JP2008305941A - Driver circuit of light emitting diode, method for detecting failure of light emitting diode, or the like - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inform failure when the failure occurs in either one of light emitting diodes, in the driver circuit of the light emitting diodes which has such a plurality of lines connected in parallel with each other that each line has the light emitting diodes connected in series with each other, and has a Zener diode connected in parallel with at least one light emitting diode whose polarity is the reverse of its polarity. <P>SOLUTION: The driver circuit C of light emitting diodes is the one which has such a plurality lines connected in parallel with each other that each line has the plurality of light emitting diodes connected in series with each other, or has at least one light emitting diode, and has a Zener diode connected in parallel with at least one light emitting diode whose polarity is the reverse of its polarity. Further, the driver circuit C has such a failure sensing circuit FC that it senses the voltage of each line, and compares mutually the sensed voltages of the respective lines, and further, senses based on the compared result the failure of either one of the light emitting diodes, and moreover, outputs an information for indicating the. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present application has a plurality of lines connected in parallel, and each of the lines is connected in parallel with a plurality of light emitting diodes connected in series and at least one Zener diode having a polarity opposite to that of the light emitting diodes. The present invention relates to a technical field such as a driver circuit for a light emitting diode.

  In a conventional multi-light LED (light emitting diode) driver circuit, when any one of a plurality of light emitting diodes connected in series (connected) is opened (opened) due to a failure, the light emitting diodes in that line are turned on. become unable. In this case, if the stabilization voltage control unit boosts the output voltage so that current flows through the line, overvoltage protection is activated and the output of the stabilization voltage is stopped. The light emitting diode will be turned off.

By the way, Patent Document 1 discloses a technique for continuing lighting of the remaining light emitting diodes in the line even if one of the light emitting diodes connected in series is opened (disconnected) due to a failure. In Patent Document 1, a Zener diode having a Zener voltage slightly larger than its forward voltage is connected in parallel to each light emitting diode, so that a current flows through the Zener diode even if a certain light emitting diode is opened due to a failure. Therefore, the remaining light emitting diodes in the line can be turned on.
JP 2005-49239 A

  However, when such a technique of Patent Document 1 is applied to the above-described multi-light LED driver circuit, even if the light emitting diode fails, it cannot be distinguished from the normal operation, so the user is notified of the failure. I can't. Therefore, it is assumed that the user continues to use the device without noticing whether or not it is a failure, while noticing that the luminance is slightly reduced or luminance unevenness occurs.

  Therefore, the present application has an object to solve such a problem, and has a plurality of lines connected in parallel, each line including a plurality of or at least one light emitting diode connected in series, and at least one light emitting diode. In the driver circuit of a light emitting diode in which a Zener diode with the pole reversed with respect to the light emitting diode is connected in parallel, if there is an abnormality such as a failure in any of the light emitting diodes, the abnormality has occurred It is an object of the present invention to provide a light emitting diode driver circuit and a light emitting diode abnormality detection method that can notify the user of the above.

  In order to solve the above problem, the invention according to claim 1 has a plurality of lines connected in parallel, and each of the lines includes a plurality of or at least one light emitting diode connected in series, and at least one light emitting diode. A light emitting diode driver circuit comprising a Zener diode connected in parallel with the poles reversed with respect to the light emitting diode, the voltage detecting means for detecting the voltage in each line, and each detected An abnormality detection means for comparing line voltages and detecting that there is an abnormality in any of the light emitting diodes based on the comparison result; and an abnormality information output means for outputting information indicating that there is an abnormality. It is characterized by providing.

  The invention according to claim 6 has a plurality of lines connected in parallel, and each line corresponds to a plurality of or at least one light emitting diode connected in series and at least one of the light emitting diodes. A method of detecting an abnormality of the light emitting diode in a driver circuit of the light emitting diode, comprising a Zener diode connected in parallel with the poles reversed, and a step of detecting a voltage in each line; Comparing a line voltage, detecting that there is an abnormality in any one of the light emitting diodes based on the comparison result, and outputting information indicating that there is an abnormality. Features.

