JP2011181616A - Led drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the abnormality of a LED array if a variation of rating is generated at each of LED constructing the LED array. <P>SOLUTION: The LED is lighted up by supplying electric power from an electric source 11 to a LED array 14 via a LED drive part 12. A memory M in a voltage comparing and detecting part 16 stores a detected voltage at a voltage detector 13 as an initial voltage Vr when the LED is lighted up. The voltage comparing and detecting part 16 compares the voltage Vd detected later at the voltage detector 13 with the initial voltage Vr stored in the memory M, and when a voltage change state to the initial voltage Vr exceeds a predetermined amount, it is determined that there is an abnormality in the LED array 14. Therefore, even if LEDs constructing the LED array 14 have variations and any voltage variation in the LED array 14 of their combination is generated, it is possible to accurately detect the abnormality in the LED by determining a value obtained when the LED based on the combination is normally lighted up as the initial value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an LED drive circuit that drives an LED array, and more particularly to reliably detect abnormality of the LED array.

  In a conventional LED drive circuit, the circuit is protected from an overcurrent / overvoltage that occurs when an LED array directly connected to a DC / DC converter is short-circuited or opened due to an external environment or the like. (For example, Patent Document 1)

JP 2006-325396 A

  The technique of the above-mentioned Patent Document 1 compares the LED voltage abnormality with a preset value. In an LED array circuit in which a plurality of LEDs are connected in series, each LED in which a plurality of LED voltage variations are connected. Therefore, there is a problem that the initial value of the life cannot be determined unless the LED array is configured and viewed.

  Further, assuming that the LEDs used in the LED array have the same maximum / minimum catalog value, there is a problem that the actual abnormality cannot be detected because it is far from the actual initial value.

  An object of the present invention is to provide an LED drive circuit capable of detecting an abnormality in an LED array even when there is a variation in catalog values among individual LEDs constituting the LED array.

  In order to solve the above-described problems, an LED drive circuit of the present invention includes a DC power supply, an LED drive unit that generates a voltage obtained by increasing or decreasing the voltage of the DC power supply, and an output voltage of the LED drive unit. An LED array composed of a plurality of LEDs connected in series to be applied and lit; storage means for storing a voltage when the LED array is normally lit as an initial voltage; and an initial voltage stored in the storage means; The detected voltage according to the lighting state of the LED array after normal lighting is compared, and if the detected voltage changes more than a predetermined value with respect to the initial voltage, it is determined as an abnormality of the LED array. And a judging means.

  According to the present invention, there are variations in the LEDs constituting the LED array, and even when variations occur in the voltage of the LED array due to these combinations, it is possible to accurately determine the value of normal lighting due to the combination as an initial value. An abnormality can be detected.

It is a schematic circuit block diagram for demonstrating one Embodiment regarding the LED lighting device of this invention. It is a circuit block diagram for demonstrating specifically the principal part of FIG. It is a schematic circuit block diagram for demonstrating other embodiment regarding the LED lighting device of this invention. It is a flowchart for demonstrating the process sequence at the time of implement | achieving the control circuit of FIG. 3 by the process of a microcomputer program. FIG. 5A is a configuration diagram for explaining another configuration example, and FIG. 5B is a configuration diagram for explaining another configuration example of the LED array used in the present invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  1 and 2 are diagrams for explaining an embodiment of the LED lighting device according to the present invention. FIG. 1 is a schematic circuit configuration diagram. FIG. 2 is a diagram for explaining a specific example of a main part of FIG. It is a circuit block diagram.

  In FIG. 1, reference numeral 11 denotes, for example, a 100 V DC power supply, which is supplied to an LED drive unit 12 having a DC / DC converter function for stepping down the DC voltage of the power supply 11. The LED drive unit 12 outputs a DC voltage obtained by dropping the voltage.

  The output of the LED drive unit 12 is connected to the reference potential point via the voltage detector 13. The output of the LED drive unit 12 is supplied to the anode of the LED 14n to which the highest voltage of the LED array 14 composed of, for example, 14 LEDs 14a to 14n connected in series as a load is applied. The cathode of the LED 14 a to which the lowest voltage of the LED array 14 is applied is connected to the reference potential point via the current detector 15.

