JPWO2017175806A1 - LED drive circuit - Google Patents

LED drive circuit Download PDF

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JPWO2017175806A1
JPWO2017175806A1 JP2018510644A JP2018510644A JPWO2017175806A1 JP WO2017175806 A1 JPWO2017175806 A1 JP WO2017175806A1 JP 2018510644 A JP2018510644 A JP 2018510644A JP 2018510644 A JP2018510644 A JP 2018510644A JP WO2017175806 A1 JPWO2017175806 A1 JP WO2017175806A1
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led
current
circuit
voltage
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JP6818013B2 (en
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後藤　聡
聡 後藤
達郎 山田
達郎 山田
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Citizen Electronics Co Ltd
Citizen Watch Co Ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
    • H05B47/10—Controlling the light source

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Abstract

ＬＥＤ駆動回路は、調光に連動して出力が変化する電源に接続された整流回路と、整流回路に接続され、複数のＬＥＤが直列に接続された第１ＬＥＤ列と、整流回路に対して第１ＬＥＤ列と並列に接続され、複数のＬＥＤが直列に接続された第２ＬＥＤ列と、第２ＬＥＤ列と直列に接続され、複数のＬＥＤが直列に接続された第３ＬＥＤ列と、第２ＬＥＤ列と第３ＬＥＤ列との間に一端が接続され、複数のＬＥＤが直列に接続された第４ＬＥＤ列と、第１ＬＥＤ列を流れる電流を制限する第１電流制限部と、第２及び第４ＬＥＤ列を流れる電流を制限する第２電流制限部とを備え、第１ＬＥＤ列の複数のＬＥＤは、第２及び第３ＬＥＤ列の複数のＬＥＤよりも低い色温度で発光し、第１ＬＥＤ列が発光するための第１閾値電圧は、第２及び第４ＬＥＤ列が発光するための第２閾値電圧よりも小さく、第２閾値電圧は、第２及び第３ＬＥＤ列が発光するための第３閾値電圧よりも小さい。The LED drive circuit includes a rectifier circuit connected to a power source whose output changes in conjunction with dimming, a first LED row connected to the rectifier circuit, and a plurality of LEDs connected in series, and A second LED string connected in parallel with one LED string, a plurality of LEDs connected in series, a third LED string connected in series with the second LED string, and a plurality of LEDs connected in series, a second LED string, and a second LED string; One LED is connected between the three LED strings, a plurality of LEDs are connected in series, a fourth LED string, a first current limiting unit that limits a current flowing through the first LED string, and a current flowing through the second and fourth LED strings A plurality of LEDs in the first LED array emit light at a lower color temperature than the plurality of LEDs in the second and third LED arrays, and the first LED array emits light for the first light emission. The threshold voltage is the second and second Smaller than the second threshold voltage for the LED strings to emit light, the second threshold voltage is less than the third threshold voltage for the second and third 3LED column emits light.

Description

本発明は、調光に連動して発光色が変化するＬＥＤ駆動回路に関する。   The present invention relates to an LED drive circuit whose emission color changes in conjunction with dimming.

商用交流電源と白熱電球の間に調光器を挿入し、白熱電球の発光量を調節することが古くから行われている。この調光器は、トライアックを含み、商用交流電源の交流波形の一部を切り取るようにして実効値を調整している。調光に際し白熱電球には、明るくすると色温度が高くなり、暗くすると色温度が低くなるという発光特性がある。このような発光特性が一般に好まれるため、白熱電球からＬＥＤ（発光ダイオード）を光源とするＬＥＤ電球への置き換えが進むなかで、白熱電球の発光特性を模したＬＥＤ照明装置が上市されるようになった。   It has long been practiced to adjust the amount of light emitted by an incandescent lamp by inserting a dimmer between the commercial AC power supply and the incandescent lamp. This dimmer includes a triac and adjusts the effective value so as to cut out a part of the AC waveform of the commercial AC power supply. When dimming, incandescent bulbs have a light emission characteristic that the color temperature increases when brightened and the color temperature decreases when darkened. Since such light emission characteristics are generally preferred, LED lighting devices that simulate the light emission characteristics of incandescent light bulbs will be put on the market as incandescent light bulbs are replaced with LED light bulbs that use LEDs (light emitting diodes) as light sources. became.

任意の強度で任意の発光色を得るには、赤色で発光する光源と緑色で発光する光源と青色で発光する光源とを準備すれば良い。このような光源にデジタル制御可能な電源などを付加すれば、様々な強度で様々な発光色が得られる。調光に連動して調色を行うには、このような照明システムを組み、調光度合に応じて各光源の発光強度を調整すれば良い。しかしながら、このような原則通り照明システムを構成すると、回路規模が大きくなり無駄が多くなる。そこで、変化できる発光色を色温度で表せる範囲内に限定し、調光度合に応じて色温度を調整するようにすれば、照明システムを小規模化できる。すなわち、高い色温度の白色光源と低い色温度の白色光源とを準備し、調光度合に応じてアナログ制御でそれぞれの光源の発光強度を変化させれば良い。   In order to obtain an arbitrary emission color with an arbitrary intensity, a light source emitting red light, a light source emitting green light, and a light source emitting blue light may be prepared. If a light source that can be digitally controlled is added to such a light source, various emission colors can be obtained with various intensities. In order to perform color adjustment in conjunction with light adjustment, such an illumination system is assembled, and the light emission intensity of each light source may be adjusted in accordance with the degree of light adjustment. However, if the lighting system is configured according to such a principle, the circuit scale becomes large and waste is increased. Therefore, if the emission color that can be changed is limited to the range that can be expressed by the color temperature, and the color temperature is adjusted according to the dimming degree, the lighting system can be reduced in scale. That is, a white light source having a high color temperature and a white light source having a low color temperature may be prepared, and the light emission intensity of each light source may be changed by analog control according to the degree of dimming.

二つの光源（ＬＥＤを直列接続した回路。以下「ＬＥＤ列」と呼ぶ。）をアナログ制御で切り換えるＬＥＤ駆動回路は、特許文献１の図５−１に示されている。そこで特許文献１の図５−１（図５Ａ）及び図５−１（図５Ｂ）を図８、９にそれぞれ再掲示し、その回路構成及び動作並びに調光に応じて調色できるようにする手法を説明する。   An LED driving circuit that switches two light sources (a circuit in which LEDs are connected in series; hereinafter referred to as “LED array”) by analog control is shown in FIG. Therefore, FIG. 5A (FIG. 5A) and FIG. 5A (FIG. 5B) of Patent Document 1 are re-displayed in FIGS. 8 and 9, respectively, and a method for adjusting the color according to the circuit configuration, operation, and dimming. Will be explained.

図８は、特許文献１のＬＥＤ駆動回路（以下「回路５００」と呼ぶ）の回路図であり、図９は、回路５００に流れる電流を示す波形図である。回路５００は、整流回路１０７と、第１光源となる第１ＬＥＤグループ５０９と、第２光源となる第２ＬＥＤグループ５１１と、デプレッション型のＦＥＴ５１３及び電流検出用の抵抗５１７からなる第１電流制限回路と、デプレッション型のＦＥＴ５１５及び電流検出用の抵抗５１９からなる第２電流制限回路とを備えている。整流回路１０７の入力側には、過渡電圧サプレッサ（ＴＶＳ）１０５と、ヒューズ１０３を介して商用交流電源１０１（ＡＣ電源）とが接続している。   FIG. 8 is a circuit diagram of an LED driving circuit (hereinafter referred to as “circuit 500”) in Patent Document 1, and FIG. 9 is a waveform diagram showing a current flowing in the circuit 500. The circuit 500 includes a rectifier circuit 107, a first LED group 509 serving as a first light source, a second LED group 511 serving as a second light source, a first current limiting circuit including a depletion type FET 513 and a current detection resistor 517. And a second current limiting circuit including a depletion type FET 515 and a current detection resistor 519. On the input side of the rectifier circuit 107, a transient voltage suppressor (TVS) 105 and a commercial AC power supply 101 (AC power supply) are connected via a fuse 103.

整流回路１０７の出力端子には、交流を全波整流した電圧が現れる（以下この電圧を「全波整流電圧」と呼ぶ）。図９に示すように、全波整流電圧が０（Ｖ）から第１ＬＥＤグループ５０９が発光するための閾値電圧（以下単に「閾値電圧」という）未満となる期間（ｔ０〜ｔ１、ｔ４〜ｔ５）では、電流は流れない。全波整流電圧が第１ＬＥＤグループ５０９の閾値電圧以上で第２ＬＥＤグループ５１１の閾値電圧未満となる期間（ｔ１〜ｔ２、ｔ３〜ｔ４）では、第１ＬＥＤグループ５０９に電流ＩＧ１（図８では「ＩＧ２」と誤記されている）が流れる。全波整流電圧が第２ＬＥＤグループ５１１の閾値電圧以上となる期間（ｔ２〜ｔ３）では、第２ＬＥＤグループ５１１に電流ＩＧ２（図８では「ＩＧ１」と誤記されている）が流れるとともに電流ＩＧ１が無くなる。なお、実際の電流ＩＧ１、ＩＧ２は、図９に示される通り過渡状態をもって切り換わる。   A voltage obtained by full-wave rectification of alternating current appears at the output terminal of the rectifier circuit 107 (hereinafter, this voltage is referred to as “full-wave rectified voltage”). As shown in FIG. 9, the period (t0 to t1, t4 to t5) in which the full-wave rectified voltage is less than the threshold voltage (hereinafter simply referred to as “threshold voltage”) for the first LED group 509 to emit light from 0 (V). Then, no current flows. In a period (t1 to t2, t3 to t4) in which the full-wave rectified voltage is equal to or higher than the threshold voltage of the first LED group 509 and lower than the threshold voltage of the second LED group 511, the current IG1 (“IG2” in FIG. 8) is supplied to the first LED group 509. Is mistakenly written). In a period (t2 to t3) in which the full-wave rectified voltage is equal to or higher than the threshold voltage of the second LED group 511, the current IG2 (indicated as “IG1” in FIG. 8) flows through the second LED group 511 and the current IG1 disappears. . The actual currents IG1 and IG2 are switched in a transient state as shown in FIG.

