JP2011233553A - Led drive circuit - Google Patents

Led drive circuit Download PDF

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JP2011233553A
JP2011233553A JP2010099706A JP2010099706A JP2011233553A JP 2011233553 A JP2011233553 A JP 2011233553A JP 2010099706 A JP2010099706 A JP 2010099706A JP 2010099706 A JP2010099706 A JP 2010099706A JP 2011233553 A JP2011233553 A JP 2011233553A
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voltage
led
converter
circuit
led units
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JP5644169B2 (en
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Yoshinori Sato
嘉典 佐藤
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Toshiba Lighting and Technology Corp
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Harison Toshiba Lighting Corp
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Abstract

PROBLEM TO BE SOLVED: To maintain lifetimes of LEDs by disallowing an excessive current to flow to an array of normal LED units even if the array of LED units enters an open state.SOLUTION: The voltage of a power source 11 is stepped down by a DC/DC converter 12 based upon a switching signal of a pulse width modulation circuit. An output voltage Vd of the converter 12 is supplied to first and second LED units 13 and 14 which are connected in parallel to make the LED units illuminate. Currents flowing to the LED units 13 and 14 are converted by resistances R1 and R2 into voltages, which are ORed by an OR circuit 16, and the output voltage Vd is controlled with a duty of switching pulses from the pulse width modulation circuit 18 which turns ON and OFF a transistor of Q of the converter 12 so that the currents flowing to the LED units 13 and 14 become constant. The voltages converted by the resistances R1 and R2 are ORed, so that the constant output voltage Vd is obtained even if one of the LED units 13 and 14 enters an open state.

Description

この発明は、複数のＬＥＤが直列接続されたＬＥＤ回路が複数並列接続された状態で駆動するＬＥＤ駆動回路に関する。   The present invention relates to an LED drive circuit that drives an LED circuit in which a plurality of LEDs are connected in series and is connected in parallel.

従来のＬＥＤ駆動回路は、図４に示すように、複数のＬＥＤを直列に接続したＬＥＤユニット１１ａ〜１１ｎを複数並列接続し、ＬＥＤユニット１１ａ〜１１ｎには定電圧回路からの電圧を供給して点灯させ、このときＬＥＤユニット１１ａ〜１１ｎに流れる総電流を検出し、検出された総電流またはＬＥＤユニット１１ａ〜１１ｎ単位の平均電流が一定になるように制御している。（例えば、特許文献１）   As shown in FIG. 4, the conventional LED driving circuit connects a plurality of LED units 11 a to 11 n in which a plurality of LEDs are connected in series, and supplies a voltage from a constant voltage circuit to the LED units 11 a to 11 n. At this time, the total current flowing through the LED units 11a to 11n is detected, and the detected total current or the average current of the LED units 11a to 11n is controlled to be constant. (For example, Patent Document 1)

特開２００７−１３４４３０公報JP 2007-134430 A

上記した特許文献１の技術は、列または複数列のＬＥＤユニットがオープン状態となり電流が流れなくなった場合、流れなくなった分の電流が正常な他の列のＬＥＤユニットに過大電流となって流れ、ＬＥＤの温度が上昇して短寿命の原因になってしまう、という問題があった。   In the technique of Patent Document 1 described above, when the LED units in a row or a plurality of rows are in an open state and the current does not flow, the current that does not flow flows as an excessive current to the LED units in other rows, There existed a problem that the temperature of LED raised and caused the short life.

この発明の目的は、ＬＥＤユニットの列がオープン状態となった場合に、正常なＬＥＤユニットの列に過大な電流が流れないようにしてＬＥＤの温度上昇を抑えて、ＬＥＤの寿命の維持が図れるＬＥＤ駆動回路を提供することにある。   The object of the present invention is to maintain the life of the LED by suppressing an increase in the temperature of the LED so that an excessive current does not flow in the normal LED unit row when the LED unit row is opened. The object is to provide an LED driving circuit.