  The invention of the abnormality detection program according to claim 7 has a plurality of lines connected in parallel, and each line includes a plurality of or at least one light emitting diode connected in series and at least one of the light emitting diodes. A computer for detecting an abnormality of the light emitting diode in a driver circuit of the light emitting diode provided with a Zener diode connected in parallel with the polarity reversed with respect to the light emitting diode, detecting a voltage in each line, and detecting the voltage And comparing the voltage of each line, detecting that there is an abnormality in any of the light emitting diodes based on the comparison result, and functioning to output information indicating that there is an abnormality. And

  Hereinafter, the best embodiment of the present application will be described with reference to the accompanying drawings. In addition, embodiment described below is embodiment at the time of applying this application with respect to a multi-lamp LED driver circuit.

  First, the configuration and function of the multi-lamp LED driver circuit will be described with reference to FIG.

  FIG. 1 is a diagram illustrating a schematic configuration example of a multi-lamp LED driver circuit.

  As shown in FIG. 1, the multi-lamp LED driver circuit C has a plurality of lines (first line to m-th line) connected in parallel, and each line includes a plurality of light emitting diodes (series connected in series). For example, in the first line, 1-1a to 1-na) and a Zener diode connected in parallel with the light emitting diode reversed (for example, 1-1b to 1-nb in the first line) It comes to be equipped with. The forward voltage of each light emitting diode is smaller (slightly smaller) than the Zener voltage of the Zener diode connected in parallel to the light emitting diode (the breakdown voltage when a reverse bias is applied).

  Further, the number of light emitting diodes in each line is the same between the lines, and the number of Zener diodes in each line is the same between the lines. In the example of FIG. 1, a configuration in which one Zener diode is connected in parallel (one-to-one connection) to one light emitting diode is shown, but in order to reduce the number of Zener diodes, they are connected in series. Alternatively, one Zener diode may be connected in parallel to a plurality of (for example, two, three,...) Light emitting diodes. Further, the number of light emitting diodes in each line may be one.

  Further, in the example of FIG. 1, current limiting circuits RC <b> 1 to RCm are connected in series to a plurality of light emitting diodes connected in series in each line. These current limiting circuits RC1 to RCm are circuits for allowing the same constant current to flow in each line in consideration of variations in the forward voltage of each light emitting diode, and even if they are resistors, they are constant current circuits. Also good.

  Further, the multi-lamp LED driver circuit C includes an abnormality detection circuit FC as an example of a voltage detection unit, an abnormality detection unit, and an abnormality information output unit. As shown in FIG. 1, the abnormality detection circuit FC is connected via a line between the light emitting diodes (1-na, m-na, etc.) at the final stage in each line and the current limiting circuits RC1 to RCm. Each voltage between them (hereinafter referred to as “feedback voltage”) is detected, the detected feedback voltages are compared, and one of the light emitting diodes is failed based on the comparison result. Is detected, and information indicating that there is an abnormality is output.

  More specifically, the abnormality detection circuit FC includes a maximum-minimum voltage difference calculation circuit 100 and a comparator 101. Then, the maximum-minimum voltage difference calculation circuit 100 detects the feedback voltage in each line, detects the maximum voltage and the minimum voltage from the detected feedback voltages, and calculates the difference between the maximum voltage and the minimum voltage. The difference voltage is calculated and output to the comparator 101. The comparator 101 compares the difference voltage from the maximum-minimum voltage difference calculation circuit 100 and a reference voltage (predetermined value). For example, the comparator 101 inputs and compares the difference voltage and the reference voltage Vref. If it is equal to or higher than the reference voltage Vref, an abnormality is detected, and a high level signal Hi is output as information indicating the abnormality to an alarm display (monitor unit), an alarm buzzer, etc. (not shown), for example. To do. As a result, an alarm is output from an alarm indicator, an alarm buzzer, or the like (for example, an indication that “LED failure has occurred” is output to the monitor unit), and the user is notified that one of the light emitting diodes has an abnormality such as a failure. Will be.

