JP2013021135A - Light-emitting element driving circuit and light-emitting element abnormality detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting element driving circuit and a light-emitting element abnormality detection method capable of improving the accuracy of abnormality detection of a light-emitting element.SOLUTION: A light-emitting element driving circuit 1 comprises element arrays 10a and 10b each including the same number of two or more light-emitting elements connected in series. The element arrays 10a and 10b are connected with each other in parallel. A comparison circuit 30 detects a voltage difference between the element arrays 10a and 10b on the basis of the respective voltages at center light-emitting element interconnection parts or at one ends of the center light-emitting elements of the element arrays 10a and 10b. The comparison circuit 30 determines that there are abnormalities in any of the light-emitting elements in the element arrays 10a and 10b in the case that the voltage difference of the element arrays 10a and 10b exceeds a predetermined range. The comparison circuit 30 notifies the outside of the light-emitting element driving circuit 1 of determination results.

Description

  The present invention relates to a light emitting element driving circuit and a light emitting element abnormality detecting method.

  Light emitting elements such as light emitting diodes (hereinafter referred to as LEDs) are used in various devices, and techniques for detecting abnormalities such as LED degradation, individual characteristics, failures, and defects have been developed. As an abnormality detection method, the current flowing through each LED is converted into a voltage using a resistor, and it is determined whether or not the voltage is within a predetermined range. There is a method of converting voltage by using and determining whether or not the voltage is within a predetermined range.

  The light emitting element driving circuit disclosed in Patent Document 1 includes a plurality of LED strings including a plurality of LEDs connected in series, and has the lowest voltage among the voltages on the cathode side of each LED string connected in parallel. To detect. When the detected voltage is lower than the reference voltage, the voltage applied to each LED array is controlled so as to be equal to the reference voltage.

  The lighting device disclosed in Patent Document 2 detects the voltage across the LED, and limits the current flowing through the LED when the detected voltage is equal to or less than a predetermined value that is defined in advance for determining short-circuiting of the LED.

  The LED lighting protection circuit disclosed in Patent Document 3 includes a plurality of LED strings composed of a plurality of LEDs connected in series, and monitors the voltage at the midpoint of each LED string connected in parallel with two transistors. When it is detected that the midpoint voltage exceeds the predetermined range, it is determined that the LED is abnormal, and the current is stopped.

JP 2010-109006 A JP 2010-129612 A JP 2010-278039 A

  In the techniques disclosed in Patent Documents 1, 2, and 3, an abnormality of the LED is detected based on whether or not the detected voltage is within a predetermined range. The forward voltage of the LED changes under the influence of the outside of the LED such as temperature. In order to prevent the LED from being erroneously determined to be abnormal even though the LED is normal, a predetermined range that is considered normal is desired in consideration of an error in voltage change due to an external influence of the LED. It must be set wider than the range. Therefore, for example, in a circuit including a large number of LEDs connected in series, a change smaller than the considered error cannot be detected as abnormal, such as a voltage change when one LED is short-circuited.

  The present invention has been made in view of the above-described situation, and an object thereof is to provide a light emitting element drive circuit and a light emitting element abnormality detection method that improve the accuracy of abnormality detection of a light emitting element.

In order to achieve the above object, a light-emitting element driving circuit according to the first aspect of the present invention includes:
Two or more light emitting element arrays connected in parallel, each including one or two or more light emitting element arrays connected in series;
For any two of the light emitting element rows, the voltage on the cathode side of the light emitting element row in one light emitting element row or on the cathode side of the light emitting element row, and the first light emitting element in the other light emitting element row A voltage difference detection means for detecting a voltage difference with a voltage at the same position as the voltage detection position in the row;
An abnormality determining means for determining that any one of the light emitting elements in the two light emitting element arrays is abnormal when the voltage difference exceeds a predetermined range;
It is characterized by providing.

A light emitting element abnormality detection method according to a second aspect of the present invention includes:
Light emitting element abnormality detection performed by a light emitting element drive circuit, comprising two or more light emitting element arrays connected in parallel, each including one or two or more light emitting element arrays connected in series A method,
For any two of the light emitting element rows, the voltage on the cathode side of the light emitting element row in one light emitting element row or on the cathode side of the light emitting element row, and the first light emitting element in the other light emitting element row A voltage difference detection step for detecting a voltage difference with a voltage at the same position as the voltage detection position in the row;
When the voltage difference exceeds a predetermined range, an abnormality determination step for determining that any one of the light emitting elements in the two light emitting element arrays is abnormal;
It is characterized by providing.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the light emitting element drive circuit and the light emitting element abnormality detection method which improve the precision of abnormality detection of a light emitting element.