調光に応じて調色できるようにするためには、回路５００において商用交流電源１０１とヒューズ１０３の間に調光器（位相制御型ディマー）が挿入され、第１ＬＥＤグループ５０９の発光色が低い色温度に、第２ＬＥＤグループ５１１の発光色が高い色温度にそれぞれ設定される。   In order to adjust the color according to the dimming, a dimmer (phase control type dimmer) is inserted between the commercial AC power supply 101 and the fuse 103 in the circuit 500, and the emission color of the first LED group 509 is low. The color temperature of the second LED group 511 is set to a high color temperature.

調光器は、商用交流電源１０１から得られる交流の一部の期間（「位相」ともいう）を切り取る（０（Ｖ）にする）。このとき整流回路１０７は、一部分が切り取られた交流波形を全波整流し、全波整流電圧の波形から一部分が切り取られた脈流電圧を出力する。調光器により明るく調光されると、脈流電圧のなかで電圧の高い期間が占める割合が多くなる。この結果、第２ＬＥＤグループ５１１の発光が支配的になり、発光色が高い色温度となる。これに対し、調光器により暗く調光されると、脈流電圧のなかで電圧の低い期間が占める割合が多くなる。この結果、第１ＬＥＤグループ５０９の発光が支配的になり、発光色が低い色温度となる。   The dimmer cuts out a period (also referred to as “phase”) of AC obtained from the commercial AC power supply 101 (sets to 0 (V)). At this time, the rectifier circuit 107 performs full-wave rectification on the AC waveform that is partially cut off, and outputs a pulsating voltage that is partially cut off from the waveform of the full-wave rectified voltage. When the light is brightly adjusted by the dimmer, the ratio of the high voltage period in the pulsating voltage increases. As a result, the light emission of the second LED group 511 becomes dominant, and the emission color has a high color temperature. On the other hand, when the dimmer is dimmed darkly, the ratio of the low voltage period to the pulsating current voltage increases. As a result, the light emission of the first LED group 509 becomes dominant, and the light emission color has a low color temperature.

図８、９に示した回路５００では、調光器がないとき、ＬＥＤ列に全波整流電圧を印加するだけの単純なＬＥＤ駆動回路に比べて、力率や高調波歪率が改善されている。特許文献１には、力率や高調波歪率を改善するという回路５００と共通の課題をもった他の回路が示されている（例えば図１−１）。そこで特許文献１の図１−１（図１Ａ）を図１０に再掲示し、その構成と動作を説明する。   In the circuit 500 shown in FIGS. 8 and 9, when there is no dimmer, the power factor and the harmonic distortion factor are improved as compared with a simple LED driving circuit that only applies a full-wave rectified voltage to the LED array. Yes. Patent Document 1 discloses another circuit having a common problem with the circuit 500 for improving the power factor and the harmonic distortion factor (for example, FIG. 1-1). Therefore, FIG. 1-1 (FIG. 1A) of Patent Document 1 is shown again in FIG.

図１０は、特許文献１の他のＬＥＤ駆動回路（以下「回路１００」と呼ぶ）の回路図である。回路１００は、第１ＬＥＤグループ１０９、第２ＬＥＤグループ１１１、ＦＥＴ１１３と抵抗１１７からなる第１電流制限回路（「バイパス回路」ともいう）、及びＦＥＴ１１５と抵抗１１９からなる第２電流制限回路（「定電流回路」ともいう）を備えている。回路１００では、第１ＬＥＤグループ１０９と第２ＬＥＤグループ１１１が直列接続している。第１電流制限回路において、電流入力端子となるＦＥＴ１１３のドレインは第１ＬＥＤグループ１０９と第２ＬＥＤグループ１１１との接続点に接続し、電流出力端子となる抵抗１１７の右端子は整流回路１０７の電流が戻る端子Ｖ−に接続している。第２電流制限回路において、電流入力端子であるＦＥＴ１１５のドレインは第２ＬＥＤグループ１１１の電流出力端子に接続し、電流出力端子である抵抗１１９の右端子は抵抗１１７に接続している。   FIG. 10 is a circuit diagram of another LED drive circuit (hereinafter referred to as “circuit 100”) in Patent Document 1. The circuit 100 includes a first LED group 109, a second LED group 111, a first current limiting circuit (also referred to as a “bypass circuit”) including an FET 113 and a resistor 117, and a second current limiting circuit including an FET 115 and a resistor 119 (“constant current”). Circuit "). In the circuit 100, the first LED group 109 and the second LED group 111 are connected in series. In the first current limiting circuit, the drain of the FET 113 serving as a current input terminal is connected to the connection point between the first LED group 109 and the second LED group 111, and the right terminal of the resistor 117 serving as a current output terminal is the current of the rectifier circuit 107. Connected to the return terminal V-. In the second current limiting circuit, the drain of the FET 115 that is a current input terminal is connected to the current output terminal of the second LED group 111, and the right terminal of the resistor 119 that is a current output terminal is connected to the resistor 117.

回路１００に全波整流電圧を印加したとき、全波整流電圧が０（Ｖ）から第１ＬＥＤグループ１０９の閾値電圧に達するまでの期間では、整流回路１０７から第１ＬＥＤグループ１０９に電流は流れ込まない。全波整流電圧が第１ＬＥＤグループ１０９の閾値電圧から第１ＬＥＤグループ１０９の閾値電圧と第２ＬＥＤグループ１１１の閾値電圧との和となる電圧に達するまでの期間では、整流回路１０７を発し、第１ＬＥＤグループ１０９及び第１電流制限回路を経て整流回路１０７に戻る電流ＩＧ１が流れる。このとき第１電流制限回路では、抵抗１１７の電圧降下がＦＥＴ１１３にフィードバックし、電流ＩＧ１が定電流化する。全波整流電圧が上記の和の電圧を超える期間では、整流回路１０７を発し、第１及び第２ＬＥＤグループ１０９、１１１、第２電流制限回路並びに抵抗１１７を経て整流回路１０７に戻る電流ＩＧ２が流れる。このとき第１電流制限回路では、抵抗１１７の電圧降下が増大するためＦＥＴ１１３はカットオフする。同時に第２電流制限回路では、抵抗１１９の電圧降下がＦＥＴ１１５にフィードバックし、電流ＩＧ２が定電流化する。全波整流電圧が低下する期間では、全波整流電圧が上昇する期間の過程とは逆の過程を辿る。   When a full-wave rectified voltage is applied to the circuit 100, no current flows from the rectifier circuit 107 into the first LED group 109 during the period from the full-wave rectified voltage reaching 0 (V) to the threshold voltage of the first LED group 109. In a period until the full-wave rectified voltage reaches the voltage that is the sum of the threshold voltage of the first LED group 109 and the threshold voltage of the second LED group 111 from the threshold voltage of the first LED group 109, the rectifier circuit 107 is generated, and the first LED group The current IG1 that returns to the rectifier circuit 107 through 109 and the first current limiting circuit flows. At this time, in the first current limiting circuit, the voltage drop of the resistor 117 is fed back to the FET 113, and the current IG1 becomes constant. In a period in which the full-wave rectified voltage exceeds the above sum voltage, the rectifier circuit 107 is emitted, and a current IG2 that returns to the rectifier circuit 107 through the first and second LED groups 109 and 111, the second current limiting circuit, and the resistor 117 flows. . At this time, in the first current limiting circuit, the voltage drop across the resistor 117 increases, so that the FET 113 is cut off. At the same time, in the second current limiting circuit, the voltage drop of the resistor 119 feeds back to the FET 115, and the current IG2 becomes constant. In the period in which the full-wave rectified voltage decreases, the process reverse to the process in the full-wave rectified voltage increases.

以上の知見に基づき本願発明者は、図８に示した回路５００に図１０に示した回路１００を適用して、さらに他のＬＥＤ駆動回路を作成した（特許文献２を参照）。図１１は、特許文献２のＬＥＤ駆動回路（以下「ＬＥＤ駆動回路３００」と呼ぶ）の回路図である。ＬＥＤ駆動回路３００は、第１ＬＥＤ列３０１、第２ＬＥＤ列３０２、第３ＬＥＤ列３０３、第１電流制限回路３１１、第２電流制限回路３１２、第３電流制限回路３１３及び整流回路３０５を備えている。図１１では、参考のため商用交流電源１２１と、位相制御型ディマーである調光器１２２とを書き加えている。   Based on the above knowledge, the present inventor applied the circuit 100 shown in FIG. 10 to the circuit 500 shown in FIG. 8 to create another LED driving circuit (see Patent Document 2). FIG. 11 is a circuit diagram of an LED drive circuit (hereinafter referred to as “LED drive circuit 300”) of Patent Document 2. The LED driving circuit 300 includes a first LED row 301, a second LED row 302, a third LED row 303, a first current limiting circuit 311, a second current limiting circuit 312, a third current limiting circuit 313, and a rectifying circuit 305. In FIG. 11, a commercial AC power supply 121 and a dimmer 122 that is a phase control dimmer are added for reference.

