JP6186918B2 - LED lighting circuit and LED lighting device - Google Patents

LED lighting circuit and LED lighting device Download PDF

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JP6186918B2
JP6186918B2 JP2013126631A JP2013126631A JP6186918B2 JP 6186918 B2 JP6186918 B2 JP 6186918B2 JP 2013126631 A JP2013126631 A JP 2013126631A JP 2013126631 A JP2013126631 A JP 2013126631A JP 6186918 B2 JP6186918 B2 JP 6186918B2
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伸一 野月
伸一 野月
秀明 岩館
秀明 岩館
知広 白木
知広 白木
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Iwasaki Denki KK
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Description

本発明はＬＥＤ点灯回路及びそれを用いたＬＥＤ照明装置に関する。   The present invention relates to an LED lighting circuit and an LED lighting device using the LED lighting circuit.

特許文献１はＬＥＤに対して定電流制御又は定電圧制御を行うＬＥＤ点灯装置を開示する。同文献のＬＥＤ点灯装置はＬＥＤ（２）及び点灯ユニット（５）を備える。点灯ユニットは、ＬＥＤの接続数が所定値未満の場合には電流検出抵抗（４０）に流れる出力電流が設定値で一定となるように定電流制御を行う。また、点灯ユニットは、ＬＥＤの接続数が所定値以上の場合には電圧検出抵抗（３０、３１）に発生する電圧が設定値以上とならないように定電圧制御を行う。これにより、直列接続されたＬＥＤの個数に応じて定電流制御又は定電圧制御が行われ、特に、複数のＬＥＤのうちの一部が短絡故障しても残りのＬＥＤが定電流制御される。   Patent Document 1 discloses an LED lighting device that performs constant current control or constant voltage control on an LED. The LED lighting device of the same document includes an LED (2) and a lighting unit (5). When the number of connected LEDs is less than a predetermined value, the lighting unit performs constant current control so that the output current flowing through the current detection resistor (40) is constant at the set value. The lighting unit performs constant voltage control so that the voltage generated in the voltage detection resistors (30, 31) does not exceed a set value when the number of connected LEDs is equal to or greater than a predetermined value. Thereby, constant current control or constant voltage control is performed according to the number of LEDs connected in series. In particular, even if a part of the plurality of LEDs is short-circuited, the remaining LEDs are constant current controlled.

特許文献２はＬＥＤの短絡故障時に、ＤＣ／ＤＣコンバータ（２）からＬＥＤ（４）に流れる電流を制限する点灯装置を開示する。点灯装置は、ＬＥＤの電圧を検出する電圧検出手段（Ｒ２、Ｒ３）と、ＬＥＤに直列接続されたスイッチング素子（ＳＷ１）と、スイッチング素子を制御する出力電圧判別部（３）とを備える。具体的には、検出電圧がＬＥＤの短絡判別用の所定値以下となった場合に出力電圧判定部によってスイッチング素子がオフ状態とされ、ＬＥＤ電流の経路が遮断される。また、スイッチング素子に並列接続された限流抵抗（Ｒｓ）により、一部のＬＥＤに短絡故障が生じてスイッチング素子が開放された場合であっても他の正常なＬＥＤに電流が流れ、減光点灯が行われる。   Patent Document 2 discloses a lighting device that limits the current flowing from the DC / DC converter (2) to the LED (4) when a short circuit failure occurs in the LED. The lighting device includes voltage detection means (R2, R3) for detecting the voltage of the LED, a switching element (SW1) connected in series with the LED, and an output voltage determination unit (3) for controlling the switching element. Specifically, when the detected voltage is equal to or lower than a predetermined value for determining the short circuit of the LED, the output voltage determining unit turns off the switching element, and the LED current path is blocked. In addition, due to a current limiting resistor (Rs) connected in parallel to the switching element, even if a short circuit failure occurs in some LEDs and the switching elements are opened, current flows to other normal LEDs, resulting in dimming Lighting is performed.

特開２００８−２８３２０６号公報JP 2008-283206 A 特開２０１０−１２９６１２号公報JP 2010-129612 A

しかし、特許文献１の構成によると、接続されたＬＥＤ全体が短絡故障した場合の動作が検討されていない。また近年では、ＬＥＤの定電流制御用のドライバＩＣが普及しているが、上記のような負荷短絡に対する保護機能を有するドライバＩＣは存在しない。ＬＥＤ全体が短絡故障した場合にＬＥＤ正常時と同様の定電流制御を行うと、不要な出力電流が回路に流れ続けることになり、この不要な出力電流によって回路部品の発熱及びそれに伴う故障が発生し得るため、回路の信頼性確保の観点から好ましくない。   However, according to the configuration of Patent Document 1, the operation in the case where the entire connected LED is short-circuited has not been studied. In recent years, driver ICs for constant current control of LEDs have become widespread, but there is no driver IC having a protection function against the load short circuit as described above. If the constant current control is performed in the same way as when the LED is normal when the entire LED has a short-circuit failure, unnecessary output current will continue to flow through the circuit, and this unnecessary output current will cause circuit component heat generation and associated failure. Therefore, it is not preferable from the viewpoint of ensuring the reliability of the circuit.

また、特許文献２の構成によると、ＬＥＤ電流を遮断するためのスイッチング素子がＬＥＤ電流の経路上に配置される。これによると、ＬＥＤの全部又は一部短絡時の過電流がスイッチング素子の開放動作により抑制されるものの、正常点灯時において導通状態が維持されるスイッチング素子での電力損失によって回路効率が低下してしまう。またさらに、スイッチング素子に限流抵抗が並列接続される構成においては、スイッチング素子開放時に限流抵抗による電力損失が発生してしまう。言い換えると、限流抵抗に定格電力の大きな抵抗を用いる必要があり、これにより回路が高コスト化及び大型化してしまう。   Further, according to the configuration of Patent Document 2, a switching element for cutting off the LED current is arranged on the LED current path. According to this, although the overcurrent at the time of short-circuiting all or part of the LED is suppressed by the opening operation of the switching element, the circuit efficiency is reduced due to the power loss in the switching element that maintains the conduction state during normal lighting. End up. Furthermore, in the configuration in which the current limiting resistor is connected in parallel to the switching element, power loss due to the current limiting resistance occurs when the switching element is opened. In other words, it is necessary to use a resistor having a large rated power as the current limiting resistor, which increases the cost and size of the circuit.