It is a block diagram which shows the structural example of the light emitting element drive circuit which concerns on Embodiment 1 of this invention. It is a block diagram which shows the structural example of the light emitting element drive circuit which concerns on Embodiment 2 of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent parts are denoted by the same reference numerals.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration example of a light emitting element driving circuit according to Embodiment 1 of the present invention. The light emitting element driving circuit 1 (hereinafter referred to as the driving circuit 1) includes light emitting element arrays (hereinafter referred to as element arrays) 10a and 10b in which LEDs as light emitting elements are connected in series. The element rows 10a and 10b are connected in parallel. The number of LEDs included in each of the element arrays 10a and 10b is the same. The drive circuit 1 determines the presence / absence of an LED abnormality based on the voltage difference between the voltage at the detection position of the element array 10a and the voltage at the detection position of the element array 10b, and notifies the determination result to the outside of the drive circuit 1. . Each part of the drive circuit 1 will be described below.

  The capacitor 21 is connected in parallel to the element rows 10a and 10b, the inductor 22 is connected in series to the cathode side of the capacitor 21 and the element rows 10a and 10b, and the other end is connected to an N-type MOS transistor 24 (hereinafter referred to as NMOS 24). And the diode 23. The cathode sides of the element rows 10a and 10b are also connected to the comparison circuit 30. The source of the NMOS 24 is grounded. The gate of the NMOS 24 is connected to the gate power supply 26.

  The voltage of the DC power supply 25 is stepped down by the capacitor 21, the inductor 22, the diode 23, and the NMOS 24. The stepped-down voltage is supplied to the anode side of the element rows 10a and 10b.

  The comparison circuit 30 detects a voltage between the central LEDs or one end of the central LED in the element array 10a. And the voltage in the same position as the detection position in the element row 10a in the element row 10b is detected. The same position means between the same LEDs or one end of the same LEDs. Between the central LEDs means a position where the number of LEDs on the anode side and the number of LEDs on the cathode side are the same from that position. The comparison circuit 30 detects the voltage difference between the element arrays 10a and 10b based on the voltage at the detection position in the element array 10a and the voltage at the detection position in the element array 10b.

  When the voltage difference between the element arrays 10a and 10b exceeds a predetermined range, the comparison circuit 30 determines that any one of the LEDs in the element arrays 10a and 10b is abnormal, and determines the determination result as a drive circuit. 1 is notified outside. The case where it exceeds the predetermined range means that the voltage difference between the element arrays 10a and 10b exceeds the reference value. The predetermined range is determined in consideration of variations in forward voltage due to individual characteristics of LEDs, for example. Since both the element arrays 10a and 10b are affected by the outside of the LED such as temperature, for example, it is not necessary to consider the influence from the outside of the LED when determining the predetermined range.

  For example, the comparison circuit 30 detects an abnormality of the LED as follows. When one of the LEDs located on the anode side is short-circuited from the voltage detection position of the element array 10a, the voltage at the detection position is increased. On the other hand, when one of the LEDs located on the cathode side has a short-circuit failure from the voltage detection position of the element array 10a, the voltage at the detection position becomes small. Further, when one of the LEDs located on the anode side has an open failure from the voltage detection position of the element array 10a, the voltage at the detection position becomes small. On the other hand, when one of the LEDs located on the cathode side has an open failure from the voltage detection position of the element array 10a, the voltage at the detection position becomes large.

  As described above, when the voltage at the voltage detection position of the element row 10a changes, the voltage difference from the voltage at the voltage detection position of the element row 10b changes. When the voltage difference between the element arrays 10a and 10b exceeds the reference value, the comparison circuit 30 determines that any one of the LEDs in the element arrays 10a and 10b is abnormal. The comparison circuit 30 notifies the determination result to the outside of the drive circuit 1.

  Although FIG. 1 shows an example of the drive circuit 1 including two element arrays 10a and 10b, the drive circuit 1 can include an arbitrary number of element arrays 10. In the example of FIG. 1, the comparison circuit 30 cannot determine which of the element rows 10a and 10b the LED included is abnormal. However, when the drive circuit 1 includes three or more element arrays 10, for example, the element array 10 having an LED abnormality can be detected as follows.

  The drive circuit 1 includes element rows 10a, 10b, and 10c. The comparison circuit 30 detects a voltage difference between the element arrays 10a and 10b, a voltage difference between the element arrays 10a and 10c, and a voltage difference between the element arrays 10b and 10c. Here, if the voltage difference between the element rows 10a and 10b and the voltage difference between the element rows 10b and 10c exceed a predetermined range, and the voltage difference between the element rows 10a and 10c is within the predetermined range, the element row 10b. It can be determined that the LED inside is abnormal.