第１、第２及び第３ＬＥＤ列３０１、３０２、３０３では、それぞれＬＥＤ３０１ａ、３０２ａ、３０３ａが直列接続している。ＬＥＤ３０１ａは低い色温度で発光し、ＬＥＤ３０２ａ、３０３ａは高い色温度で発光する。第１、第２及び第３電流制限回路３１１、３１２、３１３は、それぞれデプレッション型のＦＥＴ３１１ａ、３１２ａ、３１３ａと電流検出用の抵抗３１１ｂ、３１２ｂ、３１３ｂとからなる。整流回路３０５は４個のダイオード３０５ａのダイオードブリッジで構成されている。   In the first, second, and third LED rows 301, 302, and 303, the LEDs 301a, 302a, and 303a are connected in series, respectively. The LED 301a emits light at a low color temperature, and the LEDs 302a and 303a emit light at a high color temperature. The first, second, and third current limiting circuits 311, 312, and 313 include depletion type FETs 311 a, 312 a, and 313 a and current detection resistors 311 b, 312 b, and 313 b, respectively. The rectifier circuit 305 is constituted by a diode bridge of four diodes 305a.

整流回路３０５が全波整流電圧を出力する場合、全波整流電圧が第１ＬＥＤ列３０１の閾値電圧以上でありかつ第２ＬＥＤ列３０２の閾値電圧よりも低い期間では、第１ＬＥＤ列３０１に電流Ｉ３１が流れ、第１ＬＥＤ列３０１が低い色温度で点灯する。全波整流電圧が第２ＬＥＤ列３０２の閾値電圧以上でありかつ第２ＬＥＤ列３０２と第３ＬＥＤ列３０３との閾値電圧の和となる電圧未満となる期間では、第２ＬＥＤ列３０２に電流Ｉ３２が流れ、第２ＬＥＤ列３０２が高い色温度で点灯する。全波整流電圧が上記の和の電圧を超える期間では、第２及び第３ＬＥＤ列３０２、３０３に電流Ｉ３３が流れ、第２及び第３ＬＥＤ列３０２、３０３が高い色温度で点灯する。   When the rectifier circuit 305 outputs a full-wave rectified voltage, the current I31 is supplied to the first LED string 301 in a period in which the full-wave rectified voltage is equal to or higher than the threshold voltage of the first LED string 301 and lower than the threshold voltage of the second LED string 302. The first LED row 301 is lit at a low color temperature. In a period in which the full-wave rectified voltage is equal to or higher than the threshold voltage of the second LED string 302 and less than the voltage that is the sum of the threshold voltages of the second LED string 302 and the third LED string 303, the current I32 flows through the second LED string 302, The second LED row 302 is lit at a high color temperature. In a period in which the full-wave rectified voltage exceeds the above sum voltage, the current I33 flows through the second and third LED strings 302 and 303, and the second and third LED strings 302 and 303 are lit at a high color temperature.

調光器１２２で調光した場合、整流回路３０５は前述の脈流電圧を出力し、脈流電圧のなかで電圧の高い期間が占める割合に応じてＬＥＤ駆動回路３００の発光色が変化する。   When dimming is performed by the dimmer 122, the rectifier circuit 305 outputs the above-described pulsating voltage, and the light emission color of the LED driving circuit 300 changes according to the ratio of the high voltage period in the pulsating voltage.

特表２０１４−５１６４５２号公報（図１−１、図５−１）Japanese Translation of PCT International Publication No. 2014-516442 (FIGS. 1-1 and 5-1) 国際公開第２０１６／０３９４５７号（図１）International Publication No. 2016/039457 (FIG. 1)

前述したようにＬＥＤ駆動回路３００は、低く調光したとき、第１ＬＥＤ列３０１だけが点灯し、低い色温度で発光する。一方ＬＥＤ駆動回路３００は、高く調光したとき、第２及び第３ＬＥＤ列３０２、３０３の発光が支配的になるため、高い色温度で発光する。しかしながら、中間の調光状態では、ＬＥＤ駆動回路３００は、特定の調光度合を境にして急激に発光色が変化するため、使用者に不自然な印象を与えた。   As described above, when the LED drive circuit 300 is dimmed low, only the first LED row 301 is lit and emits light at a low color temperature. On the other hand, the LED drive circuit 300 emits light at a high color temperature because light emission of the second and third LED rows 302 and 303 becomes dominant when dimming high. However, in the middle dimming state, the LED drive circuit 300 gives an unnatural impression to the user because the emission color changes abruptly at a specific dimming degree.

そこで本発明は、上記の課題に鑑みて為されたものであり、回路構成が簡単でありながら調光に応じて発光色を滑らかに変化させられるＬＥＤ駆動回路を提供することを目的とする。   Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide an LED drive circuit capable of smoothly changing an emission color according to light control while having a simple circuit configuration.

上記の課題を解決するため、高い色温度で発光するＬＥＤと低い色温度で発光するＬＥＤを備え、調光に連動して発光色が変化するＬＥＤ駆動回路において、整流回路と、低い色温度で発光する第１及び第４ＬＥＤ列と、高い色温度で発光する第２及び第３ＬＥＤ列と、第１スイッチ素子及び第１電流検出素子を有する第１電流制限回路と、第２スイッチ素子及び第２電流検出素子を有する第２電流制限回路とを備え、整流回路の電流を出力する端子は、第１及び第２ＬＥＤ列のアノードに接続し、第１ＬＥＤ列のカソードは、第１電流制限回路の電流入力端子に接続し、第２ＬＥＤ列のカソードは、第３及び第４ＬＥＤ列のアノードに接続し、第３ＬＥＤ列のカソードは、直接又は回路素子を介して第２電流検出素子に接続し、第４ＬＥＤ列のカソードは、第２電流制限回路の電流入力端子に接続し、第２電流制限回路の電流出力端子は、第１電流検出素子に接続し、第１電流制限回路の電流出力端子は、整流回路の電流が戻る端子に接続し、第１ＬＥＤ列の閾値電圧は、第２及び第４ＬＥＤ列の閾値電圧の和となる電圧よりも小さく、第４ＬＥＤ列の閾値電圧は、第３ＬＥＤ列の閾値電圧よりも小さいことを特徴とするＬＥＤ駆動回路が提供される。   In order to solve the above problems, in an LED drive circuit that includes an LED that emits light at a high color temperature and an LED that emits light at a low color temperature, and the emission color changes in conjunction with dimming, a rectifier circuit and a low color temperature First and fourth LED rows that emit light, second and third LED rows that emit light at a high color temperature, a first current limiting circuit having a first switch element and a first current detection element, a second switch element and a second A terminal for outputting a current of the rectifier circuit is connected to the anodes of the first and second LED strings, and the cathode of the first LED string is a current of the first current limiting circuit. Connected to the input terminal, the cathode of the second LED string is connected to the anodes of the third and fourth LED strings, the cathode of the third LED string is connected to the second current detection element directly or via a circuit element, and the fourth LED Is connected to the current input terminal of the second current limiting circuit, the current output terminal of the second current limiting circuit is connected to the first current detection element, and the current output terminal of the first current limiting circuit is the rectifier circuit The threshold voltage of the first LED array is smaller than the voltage that is the sum of the threshold voltages of the second and fourth LED arrays, and the threshold voltage of the fourth LED array is less than the threshold voltage of the third LED array. An LED driving circuit is also provided that is characterized by a small size.

また、調光に連動して出力が変化する電源に接続された整流回路と、整流回路に接続され、かつ複数のＬＥＤが直列に接続された第１ＬＥＤ列と、整流回路に対して第１ＬＥＤ列と並列に接続され、かつ複数のＬＥＤが直列に接続された第２ＬＥＤ列と、第２ＬＥＤ列と直列に接続され、かつ複数のＬＥＤが直列に接続された第３ＬＥＤ列と、第２ＬＥＤ列と第３ＬＥＤ列との間に一端が接続され、かつ複数のＬＥＤが直列に接続された第４ＬＥＤ列と、第１ＬＥＤ列を流れる電流を制限する第１電流制限部と、第２及び第４ＬＥＤ列を流れる電流を制限する第２電流制限部とを備え、第１ＬＥＤ列に含まれる複数のＬＥＤは、第２及び第３ＬＥＤ列に含まれる複数のＬＥＤよりも低い色温度で発光し、第１ＬＥＤ列が発光するための第１閾値電圧は、第２及び第４ＬＥＤ列が発光するための第２閾値電圧よりも小さく、第２閾値電圧は、第２及び第３ＬＥＤ列が発光するための第３閾値電圧よりも小さいことを特徴とするＬＥＤ駆動回路が提供される。   Further, a rectifier circuit connected to a power source whose output changes in conjunction with dimming, a first LED row connected to the rectifier circuit and having a plurality of LEDs connected in series, and a first LED row with respect to the rectifier circuit A second LED string connected in parallel with each other and a plurality of LEDs connected in series; a third LED string connected in series with the second LED string; and a plurality of LEDs connected in series; a second LED string; A fourth LED string in which one end is connected between the three LED strings and a plurality of LEDs are connected in series; a first current limiting unit that limits a current flowing through the first LED string; and a second and fourth LED string. A plurality of LEDs included in the first LED array emit light at a color temperature lower than that of the plurality of LEDs included in the second and third LED arrays, and the first LED array emits light. First threshold to do The voltage is smaller than the second threshold voltage for the second and fourth LED strings to emit light, and the second threshold voltage is smaller than the third threshold voltage for the second and third LED strings to emit light. An LED driving circuit is provided.