  The detection voltage Vd detected by the voltage detector 13 is supplied to the voltage comparison / detection unit 16 as one comparison voltage, and the initial voltage Vr when the LED array 14 is turned on is stored as an initial normal voltage. Is taken into a semiconductor memory M such as a RAM (Random Access Memory), and the taken-in information is used as the other comparison voltage. The switch S is for taking the initial voltage Vr into the memory M. When the switch S is turned on, the switch S is set to a low (“L”) level and written to the memory M. The initial voltage Vr once written in the memory M maintains its value even when the power supply 11 is turned off. The voltage comparison detection unit 16 serves as a determination unit for determining whether the LED array 14 is abnormal.

  The output of the voltage comparison detection unit 16 is supplied to the PWM control unit 17 and used as on / off control information for the PWM control unit 17. The PWM control unit 17 is also supplied with the detection current of the current detector 15, and here supplies a switching pulse having a duty based on the detection current to the LED drive unit 12. The LED drive unit 12 generates and outputs an output voltage based on the switching pulse of the PWM control unit 17.

  A specific example of the main part of FIG. 1 will be described with reference to the circuit configuration diagram of FIG.

  That is, the LED drive unit 12 is connected from the positive electrode of the power supply 11 to the cathode of the diode D whose anode is grounded via one end of the inductor L via the switch element SW formed of, for example, a MOS FET transistor. The other end of the coil L is grounded via a smoothing capacitor C.

  The voltage detector 13 includes resistors R1 and R2 connected in series between the output of the LED driving unit 12 and a reference potential point, and outputs a connection point between the resistors R1 and R2 as a detection voltage of the voltage detector 13. The current detector 15 includes a resistor R3, and outputs a connection point between the resistor R3 and the cathode of the LED 14a as a voltage proportional to the detected current of the current detector 15.

  The voltage comparison detection unit 16 turns on the switch S when the LED array 14 is normally lit, and stores the detection voltage output from the voltage detector 13 as the initial voltage Vr and the initial stored in the memory M. The comparator 161 compares the voltage Vr with the detection voltage Vd output each time from the voltage detector 13.

  Now, when the power supply 11 is supplied to the LED drive unit 12, the current supplied by the power supply 11 is supplied to the LED array 14 via the inductor L. At this time, energy is stored in the inductor L. When the switch element 12 is off, power is supplied to the LED array 14 by the energy accumulated in the inductor L.

  The PWM control unit 17 repeats on / off with a duty of an on / off ratio corresponding to a predetermined constant current value detected by the current detector 15, and switches the switching element of the LED driving unit 12. SW is controlled. A voltage generated based on the resistance division of the resistors R1 and R2 of the voltage detector 13 is supplied from the voltage comparison detection unit 16, and the switch element SW of the LED drive unit 12 can be determined to be on or off.

  In the LED driving unit 12, an output current corresponding to the duty of the switching pulse supplied from the PWM control unit 17 is supplied to the LED array 14. That is, the LED drive unit 12 generates a voltage corresponding to the current flowing through the LED array 14.

  By the way, in the LED array 14, when the forward voltage Vf of one LED is 2.1 V, for example, the voltage of the LED array 14 is 2.1 V × 14 = 29.4 V. Assuming that the variation of the forward voltage Vf of the LED is ± 20%, when all the LEDs are aligned with the same variation, there is a variation range of 23.52V to 35.28V and 11.78V, and one of the LEDs is temporarily shorted. Even so, it is regarded as a normal voltage from the variation range.

  Therefore, the detection voltage output from the voltage detector 13 corresponding to the initial LED array 14 that is normally lit is taken into the memory M by turning on the switch S as the initial voltage Vr. Thereafter, a voltage corresponding to the voltage supplied to the LED array 14 is supplied to the voltage comparison detection unit 16 by the voltage detector 13 as the detection voltage Vd.

  In the voltage comparison detection unit 16, for example, when the LED 14 e of the LED array 14 is short-circuited, the voltage detector 13 detects a voltage change of the LED array 14 and supplies it as the detection voltage Vd. When the LED 14e is short-circuited, the voltage of the LED array 14 is lowered, and as a result, the detection voltage Vd is also lowered. The voltage comparison detection unit 16 outputs a stop signal from the comparator 161 and stops the output of the LED drive unit 12 when a voltage change more than a predetermined value with respect to the initial voltage Vr stored in the memory M. Thereby, the power supply to the LED array 14 can be stopped.