そこで、本発明は、ＬＥＤ点灯回路において、負荷短絡故障時に不要な回路電流を低減して適切な保護動作を行うことを可能とする構成を、回路効率を損なうことなく簡素な回路構成で提供することを課題とする。   Therefore, the present invention provides a configuration that enables an appropriate protection operation by reducing an unnecessary circuit current at the time of a load short-circuit failure in an LED lighting circuit with a simple circuit configuration without impairing circuit efficiency. This is the issue.

本発明のＬＥＤ点灯回路は、ＬＥＤに直流電流を供給する直流電源回路と、直流電源回路の出力電流を検出する電流検出回路と、直流電源回路の出力電圧を検出する電圧検出回路と、電流検出回路によって検出された出力電流に対応する電流検出値が目標値で一定となるように直流電源回路の出力電流を制御するとともに、電圧検出回路によって検出された検出電圧が所定値未満となった場合に目標値を減少させる制御回路とを備える。   The LED lighting circuit of the present invention includes a DC power supply circuit that supplies a direct current to the LED, a current detection circuit that detects an output current of the DC power supply circuit, a voltage detection circuit that detects an output voltage of the DC power supply circuit, and a current detection When the output current of the DC power supply circuit is controlled so that the current detection value corresponding to the output current detected by the circuit is constant at the target value, and the detection voltage detected by the voltage detection circuit is less than the predetermined value And a control circuit for decreasing the target value.

本発明の他のＬＥＤ点灯回路は、ＬＥＤに直流電流を供給する直流電源回路と、直流電源回路の出力電流を所定の変換比で電流検出値に変換する電流検出回路と、直流電源回路の出力電圧を検出する電圧検出回路と、電流検出値が目標値で一定となるように直流電源回路の出力電流を制御するとともに、電圧検出回路によって検出された検出電圧が所定値未満となった場合に変換比を増加させる制御回路とを備える。   Another LED lighting circuit of the present invention includes a DC power supply circuit that supplies a direct current to the LED, a current detection circuit that converts an output current of the DC power supply circuit into a current detection value at a predetermined conversion ratio, and an output of the DC power supply circuit. The voltage detection circuit that detects the voltage and the output current of the DC power supply circuit is controlled so that the current detection value is constant at the target value, and the detected voltage detected by the voltage detection circuit is less than the predetermined value And a control circuit for increasing the conversion ratio.

上記の各ＬＥＤ点灯回路によると、負荷短絡時に直流電源回路の出力電流が直流電源回路側の制御により低減される。この構成においては、負荷短絡が誤検出された場合又は複数のＬＥＤの一部が短絡故障した場合には、正常なＬＥＤが消灯されることはなく、最小限の照明機能が維持される。従って、負荷短絡故障時に不要な回路電流が低減され適切な保護動作を行うことが可能となる。また、上記の目標値又は変換比の切替えのための構成はＬＥＤ電流の経路に追加の回路部品を必要としないので、通常点灯時及び保護動作時の回路効率が不要に損なわれることはなく、かつ簡素な回路構成となる。   According to each of the LED lighting circuits described above, the output current of the DC power supply circuit is reduced by the control on the DC power supply circuit side when the load is short-circuited. In this configuration, when a load short circuit is erroneously detected or when some of the plurality of LEDs have a short circuit failure, normal LEDs are not extinguished and a minimum illumination function is maintained. Therefore, an unnecessary circuit current is reduced at the time of a load short-circuit failure, and an appropriate protection operation can be performed. In addition, since the configuration for switching the target value or the conversion ratio does not require an additional circuit component in the LED current path, circuit efficiency during normal lighting and protection operation is not unnecessarily impaired. And it becomes a simple circuit structure.

本発明のＬＥＤ照明装置は、筐体に収容された上記ＬＥＤ点灯回路と、ＬＥＤが実装され、ＬＥＤ点灯回路に配線接続されたＬＥＤユニットとを備える。これにより、負荷短絡故障後も、負荷を修理又は交換すればＬＥＤ照明装置の使用を継続することができ、保守コストが低減される。   The LED lighting device of the present invention includes the LED lighting circuit housed in a housing, and an LED unit on which the LED is mounted and connected to the LED lighting circuit by wiring. Thereby, even after a load short-circuit failure, if the load is repaired or replaced, the use of the LED lighting device can be continued, and the maintenance cost is reduced.

本発明の実施形態によるＬＥＤ点灯回路を備えたＬＥＤ照明装置を示す図である。It is a figure which shows the LED lighting apparatus provided with the LED lighting circuit by embodiment of this invention. 本発明の変形例によるＬＥＤ点灯回路を備えたＬＥＤ照明装置を示す図である。It is a figure which shows the LED lighting apparatus provided with the LED lighting circuit by the modification of this invention.

実施形態．
図１に、本発明の実施形態によるＬＥＤ照明装置を示す。ＬＥＤ照明装置１はＬＥＤ点灯回路１００及びＬＥＤユニット２００からなる。ＬＥＤ点灯回路１００は交流電源ＡＣ（例えば、商用電源）からの交流入力を直流出力に変換し、配線Ｗ１及びＷ２を介して直流出力をＬＥＤユニット２００に供給する。ＬＥＤ点灯回路１００は筐体に内包される。 Embodiment.
FIG. 1 shows an LED lighting device according to an embodiment of the present invention. The LED lighting device 1 includes an LED lighting circuit 100 and an LED unit 200. The LED lighting circuit 100 converts an alternating current input from an alternating current power source AC (for example, commercial power source) into a direct current output, and supplies the direct current output to the LED unit 200 via the wirings W1 and W2. The LED lighting circuit 100 is included in the housing.

ＬＥＤ点灯回路１００は、入力端子Ｔ１及びＴ２と出力端子Ｔ３及びＴ４の間に、入力回路１１０、直流電源回路１２０、電流検出回路１３０、電圧検出回路１４０及び制御回路１５０を備える。出力端子Ｔ３及びＴ４にはそれぞれ配線Ｗ１及びＷ２が接続される。なお、本明細書における説明において、各回路素子が上記のどの回路に属するかは便宜的なものであり、本発明を拘束するものではない。   The LED lighting circuit 100 includes an input circuit 110, a DC power supply circuit 120, a current detection circuit 130, a voltage detection circuit 140, and a control circuit 150 between input terminals T1 and T2 and output terminals T3 and T4. Wirings W1 and W2 are connected to the output terminals T3 and T4, respectively. In the description in this specification, it is convenient for each circuit element to belong to which circuit, and the present invention is not bound thereto.