全波整流電圧が０（Ｖ）から第１ＬＥＤ列の閾値電圧（第１閾値電圧）まで上昇する位相では、整流回路は電流を出力しない。全波整流電圧が第１ＬＥＤ列の閾値電圧から第２及び第４ＬＥＤ列の閾値電圧の和となる電圧（第２閾値電圧）まで上昇する位相では、第１ＬＥＤ列に電流が流れ、第１ＬＥＤ列は低い色温度で発光する。全波整流電圧が第２及び第４ＬＥＤ列の閾値電圧の和となる電圧から第２及び第３ＬＥＤ列の閾値電圧の和となる電圧（第３閾値電圧）まで上昇する位相では、第２及び第４ＬＥＤ列に電流が流れ、第２及び第４ＬＥＤ列はそれぞれ高い色温度及び低い色温度で発光する。全波整流電圧が第２及び第３ＬＥＤ列の閾値電圧の和となる電圧よりも高い電圧となる位相では、第２及び第３ＬＥＤ列に電流が流れ、第２及び第３ＬＥＤ列は高い色温度で発光する。全波整流電圧が低下する位相では、全波整流電圧が上昇する位相とは逆の過程を辿る。   In the phase in which the full-wave rectified voltage rises from 0 (V) to the threshold voltage (first threshold voltage) of the first LED string, the rectifier circuit does not output current. In the phase in which the full-wave rectified voltage rises from the threshold voltage of the first LED string to the voltage (second threshold voltage) that is the sum of the threshold voltages of the second and fourth LED strings, current flows through the first LED string, Emits light at a low color temperature. In the phase in which the full-wave rectified voltage rises from the voltage that is the sum of the threshold voltages of the second and fourth LED strings to the voltage that is the sum of the threshold voltages of the second and third LED strings (third threshold voltage), the second and second A current flows through the 4 LED rows, and the second and fourth LED rows emit light at a high color temperature and a low color temperature, respectively. In the phase in which the full-wave rectified voltage is higher than the voltage that is the sum of the threshold voltages of the second and third LED strings, current flows through the second and third LED strings, and the second and third LED strings have a high color temperature. Emits light. The phase in which the full-wave rectified voltage decreases follows a process opposite to the phase in which the full-wave rectified voltage increases.

商用交流電源が出力する交流の位相の一部が調光器により切り取られた電圧波形が整流回路に入力されると、整流回路は電圧波形を全波整流した脈流電圧を出力する。調光度が低いときには、脈流電圧では電圧の低い位相の割合が多くなるので、第１ＬＥＤ列の発光が支配的となり、ＬＥＤ駆動回路の発光色の色温度は低くなる。反対に、調光度が高いときには、脈流電圧では電圧の高い位相の割合が多くなるので、第２及び第３ＬＥＤ列の発光が支配的となり、ＬＥＤ駆動回路の発光色の色温度は高くなる。調光度が中間的な状態にあるときには、脈流電圧では第２及び第４ＬＥＤ列が発光する位相の割合が多くなるので、ＬＥＤ駆動回路の発光色の色温度は中間的になる。   When a voltage waveform in which part of the AC phase output from the commercial AC power supply is cut off by the dimmer is input to the rectifier circuit, the rectifier circuit outputs a pulsating voltage obtained by full-wave rectifying the voltage waveform. When the dimming degree is low, since the ratio of the low voltage phase increases in the pulsating voltage, the light emission of the first LED row becomes dominant, and the color temperature of the light emission color of the LED drive circuit becomes low. On the other hand, when the dimming degree is high, the ratio of the high voltage phase increases in the pulsating voltage, so that the light emission of the second and third LED arrays becomes dominant, and the color temperature of the light emission color of the LED drive circuit becomes high. When the dimming degree is in an intermediate state, the pulsating voltage increases the ratio of the phase at which the second and fourth LED arrays emit light, so that the color temperature of the light emission color of the LED drive circuit is intermediate.

第１電流制限部は、整流回路の出力電圧が第１範囲内にあるときに、第１ＬＥＤ列を流れる電流を制限し、第２電流制限部は、出力電圧が第１範囲よりも高い第２範囲内にあるときに、第２及び第４ＬＥＤ列を流れる電流を制限し、整流回路の電流出力端子は、第１及び第２ＬＥＤ列のアノードに接続し、第１ＬＥＤ列のカソードは、第１電流制限部の電流入力端子に接続し、第２ＬＥＤ列のカソードは、第３及び第４ＬＥＤ列のアノードに接続し、第３ＬＥＤ列のカソード並びに第１及び第２電流制限部の電流出力端子は、直接又は回路素子を介して整流回路の電流が戻る端子に接続し、第４ＬＥＤ列のカソードは、第２電流制限部の電流入力端子に接続しても良い。   The first current limiting unit limits the current flowing through the first LED string when the output voltage of the rectifier circuit is within the first range, and the second current limiting unit is a second current whose output voltage is higher than the first range. When in range, the current through the second and fourth LED strings is limited, the current output terminal of the rectifier circuit is connected to the anodes of the first and second LED strings, and the cathode of the first LED string is the first current The cathode of the second LED row is connected to the anodes of the third and fourth LED rows, and the cathode of the third LED row and the current output terminals of the first and second current limiting portions are directly connected Alternatively, it may be connected to a terminal to which the current of the rectifier circuit returns via a circuit element, and the cathode of the fourth LED array may be connected to the current input terminal of the second current limiting unit.

第１電流制限部は、第１スイッチ素子及び第１電流検出素子を有し、第２電流制限部は、第２スイッチ素子及び第２電流検出素子を有し、第３ＬＥＤ列のカソードは、直接又は回路素子を介して第２電流検出素子に接続し、第２電流制限部の電流出力端子は、第１電流検出素子に接続し、第１電流制限部の電流出力端子は、整流回路の電流が戻る端子に接続しても良い。   The first current limiter includes a first switch element and a first current detection element, the second current limiter includes a second switch element and a second current detection element, and the cathode of the third LED array is directly Alternatively, it is connected to the second current detection element via a circuit element, the current output terminal of the second current limiting unit is connected to the first current detection element, and the current output terminal of the first current limiting unit is the current of the rectifier circuit It may be connected to the terminal that returns.

第３ＬＥＤ列のカソードは、第３スイッチ素子及び第３電流検出素子を有する第３電流制限回路を介して第２電流検出素子に接続しても良い。   The cathode of the third LED array may be connected to the second current detection element via a third current limiting circuit having a third switch element and a third current detection element.

整流回路の電流出力端子と第２ＬＥＤ列のアノードの間に挿入された逆流防止用ダイオードと、第２ＬＥＤ列と並列接続されたコンデンサをさらに備えても良い。   You may further provide the backflow prevention diode inserted between the current output terminal of the rectifier circuit and the anode of the second LED row, and a capacitor connected in parallel with the second LED row.

第１スイッチ素子と第１電流検出素子の間又は第２スイッチ素子と第２電流検出素子の間に接続された抵抗をさらに有しても良い。   You may further have the resistance connected between the 1st switch element and the 1st current detection element, or between the 2nd switch element and the 2nd current detection element.

第２ＬＥＤ列を流れる電流が第１スイッチ素子をカットオフし、第３ＬＥＤ列を流れる電流が第２スイッチ素子をカットオフしても良い。   The current flowing through the second LED string may cut off the first switch element, and the current flowing through the third LED string may cut off the second switch element.

第１電流制限部は、出力電圧が第１範囲内にあるときに導通する第１スイッチであり、第２電流制限部は、出力電圧が第２範囲内にあるときに導通する第２スイッチでも良い。   The first current limiter is a first switch that conducts when the output voltage is within the first range, and the second current limiter is a second switch that conducts when the output voltage is within the second range. good.

第４ＬＥＤ列に含まれる複数のＬＥＤは、第２及び第３ＬＥＤ列に含まれる複数のＬＥＤよりも低い色温度で発光しても良い。   The plurality of LEDs included in the fourth LED array may emit light at a lower color temperature than the plurality of LEDs included in the second and third LED arrays.