  In addition, you may comprise so that the voltage in element row | line | columns 10a and 10b may be detected between arbitrary LED or the cathode side of element row | line | columns 10a and 10b besides the position mentioned above. When detecting on the cathode side of the element rows 10a and 10b, resistors having the same resistance value are connected in series to the cathode sides of the element rows 10a and 10b, and the voltage on the cathode side of the element rows 10a and 10b is detected. . The element rows 10a and 10b can include any number of LEDs. When one LED is included in the element rows 10a and 10b, as described above, the voltage of the element rows 10a and 10b is detected on the cathode side of the element rows 10a and 10b.

  As described above, the drive circuit 1 according to Embodiment 1 of the present invention determines whether the detected voltage difference is within a predetermined range based on the voltage at the detection position of the voltage in the two element arrays. Based on this, an abnormality of the LED is detected. Therefore, in the drive circuit 1 according to the first embodiment, when determining a predetermined range that is considered normal, there is no need to consider an error in voltage change due to an external influence of the LED, and the accuracy of detecting an abnormality of the light emitting element is improved. Can be made.

(Embodiment 2)
FIG. 2 is a block diagram showing a configuration example of the light emitting element driving circuit according to Embodiment 2 of the present invention. Similarly to the first embodiment, the drive circuit 1 according to the second embodiment detects an abnormality of the LED, and when an abnormality is detected, the current flowing through the element rows 10a and 10b and / or the element rows 10a and 10b. The protective voltage is applied by changing the voltage applied to. Each part of the drive circuit 1 that is different from the first embodiment will be described below.

  The drive circuit 1 includes a resistor 27 and a control circuit 40 in addition to the drive circuit 1 of the first embodiment. The gate of the NMOS 24 is connected to the control circuit 40 via the GATE terminal. The NMOS 24 is grounded via a resistor 27. The resistor 27 is used for voltage conversion of the total amount of current flowing through the element arrays 10a and 10b. The voltage drop generated by the resistor 27 is sent to the control circuit via the CS terminal. One end of the control circuit 40 is grounded via a GND terminal.

  As in the first embodiment, the comparison circuit 30 determines whether there is an abnormality in the LED based on the voltage difference between the element arrays 10a and 10b. For example, the voltage difference between the element arrays 10a and 10b deviates from a predetermined range. Is sent to the control circuit 40 via the FB terminal.

  The control circuit 40 performs a protection operation as follows, for example. The control circuit 40 controls the gate power supply 26 based on the input of the FB terminal. When the gate power supply 26 is controlled, the gate voltage of the NMOS 24 changes, and the drain current of the NMOS 24 changes accordingly, and the total amount of current flowing through the element arrays 10a and 10b can be reduced. As described in the first embodiment, when the drive circuit 1 includes three or more element arrays 10, the element array 10 in which the abnormality of the LED has occurred may be identified. Therefore, a switch or a switching element may be provided in each element row 10 and control may be performed so that no current flows through the element row 10 in which the abnormality of the LED has occurred.

  The voltage applied to the element arrays 10a and 10b may be controlled by controlling the gate power supply 26 and controlling the time when the gate voltage of the NMOS 24 exceeds and does not exceed the threshold value. Further, for example, when an abnormality of the LED is detected by the comparison circuit 30, the voltage applied to the element arrays 10a and 10b is controlled so that the voltage applied to each LED in the element arrays 10a and 10b is smaller than the rising voltage. You may comprise.

  Furthermore, the control circuit 40 may be configured to take into account the input of the CS terminal in the above-described control, for example, as follows. The input of the CS terminal is the result of voltage conversion of the total current flowing through the element arrays 10 a and 10 b using the resistor 27. The control circuit 40 may be configured to determine whether the input of the CS terminal is within a predetermined range, and to control the gate power supply 26 in consideration of the determination result. The predetermined range is a range in which the current flowing through the element arrays 10a and 10b does not become an overcurrent.

  As described above, the drive circuit 1 according to the second embodiment of the present invention can improve the accuracy of detecting an abnormality of the light emitting element as in the first embodiment. Furthermore, if an abnormality is detected, the drive circuit 1 according to Embodiment 2 can control the current flowing through the light emitting element array and / or the voltage applied to the light emitting element array.

  The embodiment of the present invention is not limited to the above-described embodiment. In the example of FIGS. 1 and 2, the step-down circuit is provided, but a step-up circuit may be provided.

  A part or all of the above-described embodiment can be described as in the following supplementary notes, but is not limited thereto.