ＬＥＤユニット２００は入力端子Ｔ５及びＴ６を有し、入力端子Ｔ５−Ｔ６間にはＬＥＤ２０１が実装される。ＬＥＤ２０１のアノード端は、入力端子Ｔ５及び配線Ｗ１を介してＬＥＤ点灯回路１００の出力端子Ｔ３に接続され、ＬＥＤ２０１のカソード端は、入力端子Ｔ６及び配線Ｗ２を介して出力端子Ｔ４に接続される。なお、図１においては１つのＬＥＤ２０１が図示されているが、複数のＬＥＤ２０１が直列接続されていてもよい。   The LED unit 200 has input terminals T5 and T6, and an LED 201 is mounted between the input terminals T5 and T6. The anode end of the LED 201 is connected to the output terminal T3 of the LED lighting circuit 100 via the input terminal T5 and the wiring W1, and the cathode end of the LED 201 is connected to the output terminal T4 via the input terminal T6 and the wiring W2. In addition, although one LED 201 is illustrated in FIG. 1, a plurality of LEDs 201 may be connected in series.

ここで、以降の説明において、「負荷」とは、ＬＥＤ点灯回路１００の出力端子Ｔ３及びＴ４よりもＬＥＤユニット２００側の構成要素を総称したものと定義する。即ち、負荷は、ＬＥＤユニット２００、ＬＥＤ２０１並びに配線Ｗ１及びＷ２の１以上を含むものとする。従って、「負荷短絡」とは、ＬＥＤユニット２００内部でのＬＥＤ２０１の短絡、ＬＥＤユニット２００の端子Ｔ５−Ｔ６間又は配線Ｗ１−Ｗ２間の偶発的な短絡等を含むものとする。   Here, in the following description, “load” is defined as a general term for components on the LED unit 200 side of the output terminals T3 and T4 of the LED lighting circuit 100. That is, the load includes one or more of the LED unit 200, the LED 201, and the wirings W1 and W2. Therefore, the “load short circuit” includes a short circuit of the LED 201 inside the LED unit 200, an accidental short circuit between the terminals T5-T6 of the LED unit 200 or between the wirings W1-W2.

入力回路１１０は、電流ヒューズ１１１、コンデンサ１１２、ダイオードブリッジ１１３、コンデンサ１１４、及び必要に応じてノイズフィルタを備える。入力回路１１０には交流電源ＡＣからの交流電圧が入力され、ダイオードブリッジ１１３による全波整流出力が出力される。   The input circuit 110 includes a current fuse 111, a capacitor 112, a diode bridge 113, a capacitor 114, and a noise filter as necessary. An AC voltage from the AC power supply AC is input to the input circuit 110, and a full-wave rectified output from the diode bridge 113 is output.

直流電源回路１２０は、本実施形態では絶縁型フライバックコンバータからなり、力率改善機能を持つ所謂ワンコンバータ方式のフライバック降圧回路を構成する。直流電源回路１２０は、トランス１２１、スイッチング素子１２２、ダイオード１２３及び平滑コンデンサ１２４を備える。スイッチング素子１２２のオン期間にトランス１２１の一次巻線１２１ａによって全波整流出力からのエネルギーが蓄積され、スイッチング素子１２２のオフ期間にそのエネルギーが二次巻線１２１ｂ側からダイオード１２３を介して平滑コンデンサ１２４に充電される。トランス１２１における一次電圧から二次電圧への降圧比は一次巻線１２１ａに対する二次巻線１２１ｂの巻数比によって決まり、出力電流値はスイッチング素子１２２のオンデューティ（オン期間幅）によって決まる。   In the present embodiment, the DC power supply circuit 120 is composed of an isolated flyback converter, and constitutes a so-called one-converter flyback step-down circuit having a power factor correction function. The DC power supply circuit 120 includes a transformer 121, a switching element 122, a diode 123, and a smoothing capacitor 124. The energy from the full-wave rectified output is accumulated by the primary winding 121a of the transformer 121 during the ON period of the switching element 122, and the smoothing capacitor passes through the diode 123 from the secondary winding 121b side during the OFF period of the switching element 122. 124 is charged. The step-down ratio from the primary voltage to the secondary voltage in the transformer 121 is determined by the turn ratio of the secondary winding 121b to the primary winding 121a, and the output current value is determined by the on-duty (on period width) of the switching element 122.

電流検出回路１３０は低抵抗素子からなる電流検出抵抗（以下、「電流検出抵抗１３０」ともいう）からなり、ＬＥＤ２０１に直列接続される。ＬＥＤ２０１に流れるＬＥＤ電流ＩＬＥＤは、電流検出抵抗１３０の抵抗値Ｒ１３０で決まる変換比で電流検出値（＝ＩＬＥＤ×Ｒ１３０）に変換される。 The current detection circuit 130 includes a current detection resistor (hereinafter, also referred to as “current detection resistor 130”) made of a low resistance element, and is connected in series to the LED 201. The LED current I LED flowing through the LED 201 is converted into a current detection value (= I LED × R 130 ) at a conversion ratio determined by the resistance value R 130 of the current detection resistor 130.

電圧検出回路１４０は分圧回路からなり、平滑コンデンサ１２４に並列接続された分圧抵抗１４１及び１４２並びにコンデンサ１４３からなる。コンデンサ１４３は分圧ノードＮ１の過渡的な電圧変動を平滑化するために設けられる。なお、図１においては、高電位側の分圧抵抗１４１を１つの抵抗素子で示しているが、分圧抵抗１４１は直列接続された複数の抵抗素子からなるものであってもよい。   The voltage detection circuit 140 includes a voltage dividing circuit, and includes voltage dividing resistors 141 and 142 and a capacitor 143 connected in parallel to the smoothing capacitor 124. Capacitor 143 is provided to smooth transient voltage fluctuations at voltage dividing node N1. In FIG. 1, the voltage dividing resistor 141 on the high potential side is shown as one resistor element, but the voltage dividing resistor 141 may be composed of a plurality of resistor elements connected in series.

制御回路１５０は、トランス１２１の三次巻線１２１ｃ、ダイオード１５１、コンデンサ１５２、抵抗１５３、オペアンプ１５４、帰還素子１５５、抵抗１５６、フォトカプラ１５７、ＰＷＭ制御回路１５８、抵抗１５９、シャントレギュレータ１６０、抵抗１６１〜１６３、トランジスタ１６４〜１６５、抵抗１６６及びツェナーダイオード１６７を備える。   The control circuit 150 includes a tertiary winding 121c of the transformer 121, a diode 151, a capacitor 152, a resistor 153, an operational amplifier 154, a feedback element 155, a resistor 156, a photocoupler 157, a PWM control circuit 158, a resistor 159, a shunt regulator 160, and a resistor 161. 163, transistors 164 to 165, a resistor 166, and a Zener diode 167.