また、高い色温度で発光するＬＥＤと低い色温度で発光するＬＥＤを備え、調光に連動して発光色が変化するＬＥＤ駆動回路において、整流回路と、低い色温度で発光する第５及び第８ＬＥＤ列と、高い色温度で発光する第６及び第７ＬＥＤ列と、整流回路が低い電圧を出力しているとき導通する第４スイッチと、整流回路が中間の電圧を出力しているときに導通する第５スイッチとを備え、整流回路の電流を出力する端子は、第５及び第６ＬＥＤ列のアノードに接続し、第５ＬＥＤ列のカソードは、第４スイッチの電流入力端子に接続し、第６ＬＥＤ列のカソードは、第７及び第８ＬＥＤ列のアノードに接続し、第８ＬＥＤ列のカソードは、第５スイッチの電流入力端子に接続し、第７ＬＥＤ列のカソード並びに第４及び第５スイッチの電流出力端子は、直接又は回路素子を介して整流回路の電流が戻る端子に接続することを特徴とするＬＥＤ駆動回路が提供される。   Further, in an LED drive circuit that includes an LED that emits light at a high color temperature and an LED that emits light at a low color temperature, and the emission color changes in conjunction with dimming, a rectifier circuit, and fifth and fifth light sources that emit light at a low color temperature. 8 LED strings, sixth and seventh LED strings that emit light at a high color temperature, a fourth switch that is conductive when the rectifier circuit outputs a low voltage, and a conductive switch when the rectifier circuit outputs an intermediate voltage A terminal for outputting a current of the rectifier circuit is connected to the anodes of the fifth and sixth LED strings, and a cathode of the fifth LED string is connected to a current input terminal of the fourth switch, The cathode of the column is connected to the anodes of the seventh and eighth LED columns, the cathode of the eighth LED column is connected to the current input terminal of the fifth switch, and the cathodes of the seventh LED column and the electric currents of the fourth and fifth switches are connected. Output terminals, LED driving circuit characterized in that connected to the current return terminal of the rectifier circuit directly or through circuit elements are provided.

上記のＬＥＤ駆動回路は、回路構成が簡単でありながら調光に応じて発光色を滑らかに変化させることができる。   The above LED drive circuit can change the emission color smoothly according to the light control while having a simple circuit configuration.

ＬＥＤ駆動回路１０の回路図である。2 is a circuit diagram of an LED drive circuit 10. FIG. ＬＥＤ駆動回路１０の動作を説明するための波形図である。4 is a waveform diagram for explaining the operation of the LED drive circuit 10. FIG. 他のＬＥＤ駆動回路２０の回路図である。FIG. 6 is a circuit diagram of another LED drive circuit 20. 比較例として示すＬＥＤ駆動回路２５の回路図である。It is a circuit diagram of the LED drive circuit 25 shown as a comparative example. ＬＥＤ駆動回路２０、２５の発光色と調光度の関係を示すグラフである。It is a graph which shows the relationship between the luminescent color of the LED drive circuits 20 and 25, and the light control degree. さらに他のＬＥＤ駆動回路３０の回路図である。4 is a circuit diagram of still another LED drive circuit 30. FIG. さらに他のＬＥＤ駆動回路４０の回路図である。FIG. 6 is a circuit diagram of still another LED drive circuit 40. 特許文献１のＬＥＤ駆動回路の回路図である。FIG. 11 is a circuit diagram of an LED drive circuit disclosed in Patent Document 1. 図８のＬＥＤ駆動回路に流れる電流を示す波形図である。It is a wave form diagram which shows the electric current which flows into the LED drive circuit of FIG. 特許文献１の他のＬＥＤ駆動回路の回路図である。FIG. 11 is a circuit diagram of another LED drive circuit in Patent Document 1. 特許文献２のＬＥＤ駆動回路の回路図である。FIG. 11 is a circuit diagram of an LED drive circuit disclosed in Patent Document 2.

以下、図１〜７を参照しながらＬＥＤ駆動回路の好適な実施形態について詳細に説明する。なお、図面の説明において、同一又は相当要素には同一の符号を付し、重複する説明は省略する。請求の範囲に記載した発明特定事項をカッコ内に記載している。   Hereinafter, a preferred embodiment of the LED drive circuit will be described in detail with reference to FIGS. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted. The invention-specific matters described in the claims are described in parentheses.

（第１実施形態）
図１は、ＬＥＤ駆動回路１０の回路図である。図２は、ＬＥＤ駆動回路１０の動作を説明するための波形図であり、（ａ）は１周期分の全波整流電圧を、（ｂ）は全波整流電圧に対する回路電流を、（ｃ）は調光時の脈流電圧と回路電流との関係を示す。図２において、（ａ）の縦軸は電圧Ｖ、（ｂ）の縦軸は電流Ｉ、（ｃ）の縦軸は電圧Ｖと電流Ｉである。また図２において、（ａ）、（ｂ）及び（ｃ）の横軸は時間ｔを示し、共通の時間軸となる。(First embodiment)
FIG. 1 is a circuit diagram of the LED drive circuit 10. FIG. 2 is a waveform diagram for explaining the operation of the LED drive circuit 10, where (a) shows a full-wave rectified voltage for one cycle, (b) shows a circuit current with respect to the full-wave rectified voltage, and (c). Indicates the relationship between the pulsating voltage and the circuit current during dimming. In FIG. 2, the vertical axis of (a) is voltage V, the vertical axis of (b) is current I, and the vertical axis of (c) is voltage V and current I. In FIG. 2, the horizontal axes of (a), (b) and (c) indicate time t, which is a common time axis.

図１に示すように、ＬＥＤ駆動回路１０は、整流回路１５、ＬＥＤ列１１（第１ＬＥＤ列）、ＬＥＤ列１２（第２ＬＥＤ列）、ＬＥＤ列１３（第３ＬＥＤ列）、ＬＥＤ列１４（第４ＬＥＤ列）、バイパス回路１６（第１電流制限部、第１電流制限回路）、バイパス回路１７（第２電流制限部、第２電流制限回路）及び定電流回路１８（第３電流制限回路）を備えている。図１では、参考のため商用交流電源１２１と、位相制御型ディマーである調光器１２２とを書き加えている。   As shown in FIG. 1, the LED drive circuit 10 includes a rectifier circuit 15, an LED array 11 (first LED array), an LED array 12 (second LED array), an LED array 13 (third LED array), and an LED array 14 (fourth LED array). Column), bypass circuit 16 (first current limiting unit, first current limiting circuit), bypass circuit 17 (second current limiting unit, second current limiting circuit) and constant current circuit 18 (third current limiting circuit). ing. In FIG. 1, a commercial AC power supply 121 and a dimmer 122 which is a phase control dimmer are added for reference.

整流回路１５は４個のダイオード１５ａのダイオードブリッジで構成されている。整流回路１５の一方の入力端子１５１には調光器１２２を介して商用交流電源１２１が接続し、他方の入力端子１５２には商用交流電源１２１が直接接続している。すなわち、整流回路１５は、２つの入力端子１５１、１５２を介して、調光に連動して出力が変化する電源（商用交流電源１２１及び調光器１２２）に接続されている。なお、ヒューズや過電圧サプレッサなどの安全に係る回路は図示していない。   The rectifier circuit 15 is composed of a diode bridge of four diodes 15a. The commercial AC power supply 121 is connected to one input terminal 151 of the rectifier circuit 15 via the dimmer 122, and the commercial AC power supply 121 is directly connected to the other input terminal 152. That is, the rectifier circuit 15 is connected via two input terminals 151 and 152 to a power source (commercial AC power source 121 and dimmer 122) whose output changes in conjunction with dimming. Note that safety-related circuits such as a fuse and an overvoltage suppressor are not shown.

ＬＥＤ列１１、１２、１３、１４では、それぞれＬＥＤ１１ａ、１２ａ、１３ａ、１４ａが直列接続している。ＬＥＤ１１ａ、１４ａは、ＬＥＤ１２ａ、１３ａよりも低い色温度で発光し、ＬＥＤ１２ａ、１３ａは、ＬＥＤ１１ａ、１４ａよりも高い色温度で発光する。すなわち、ＬＥＤ列１１、１４はＬＥＤ列１２、１３よりも低い色温度で発光し、ＬＥＤ列１２、１３はＬＥＤ列１１、１４よりも高い色温度で発光する。   In the LED rows 11, 12, 13, and 14, the LEDs 11a, 12a, 13a, and 14a are connected in series, respectively. The LEDs 11a and 14a emit light at a lower color temperature than the LEDs 12a and 13a, and the LEDs 12a and 13a emit light at a higher color temperature than the LEDs 11a and 14a. That is, the LED rows 11 and 14 emit light at a lower color temperature than the LED rows 12 and 13, and the LED rows 12 and 13 emit light at a higher color temperature than the LED rows 11 and 14.

ＬＥＤ列１１の閾値電圧は、ＬＥＤ１１ａの順方向ドロップ電圧とＬＥＤ列１１におけるＬＥＤ１１ａの直列段数との積である。同様に、ＬＥＤ列１２〜１４の閾値電圧は、それぞれＬＥＤ１２ａ〜１４ａの順方向ドロップ電圧とＬＥＤ列１２〜１４におけるＬＥＤ１２ａ〜１４ａの直列段数との積である。ＬＥＤ列１１の閾値電圧（第１閾値電圧）は、ＬＥＤ列１２、１４の閾値電圧の和となる電圧（第２閾値電圧）よりも小さく、ＬＥＤ列１４の閾値電圧はＬＥＤ列１３の閾値電圧よりも小さい。また、ＬＥＤ列１２、１４の閾値電圧の和は、ＬＥＤ列１２、１３の閾値電圧の和となる電圧（第３閾値電圧）よりも小さい。   The threshold voltage of the LED array 11 is a product of the forward drop voltage of the LED 11 a and the number of series stages of the LEDs 11 a in the LED array 11. Similarly, the threshold voltage of the LED strings 12 to 14 is the product of the forward drop voltage of the LEDs 12a to 14a and the number of series stages of the LEDs 12a to 14a in the LED strings 12 to 14, respectively. The threshold voltage (first threshold voltage) of the LED array 11 is smaller than the voltage (second threshold voltage) that is the sum of the threshold voltages of the LED arrays 12 and 14, and the threshold voltage of the LED array 14 is the threshold voltage of the LED array 13. Smaller than. Further, the sum of the threshold voltages of the LED strings 12 and 14 is smaller than a voltage (third threshold voltage) which is the sum of the threshold voltages of the LED strings 12 and 13.