  Next, with reference to FIG. 2, the operation of the multi-lamp LED driver circuit C when one of the light emitting diodes is opened will be described.

  FIG. 2 is a diagram illustrating a state of the multi-lamp LED driver circuit C when one of the light emitting diodes is opened.

  In FIG. 2, the forward voltage of the n-th light emitting diode m-na in the m-th line is Vfmn. If light emitting diodes of the same type and the same lot are used, Vf11 = Vf12 =... Vfm1 =... = Vf1n (hereinafter referred to as Vf). Vzd. Further, the power supply voltage is E, and the voltages input to the abnormality detection circuit FC are Vr1,..., Vrm, respectively. The Vrm of the m-th line that is normally operating is Vrm = E−n × Vf. Similarly, the other lines are E−n × Vf.

  As shown in the figure, if the second light emitting diode 1-2a in the first line is broken and opened, Vr1 = E− (n−1) × Vf−Vzd. Here, since Vf <Vzd, the voltage drop of the line increases by Vzd−Vf, and the feedback voltage decreases accordingly. Therefore, assuming that Vrm> Vr1 and the abnormality detection circuit FC selects the maximum voltage Vrm and the minimum voltage Vr1, the maximum voltage−minimum voltage = Vrm−Vr1 = E−n × Vf− (E− (n− 1) × Vf−Vzd) = Vzd−Vf.

  That is, if the Zener diode and the reference voltage are set so that Vzd−Vf> reference voltage Vref, the abnormality detection circuit FC outputs the high level signal Hi when the light emitting diode is open, and the abnormality is detected. The user will be notified of this. At this time, since the current in the first line is bypassed by the Zener diode connected in parallel to the failed second light emitting diode, the light emitting diodes other than the failed light can continue to be lit.

  Next, the operation of the multi-lamp LED driver circuit C when one of the light emitting diodes is short-circuited will be described with reference to FIG.

  FIG. 3 is a diagram illustrating a state of the multi-lamp LED driver circuit C when one of the light emitting diodes is short-circuited.

  In FIG. 3, if the second light emitting diode 1-2a in the first line is broken and short-circuited, Vr1 = E- (n-1) * Vf. On the other hand, in the line having no failure, Vrm = E−n × Vf, so Vrm <Vr1, and if the maximum voltage Vr1 and the minimum voltage Vrm are selected by the abnormality detection circuit FC, the maximum voltage−minimum Voltage = Vr1-Vrm = Vf.

  In other words, if the reference voltage is set so that Vf> reference voltage Vref, the abnormality detection circuit FC outputs a high level signal Hi when the light emitting diode is short-circuited. Will be notified.

  By setting Vzd−Vf> reference voltage Vref, it is possible to detect both an open failure and a short-circuit failure of a light emitting diode without stopping light emission of other light emitting diodes.

  However, in reality, each light emitting diode has a tolerance of Vf. Assuming that the maximum voltage VfMAX−minimum voltage VfMIN = Vdif and the first line is composed of light emitting diodes with the minimum voltage VfMIN, and the other lines are all composed of the maximum voltage VfMAX, Vrm A voltage difference of −Vr1 = E−n × VfMAX− (E−n × VfMIN) = n × Vdif is generated. In order not to make a failure determination based on this voltage difference, Vf> reference voltage Vref> n × Vdif should be satisfied. That is, the number n of light emitting diodes is limited in order to reliably detect an abnormality.

  As described above, according to the above-described embodiment, it has a plurality of lines connected in parallel, and each line has a plurality of light-emitting diodes connected in series and a polarity opposite to that of the light-emitting diodes. The multi-lamp LED driver circuit C including the Zener diodes connected in parallel detects the feedback voltage in each line, compares the detected feedback voltages, and selects any one of the light emitting diodes based on the comparison result. It is configured to detect that there is an abnormality such as a failure, and to output information indicating that there is an abnormality. It can be notified that there is an abnormality such as a failure in the light emitting diode.