トランス１２１の一次電圧が、一次巻線１２１ａに対する三次巻線１２１ｃの巻数比に応じて降圧され、この降圧電圧がダイオード１５１を介してコンデンサ１５２に充電される。これにより、制御回路１５０の制御電源が確保される。   The primary voltage of the transformer 121 is stepped down in accordance with the turn ratio of the tertiary winding 121c with respect to the primary winding 121a, and the stepped down voltage is charged to the capacitor 152 via the diode 151. Thereby, the control power supply of the control circuit 150 is ensured.

オペアンプ１５４の負入力端子（−）には、電流検出回路１３０からの電流検出値が抵抗１５３を介して入力され、オペアンプ１５４の正入力端子（＋）には、後述する目標値が入力される。オペアンプ１５４の負入力端子と出力端子間には帰還素子１５５（本実施形態においては抵抗とコンデンサの直列回路）が接続され、負入力端子電圧と正入力端子電圧の誤差が出力端子において出力される。オペアンプ１５４の出力はフォトカプラ１５７の入力フォトダイオードのカソードに接続される。フォトカプラ１５７の入力フォトダイオードのアノードは抵抗１５６を介して制御電源に接続される。フォトカプラ１５７では、制御電源から抵抗１５６を介して入力フォトダイオードに流れる電流に応じて出力フォトトランジスタの出力状態が決定され、その出力がＰＷＭ制御回路１５８に入力される。   A current detection value from the current detection circuit 130 is input to the negative input terminal (−) of the operational amplifier 154 via the resistor 153, and a target value to be described later is input to the positive input terminal (+) of the operational amplifier 154. . A feedback element 155 (in this embodiment, a series circuit of a resistor and a capacitor) is connected between the negative input terminal and the output terminal of the operational amplifier 154, and an error between the negative input terminal voltage and the positive input terminal voltage is output at the output terminal. . The output of the operational amplifier 154 is connected to the cathode of the input photodiode of the photocoupler 157. The anode of the input photodiode of the photocoupler 157 is connected to the control power supply via the resistor 156. In the photocoupler 157, the output state of the output phototransistor is determined according to the current flowing from the control power supply to the input photodiode via the resistor 156, and the output is input to the PWM control circuit 158.

ＰＷＭ制御回路１５８は一般的なＬＥＤドライバＩＣ及びその周辺回路からなる。ＰＷＭ制御回路１５８はフォトカプラ１５７の出力状態に基づくオン幅でスイッチング素子１２２をＰＷＭ制御する。これにより、制御回路１５０によって、電流検出値が目標値で一定となるように直流電源回路１２０の出力がフィードバック制御され、即ち、定電流制御が行われる。   The PWM control circuit 158 includes a general LED driver IC and its peripheral circuits. The PWM control circuit 158 performs PWM control of the switching element 122 with an ON width based on the output state of the photocoupler 157. Thereby, the control circuit 150 performs feedback control of the output of the DC power supply circuit 120 so that the detected current value becomes constant at the target value, that is, constant current control is performed.

シャントレギュレータ１６０は抵抗１５９を介して制御電源に接続される。オペアンプ１５４の正入力端子に入力される目標値は、シャントレギュレータ１６０の出力電圧（以下、「基準電圧」という）の分圧値によって決定され、その分圧値はトランジスタ１６４の動作状態によって決まる。トランジスタ１６４のオフ時には基準電圧が抵抗１６１及び１６２によって分圧され、抵抗１６２に発生する電圧がオペアンプ１５４の正入力端子に目標値として入力される。一方、トランジスタ１６４のオン時には基準電圧が抵抗１６１、１６２及び１６３によって分圧され、抵抗１６２及び１６３の並列回路に発生する電圧がオペアンプ１５４の正入力端子に目標値として入力される。   The shunt regulator 160 is connected to the control power supply via the resistor 159. The target value input to the positive input terminal of the operational amplifier 154 is determined by the divided value of the output voltage (hereinafter referred to as “reference voltage”) of the shunt regulator 160, and the divided value is determined by the operating state of the transistor 164. When the transistor 164 is off, the reference voltage is divided by the resistors 161 and 162, and the voltage generated in the resistor 162 is input to the positive input terminal of the operational amplifier 154 as a target value. On the other hand, when the transistor 164 is on, the reference voltage is divided by the resistors 161, 162, and 163, and the voltage generated in the parallel circuit of the resistors 162 and 163 is input to the positive input terminal of the operational amplifier 154 as a target value.

トランジスタ１６４の動作状態はトランジスタ１６５の動作状態によって決まる。即ち、トランジスタ１６５がオン状態の場合には、トランジスタ１６４の制御端子と出力端子が短絡され、トランジスタ１６４はオフ状態となる。一方、トランジスタ１６５がオフ状態の場合には、トランジスタ１６４の制御端子には抵抗１６６を介して制御電源が供給され、トランジスタ１６４はオン状態となる。なお、本明細書において、トランジスタの制御端子、入力端子及び出力端子とは、トランジスタがバイポーラトランジスタの場合にはそれぞれベース端子、コレクタ端子及びエミッタ端子のことをいい、ＦＥＴの場合にはそれぞれゲート端子、ドレイン端子及びソース端子のことをいうものとする。   The operation state of the transistor 164 depends on the operation state of the transistor 165. That is, when the transistor 165 is on, the control terminal and the output terminal of the transistor 164 are short-circuited, and the transistor 164 is turned off. On the other hand, when the transistor 165 is off, control power is supplied to the control terminal of the transistor 164 via the resistor 166, and the transistor 164 is turned on. In this specification, the control terminal, input terminal, and output terminal of a transistor refer to a base terminal, a collector terminal, and an emitter terminal, respectively, when the transistor is a bipolar transistor, and a gate terminal when the transistor is an FET. , Drain terminal and source terminal.