ＬＥＤ列１１に含まれる初段のＬＥＤ１１ａのアノード（以下「ＬＥＤ列１１のアノード」と呼ぶ。以下同様。）は、整流回路１５の電流を出力する端子（以下「出力端子」と呼ぶ）及びＬＥＤ列１２のアノードに接続している。ＬＥＤ列１２に含まれる最終段のＬＥＤ１２ａのカソード（以下「ＬＥＤ列１２のカソード」と呼ぶ。以下同様。）は、ＬＥＤ列１３、１４のアノードに接続している。   The anode of the first stage LED 11a included in the LED array 11 (hereinafter referred to as “the anode of the LED array 11”, and so on) is a terminal for outputting the current of the rectifier circuit 15 (hereinafter referred to as “output terminal”) and the LED array. 12 anodes are connected. The cathode of the last stage LED 12a included in the LED array 12 (hereinafter referred to as “the cathode of the LED array 12”, and so on) is connected to the anodes of the LED arrays 13 and 14.

バイパス回路１６は、デプレッション型のＦＥＴ１６ａ（第１スイッチ素子）と抵抗１６ｂ（第１電流検出素子）からなる。バイパス回路１７は、デプレッション型のＦＥＴ１７ａ（第２スイッチ素子）と抵抗１７ｂ（第２電流検出素子）からなる。定電流回路１８は、デプレッション型のＦＥＴ１８ａ（第３スイッチ素子）と抵抗１８ｂ（第３電流検出素子）からなる。バイパス回路１６、１７及び定電流回路１８では、それぞれＦＥＴ１６ａ〜１８ａのドレインが電流入力端子、抵抗１６ｂ〜１８ｂの左端子が電流出力端子であり、ＦＥＴ１６ａ〜１８ａのソース及びゲートはそれぞれ抵抗１６ｂ〜１８ｂの右端子及び左端子に接続している。ＬＥＤ列１１、１４、１３のカソードはそれぞれＦＥＴ１６ａ、１７ａ、１８ａのドレインに接続している。抵抗１８ｂの左端子と抵抗１７ｂの右端子、抵抗１７ｂの左端子と抵抗１６ｂの右端子、抵抗１６ｂの左端子と整流回路１５の電流が戻る端子（以下「グランド端子」と呼ぶ）がそれぞれ接続している。   The bypass circuit 16 includes a depletion type FET 16a (first switch element) and a resistor 16b (first current detection element). The bypass circuit 17 includes a depletion type FET 17a (second switch element) and a resistor 17b (second current detection element). The constant current circuit 18 includes a depletion type FET 18a (third switch element) and a resistor 18b (third current detection element). In the bypass circuits 16 and 17 and the constant current circuit 18, the drains of the FETs 16a to 18a are current input terminals, the left terminals of the resistors 16b to 18b are current output terminals, and the sources and gates of the FETs 16a to 18a are resistors 16b to 18b, respectively. Are connected to the right and left terminals. The cathodes of the LED strings 11, 14, and 13 are connected to the drains of the FETs 16a, 17a, and 18a, respectively. The left terminal of the resistor 18b and the right terminal of the resistor 17b, the left terminal of the resistor 17b and the right terminal of the resistor 16b, and the left terminal of the resistor 16b and a terminal to which the current of the rectifier circuit 15 returns (hereinafter referred to as a “ground terminal”) are connected. doing.

次に図２によりＬＥＤ駆動回路１０の動作を説明する。なお、特別な明示なしに図１に含まれる部品を参照する。図２（ａ）に示した全波整流電圧Ｖ０は、整流回路１５のグランド端子を０（Ｖ）としたとき出力端子に現れる電圧である。図２（ａ）に示す位相ｔ１は、全波整流電圧Ｖ０が０（Ｖ）からＬＥＤ列１１の閾値電圧に等しい電圧Ｖ１になるまでの期間である。図２（ｂ）に示すように、位相ｔ１においてＬＥＤ駆動回路１０に電流は流れない。   Next, the operation of the LED drive circuit 10 will be described with reference to FIG. It should be noted that the parts included in FIG. The full-wave rectified voltage V0 shown in FIG. 2A is a voltage that appears at the output terminal when the ground terminal of the rectifier circuit 15 is 0 (V). A phase t1 shown in FIG. 2A is a period from when the full-wave rectified voltage V0 becomes 0 (V) to a voltage V1 equal to the threshold voltage of the LED array 11. As shown in FIG. 2B, no current flows through the LED drive circuit 10 at the phase t1.

位相ｔ２は、全波整流電圧Ｖ０が電圧Ｖ１からＬＥＤ列１２、１４の閾値電圧の和となる電圧Ｖ２まで上昇する期間である。位相ｔ２では、整流回路１５の出力端子を発し、ＬＥＤ列１１、ＦＥＴ１６ａのドレイン−ソース間、及び抵抗１６ｂを経てグランド端子に至る電流Ｉ１が流れ、ＬＥＤ列１１が低い色温度で発光する。図２（ｂ）に示すように、電流Ｉ１は、位相ｔ２の最初のタイミングで急激に増加し、その後定電流Ｉ１１となる。抵抗１６ｂは電流検出抵抗として機能する。電流Ｉ１により発生する抵抗１６ｂの電圧降下がＦＥＴ１６ａにフィードバックし、ＦＥＴ１６ａのドレイン−ソース間電流が定電流化する。   The phase t2 is a period in which the full-wave rectified voltage V0 rises from the voltage V1 to the voltage V2 that is the sum of the threshold voltages of the LED strings 12 and 14. In the phase t2, the current I1 that is emitted from the output terminal of the rectifier circuit 15 and flows to the ground terminal through the LED string 11, the drain-source of the FET 16a, and the resistor 16b flows, and the LED string 11 emits light at a low color temperature. As shown in FIG. 2B, the current I1 increases rapidly at the first timing of the phase t2, and then becomes a constant current I11. The resistor 16b functions as a current detection resistor. The voltage drop of the resistor 16b generated by the current I1 is fed back to the FET 16a, and the drain-source current of the FET 16a becomes constant.

位相ｔ３は、全波整流電圧Ｖ０が電圧Ｖ２からＬＥＤ列１２、１３の閾値電圧の和となる電圧Ｖ３まで上昇する期間である。位相ｔ３では、整流回路１５の出力端子を発し、ＬＥＤ列１２、１４、ＦＥＴ１７ａのドレイン−ソース間、及び抵抗１７ｂ、１６ｂを経てグランド端子に至る電流Ｉ２が流れ、ＬＥＤ列１２、１４がそれぞれ高い色温度及び低い色温度で発光する。図２（ｂ）に示すように、位相ｔ３の最初のタイミングでは、電流Ｉ２が抵抗１６ｂに流れ込むため電流Ｉ１が急激に減少し、これと同時に電流Ｉ２が急激に増加する。その後、電流Ｉ１は０（Ａ）となり、電流Ｉ２は定電流Ｉ１２となる。抵抗１７ｂは、電流検出抵抗として機能し、電流Ｉ２による抵抗１７ｂの電圧降下でＦＥＴ１７ａのドレイン−ソース間電流を定電流化する。   The phase t3 is a period in which the full-wave rectified voltage V0 rises from the voltage V2 to the voltage V3 that is the sum of the threshold voltages of the LED strings 12 and 13. At phase t3, the output terminal of the rectifier circuit 15 is emitted, the current I2 flows between the LED strings 12 and 14, the drain and source of the FET 17a, and through the resistors 17b and 16b to the ground terminal, and the LED strings 12 and 14 are high. Emits light at low and low color temperatures. As shown in FIG. 2B, at the first timing of the phase t3, the current I2 flows into the resistor 16b, so that the current I1 decreases rapidly, and at the same time, the current I2 increases rapidly. Thereafter, the current I1 becomes 0 (A), and the current I2 becomes the constant current I12. The resistor 17b functions as a current detection resistor, and makes the drain-source current of the FET 17a constant by the voltage drop of the resistor 17b due to the current I2.

位相ｔ４は、全波整流電圧Ｖ０が電圧Ｖ３を超える期間である。位相ｔ４では、整流回路１５の出力端子を発し、ＬＥＤ列１２、１３、ＦＥＴ１８ａのドレイン−ソース間、及び抵抗１８ｂ、１７ｂ、１６ｂを経てグランド端子に至る電流Ｉ３が流れ、ＬＥＤ列１２、１３が高い色温度で発光する。図２（ｂ）に示すように、位相ｔ４の最初のタイミングでは電流Ｉ３が増加し、その後電流Ｉ３は定電流Ｉ１３となる。なお、位相ｔ４の最初のタイミングでは、電流Ｉ３により抵抗１７ｂの電圧降下が増大するため、ＦＥＴ１７ａのドレイン−ソース間はカットオフする（ＦＥＴ１６ａのドレイン−ソース間はカットオフが維持される）。抵抗１８ｂは電流検出抵抗として機能し、電流Ｉ３による抵抗１８ｂの電圧降下でＦＥＴ１８ａのドレイン−ソース間電流を定電流化する。   Phase t4 is a period in which full-wave rectified voltage V0 exceeds voltage V3. At phase t4, the output terminal of the rectifier circuit 15 is emitted, and the current I3 flows between the LED strings 12 and 13, the drain-source of the FET 18a, and the resistors 18b, 17b, and 16b to the ground terminal. Emits light at a high color temperature. As shown in FIG. 2B, the current I3 increases at the first timing of the phase t4, and then the current I3 becomes a constant current I13. At the first timing of phase t4, the voltage drop of the resistor 17b increases due to the current I3, so that the drain-source of the FET 17a is cut off (the cutoff is maintained between the drain-source of the FET 16a). The resistor 18b functions as a current detection resistor, and makes the drain-source current of the FET 18a constant by the voltage drop of the resistor 18b due to the current I3.