上記した課題を解決するために、この発明のＬＥＤ駆動回路は、スイッチング信号に基づき、入力直流電圧を降圧または昇圧させ、所望の直流電圧に変換して出力するコンバータと、前記コンバータの出力電圧を供給する複数のＬＥＤを直列接続した第１のＬＥＤユニットと、前記第１のＬＥＤユニットと並列接続し、前記コンバータの出力電圧を供給する複数のＬＥＤを直列接続した第２のＬＥＤユニットと、前記第１および第２のＬＥＤユニットに流れる電流を電圧に変換し、それぞれ電圧のオアをとって、前記第１および第２のＬＥＤユニットに流れる電流が一定となるように前記コンバータの出力電圧を制御する制御手段と、を具備したことを特徴とする。   In order to solve the above-described problems, an LED drive circuit according to the present invention includes a converter that steps down or boosts an input DC voltage based on a switching signal, converts the input DC voltage to a desired DC voltage, and outputs the output voltage of the converter. A first LED unit in which a plurality of LEDs to be supplied are connected in series; a second LED unit in which a plurality of LEDs that are connected in parallel with the first LED unit and supply the output voltage of the converter are connected in series; The current flowing through the first and second LED units is converted into a voltage, and the output voltage of the converter is controlled so that the current flowing through the first and second LED units is constant by taking the voltage OR. And a control means.

この発明によれば、ＬＥＤユニットの列がオープン状態となった場合でも、正常なＬＥＤユニットの列に過大な電流が流れないようにしたことでＬＥＤの寿命を維持することが可能となる。   According to the present invention, even when the LED unit row is in an open state, it is possible to maintain the life of the LED by preventing an excessive current from flowing through the normal LED unit row.

この発明のＬＥＤ駆動回路に関する一実施形態について説明するための回路構成図である。It is a circuit block diagram for demonstrating one Embodiment regarding the LED drive circuit of this invention. この発明のＬＥＤ駆動回路に関する他の実施形態について説明するための回路構成図である。It is a circuit block diagram for demonstrating other embodiment regarding the LED drive circuit of this invention. この発明の一実施形態の変形例について説明するための回路構成図である。It is a circuit block diagram for demonstrating the modification of one Embodiment of this invention. 従来のＬＥＤ駆動回路について説明するための回路構成図である。It is a circuit block diagram for demonstrating the conventional LED drive circuit.

以下、この発明を実施するための形態について、図面を参照しながら詳細に説明する。   Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

図１は、この発明のＬＥＤ駆動回路に関する一実施形態について説明するための回路構成図である。   FIG. 1 is a circuit configuration diagram for explaining an embodiment relating to an LED drive circuit of the present invention.

図１において、１１は直流電源であり、この電源１１の正極は、ＭＯＳ型のスイッチング用トランジスタＱのソースを接続する。トランジスタＱのドレインは、電源１１から供給されるエネルギーを蓄えるインダクタＬの一端に接続するとともに、アノードが基準電位点に接続された整流用のダイオードＤ１のカソードに接続する。インダクタＬの他端は、平滑用のコンデンサＣを介して基準電位点に接続する。トランジスタＱ、インダクタＬ、ダイオードＤ１、コンデンサＣは、トランジスタＱのオン・オフに基づき入力直流電圧を降圧させ、所望の直流電圧に変換して出力するＤＣ／ＤＣコンバータ１２を構成している。   In FIG. 1, 11 is a DC power supply, and the positive electrode of the power supply 11 is connected to the source of a MOS type switching transistor Q. The drain of the transistor Q is connected to one end of an inductor L that stores energy supplied from the power supply 11, and the anode is connected to the cathode of a rectifying diode D1 connected to a reference potential point. The other end of the inductor L is connected to a reference potential point via a smoothing capacitor C. The transistor Q, the inductor L, the diode D1, and the capacitor C constitute a DC / DC converter 12 that steps down the input DC voltage based on the on / off state of the transistor Q, converts it to a desired DC voltage, and outputs it.

