-20993 A

  In view of the above situation, an object of the present invention is to solve the conventional problems and to provide a failure detection device that can detect a failure even when one LED is short-circuited or disconnected.

The present invention is a failure detection device for detecting a load failure formed by connecting a plurality of LEDs driven by an output voltage of a DC power supply in series,
A switch circuit in which switch elements are connected in parallel to each or any number of the LEDs;
A switch control circuit that turns on each switch element of the switch circuit and short-circuits the LEDs connected in parallel with the switch element while sequentially cycling according to a predetermined period (T1) for a fixed time (t1) within the period (T1). ,
An output voltage monitoring circuit that is connected to the output terminal of the DC power supply, monitors the change in the output voltage, and outputs an abnormal signal when there is no change in the output voltage within the period (T1). Features.

  In the failure detection apparatus of the present invention, the switch control circuit includes a clock circuit that generates a clock signal of a reference frequency, a ring counter circuit that receives the clock signal and sequentially outputs signals corresponding to the number of LEDs, A differentiation circuit to which a plurality of signals sequentially output from the ring counter circuit are input, and an output circuit for adding the output of each differentiation circuit to each switch element can be formed.

  In addition, the power source of the switch control circuit can be taken from both ends of the load or between any LED connection point and the zero potential end.

  According to the present invention, when each switch element is turned on by the switch control circuit and the corresponding LED is short-circuited, when the LED is in a normal operation state, the switch element is turned on from the forward voltage of the LED. The voltage value is obtained by subtracting the voltage of. Here, when the LED is short-circuited, the output voltage does not change even if the LED is short-circuited by the switch element. Accordingly, when there is no change in the output voltage of the DC power supply within the period, the output voltage monitoring circuit determines that the LED is a short circuit failure and outputs an abnormal signal. When the LED breaks down, the output voltage does not change even if the switch element short-circuits a normal LED that is not broken, so the output voltage monitoring circuit determines that it is abnormal. Therefore, the disconnection failure of the LED is also detected as an abnormality.

  As described above, since it is possible to detect even a failure in which one LED is short-circuited, it is possible to promptly notify the user of the failure. Moreover, while detecting the disconnection failure of LED, the case where the wiring between a power supply and a lamp is disconnected can also be detected. It is not necessary to set an output limit voltage having a value higher than necessary for detecting such a disconnection failure, and performance degradation and cost increase can be prevented.

  Further, since the failure of the LED is detected by a change in the output voltage from the DC power supply, a conventional current detection resistor is unnecessary, and the efficiency is not reduced by that amount.

  In the conventional method, when the voltage drop of the wiring from the power source to the lamp is large, it is necessary to change the detection voltage according to the voltage value of the voltage drop, but in the present invention, the absolute value of the voltage change is detected. Since the failure of the LED is detected, the failure of the LED can be detected without being affected by the voltage drop of the wiring, no matter how far the power supply and the lamp are separated.

  When the DC power supply is a power supply in which a resistance element is connected to a battery or a DC constant voltage power supply, the output voltage fluctuates and varies, but the LED changes by detecting the voltage change during the switch-on time that occurs in the above cycle. Therefore, the failure of the LED can be detected stably without being affected by fluctuations or variations in the output voltage.

  It is also possible to provide one switch element for a plurality of LEDs. In that case, short-circuit faults of individual LEDs cannot be detected, but disconnection faults can be detected. Since the number of switch elements is reduced and the switch control circuit is simplified, the cost can be reduced. Therefore, a decrease in luminous intensity is not a fatal problem as a lamp, and it can be effectively used when a plurality of LED sets constituting the lamp are used as a single function.

  Furthermore, since the power of the switch circuit and the switch control circuit can be supplied within the lamp, no wiring for a failure detection device between the power and the lamp is required. In addition, since the power of the switch control circuit can be supplied from the intermediate connection point of the LEDs connected in series, the minimum power supply voltage can be supplied to the power supply of the switch control circuit, minimizing power loss. It is done.

  INDUSTRIAL APPLICABILITY The present invention is suitably used for automobile lamps using LEDs, general lighting equipment, display devices, backlights for display devices, and the like.

  FIG. 1 shows a circuit configuration of a lighting circuit 4 that constitutes an LED failure detection apparatus according to an embodiment of the present invention and a lamp 1 that is supplied with an output voltage thereof. Here, the lighting circuit 4 includes a DC constant current power supply 10 and an output voltage monitoring circuit 20 that outputs an abnormal signal when the output voltage Vout is monitored and an abnormality is detected. The configuration will be described later.