トランジスタ１６５の動作状態は電圧検出回路１４０の出力状態によって決まる。即ち、直流電源回路１２０の出力電圧が所定値以上の場合には、ツェナーダイオード１６７がオン状態となり、かつそのアノード電圧がトランジスタ１６５の閾値以上となり、トランジスタ１６５がオン状態となる。一方、直流電源回路１２０の出力電圧が所定値未満の場合には、ツェナーダイオード１６７がオフ状態となり、又はオン状態であってもそのアノード電圧がトランジスタ１６５の閾値未満となり、トランジスタ１６５がオフ状態となる。言い換えると、負荷が正常な出力電圧で駆動されている場合にはトランジスタ１６５がオンし、負荷電圧の異常な低下が検出された場合にトランジスタ１６５がオフするように、ツェナーダイオード１６７のツェナー電圧が決定される。   The operation state of the transistor 165 is determined by the output state of the voltage detection circuit 140. That is, when the output voltage of the DC power supply circuit 120 is equal to or higher than a predetermined value, the Zener diode 167 is turned on, and its anode voltage is equal to or higher than the threshold value of the transistor 165, so that the transistor 165 is turned on. On the other hand, when the output voltage of the DC power supply circuit 120 is less than a predetermined value, the Zener diode 167 is turned off, or the anode voltage is less than the threshold value of the transistor 165 even when it is turned on, and the transistor 165 is turned off. Become. In other words, the zener voltage of the zener diode 167 is such that the transistor 165 is turned on when the load is driven with a normal output voltage, and the transistor 165 is turned off when an abnormal drop in the load voltage is detected. It is determined.

上記をまとめると、負荷が正常に駆動されている場合、電圧検出回路１４０の抵抗１４２の電圧によってトランジスタ１６５がオン状態、トランジスタ１６４がオフ状態となり、基準電圧が抵抗１６１及び１６２によって分圧される。これにより、通常出力用の分圧値がオペアンプ１５４の正入力端子に目標値として入力される。一方、負荷短絡故障が発生し、直流電源回路１２０の出力電圧が所定値未満となった場合、トランジスタ１６５がオフ状態、トランジスタ１６４がオン状態となり、基準電圧が抵抗１６１、１６２及び１６３によって分圧される。これにより、出力電流低減用の低い分圧値が目標値としてオペアンプ１５４の正入力端子に入力される。   In summary, when the load is driven normally, the transistor 165 is turned on and the transistor 164 is turned off by the voltage of the resistor 142 of the voltage detection circuit 140, and the reference voltage is divided by the resistors 161 and 162. . As a result, the divided voltage value for normal output is input to the positive input terminal of the operational amplifier 154 as a target value. On the other hand, when a load short circuit failure occurs and the output voltage of the DC power supply circuit 120 becomes less than a predetermined value, the transistor 165 is turned off, the transistor 164 is turned on, and the reference voltage is divided by the resistors 161, 162, and 163. Is done. As a result, a low voltage division value for reducing the output current is input to the positive input terminal of the operational amplifier 154 as a target value.

このように、制御回路１５０は、電流検出回路１３０によるＬＥＤ電流の検出値が目標値で一定となるように直流電源回路１２０の出力電流を制御するとともに、電圧検出回路１４０による検出電圧が所定値未満となった場合に目標値を減少させる。即ち、負荷において短絡故障が発生して直流電源回路１２０の出力電圧が所定値未満となった場合、制御回路１５０において定電流制御の目標値が低減される。これにより、負荷短絡時に、スイッチング素子１２２の駆動におけるＰＷＭ幅（オンデューティ）が減少し、直流電源回路１２０の出力電流が低減される。   In this way, the control circuit 150 controls the output current of the DC power supply circuit 120 so that the detected value of the LED current by the current detecting circuit 130 is constant at the target value, and the detected voltage by the voltage detecting circuit 140 is a predetermined value. Decrease target value when less than. That is, when a short circuit failure occurs in the load and the output voltage of the DC power supply circuit 120 becomes less than a predetermined value, the control circuit 150 reduces the target value for constant current control. Thereby, when the load is short-circuited, the PWM width (on duty) in driving the switching element 122 is reduced, and the output current of the DC power supply circuit 120 is reduced.

従って、負荷短絡時に不要な回路電流が抑制される。この構成においては、負荷短絡が誤検出された場合には正常なＬＥＤが消灯されずに減光駆動され、最小限の照明機能が維持される。即ち、ＬＥＤ２０１が正常であるにもかかわらずノイズ等の外乱によって保護動作が行われたとしてもＬＥＤ２０１は減光点灯され、消灯されることはない。そして、誤検出状態をもたらすノイズ等の外乱が除去された後は再び通常点灯が行われる。このように、ＬＥＤ点灯回路１００によると、負荷短絡時の適切な保護動作が実現される。   Therefore, unnecessary circuit current is suppressed when the load is short-circuited. In this configuration, when a load short circuit is erroneously detected, a normal LED is not turned off but is dimmed and the minimum illumination function is maintained. That is, even if the LED 201 is normal, even if the protection operation is performed due to disturbance such as noise, the LED 201 is dimmed and not turned off. Then, after the disturbance such as noise causing the erroneous detection state is removed, the normal lighting is performed again. Thus, according to the LED lighting circuit 100, an appropriate protection operation when a load is short-circuited is realized.

また、上記においては、負荷短絡の一態様としてＬＥＤ２０１全体の短絡を検出するように出力電圧検出における所定値が決定されるものとした。ここで、ＬＥＤ２０１が複数の直列接続されたＬＥＤ素子からなる場合には、その一部短絡時の出力電圧が所定値に相当するように電圧検出回路１４０の分圧比が決定されてもよい。この場合、ＬＥＤ２０１の一部が短絡故障して出力電圧が所定値未満となった場合には、残りのＬＥＤについて減光点灯が行われることになる。ここで、一部のＬＥＤが短絡した場合に、仮に残りの正常なＬＥＤが定格電流で点灯されたとしてもＬＥＤユニット２００全体としては設計照度を出力していることにはならないため、ＬＥＤユニット２００は交換されることが望ましい。上記実施形態では、残りの正常なＬＥＤが減光駆動されるので、残りの正常なＬＥＤが定格駆動される場合よりも、ＬＥＤユニット２００の照度はさらに低下する。このように、ＬＥＤ２０１の一部短絡時に、ＬＥＤ点灯回路１００はＬＥＤユニット２００を非常に低い照度で減光駆動させるので、ユーザに対して最低限の照明機能を提供しつつもＬＥＤユニット２００の故障を報知し、その交換を促すことができる。   Moreover, in the above, the predetermined value in output voltage detection shall be determined so that the short circuit of the whole LED201 may be detected as one aspect | mode of load short circuit. Here, when the LED 201 is composed of a plurality of LED elements connected in series, the voltage dividing ratio of the voltage detection circuit 140 may be determined so that the output voltage when the LED 201 is partially short-circuited corresponds to a predetermined value. In this case, when a part of the LED 201 is short-circuited and the output voltage becomes less than a predetermined value, dimming lighting is performed for the remaining LEDs. Here, when some LEDs are short-circuited, even if the remaining normal LEDs are lit at the rated current, the LED unit 200 as a whole does not output the design illuminance. Is preferably replaced. In the above embodiment, since the remaining normal LEDs are driven to dimm, the illuminance of the LED unit 200 is further reduced as compared with the case where the remaining normal LEDs are rated-driven. As described above, when the LED 201 is partially short-circuited, the LED lighting circuit 100 causes the LED unit 200 to be dimmed at a very low illuminance, so that the failure of the LED unit 200 is provided while providing a minimum illumination function to the user. Can be urged to be exchanged.