ＤＣ／ＤＣコンバータ１２の出力は、直列接続のＬＥＤ（発光ダイオード）１３１〜１３１ｎから構成のＬＥＤユニット１３の最上の電圧が印加されるＬＥＤ１３１ｎのアノードに、ＬＥＤユニット１３に並列接続される直列接続のＬＥＤ１４１〜１４１ｎから構成のＬＥＤユニット１４の最上の電圧が印加されるＬＥＤ１４１ｎのアノードにそれぞれ接続される。   The output of the DC / DC converter 12 is connected in series to the LED unit 13 in parallel to the anode of the LED 131n to which the highest voltage of the LED unit 13 configured from LEDs (light emitting diodes) 131 to 131n connected in series is applied. Each of the LEDs 141 to 141n is connected to the anode of the LED 141n to which the highest voltage of the LED unit 14 is applied.

ＬＥＤユニット１３の最下の電圧が印加されるＬＥＤ１３１のカソードは、抵抗Ｒ１を介して基準電位点に、ＬＥＤユニット１４の最下の電圧が印加されるＬＥＤ１４１のカソードは、抵抗Ｒ２を介して基準電位点にそれぞれ接続される。   The cathode of the LED 131 to which the lowest voltage of the LED unit 13 is applied is a reference potential point via the resistor R1, and the cathode of the LED 141 to which the lowest voltage of the LED unit 14 is applied is a reference via the resistor R2. Each is connected to a potential point.

１５は演算増幅器であり、この演算増幅器１５の反転入力＋は、基準電圧Ｖｒｅｆを介して基準電位点に接続される。演算増幅器１５の非反転入力−には、ＬＥＤユニット１３のＬＥＤ１３１のカソードと抵抗Ｒ１との接続点にアノードが接続されたダイオードＤ２のカソードおよびＬＥＤユニット１４のＬＥＤ１４１のカソードと抵抗Ｒ２との接続点にアノードが接続されたダイオードＤ３のカソードがそれぞれ接続される。   Reference numeral 15 denotes an operational amplifier. An inverting input + of the operational amplifier 15 is connected to a reference potential point via a reference voltage Vref. The non-inverting input − of the operational amplifier 15 includes a cathode of the diode D2 having an anode connected to a connection point between the cathode of the LED 131 of the LED unit 13 and the resistor R1, and a connection point of the cathode of the LED 141 of the LED unit 14 and the resistor R2. Are connected to the cathodes of the diodes D3, to which the anodes are connected, respectively.

ところで、ダイオードＤ２，Ｄ３は、ＯＲ回路１６を構成しており、いずれか一方の出力が演算増幅器１５の反転入力−に供給されている状態での演算増幅器１５の出力は、負荷であるＬＥＤユニット１３，１４は通常の状態にあると判断し、制御回路１７に出力を供給する。   By the way, the diodes D2 and D3 constitute an OR circuit 16, and the output of the operational amplifier 15 in a state where one of the outputs is supplied to the inverting input − of the operational amplifier 15 is an LED unit that is a load. 13 and 14 are determined to be in a normal state, and an output is supplied to the control circuit 17.

そして演算増幅器１５の出力は、制御回路１７に供給し、ここで演算増幅器１５の出力情報に基づいた制御パルスを生成し、パルス幅変調回路１８に供給し、制御パルスのパルス幅に基づいたスイッチング信号をトランジスタＱのゲートに供給する。   The output of the operational amplifier 15 is supplied to the control circuit 17, where a control pulse based on the output information of the operational amplifier 15 is generated, supplied to the pulse width modulation circuit 18, and switched based on the pulse width of the control pulse. A signal is supplied to the gate of transistor Q.

なお、ＬＥＤユニット１３，１４の電流を電圧にそれぞれ変換し、これらをＯＲ回路１６でオアをとった電圧と基準電位Ｖｒｅｆとの演算を演算増幅器１５で行い、演算増幅器１５の出力情報に基づいた制御信号を制御回路１７からパルス幅変調回路１８に供給し、ここで制御信号に基づいたデューティのスイッチングパルスを生成し、トランジスタＱのゲートに供給するルーチンで制御手段を構成している。   The currents of the LED units 13 and 14 are converted into voltages, respectively, and the OR circuit 16 takes the ORed voltage and the reference potential Vref is calculated by the operational amplifier 15, which is based on the output information of the operational amplifier 15. The control signal is supplied from the control circuit 17 to the pulse width modulation circuit 18, where a switching pulse having a duty based on the control signal is generated and supplied to the gate of the transistor Q to constitute control means.