  The lamp 1 has five LEDs connected in series as a load, and a switch circuit 21 including five switch elements 21a to 21e connected in parallel to each LED, and on / off of each switch element. And a switch control circuit 22 for controlling.

  As shown in FIG. 2, the switch control circuit 22 includes a clock circuit 30 that generates a clock signal having a reference frequency, a ring counter circuit 31 to which the clock signal is input, and 5 that are sequentially output from the counter circuit 31. Five output circuits 33a to 33e including five differentiating circuits 32a to 32e to which one ring counter output R1 to R5 is inputted and an interface circuit for adding the outputs D1 to D5 of the differentiating circuits to the respective switch elements 21a to 21e. It consists of.

  The clock circuit 30 generates a clock signal having a period T 1 and supplies it to the ring counter circuit 31. The ring counter circuit 31 has outputs R1 to R5 corresponding to the number of LEDs (5 in the illustrated example), and each output is a signal that is turned on (H) by one cycle (T1) every five cycles. Is output. Differentiating circuits 32a to 32e differentiate the output waveform of the ring counter circuit 31, and generate pulse outputs D1 to D5 of the on-time t1. Each output circuit 33a-e outputs the output D1-D5 of each differentiation circuit as a signal which drives each switch element 21a-e.

  In the above circuit, the clock circuit 30 and the ring counter 31 are configured using a logic IC. Each of the differentiating circuits 32a to 32e is configured using an operational amplifier or a logic IC. However, a similar function may be configured using a programmable logic array or a microcomputer.

  The switch control circuit 22 may be supplied from an auxiliary power source or an input power source constituting the DC power source of the lighting circuit 4 or from the lamp 1. In the latter case, the light can be supplied from both ends of the LED or from any connection point of the LEDs connected in series and the zero potential end. When the forward voltage of the LED is 3V, if the power supply voltage of the switch control circuit 22 is 5V, the power can be supplied by two or three LEDs. Alternatively, an appropriate voltage can be supplied via a three-terminal regulator or the like.

  FIG. 3 is a timing chart showing the waveforms of signals output from the respective circuit units constituting the switch control circuit 22.

  The clock signal CK output from the clock circuit 30 is a signal that repeats on (H) and off (L) in a cycle of T1, and the ring counter circuit 31 has one cycle (T1) every five cycles of the clock signal CK. The signals R1 to R5 that are turned on (H) one by one are sequentially output. The outputs are differentiated by the corresponding differentiating circuits 32a to 32e to become pulse signals D1 to D5 of the on-time t1, and are output from the output circuits 33a to 33e. With these pulse signals D1 to D5, the switch elements 21a to 21e of the switch circuit 21 are sequentially turned on, and the LEDs are sequentially short-circuited.

  The voltage change when each switch element 21a-e is turned on and the corresponding LED is short-circuited is a voltage value obtained by subtracting the voltage when the switch element is turned on from the forward voltage of the LED when the LED is in a normal operation state. It becomes. For example, if the forward voltage (Vf) of each LED is 3V, the output voltage of the DC constant current power supply 10 is Vout = 3V × 5 = 15V when all the switch elements 21a to 21e are off. When each switch element 21a-e is turned on, one corresponding LED is short-circuited, so that the output voltage becomes Vout≈15V-3V = 12V and changes by about 3V. When an LED is short-circuited, the output voltage does not change even if the LED is short-circuited by a switch element.

  Since the output voltage does not change, the output voltage monitoring circuit 20 connected to the output of the DC power supply 10 outputs an abnormal signal to the outside when it is determined that the LED is short-circuited. For this reason, a timer (time T2: T1.ltoreq.T2 <2T1) having a cycle of T1 or more and less than (T1.times.2) time is started to monitor the change in the output voltage. When the LED is operating normally, the output voltage changes for t1 time every T1 time. If the voltage value for this change is equal to or higher than the preset reference voltage value, the timer for T2 time is reset. Continue monitoring the change in output voltage. For this reason, the timer of time T2 does not time up and an abnormal signal is not output. On the other hand, if there is no change in the output voltage within the time T1, the timer for the time T2 times out and outputs an abnormal signal to the outside.