位相ｔ５、ｔ６、ｔ７は、それぞれ全波整流電圧Ｖ０が、電圧Ｖ３から電圧Ｖ２、電圧Ｖ２から電圧Ｖ１、電圧Ｖ１から０（Ｖ）に下降する期間である。全波整流電圧Ｖ０が低下する位相ｔ５、ｔ６、ｔ７では、全波整流電圧Ｖ０が上昇する位相ｔ１、ｔ２、ｔ３とは逆の過程を辿る。   Phases t5, t6, and t7 are periods in which full-wave rectified voltage V0 drops from voltage V3 to voltage V2, from voltage V2 to voltage V1, and from voltage V1 to 0 (V), respectively. In phases t5, t6, and t7 in which the full-wave rectified voltage V0 decreases, the processes reverse to the phases t1, t2, and t3 in which the full-wave rectified voltage V0 increases.

調光器１２２は、商用交流電源１２１が出力する交流の位相の一部を切り取る（０（Ｖ）にする）。図２（ｃ）に示すように、整流回路１５は、調光器１２２の出力する電圧波形を全波整流し脈流電圧Ｖ０ａを出力する。脈流電圧Ｖ０ａは、全波整流電圧Ｖ０（破線）の先頭部分を切り取ったものであり、調光度合に応じて切り取る部分が増減する。なお、図２（ｃ）で例示した脈流電圧Ｖ０ａでは、ＬＥＤ駆動回路１０に、電流Ｉ３ａ、Ｉ２ａ、Ｉ１ａが流れる。電流Ｉ３ａ、Ｉ２ａ、Ｉ１ａは、脈流電圧Ｖ０ａが存在する期間における電流Ｉ３、Ｉ２、Ｉ１である。   The dimmer 122 cuts off a part of the AC phase output from the commercial AC power supply 121 (sets to 0 (V)). As shown in FIG. 2C, the rectifier circuit 15 performs full-wave rectification on the voltage waveform output from the dimmer 122 and outputs a pulsating voltage V0a. The pulsating voltage V0a is obtained by cutting off the leading portion of the full-wave rectified voltage V0 (broken line), and the portion to be cut off increases or decreases depending on the degree of dimming. 2C, currents I3a, I2a, and I1a flow through the LED drive circuit 10. In the pulsating voltage V0a illustrated in FIG. The currents I3a, I2a, and I1a are the currents I3, I2, and I1 during the period in which the pulsating voltage V0a is present.

調光度が低いとき、脈流電圧Ｖ０ａでは、切り取られる部分が大きくなるため電圧の低い部分（位相ｔ６）の割合が多くなる。これは、例えば、図２（ｃ）において例示した脈流電圧Ｖ０ａよりも全波整流電圧Ｖ０が大きく切り取られ、脈流電圧Ｖ０ａに位相ｔ６の一部と位相ｔ７だけが含まれるような状態である。このときＬＥＤ列１１の発光が支配的となり、ＬＥＤ駆動回路１０の発光色の色温度は低くなる。   When the dimming degree is low, in the pulsating current voltage V0a, the portion to be cut off becomes large, so the proportion of the low voltage portion (phase t6) increases. This is because, for example, the full-wave rectified voltage V0 is cut larger than the pulsating voltage V0a illustrated in FIG. 2C, and the pulsating voltage V0a includes only a part of the phase t6 and the phase t7. is there. At this time, the light emission of the LED row 11 becomes dominant, and the color temperature of the light emission color of the LED drive circuit 10 becomes low.

調光度が中間的な状態にあるとき、脈流電圧Ｖ０では中間の電圧となる期間（位相ｔ５）の割合が多くなる。これは、例えば、図２（ｃ）において例示した脈流電圧Ｖ０ａよりももう少し大きく全波整流電圧が切り取られ、脈流電圧Ｖ０ａに位相ｔ５の一部と位相ｔ６、ｔ７だけが含まれるような状態である。位相ｔ５では、ＬＥＤ列１２が高い色温度で発光する一方、ＬＥＤ列１４は低い色温度で発光する。この結果、ＬＥＤ駆動回路１０としては中間的な色温度で発光する。なお、この脈流電圧Ｖ０ａでも位相ｔ６でＬＥＤ列１１が発光する。しかしながら、位相ｔ５における電流Ｉ２ａの値並びにＬＥＤ１２ａ及びＬＥＤ１４ａの数が、位相ｔ６における電流Ｉ１ａ及びＬＥＤ１１ａの数よりも大きいので、ＬＥＤ列１１の発光が色温度に与える影響が小さくなり、位相ｔ５における発光が支配的になる。   When the dimming degree is in an intermediate state, the ratio of the period (phase t5) in which the pulsating voltage V0 is an intermediate voltage increases. For example, the full-wave rectified voltage is cut off a little larger than the pulsating voltage V0a illustrated in FIG. 2C, and the pulsating voltage V0a includes only a part of the phase t5 and the phases t6 and t7. State. At phase t5, the LED array 12 emits light at a high color temperature, while the LED array 14 emits light at a low color temperature. As a result, the LED drive circuit 10 emits light at an intermediate color temperature. Note that the LED array 11 emits light at the phase t6 even with this pulsating voltage V0a. However, since the value of the current I2a at the phase t5 and the number of the LEDs 12a and 14a are larger than the number of the current I1a and the LED 11a at the phase t6, the influence of the light emission of the LED array 11 on the color temperature is reduced, and the light emission at the phase t5 Becomes dominant.

調光度が高いとき、脈流電圧Ｖ０ａは電圧のもっとも高い期間（位相ｔ４）を多く含むようになり、ＬＥＤ駆動回路１０の発光色の色温度が高くなる（図２（ｃ）の脈流電圧Ｖ０ａ）。なお、脈流電圧Ｖ０ａでは位相ｔ５、ｔ６でＬＥＤ列１４、１１がそれぞれ発光する。しかしながら、位相ｔ４における電流Ｉ３ａの値並びにＬＥＤ１２ａ及びＬＥＤ１３ａの数が、位相ｔ５、ｔ６における電流Ｉ２ａ、Ｉ１ａの値及びＬＥＤ１４ａ、１１ａの数よりも大きいので、ＬＥＤ列１１、１４の発光が色温度に与える影響は小さくなり、位相ｔ４におけるＬＥＤ列１２、１３の発光が支配的となる。なお、さらに調光度を上げ、脈流電圧Ｖ０ａに位相ｔ２、ｔ３が含まれるようになると、ＬＥＤ駆動回路１０の輝度は上昇する一方で、位相ｔ２、ｔ３におけるＬＥＤ列１１、１４の点灯により色温度が若干下がる（図５の発光特性５１を参照）。   When the dimming degree is high, the pulsating voltage V0a includes many periods of the highest voltage (phase t4), and the color temperature of the light emission color of the LED drive circuit 10 becomes high (the pulsating voltage shown in FIG. 2C). V0a). In the pulsating voltage V0a, the LED rows 14 and 11 emit light at phases t5 and t6, respectively. However, since the value of the current I3a in the phase t4 and the number of the LEDs 12a and 13a are larger than the values of the currents I2a and I1a and the number of the LEDs 14a and 11a in the phases t5 and t6, the light emission of the LED rows 11 and 14 becomes the color temperature. The effect is small, and the light emission of the LED strings 12 and 13 at the phase t4 becomes dominant. When the dimming degree is further increased and the pulsating voltage V0a includes the phases t2 and t3, the luminance of the LED drive circuit 10 is increased, while the LEDs 11 and 14 are turned on at the phases t2 and t3. The temperature drops slightly (see the light emission characteristic 51 in FIG. 5).

ＬＥＤ駆動回路１０は、全波整流電圧Ｖ０が低い位相ｔ２、ｔ６、中間的な位相ｔ３、ｔ５、高い位相ｔ４に対し、低い色温度、中間の色温度、高い色温度で発光する。調光のため全波整流電圧Ｖ０の一部分の位相を切り取った脈流電圧Ｖ０ａに対し、ＬＥＤ駆動回路１０は、低い調光状態では低い色温度での発光を支配的にし、中間的な調光状態では中間の色温度での発光を支配的にしている。またＬＥＤ駆動回路１０は、高い調光状態では高い色温度での発光を支配的にするため、位相ｔ４においてＬＥＤ列１４を消灯し、ＬＥＤ列１２、１３だけを発光させている。以上のようにしてＬＥＤ駆動回路１０は、回路構成が簡単でありながら調光に応じて発光色を滑らかに変化させることができる。   The LED drive circuit 10 emits light at a low color temperature, an intermediate color temperature, and a high color temperature with respect to the phases t2, t6, the intermediate phases t3, t5, and the high phase t4 where the full-wave rectified voltage V0 is low. The LED drive circuit 10 dominates light emission at a low color temperature in a low dimming state with respect to the pulsating voltage V0a obtained by cutting off a part of the phase of the full-wave rectified voltage V0 for dimming. In the state, light emission at an intermediate color temperature is dominant. Further, the LED drive circuit 10 makes the light emission at a high color temperature dominant in the high dimming state, so that the LED row 14 is turned off at the phase t4 and only the LED rows 12 and 13 are caused to emit light. As described above, the LED drive circuit 10 can change the emission color smoothly according to the light control while having a simple circuit configuration.