ここで、図１の動作について説明する。トランジスタＱは、電源１１の直流電圧をパルス幅変調回路１８の出力に基づいてスイッチングし、スイッチング出力を所定の直流電圧に変換して出力する。インダクタＬは、トランジスタＱがオンのときに電源１１から電流が流れてエネルギーが蓄積される。トランジスタＱがオフのとき、ダイオードＤ１を介してインダクタＬに電流が流れ込み、一定の出力電圧Ｖｄが維持される。また、コンデンサＣにより、出力電圧Ｖｄが平滑される。   Here, the operation of FIG. 1 will be described. The transistor Q switches the DC voltage of the power supply 11 based on the output of the pulse width modulation circuit 18, converts the switching output into a predetermined DC voltage, and outputs it. Inductor L accumulates energy as a current flows from power supply 11 when transistor Q is on. When the transistor Q is off, a current flows into the inductor L via the diode D1, and a constant output voltage Vd is maintained. Further, the output voltage Vd is smoothed by the capacitor C.

ＤＣ／ＤＣコンバータ１２の出力電圧Ｖｄは、ＬＥＤユニット１３，１４に供給して電流を流し、これらを点灯する。ＬＥＤユニット１３の１３１〜１３１ｎに流れた電流は、抵抗Ｒ１により電圧に変換し、ダイオードＤ２に介して演算増幅器１５の反転入力−に、ＬＥＤユニット１４の１４１〜１４１ｎに流れた電流は、抵抗Ｒ２により電圧に変換し、ダイオードＤ３に介して演算増幅器１５の反転入力−にそれぞれ供給する。演算増幅器１５は、反転入力−のＯＲ回路１６の出力電圧と非反転入力＋の基準電圧Ｖｒｅｆとの比較を行い、演算増幅器１５の出力が基準電圧Ｖｒｅｆに相当する定電圧が制御回路１７に供給される。   The output voltage Vd of the DC / DC converter 12 is supplied to the LED units 13 and 14 so that a current flows, and these are turned on. The current flowing through 131-131n of the LED unit 13 is converted into a voltage by the resistor R1, and the current flowing through 141-141n of the LED unit 14 through the diode D2 to the inverting input − of the operational amplifier 15 is converted into the resistor R2. The voltage is converted to a voltage and supplied to the inverting input − of the operational amplifier 15 through the diode D3. The operational amplifier 15 compares the output voltage of the OR circuit 16 of the inverting input − with the reference voltage Vref of the non-inverting input +, and the output of the operational amplifier 15 supplies a constant voltage corresponding to the reference voltage Vref to the control circuit 17. Is done.

演算増幅器１５の出力が供給された制御回路１７では、演算増幅器１５の出力情報に基づいた制御信号をパルス幅変調回路１８に供給する。パルス幅変調回路１８では制御信号に基づいたデューティのスイッチングパルスを生成し、トランジスタＱのゲートに供給し、ＤＣ／ＤＣコンバータ１２の出力電圧Ｖｄを決定する。つまり、出力電圧Ｖｄは、基準電圧Ｖｒｅｆで決まる定電圧を、ＬＥＤユニット１３，１４にそれぞれ供給し、それぞれのＬＥＤを点灯する。   The control circuit 17 supplied with the output of the operational amplifier 15 supplies a control signal based on the output information of the operational amplifier 15 to the pulse width modulation circuit 18. The pulse width modulation circuit 18 generates a duty switching pulse based on the control signal, supplies it to the gate of the transistor Q, and determines the output voltage Vd of the DC / DC converter 12. That is, as the output voltage Vd, a constant voltage determined by the reference voltage Vref is supplied to the LED units 13 and 14, respectively, and each LED is turned on.