  Similarly, not only when the LED array 14 is short-circuited but also when it is disconnected, a voltage change can be detected, and the LED driving unit 12 can be stopped based on the change. In the case of disconnection, the change amount of the detection voltage Vd is larger.

  In this embodiment, the voltage across the LED array when normally lit is stored in the memory in advance, and the LED array is abnormal when there is a voltage change greater than or equal to the voltage value stored in the memory. It becomes possible to recognize this reliably.

  3 and 4 are diagrams for explaining another embodiment of the discharge lamp lighting device according to the present invention. FIG. 3 is a circuit configuration diagram, and FIG. 4 uses a microcomputer program as the control circuit of FIG. It is a flowchart for demonstrating the process sequence in a case. In addition, the same code | symbol is attached | subjected to the component same as embodiment mentioned above, and description here is abbreviate | omitted.

  In this embodiment, the voltage comparison detection unit 16 is replaced with a control circuit 31 constituted by, for example, a microcomputer.

  In FIG. 3, the detection voltage information from the voltage detector 13 is input to the control circuit 31, where it is processed based on the detection voltage information. Further, the control circuit 31 is provided with a semiconductor memory M such as a RAM which is a storage means for storing and storing the initial voltage Vr. In the memory M, the captured initial voltage Vr is converted into digital data in the control circuit 31 and written based on a write address preset in the control circuit 31.

  After the initial voltage Vr information is written in the memory M, the detection voltage Vd output from the voltage detector 13 is supplied to the control circuit 31, where it is converted into digital data.

  The control circuit 31 compares the initial voltage Vr and the detection voltage Vd, and supplies a drive voltage to the PWM controller 17 when the initial voltage Vr is within a predetermined range of change. The power supply to the LED array 14 is continued. During this time, the current of the LED array 14 is detected by the current detector 15, and the duty of the switching pulse output from the PWM control unit 17 is controlled according to the change.

  When the value of the detection voltage Vd changes above or below a predetermined amount with respect to the initial voltage Vr, the LED array 14 is determined to be abnormal, the drive voltage supply to the PWM control unit 17 is stopped, and the LED The drive of the drive part 12 is stopped. As an abnormality of the LED array 14, a case where at least one LED constituting the LED array 14 is short-circuited or disconnected may be considered.

  Next, the processing procedure of the control circuit 31 will be described with reference to FIG.

  First, the control circuit 31 checks whether or not the switch S is in an on state (S1). When it is confirmed that the LED array 14 is normally lit, the switch S is turned on. When the line to which the switch S is connected becomes L level, the control circuit 31 determines the detection voltage of the voltage detector 13. The initial voltage Vr is taken in (S2).

  Next, the control circuit 31 takes in the detection voltage Vd of the voltage detector 13 (S3) and sets it as a comparison target with the initial voltage Vr. The detected voltage Vd and the initial voltage Vr are compared, and if the difference is within 10%, for example, it is determined that the lighting state is normal, and if the difference exceeds ± 10%, it is determined that the state is abnormal (S4). ). If it is determined in step S4 that the state is abnormal, supply of the drive voltage to the PWM control unit 17 is stopped (S5).

  In this way, the initial voltage Vr is taken in, the comparison between the initial voltage Vr and the detection voltage Vd generated based on the state of the LED array 14 thereafter is performed by the control circuit 31, and the detection voltage Vd is a predetermined value of the initial voltage. A case where the voltage changes above or below can be determined as abnormal.

  Also in this embodiment, it is possible to reliably detect an abnormality in the LED array by storing the initial voltage and comparing and determining with the control circuit the detection voltage corresponding to the subsequent lighting of the LED array. . As a result, even when the LED variation occurs and occurs in various combinations, it is possible to accurately detect the abnormality of the LED by determining the normal lighting value by the combination as the initial value.

  5 (a) and 5 (b) are diagrams of LED arrays serving as loads of the LED drive unit 12, respectively, FIG. 5 (a) is a configuration diagram for explaining another specific example, and FIG. 5 (b) is another diagram. It is a block diagram for demonstrating one other specific example.