  Here, the forward voltage of the LED is expected to fluctuate by about ± 20% due to a temperature change and a change with time even when the LED is driven with a constant current. Also, variations and fluctuations are expected in the voltage when the switch element is turned on. Therefore, the reference voltage is set to a voltage value having a sufficient margin for these changes.

  For example, if the forward voltage of the LED is 3V, the minimum forward voltage is about 2.6V. If the voltage when the switch element is on is 1V, the voltage change when the LED is short-circuited is 1.6V. In this case, it is desirable that the reference voltage be an intermediate value around 0.8V.

FIG. 4 shows a configuration example of the switch element 21.
In the circuit configuration of (A), the switch element includes a transistor Tr1 in which an LED is connected between the collector and the emitter, series-connected resistors R1 and R2 that change the base voltage of the transistor Tr2, and a transistor Tr2, which is connected between the base and emitter of the transistor. The resistor R3 and the resistor R4 connected to the base of the transistor Tr2, and the output of the switch control circuit 22 is applied to the base of the transistor Tr2 through the resistor R4.

Accordingly, when the switch control circuit 22 outputs an H level signal, the transistor Tr2 is turned on by this signal, and the base voltage of the transistor Tr1 becomes L level and the transistor Tr1 is turned on, so that the LEDs connected in parallel to this are short-circuited. To do. On the other hand, when the output of the switch control circuit 22 is an L level signal, the transistor Tr2 is turned off, the transistor Tr1 is also turned off, and the LED is normally lit.
(B) is a circuit that implements a similar function using a photocoupler PC. This is because the resistors R1 and R2 are disconnected in the circuit (A), and the light receiving portion of the photocoupler PC is connected to the resistor R1, while the light emitting portion of the photocoupler PC is connected between the resistor R2 and the transistor Tr2. It is. In this case, a power source is required, but the power source of the switch control circuit 22 can be used as a common power source.
(C) is a switch element for the LED on the zero potential side that does not need to be floated. The emitter of the transistor Tr1 connected between the collector and the emitter is connected to the zero potential, and the base emitter of the transistor Tr1 is connected. A resistor R1 is connected between them, and a resistor R2 is connected to the base of the transistor Tr2.

  Accordingly, when the switch control circuit 22 outputs an H level signal, the transistor Tr1 is turned on by this signal, thereby short-circuiting the LEDs connected in parallel thereto.

  Next, although the DC constant voltage power supply 10 is used in the lighting circuit 4 of FIG. 1, other DC power supplies may be used. An example is shown in FIG. (A) shows the case where the current limiting circuit 15 is connected to the DC constant voltage power supply 10, and (B) shows the case where the current limiting circuit 15 is connected to the battery. The current limiting circuit 15 is configured by a constant current circuit, a resistance element, or the like having a function of making the current flowing through the LED constant or substantially constant.

  FIG. 6 shows the configuration of the output voltage monitoring circuit 20 in the embodiment of FIG. This output voltage monitoring circuit 20 has a (−) terminal via a series circuit of a capacitor C1 and a resistor R1 connected between terminals to which the output voltage of the DC power supply 10 is input, and a resistor R2 connected to these connection points. The operational amplifier 41 to which the input is applied, the resistor R3 connected between the output terminal and the (−) terminal, the comparator 42 for comparing the output voltage of the operational amplifier 41 with the reference voltage V, and the output terminal A series circuit of a capacitor C2 and a resistor R4 connected to each other, a series circuit of a capacitor C3 and a resistor R5 connected to a common power source, and an output of the comparator 42 and a junction voltage of the capacitor C3 and the resistor R5. An AND gate 43 that outputs an AND is output.

  Here, the resistor R4, the capacitor C2, and the AND gate 43 constitute a timer for T2, and the resistor R5, the capacitor C3, and the AND gate 43 constitute a dead time for avoiding unstable operation at the time of rising of the DC power supply. It constitutes a timer for setting T3 (determined by the time constant of the resistor R5 and the capacitor C3).

  According to the output voltage monitoring circuit 20, the DC component is removed by the capacitor C1 connected to the positive side of the DC voltage output, and the change in the output voltage is extracted. By taking the on-time t1 sufficiently short with respect to the above-described period T1, a negative pulse based on the zero potential indicating the voltage change when the LED is short-circuited can be obtained.