ここで、例えばＬＥＤユニット１４がオープンになった場合は、ＬＥＤユニット１４には電流が流れなくなり、抵抗Ｒ２により電圧が発生しない。しかし、オープン状態にないＬＥＤユニット１３に流れた電流は、抵抗Ｒ１により変換された電圧がダイオードＤ２を介して演算増幅器１５の非反転入力−に供給される。このときに演算増幅器１５には、基準電圧Ｖｒｅｆに相当する定電圧が制御回路１７に供給される。   Here, for example, when the LED unit 14 is opened, no current flows through the LED unit 14, and no voltage is generated by the resistor R2. However, as for the current flowing through the LED unit 13 that is not in the open state, the voltage converted by the resistor R1 is supplied to the non-inverting input − of the operational amplifier 15 via the diode D2. At this time, a constant voltage corresponding to the reference voltage Vref is supplied to the operational amplifier 15 to the control circuit 17.

従って、ＤＣ／ＤＣコンバータ１２の出力電圧Ｖｄとしては変化がないことから、結果としてＬＥＤユニット１３に過大な電流が流れることがなく、ＬＥＤユニット１３の発熱を抑え、ＬＥＤの寿命を維持させることができる。   Therefore, since there is no change in the output voltage Vd of the DC / DC converter 12, as a result, an excessive current does not flow through the LED unit 13, and heat generation of the LED unit 13 can be suppressed and the life of the LED can be maintained. it can.

図２は、この発明のＬＥＤ駆動回路に関する他の実施形態について説明するための回路構成図である。上記実施形態と同一の機能部分には同一の符号を付し、ここでの説明は省略する。   FIG. 2 is a circuit configuration diagram for explaining another embodiment relating to the LED drive circuit of the present invention. The same functional parts as those in the above embodiment are denoted by the same reference numerals, and description thereof is omitted here.

この実施形態は、演算増幅器１５の基準電圧Ｖｒｅｆと直列に、ＯＲ回路１６のダイオードＤ２，Ｄ３と同じ温度特性を有するダイオードＤ４を接続した構成部分が、図１と異なる。   This embodiment is different from that shown in FIG. 1 in that a diode D4 having the same temperature characteristics as the diodes D2 and D3 of the OR circuit 16 is connected in series with the reference voltage Vref of the operational amplifier 15.

演算増幅器１５の非反転入力−に接続されたダイオードＤ２，Ｄ３は、ダイオードＤ２，Ｄ３の順方向電圧が温度により変化する特性を有している。演算増幅器１５の反転入力＋に接続されたダイオードＤ４は、ダイオードＤ２，Ｄ３と同じように順方向電圧が温度により変化する特性を有している。従って、温度変化に対して、演算増幅器１５の非反転入力−と反転入力＋は同条件となる。   The diodes D2 and D3 connected to the non-inverting input − of the operational amplifier 15 have a characteristic that the forward voltage of the diodes D2 and D3 changes with temperature. The diode D4 connected to the inverting input + of the operational amplifier 15 has a characteristic that the forward voltage changes with temperature, like the diodes D2 and D3. Therefore, the non-inverting input − and the inverting input + of the operational amplifier 15 have the same condition with respect to the temperature change.

従って、温度が上昇すると順方向電圧が下がるため検出抵抗Ｒ１、Ｒ２で検出された電流が変化していないにもかかわらず演算増幅器に入力する電圧は低下する。基準電圧Ｖｒｅｆも下げることでＬＥＤユニット１３，１４の定電流を保持する。   Accordingly, since the forward voltage decreases as the temperature rises, the voltage input to the operational amplifier decreases even though the currents detected by the detection resistors R1 and R2 have not changed. The constant current of the LED units 13 and 14 is held by lowering the reference voltage Vref.

すなわち、ダイオードＤ２，Ｄ３と同じ温度特性のダイオードＤ４は、ダイオードＤ２，Ｄ３の温度特性による順方向電圧の変化によるＬＥＤユニット１３，１４を流れる電流の誤検出を、温度によるＬＥＤユニット１３，１４の照度の変化を抑えることが可能となる。   That is, the diode D4 having the same temperature characteristics as the diodes D2 and D3 detects erroneous detection of the current flowing through the LED units 13 and 14 due to a change in the forward voltage due to the temperature characteristics of the diodes D2 and D3. It becomes possible to suppress a change in illuminance.