  First, the LED array 141 shown in FIG. 5A is formed by connecting in parallel three groups of LED groups 1411 to 1413 in which 14 LEDs 14a to 14n are connected in series. The anodes of the LEDs 14n of the LED groups 1411 to 1413 are commonly connected to the output of the LED driving unit 12, and the cathodes of the LEDs 14a of the LED groups 1411 to 1413 are commonly connected to the reference potential via the current detector 15. Connect to the point.

  When this LED 141 is connected as a load of the LED drive unit 12, for example, when the LEDs in the LED group 1412 of the LED groups 1411 to 1413 are short-circuited, only the shorted LED is turned off, and the others are turned on. To do. However, the voltage of the LED array 141 changes due to the short circuit, and it can be detected that the comparison with the voltage change amount when the LED whose short circuit is short is normal becomes a predetermined value or more. .

  For example, when an LED in the LED group 1412 is disconnected, the entire LED group 1412 is turned off. Also in this case, the abnormality of the LED array 141 can be detected.

  The LED array 142 shown in FIG. 5B includes LED groups 1421 to 1423 in which 14 LEDs 14a to 14n are connected in series and connected in parallel. The anodes of the LEDs 14n of the LED groups 1421 to 1423 are commonly connected to the output of the LED driving unit 12, and the cathodes of the LEDs 14a of the LED groups 1421 to 1423 are commonly connected to the reference potential via the current detector 15. Connect to the point.

  When this LED 142 is connected as a load of the LED drive unit 12, for example, when an LED in the LED group 1423 of the LED groups 1421 to 1423 is short-circuited, the shorted LED is simply turned off, and the others are turned on. To do. However, the voltage of the LED array 142 changes with the short circuit, and it can be detected that the comparison with the amount of voltage change when the shorted LED is normal is equal to or greater than a predetermined value. .

  For example, even when an LED in the LED group 1422 is disconnected, the entire LED group 1423 is not turned off. Also in this case, the abnormality of the LED array 142 can be detected.

  The present invention is not limited to the above-described embodiment. For example, although 14 examples of LED arrays are given in the series direction, they may be more or less than this. Further, although the normal voltage is taken into the memory at the timing of manual switching, it may be automatically performed in synchronism with an external electric signal.

  Furthermore, although the output voltage of the LED driving unit has been described with respect to the example in which the power supply voltage is lowered, the output voltage may be increased, and is determined based on the forward voltage of the LED array as a load.

DESCRIPTION OF SYMBOLS 11 DC power supply 12 LED drive part 13 Voltage detector 14,141,142 LED array 14a-14n LED
15 current detector 16 voltage comparison detection unit 17 PWM control unit M memory S switches 1411 to 1413, 1421 to 1423 LED group

Claims (8)

DC power supply,
An LED driving unit that generates a voltage obtained by raising or lowering the voltage of the DC power supply;
An LED array composed of a plurality of LEDs connected in series to apply an output voltage of the LED drive unit and turn it on;
Storage means for storing a voltage when the LED array is normally lit as an initial voltage;
When the initial voltage stored in the storage means is compared with the detection voltage corresponding to the lighting state of the LED array after normal lighting, and the detected voltage has a voltage change greater than or equal to a predetermined value with respect to the initial voltage An LED driving circuit comprising: a determination unit that determines that the LED array is abnormal.   The determination unit determines whether the LED array is abnormal based on a change in a detection voltage based on a change in a predetermined value by comparison with a detection voltage during normal lighting with the initial voltage as a reference. Item 2. An LED drive circuit according to Item 1.   3. The LED drive circuit according to claim 1, wherein the LED array is configured by connecting a plurality of LEDs in series.   3. The LED drive circuit according to claim 1, wherein the LED array includes a plurality of LEDs connected in series, and a plurality of the LED groups are connected in parallel.   3. The LED array according to claim 1, wherein a plurality of LEDs are connected in series, and a plurality of the LED groups are connected in parallel, and cathodes of the LEDs of each LED group are connected to each other. LED drive circuit.   3. The LED driving circuit according to claim 1, wherein the LED lighting voltage is stored as a voltage when the LED array is first turned on.   3. The LED driving circuit according to claim 1, wherein the LED lighting voltage is stored by a manual switch.   3. The LED driving circuit according to claim 1, wherein the LED lighting voltage is stored in synchronization with an external electric signal.

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