  The change voltage is inverted in polarity by the operational amplifier 41 and input to the comparator 42. When the change voltage is equal to or higher than the reference voltage (normal state), the comparator 42 outputs an L level signal during the on-time t1 in the cycle T1.

  Since the input of the AND gate 43 is at the L level during the dead time T3 after the power is turned on, the output of the AND gate 43 is at the L level regardless of which level is input to the other input. Indicates the state. When the dead time after the power is turned on, the timer side constituting the dead time of the input of the AND gate 43 becomes H level, and when the input of the AND gate 43 on the side of the resistor R4 and the capacitor C2 becomes H level, the AND gate 43 outputs an H level signal as an abnormal signal.

  In a normal operation state, the transistor C2 is short-circuited and discharged by turning on the open collector output transistor in the comparator 42 for the on time t1 within the time T1, so that the resistor R4 and the AND gate on the capacitor C2 side are discharged. The input of 43 does not become H level, and the AND gate 43 does not output an abnormal signal. When the LED is short-circuited or another LED is disconnected, the short-circuit operation of the capacitor C2 that occurs every T1 time does not occur, and after the time T2 elapses, the input of the resistor R4 and the AND gate 43 on the capacitor C2 side is It becomes H level, and the AND gate 43 outputs a signal of H level as an abnormal signal.

  The abnormal signal output may be output to the outside as an input for displaying an abnormal state or for processing by an external computer or the like. It may be used as a signal for stopping the power supply by stopping the DC power supply inside the power supply or cutting off the DC power supply from the input power supply.

  Preferably, a latch circuit (not shown) is added to the output side of the output voltage monitoring circuit 20 so that after the output voltage monitoring circuit 20 outputs an abnormal signal, a normal operation state is detected by the next LED and the capacitor is detected. Even if C2 is short-circuited and the input of the AND gate 43 becomes L level, the output of the abnormal signal can be continued.

  The power supply of the output voltage monitoring circuit 20 may share an auxiliary power source of a DC power source that drives the LED, or may be directly supplied from an input power source. Further, when the above latch circuit is added, it is directly supplied from the input power supply.

  Although the embodiment has been described as described above, the present invention is not limited to this. For example, in the above-described embodiment, one switch element is provided for one LED, but a configuration in which one switch element is provided for an arbitrary plurality of LEDs is also possible. In this case, the reference voltage may be set similarly to the case of one LED, or may be set by the method of setting the detection voltage described in the problem of the prior art with respect to the number of LEDs.

The figure which shows the circuit structure of embodiment of this invention. The figure which shows the structure of the switch control circuit contained in a lamp. The timing chart which shows the signal waveform output from each circuit part of a switch control circuit. The figure which shows the structural example of a switch element. The figure which shows the example of DC power supply. The figure which shows the structure of the output voltage monitoring circuit contained in the lighting circuit of FIG. The figure which shows the structure of the LED lighting circuit of the prior art example using a direct-current constant current power supply. The figure which shows another structure of the conventional LED lighting circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lamp, 2, 3, 4 ... Lighting circuit, 10 ... DC power supply, 20 ... Output voltage monitoring circuit, 21 ... Switch circuit, 22 ... Switch control circuit

Claims (3)

A failure detection device for detecting a load failure by connecting a plurality of LEDs driven by an output voltage of a DC power supply in series,
A switch circuit in which a switch element is connected in parallel to each of the plurality of LEDs or an arbitrary number;
A switch control circuit that short-circuits the LEDs connected in parallel with the switch element by turning on the switch element for a certain time (t1) within the period (T1) while sequentially circulating according to a predetermined period (T1);
An output voltage monitoring circuit connected to the output terminal of the DC power supply, monitoring an output voltage change, and outputting an abnormal signal when there is no change in the output voltage within the period (T1). Failure detection device.   2. The LED failure detection apparatus according to claim 1, wherein the switch control circuit includes a clock circuit that generates a clock signal having a reference frequency, and a ring counter that receives the clock signal and sequentially outputs signals corresponding to the number of LEDs. A failure detection apparatus comprising: a circuit; a differentiation circuit to which a plurality of signals sequentially output from the ring counter circuit are input; and an output circuit for adding an output of each differentiation circuit to each switch element. In the failure detection device according to claim 1 or 2,
An LED failure detection apparatus characterized in that the power source of the switch control circuit is taken from both ends of the load or between an arbitrary LED connection point and a zero potential end.

Images