また、制御回路１５０における目標値の切替えのための構成はＬＥＤ電流の経路上に追加の回路部品を必要としないので、通常点灯時及び保護動作時の回路効率が不要に損なわれることはない。言い換えると、ＬＥＤ電流の経路上に定格電流又は定格電力の高い部品を配置する必要がなく、回路の大型化及び高コスト化が回避される。   In addition, since the configuration for switching the target value in the control circuit 150 does not require an additional circuit component on the LED current path, circuit efficiency during normal lighting and protection operation is not unnecessarily impaired. In other words, it is not necessary to arrange a part having a high rated current or high power on the LED current path, and an increase in circuit size and cost can be avoided.

上述したように、負荷短絡時においても、直流電源回路１２０が過負荷となることはなく、ＬＥＤ点灯回路１００の故障が誘引されることはない。即ち、短絡故障した負荷（例えば、ＬＥＤユニット２００）が修理又は交換された後は、ＬＥＤ点灯回路１００を含むＬＥＤ照明装置１は負荷短絡故障前と同様に使用可能である。このように、ＬＥＤ照明装置１において、負荷短絡故障時に、ＬＥＤ点灯回路１００の修理又は交換が必要となることがないため、保守コストの低減が実現される。例えば、ＬＥＤ点灯回路１００が地面に立設されたポール部に内蔵されるとともにＬＥＤユニット２００がポール部の上方端部の灯具部に配置される道路灯等のようにＬＥＤ点灯回路１００とＬＥＤユニット２００が別置されるＬＥＤ照明装置において、上記の保守容易性は特に有利なものとなる。   As described above, even when the load is short-circuited, the DC power supply circuit 120 is not overloaded, and a failure of the LED lighting circuit 100 is not induced. In other words, after a load having a short circuit failure (for example, the LED unit 200) is repaired or replaced, the LED lighting device 1 including the LED lighting circuit 100 can be used in the same manner as before the load short circuit failure. As described above, in the LED lighting device 1, it is not necessary to repair or replace the LED lighting circuit 100 when a load short-circuit failure occurs, so that the maintenance cost can be reduced. For example, the LED lighting circuit 100 and the LED unit, such as a road lamp in which the LED lighting circuit 100 is built in a pole portion standing on the ground and the LED unit 200 is disposed in a lamp portion at the upper end of the pole portion. In the LED lighting device in which 200 is separately provided, the above-described ease of maintenance is particularly advantageous.

変形例．
上記実施形態では、検出電圧が所定値未満となった場合にオペアンプ１５４の正入力端子の入力値、即ち、目標値を低減する構成を示したが、本変形例では、オペアンプ１５４の負入力端子の入力値、即ち、電流検出値側を増加させる構成を示す。 Modified example.
In the above-described embodiment, the configuration has been described in which the input value of the positive input terminal of the operational amplifier 154, that is, the target value is reduced when the detection voltage becomes less than the predetermined value. However, in this modification, the negative input terminal of the operational amplifier 154 is shown. The structure which increases the input value of, ie, the electric current detection value side, is shown.

図２に、本発明の変形例によるＬＥＤ点灯回路を備えたＬＥＤ照明装置を示す。本変形例のＬＥＤ照明回路１００は制御回路の構成が上記実施形態のものと異なる。なお、実施形態と同様の構成要素には同様の符号を付し、その詳細な説明を省略する。本変形例のＬＥＤ照明装置１はＬＥＤ点灯回路１００及びＬＥＤユニット２００からなり、ＬＥＤ点灯回路１００は、入力回路１１０、直流電源回路１２０、電流検出回路１３０、電圧検出回路１４０及び制御回路１７０を備える。   FIG. 2 shows an LED lighting device including an LED lighting circuit according to a modification of the present invention. The LED illumination circuit 100 of this modification is different from that of the above embodiment in the configuration of the control circuit. In addition, the same code | symbol is attached | subjected to the component similar to embodiment, and the detailed description is abbreviate | omitted. The LED lighting device 1 according to this modification includes an LED lighting circuit 100 and an LED unit 200. The LED lighting circuit 100 includes an input circuit 110, a DC power supply circuit 120, a current detection circuit 130, a voltage detection circuit 140, and a control circuit 170. .

制御回路１７０は、トランス１２１の三次巻線１２１ｃ、ダイオード１５１、コンデンサ１５２、オペアンプ１５４、帰還素子１５５、抵抗１５６、フォトカプラ１５７、ＰＷＭ制御回路１５８、抵抗１５９、シャントレギュレータ１６０、抵抗１６１及び１６２、ツェナーダイオード１６７、抵抗１７１及び１７２並びにトランジスタ１７３を備える。   The control circuit 170 includes a tertiary winding 121c of the transformer 121, a diode 151, a capacitor 152, an operational amplifier 154, a feedback element 155, a resistor 156, a photocoupler 157, a PWM control circuit 158, a resistor 159, a shunt regulator 160, resistors 161 and 162, A Zener diode 167, resistors 171 and 172, and a transistor 173 are provided.

オペアンプ１５４の負入力端子（−）には、後述する電流検出値が入力され、オペアンプ１５４の正入力端子（＋）には、目標値が入力される。目標値は、基準電圧の抵抗１６１及び１６２による分圧値、即ち、抵抗１６２に発生する電圧である。オペアンプ１５４の負入力端子と出力端子間には帰還素子１５５（本実施形態においては抵抗とコンデンサの直列回路）が接続され、負入力端子電圧と正入力端子電圧の誤差が出力端子において出力される。   A current detection value described later is input to the negative input terminal (−) of the operational amplifier 154, and a target value is input to the positive input terminal (+) of the operational amplifier 154. The target value is a divided value of the reference voltage by the resistors 161 and 162, that is, a voltage generated in the resistor 162. A feedback element 155 (in this embodiment, a series circuit of a resistor and a capacitor) is connected between the negative input terminal and the output terminal of the operational amplifier 154, and an error between the negative input terminal voltage and the positive input terminal voltage is output at the output terminal. .