この実施形態では、温度変化があっても、それに対応して基準電圧を変化させることができ、ＬＥＤユニットに流す電流を定電流に保持できることから温度による影響を軽減させることが可能となる。   In this embodiment, even if there is a temperature change, the reference voltage can be changed correspondingly, and since the current flowing through the LED unit can be held at a constant current, the influence of temperature can be reduced.

図３は、この発明の一実施形態の変形例について説明するための回路構成図である。上記した各実施形態では、ＤＣ／ＤＣコンバータ１２から出力される駆動電圧Ｖｄが電源１１に対して降圧される例について説明した。この変形例は、図１の回路構成のＤＣ／ＤＣコンバータ１２を、昇圧させるＤＣ／ＤＣコンバータ１２１で構成したものである。   FIG. 3 is a circuit configuration diagram for explaining a modification of the embodiment of the present invention. In each of the above-described embodiments, the example in which the drive voltage Vd output from the DC / DC converter 12 is stepped down with respect to the power supply 11 has been described. In this modification, the DC / DC converter 12 having the circuit configuration of FIG. 1 is configured with a DC / DC converter 121 that boosts the voltage.

すなわち、ＤＣ／ＤＣコンバータ１２１は、電源１１とＤＣ／ＤＣコンバータ１２１のライン間に、インダクタＬとダイオードＤ１を直列の状態で介装接続し、インダクタＬとダイオードＤ１の接続点と基準電位点との間にスイッチングトランジスタＱのドレインとソース間を介装接続している。   That is, the DC / DC converter 121 connects the inductor L and the diode D1 in series between the power supply 11 and the DC / DC converter 121, and connects the connection point between the inductor L and the diode D1 and the reference potential point. Between the drain and the source of the switching transistor Q.

トランジスタＱのゲートをパルス幅変調回路１８から出力されるスイッチングパルスに基づいてスイッチングすることにより、ＤＣ／ＤＣコンバータ１２１の出力からは、電源１１の直流電圧値よりも昇圧された出力電圧Ｖｄを導出でき、ＬＥＤユニット１３，１４のそれぞれの最上の電圧で動作するＬＥＤの点灯させることができる。   By switching the gate of the transistor Q based on the switching pulse output from the pulse width modulation circuit 18, the output voltage Vd boosted from the DC voltage value of the power supply 11 is derived from the output of the DC / DC converter 121. The LEDs operating at the highest voltage of each of the LED units 13 and 14 can be turned on.

なお、図３の変形例では、演算増幅器１４の基準電圧Ｖｒｅｆに直列に、図２の実施形態のように、ダイオードＤ２，Ｄ３の温度特性による順方向電圧の変化による検出電圧の誤検出を防止するために、ダイオードＤ２，Ｄ３と同特性のダイオードを接続しても構わない。   In the modification of FIG. 3, the detection voltage is not erroneously detected due to the change of the forward voltage due to the temperature characteristics of the diodes D2 and D3 in series with the reference voltage Vref of the operational amplifier 14 as in the embodiment of FIG. Therefore, a diode having the same characteristics as the diodes D2 and D3 may be connected.

この発明は、上記した実施形態に限定されるものではない。例えば、ＬＥＤユニットは説明を簡単にするために２列だけを図示したが、ＬＥＤユニット３列以上であっても、追加のＬＥＤユニットに電圧変換用の抵抗とこの抵抗により検出された電圧をダイオードを介して演算増幅器の非反転入力に供給する構成にすればよい。   The present invention is not limited to the above-described embodiment. For example, although only two rows of LED units are shown for simplicity of explanation, even if there are three or more rows of LED units, a resistor for voltage conversion and a voltage detected by this resistor are added to the additional LED unit as a diode. It may be configured to supply to the non-inverting input of the operational amplifier via the.