(Appendix 1)
Two or more light emitting element arrays connected in parallel, each including one or two or more light emitting element arrays connected in series;
For any two of the light emitting element rows, the voltage on the cathode side of the light emitting element row in one light emitting element row or on the cathode side of the light emitting element row, and the first light emitting element in the other light emitting element row A voltage difference detection means for detecting a voltage difference with a voltage at the same position as the voltage detection position in the row;
An abnormality determining means for determining that any one of the light emitting elements in the two light emitting element arrays is abnormal when the voltage difference exceeds a predetermined range;
A light-emitting element driving circuit comprising:

(Appendix 2)
The light emitting element array includes two or more light emitting elements,
The voltage difference detection means detects a voltage difference based on a voltage at one end of the light emitting elements in the light emitting element row or between the central light emitting elements.
The light-emitting element driving circuit according to appendix 1, wherein:

(Appendix 3)
Circuit protection means for performing a protection operation by changing the current flowing through the second light emitting element array and / or the voltage applied to the second light emitting element array when the abnormality determining means determines that there is an abnormality. Prepare
The light-emitting element drive circuit according to appendix 1 or 2, wherein

(Appendix 4)
Light emitting element abnormality detection performed by a light emitting element drive circuit, comprising two or more light emitting element arrays connected in parallel, each including one or two or more light emitting element arrays connected in series A method,
For any two of the light emitting element rows, the voltage on the cathode side of the light emitting element row in one light emitting element row or on the cathode side of the light emitting element row, and the first light emitting element in the other light emitting element row A voltage difference detection step for detecting a voltage difference with a voltage at the same position as the voltage detection position in the row;
When the voltage difference exceeds a predetermined range, an abnormality determination step for determining that any one of the light emitting elements in the two light emitting element arrays is abnormal;
A light emitting element abnormality detection method comprising:

(Appendix 5)
The light emitting element array includes two or more light emitting elements,
In the voltage difference detection step, a voltage difference is detected based on a voltage between the central light emitting elements or one end of the central light emitting element in the light emitting element array.
The light emitting element abnormality detection method according to appendix 4, wherein

(Appendix 6)
In the abnormality determination step, when it is determined that there is an abnormality, a circuit protection step is further performed in which a protection operation is performed by changing a current flowing through the second light emitting element array and / or a voltage applied to the second light emitting element array. Prepare
The light emitting element abnormality detection method according to appendix 4 or 5, characterized in that:

1 Light-Emitting Element Drive Circuit 10, 10a, 10b Light-Emitting Element Row
21 capacitor
22 Inductor
23 Diode
24 N-type MOS transistor
25 DC power supply
26 Gate power supply
27 Resistance
30 Comparison circuit
40 Control circuit

Claims (6)

Two or more light emitting element arrays connected in parallel, each including one or two or more light emitting element arrays connected in series;
For any two of the light emitting element rows, the voltage on the cathode side of the light emitting element row in one light emitting element row or on the cathode side of the light emitting element row, and the first light emitting element in the other light emitting element row A voltage difference detection means for detecting a voltage difference with a voltage at the same position as the voltage detection position in the row;
An abnormality determining means for determining that any one of the light emitting elements in the two light emitting element arrays is abnormal when the voltage difference exceeds a predetermined range;
A light-emitting element driving circuit comprising: The light emitting element array includes two or more light emitting elements,
The voltage difference detection means detects a voltage difference based on a voltage at one end of the light emitting elements in the light emitting element row or between the central light emitting elements.
The light-emitting element driving circuit according to claim 1. Circuit protection means for performing a protection operation by changing the current flowing through the second light emitting element array and / or the voltage applied to the second light emitting element array when the abnormality determining means determines that there is an abnormality. Prepare
The light-emitting element drive circuit according to claim 1 or 2. Light emitting element abnormality detection performed by a light emitting element drive circuit, comprising two or more light emitting element arrays connected in parallel, each including one or two or more light emitting element arrays connected in series A method,
For any two of the light emitting element rows, the voltage on the cathode side of the light emitting element row in one light emitting element row or on the cathode side of the light emitting element row, and the first light emitting element in the other light emitting element row A voltage difference detection step for detecting a voltage difference with a voltage at the same position as the voltage detection position in the row;
When the voltage difference exceeds a predetermined range, an abnormality determination step for determining that any one of the light emitting elements in the two light emitting element arrays is abnormal;
A light emitting element abnormality detection method comprising: The light emitting element array includes two or more light emitting elements,
In the voltage difference detection step, a voltage difference is detected based on a voltage between the central light emitting elements or one end of the central light emitting element in the light emitting element array.
The light emitting element abnormality detection method according to claim 4. In the abnormality determination step, when it is determined that there is an abnormality, a circuit protection step is further performed in which a protection operation is performed by changing a current flowing through the second light emitting element array and / or a voltage applied to the second light emitting element array. Prepare
The light emitting element abnormality detection method according to claim 4 or 5.

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