電流検出値は、電流検出抵抗１３０によって検出される電圧と、トランジスタ１７３の動作状態によって決まる。トランジスタ１７３がオン状態の場合には、電流検出抵抗１３０に発生する電圧が抵抗１７１及び１７２で分圧され、抵抗１７２に発生する電圧が電流検出値となる。一方、トランジスタ１７３がオフ状態の場合には、電流検出抵抗１３０に発生する電圧が電流検出値となる。即ち、直流電源回路１２０の出力電流（即ち、ＬＥＤ電流）から電流検出値への変換比は、トランジスタ１７３がオンの場合を１とすると、トランジスタ１７３がオフの場合には（Ｒ１７１＋Ｒ１７２）／Ｒ１７２となる。なお、Ｒ１７１及びＲ１７２はそれぞれ抵抗１７１及び抵抗１７２の抵抗値である。即ち、トランジスタ１７３のオン時よりもオフ時において上記変換比が増加する。 The current detection value is determined by the voltage detected by the current detection resistor 130 and the operating state of the transistor 173. When the transistor 173 is on, the voltage generated in the current detection resistor 130 is divided by the resistors 171 and 172, and the voltage generated in the resistor 172 becomes the current detection value. On the other hand, when the transistor 173 is off, the voltage generated in the current detection resistor 130 becomes the current detection value. That is, the conversion ratio from the output current (that is, the LED current) of the DC power supply circuit 120 to the current detection value is 1 when the transistor 173 is on, and (R 171 + R 172 ) when the transistor 173 is off. / R 172 . R 171 and R 172 are resistance values of the resistor 171 and the resistor 172, respectively. That is, the conversion ratio increases when the transistor 173 is off rather than on.

トランジスタ１７３の動作状態は電圧検出回路１４０の出力状態によって決まる。即ち、直流電源回路１２０の出力電圧が所定値以上の場合には、ツェナーダイオード１６７がオン状態となり、かつそのアノード電圧がトランジスタ１７３の閾値以上となり、トランジスタ１７３がオン状態となる。一方、直流電源回路１２０の出力電圧が所定値未満の場合には、ツェナーダイオード１６７がオフ状態となり、又はオン状態であってもそのアノード電圧がトランジスタ１７３の閾値未満となり、トランジスタ１７３がオフ状態となる。言い換えると、負荷であるＬＥＤユニット２００が正常駆動されている場合にはトランジスタ１７３がオン状態となり、ＬＥＤユニット２００の電圧に異常な低下が検出された場合にトランジスタ１７３がオフ状態となるように、ツェナーダイオード１６７のツェナー電圧が決定される。   The operation state of the transistor 173 is determined by the output state of the voltage detection circuit 140. That is, when the output voltage of the DC power supply circuit 120 is equal to or higher than a predetermined value, the Zener diode 167 is turned on, and its anode voltage is equal to or higher than the threshold value of the transistor 173, so that the transistor 173 is turned on. On the other hand, when the output voltage of the DC power supply circuit 120 is less than a predetermined value, the Zener diode 167 is turned off, or even when the Zener diode 167 is turned on, the anode voltage is less than the threshold value of the transistor 173 and the transistor 173 is turned off. Become. In other words, the transistor 173 is turned on when the LED unit 200 as a load is normally driven, and the transistor 173 is turned off when an abnormal drop in the voltage of the LED unit 200 is detected. A Zener voltage of the Zener diode 167 is determined.

上記をまとめると、負荷が正常に駆動される場合、電圧検出回路１４０の抵抗１４２の電圧によってトランジスタ１７３がオン状態となり、電流検出抵抗１３０に発生する電圧の抵抗１７１及び１７２による分圧値がオペアンプ１５４の負入力端子に入力される。一方、負荷短絡故障が発生し、直流電源回路１２０の出力電圧が所定値未満となった場合、トランジスタ１７３がオフ状態となり、電流検出抵抗１３０に発生する電圧がオペアンプ１５４の負入力端子に入力される。これにより、負荷短絡故障時には、正常時よりも高い変換比で電流検出値がオペアンプ１５４の負入力端子に入力される。   In summary, when the load is driven normally, the transistor 173 is turned on by the voltage of the resistor 142 of the voltage detection circuit 140, and the voltage divided by the resistors 171 and 172 of the voltage generated in the current detection resistor 130 is the operational amplifier. 154 is input to the negative input terminal. On the other hand, when a load short-circuit failure occurs and the output voltage of the DC power supply circuit 120 becomes less than a predetermined value, the transistor 173 is turned off, and the voltage generated in the current detection resistor 130 is input to the negative input terminal of the operational amplifier 154. The Thereby, at the time of a load short-circuit failure, the current detection value is input to the negative input terminal of the operational amplifier 154 at a higher conversion ratio than in the normal state.

このように、制御回路１７０は、電流検出回路１３０によるＬＥＤ電流の検出値が目標値で一定となるように直流電源回路１２０の出力電流を制御するとともに、電圧検出回路１４０による検出電圧が所定値未満となった場合に電流検出抵抗１３０における検出電流から電流検出値への変換比を増加させる。即ち、負荷短絡故障が発生して直流電源回路１２０の出力電圧が所定値未満となった場合、制御回路１７０において定電流制御における電流検出値が過大評価される。従って、負荷短絡時に、直流電源回路１２０のスイッチング素子１２２の駆動におけるＰＷＭ幅（オンデューティ）が減少し、直流電源回路１２０の出力電流が低減される。これにより、本変形例においても上記実施形態と同様の効果を得ることができる。また、制御回路１７０における上記変換比の切替えのための構成はＬＥＤ電流の経路上に追加の回路部品を必要としないので、通常点灯時及び保護動作時の回路効率が不要に損なわれることはない。言い換えると、上記実施形態と同様に、ＬＥＤ電流の経路上に定格電流又は定格電力の高い部品を配置する必要がなく、回路の大型化及び高コスト化が回避される。   As described above, the control circuit 170 controls the output current of the DC power supply circuit 120 so that the detection value of the LED current by the current detection circuit 130 is constant at the target value, and the detection voltage by the voltage detection circuit 140 is a predetermined value. When it becomes less than, the conversion ratio from the detection current to the current detection value in the current detection resistor 130 is increased. That is, when a load short circuit failure occurs and the output voltage of the DC power supply circuit 120 becomes less than a predetermined value, the control circuit 170 overestimates the current detection value in constant current control. Therefore, when the load is short-circuited, the PWM width (on duty) in driving the switching element 122 of the DC power supply circuit 120 is reduced, and the output current of the DC power supply circuit 120 is reduced. Thereby, also in this modification, the effect similar to the said embodiment can be acquired. Further, since the configuration for switching the conversion ratio in the control circuit 170 does not require an additional circuit component on the LED current path, circuit efficiency during normal lighting and protection operation is not unnecessarily impaired. . In other words, similarly to the above-described embodiment, it is not necessary to arrange a part having a high rated current or high rated power on the LED current path, and an increase in circuit size and cost can be avoided.