また、ＬＥＤユニットに直列に接続された電圧変換用の抵抗を可変抵抗とし、演算増幅器の出力が基準電圧に基づくように調整することで、ＬＥＤユニットの通常の点灯時における出力電圧Ｖｄの一定化させることで、ＬＥＤユニットの照度の一定化を図ることができる。   Further, the voltage conversion resistor connected in series with the LED unit is a variable resistor, and the output voltage Vd during normal lighting of the LED unit is made constant by adjusting the output of the operational amplifier based on the reference voltage. By doing so, the illuminance of the LED unit can be made constant.

１１ 電源
１２、１２１ ＤＣ／ＤＣコンバータ
１３，１４ ＬＥＤユニット
１３１〜１３ｎ，１４１〜１４ｎ ＬＥＤ
１５ 演算増幅器
１６ ＯＲ回路
１７ 制御回路
１８ パルス幅変調回路
Ｑ スイッチングトランジスタ
Ｖｒｅｆ 基準電圧
Ｄ２〜Ｄ３ ダイオード 11 Power supply 12, 121 DC / DC converter 13, 14 LED unit 131-13n, 141-14n LED
15 operational amplifier 16 OR circuit 17 control circuit 18 pulse width modulation circuit Q switching transistor Vref reference voltage D2 to D3 diode

Claims (3)

スイッチング信号に基づき、入力直流電圧を降圧または昇圧させ、所望の直流電圧に変換して出力するコンバータと、
前記コンバータの出力電圧を供給する複数のＬＥＤを直列接続した第１のＬＥＤユニットと、
前記第１のＬＥＤユニットと並列接続し、前記コンバータの出力電圧を供給する複数のＬＥＤを直列接続した第２のＬＥＤユニットと、
前記第１および第２のＬＥＤユニットに流れる電流を電圧に変換し、それぞれ電圧のオアをとって、前記第１および第２のＬＥＤユニットに流れる電流が一定となるように前記コンバータの出力電圧を制御する制御手段と、を具備したことを特徴とするＬＥＤ駆動回路。 A converter that steps down or boosts an input DC voltage based on a switching signal, converts the input DC voltage to a desired DC voltage, and outputs it;
A first LED unit in which a plurality of LEDs that supply the output voltage of the converter are connected in series;
A second LED unit that is connected in parallel with the first LED unit, and a plurality of LEDs that supply the output voltage of the converter are connected in series;
The current flowing through the first and second LED units is converted into a voltage, and the output voltage of the converter is adjusted so that the current flowing through the first and second LED units is constant by taking the voltage OR. And an LED driving circuit comprising: a control means for controlling. 制御手段は、前記第１および第２のＬＥＤユニットにそれぞれ流れる電流を電圧に変換する電圧変換手段と、該電圧変換手段の出力をオア出力とるＯＲ回路と、該ＯＲ回路の出力を非反転入力に、基準電位を反転入力に供給した演算増幅器と、該演算増幅器の出力情報に基づき制御信号を生成する制御回路と、該制御回路からの制御信号に基づいたデューティのスイッチングパルスを生成するパルス幅変調回路と、から構成し、前記コンバータのスイッチングパルスのデューティを制御し、前記コンバータの出力電圧を制御するようにしたことを特徴する請求項１記載のＬＥＤ駆動回路。   The control means includes a voltage conversion means for converting the currents flowing through the first and second LED units into voltages, an OR circuit for taking an OR output from the voltage conversion means, and a non-inverting input for the output of the OR circuit. An operational amplifier that supplies a reference potential to an inverting input, a control circuit that generates a control signal based on output information of the operational amplifier, and a pulse width that generates a switching pulse with a duty based on the control signal from the control circuit The LED driving circuit according to claim 1, further comprising: a modulation circuit, wherein a duty of a switching pulse of the converter is controlled to control an output voltage of the converter. 前記ＯＲ回路はダイオードで構成し、該ダイオードの順方向の温度特性と同特性のダイオードを、前記基準電位に直列に接続したことを特徴とする請求項２記載のＬＥＤ駆動回路。   3. The LED drive circuit according to claim 2, wherein the OR circuit is constituted by a diode, and a diode having the same characteristic as the forward temperature characteristic of the diode is connected in series to the reference potential.
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