  Moreover, since the difference between the maximum voltage and the minimum voltage among the detected feedback voltages of each line is calculated, and the difference is greater than or equal to a predetermined value, it is configured to detect that there is an abnormality. The abnormality can be detected efficiently with a simpler configuration.

  Note that the abnormality detection circuit FC in the above embodiment may be configured by a hardware circuit or may be configured by software. When configured by software, a CPU as a computer reads a light emitting diode abnormality detection program recorded on a recording medium such as a ROM, detects a voltage in each line, and compares the detected voltage in each line. Based on the comparison result, it is detected that any one of the light emitting diodes is abnormal, and functions to output information indicating that the abnormality is present.

  The multi-light LED driver circuit C is applicable to backlights, traffic lights, brake lamps, and other lighting devices.

It is a figure which shows the example of a schematic structure of a multilamp LED driver circuit. It is a figure which shows the mode of the multi-lamp LED driver circuit C when one of the light emitting diodes opens (opens). It is a figure which shows the mode of the multi-lamp LED driver circuit C when one of the light emitting diodes is short-circuited (short-circuited).

Explanation of symbols

1-1a to m-na Light emitting diode 1-1b to m-nb Zener diode 100 Maximum-minimum voltage difference calculation circuit 101 Comparator RC1 to RCm Current limiting circuit FC Abnormality detection circuit C Multiple lamp LED driver circuit

Claims (8)

A plurality of lines connected in parallel, wherein each line includes a plurality or at least one light emitting diode connected in series, and a Zener connected in parallel with a polarity opposite to the at least one light emitting diode; A light emitting diode driver circuit comprising a diode,
Voltage detecting means for detecting a voltage in each line;
An abnormality detection means for comparing the detected voltage of each line and detecting that any of the light emitting diodes is abnormal based on the comparison result;
Abnormality information output means for outputting information indicating that the abnormality has occurred;
A light-emitting diode driver circuit comprising: The light emitting diode driver circuit according to claim 1,
The abnormality detection means calculates a difference between a maximum voltage and a minimum voltage among the detected voltages of each line, and detects that the abnormality has occurred when the difference is a predetermined value or more. A light emitting diode driver circuit characterized by the above. In the driver circuit of the light emitting diode according to claim 1 or 2,
A light emitting diode driver circuit, wherein a forward voltage of the light emitting diode is smaller than a Zener voltage of a Zener diode connected in parallel with a polarity opposite to the light emitting diode. In the driver circuit of the light emitting diode according to any one of claims 1 to 3,
A light emitting diode driver circuit, wherein the number of light emitting diodes in each line is the same between the lines, and the number of Zener diodes in each line is the same between the lines. In the driver circuit of the light emitting diode according to any one of claims 1 to 4,
A light emitting diode driver circuit, wherein a current limiting circuit is connected in series to each of the plurality of or at least one light emitting diode connected in series in each line. A plurality of lines connected in parallel, wherein each line includes a plurality or at least one light emitting diode connected in series, and a Zener connected in parallel with a polarity opposite to the at least one light emitting diode; There is a method of detecting an abnormality of the light emitting diode in a driver circuit of the light emitting diode provided with a diode,
Detecting a voltage in each line;
Comparing the detected voltage of each line, and detecting that any of the light emitting diodes is abnormal based on the comparison result;
Outputting information indicating that the abnormality has occurred;
An abnormality detection method for a light emitting diode, comprising: A plurality of lines connected in parallel, wherein each line includes a plurality or at least one light emitting diode connected in series, and a Zener connected in parallel with a polarity opposite to the at least one light emitting diode; A computer for detecting an abnormality of the light emitting diode in a driver circuit of the light emitting diode provided with a diode;
Detecting the voltage in each line,
Compare the detected voltage of each line, based on the comparison result, detect that there is an abnormality in any of the light-emitting diodes,
An abnormality detection program for a light emitting diode, which functions to output information indicating that the abnormality has occurred.   A recording medium in which the abnormality detection program for a light emitting diode according to claim 7 is recorded so as to be readable by a computer.

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