なお、上記において本発明の最も好適な実施形態等を示したが、本発明は上記構成に限られず、さらに種々の変形が可能である。   Although the most preferred embodiment of the present invention has been described above, the present invention is not limited to the above configuration, and various modifications can be made.

（１）入力回路及び直流電源回路の変形
上記実施形態及び変形例では直流電源回路に交流電圧が入力される構成を示したが、バッテリ等の直流電圧が入力される構成にも本発明は適用可能である。この場合、入力回路１１０の特に整流回路１１３は不要となり、直流電源回路１２０はＤＣ／ＤＣコンバータとなる。また、上記実施形態及び変形例では、直流電源回路１２０が絶縁型フライバック回路からなる構成を示したが、直流電力を出力することができれば他の方式のコンバータ回路からなるものであってもよい。例えば、絶縁型フライバック回路の前段に力率改善回路（昇圧チョッパ回路）を設け、フライバック回路には降圧機能のみを持たせる構成としてもよいし、絶縁型フライバック回路の代わりに非絶縁型の降圧チョッパ回路を用いる構成としてもよい。 (1) Modification of input circuit and DC power supply circuit In the above-described embodiment and modification, a configuration in which an AC voltage is input to the DC power supply circuit has been described, but the present invention is also applied to a configuration in which a DC voltage such as a battery is input. Is possible. In this case, the rectifier circuit 113 of the input circuit 110 is unnecessary, and the DC power supply circuit 120 is a DC / DC converter. Moreover, in the said embodiment and modification, although the direct-current power supply circuit 120 showed the structure which consists of an insulation type flyback circuit, if it can output direct-current power, it may consist of a converter circuit of another system. . For example, a power factor correction circuit (boost chopper circuit) may be provided in front of the isolated flyback circuit, and the flyback circuit may have only a step-down function, or a non-insulated type instead of the isolated flyback circuit The step-down chopper circuit may be used.

（２）制御回路の変形
上記実施形態及び変形例をそれぞれ個別の回路として示したが、実施形態の制御回路１５０と変形例の制御回路１７０を組み合わせて採用してもよい。即ち、電圧検出回路１４０による検出電圧が所定値未満となった場合に目標値を減少させるとともに、電流検出抵抗１３０における検出電流から電流検出値への変換比を増加させるように制御回路が構成されてもよい。 (2) Modification of Control Circuit Although the above embodiment and the modification are shown as individual circuits, the control circuit 150 according to the embodiment and the control circuit 170 according to the modification may be used in combination. That is, the control circuit is configured to decrease the target value and increase the conversion ratio from the detected current to the detected current value in the current detection resistor 130 when the detection voltage by the voltage detection circuit 140 becomes less than a predetermined value. May be.

１ ＬＥＤ照明装置
１００ ＬＥＤ点灯回路
１２０ 直流電源回路
１３０ 電流検出回路
１４０ 電圧検出回路
１５０、１７０ 制御回路
２００ ＬＥＤユニット
２０１ ＬＥＤ DESCRIPTION OF SYMBOLS 1 LED lighting apparatus 100 LED lighting circuit 120 DC power supply circuit 130 Current detection circuit 140 Voltage detection circuit 150, 170 Control circuit 200 LED unit 201 LED

Claims (2)

ＬＥＤ点灯回路であって、
ＬＥＤに直流電流を供給する直流電源回路と、
前記直流電源回路の出力電流を所定の変換比で電流検出値に変換する電流検出回路と、
前記直流電源回路の出力電圧を検出する電圧検出回路と、
前記電流検出値が目標値で一定となるように前記直流電源回路の出力電流を制御するとともに、前記電圧検出回路によって検出された検出電圧が所定値未満となった場合に前記変換比を増加させる制御回路と
を備え、
前記電流検出回路が、前記ＬＥＤに直列接続された電流検出抵抗を備え、
前記制御回路がオペアンプと、第１の抵抗、第２の抵抗及びトランジスタの直列回路と、ツェナーダイオードとを備え、前記直列回路が前記電流検出抵抗に並列接続され、前記オペアンプの負入力端子が前記第１の抵抗と第２の抵抗の接続点に接続されるとともに前記第１の抵抗を介して前記電流検出抵抗に接続され、前記オペアンプの正入力端子に前記目標値が入力され、前記トランジスタの制御端子に前記ツェナーダイオードを介して前記検出電圧が入力され、前記トランジスタが、前記検出電圧が前記所定値以上の場合にオンし、前記検出電圧が前記所定値未満の場合にオフするように構成され、前記オペアンプの出力に応じて前記直流電源回路が制御されるように構成された、ＬＥＤ点灯回路。 An LED lighting circuit,
A DC power supply circuit for supplying a direct current to the LED;
A current detection circuit that converts an output current of the DC power supply circuit into a current detection value at a predetermined conversion ratio; and
A voltage detection circuit for detecting an output voltage of the DC power supply circuit;
The output current of the DC power supply circuit is controlled so that the detected current value is constant at a target value, and the conversion ratio is increased when the detected voltage detected by the voltage detecting circuit becomes less than a predetermined value. for example Bei and a control circuit,
The current detection circuit includes a current detection resistor connected in series to the LED;
The control circuit includes an operational amplifier, a series circuit of a first resistor, a second resistor and a transistor, and a Zener diode, the series circuit is connected in parallel to the current detection resistor, and a negative input terminal of the operational amplifier is Connected to the connection point of the first resistor and the second resistor and connected to the current detection resistor via the first resistor, the target value is input to the positive input terminal of the operational amplifier, The detection voltage is input to the control terminal via the Zener diode, and the transistor is turned on when the detection voltage is equal to or higher than the predetermined value, and is turned off when the detection voltage is lower than the predetermined value. And an LED lighting circuit configured to control the DC power supply circuit in accordance with an output of the operational amplifier . 筐体に収容された請求項１に記載のＬＥＤ点灯回路と、
前記ＬＥＤが実装され、前記ＬＥＤ点灯回路に対して着脱可能なＬＥＤユニットと
を備えたＬＥＤ照明装置。
The LED lighting circuit according to claim 1 housed in a housing;
An LED lighting device comprising: an LED unit mounted with the LED and detachable from the LED lighting circuit.
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