ＬＥＤ駆動回路１０のＬＥＤ列１３のカソードは、定電流回路１８を介してバイパス回路１７に含まれる電流検出用の抵抗１７ｂに接続している。ただし、ＬＥＤ列１３のカソードは、直接又は電流制限抵抗や定電流ダイオードを介して抵抗１７ｂに接続しても良い。なお、定電流回路１８には、素子数が少なく、定電流Ｉ１３の値を抵抗１８ｂの値で調整できるという特徴がある。また定電流回路１８の代わりに、スイッチ素子用のエンハンスメント型ＦＥＴ、反転増幅用のバイポーラトランジスタ、電流検出抵抗及びプルアップ抵抗からなる良く知られた電流制限回路を用いても良い（バイパス回路１６、１７も同様）。   The cathode of the LED row 13 of the LED drive circuit 10 is connected to a current detection resistor 17 b included in the bypass circuit 17 via a constant current circuit 18. However, the cathode of the LED array 13 may be connected to the resistor 17b directly or via a current limiting resistor or a constant current diode. The constant current circuit 18 has a feature that the number of elements is small and the value of the constant current I13 can be adjusted by the value of the resistor 18b. Further, instead of the constant current circuit 18, a well-known current limiting circuit including an enhancement type FET for a switching element, a bipolar transistor for inverting amplification, a current detection resistor and a pull-up resistor may be used (bypass circuit 16, 17 is the same).

（第２実施形態及び比較例）
図３は、他のＬＥＤ駆動回路２０の回路図である。図４は、比較例として示すＬＥＤ駆動回路２５の回路図である。図５は、ＬＥＤ駆動回路２０、２５の発光色と調光度の関係を示すグラフである。図５の縦軸は色温度（ＣＣＴ（Ｋ））、横軸は調光度（Ｐｏｗｅｒ（％））であり、図５では、ＬＥＤ駆動回路２０の発光特性５１とＬＥＤ駆動回路２５の発光特性５２に加えて、参考のため白熱電球の発光特性５３とハロゲンランプの発光特性５４を示している。(Second embodiment and comparative example)
FIG. 3 is a circuit diagram of another LED drive circuit 20. FIG. 4 is a circuit diagram of an LED drive circuit 25 shown as a comparative example. FIG. 5 is a graph showing the relationship between the emission color of the LED drive circuits 20 and 25 and the dimming degree. The vertical axis in FIG. 5 is the color temperature (CCT (K)) and the horizontal axis is the dimming degree (Power (%)). In FIG. 5, the light emission characteristic 51 of the LED drive circuit 20 and the light emission characteristic 52 of the LED drive circuit 25 are shown. In addition, for the sake of reference, the light emission characteristic 53 of an incandescent bulb and the light emission characteristic 54 of a halogen lamp are shown.

ＬＥＤ駆動回路２０では、図１に示したＬＥＤ駆動回路１０に対し、逆流防止用ダイオード２１と、コンデンサ２２と、ゲート保護抵抗１６ｃ、１７ｃ、１８ｃとが追加されている。ＬＥＤ駆動回路２５は、ＬＥＤ駆動回路２０とは、ＬＥＤ列１４を備えていないところだけが相違している。コンデンサ２２は、ＬＥＤ列１２に並列接続され、位相ｔ１、ｔ７（図２（ｂ）参照）において放電してＬＥＤ列１２を点灯させる。逆流防止用ダイオード２１は、整流回路１５の出力端子とＬＥＤ列１２のアノードの間に挿入され、コンデンサ２２の放電に際し予期しない電流経路が発生しないようにする。ゲート保護抵抗１６ｃ、１７ｃ、１８ｃは、ＦＥＴ１６ａ、１７ａ、１８ａのゲートに接続され、それらのゲートを静電気やサージから保護する。   In the LED drive circuit 20, a backflow prevention diode 21, a capacitor 22, and gate protection resistors 16c, 17c, and 18c are added to the LED drive circuit 10 shown in FIG. The LED drive circuit 25 is different from the LED drive circuit 20 only in that the LED row 14 is not provided. The capacitor 22 is connected in parallel to the LED string 12, and discharges at the phases t1 and t7 (see FIG. 2B) to light the LED string 12. The backflow prevention diode 21 is inserted between the output terminal of the rectifier circuit 15 and the anode of the LED string 12 so that an unexpected current path is not generated when the capacitor 22 is discharged. The gate protection resistors 16c, 17c, and 18c are connected to the gates of the FETs 16a, 17a, and 18a, and protect those gates from static electricity and surge.

ＬＥＤ駆動回路２０、２５の動作は、基本的に図１に示したＬＥＤ駆動回路１０及び図１１に示したＬＥＤ駆動回路３００と等しく、位相ｔ１、ｔ７においてコンデンサ２２の放電によりＬＥＤ列１２が点灯するところだけが異なる。ＬＥＤ駆動回路２０は、位相ｔ１、ｔ７におけるフリッカが軽減される点で、ＬＥＤ駆動回路１０に比べて改善されている。   The operation of the LED drive circuits 20 and 25 is basically the same as that of the LED drive circuit 10 shown in FIG. 1 and the LED drive circuit 300 shown in FIG. 11, and the LED row 12 is turned on by the discharge of the capacitor 22 at the phases t1 and t7. Only the place to do is different. The LED drive circuit 20 is improved compared to the LED drive circuit 10 in that flicker at phases t1 and t7 is reduced.

ＬＥＤ１１ａ、１４ａの発光色は２０００Ｋ、ＬＥＤ１２ａ、１３ａの発光色は３０００Ｋである。ＬＥＤ列１１、１２、１３、１４の直列段数は、それぞれ、５段、１４段、７段、４段である。図５を参照すると、ＬＥＤ駆動回路２０の発光特性５１では、ＬＥＤ駆動回路２５の発光特性５２に比べて調光度に応じて色温度が滑らかに変わっていることが分かる。   The emission color of the LEDs 11a and 14a is 2000K, and the emission color of the LEDs 12a and 13a is 3000K. The number of serial stages of the LED strings 11, 12, 13, and 14 is 5, 14, 14, 7, and 4, respectively. Referring to FIG. 5, it can be seen that in the light emission characteristic 51 of the LED drive circuit 20, the color temperature changes smoothly according to the dimming degree as compared with the light emission characteristic 52 of the LED drive circuit 25.

（第３実施形態）
図６は、さらに他のＬＥＤ駆動回路３０の回路図である。図６に示すように、ＬＥＤ駆動回路３０は、図１に示したＬＥＤ駆動回路１０とは、ＦＥＴ１６ａと抵抗１６ｂの間、及びＦＥＴ１７ａと抵抗１７ｂの間にそれぞれ抵抗１６ｄ、１７ｄが追加されているところだけが相違している。抵抗１６ｄ、１７ｄを挿入すると、位相ｔ３の最初のタイミング、位相ｔ４の最初と最後のタイミング、及び位相ｔ５の最後のタイミングにおける電流Ｉ１、Ｉ２、Ｉ３の変化（図２を参照）が緩やかになる。この結果、ＬＥＤ駆動回路３０では、ＬＥＤ駆動回路１０に比べて調光に応じて発光色の色温度がより滑らかに変化する。(Third embodiment)
FIG. 6 is a circuit diagram of still another LED driving circuit 30. As shown in FIG. 6, the LED drive circuit 30 is different from the LED drive circuit 10 shown in FIG. 1 in that resistors 16d and 17d are added between the FET 16a and the resistor 16b and between the FET 17a and the resistor 17b, respectively. Only the difference is. When the resistors 16d and 17d are inserted, changes in the currents I1, I2, and I3 (see FIG. 2) at the first timing of the phase t3, the first and last timings of the phase t4, and the last timing of the phase t5 (see FIG. 2) are moderated. . As a result, in the LED drive circuit 30, the color temperature of the emitted color changes more smoothly according to the light control than in the LED drive circuit 10.

（第４実施形態）
図７は、さらに他のＬＥＤ駆動回路４０の回路図である。図７に示すように、ＬＥＤ駆動回路４０は、図１に示したＬＥＤ駆動回路１０のバイパス回路１６、１７をスイッチ４６（第１電流制限部、第１又は第４スイッチ）及びスイッチ４７（第２電流制限部、第２又は第５スイッチ）に置き換え、ＬＥＤ駆動回路１０の定電流回路１８を取り去ったものである。ＬＥＤ駆動回路４０は、整流回路１５と、低い色温度で発光するＬＥＤ列１１（第１又は第５ＬＥＤ列）及びＬＥＤ列１４（第４又は第８ＬＥＤ列）と、高い色温度で発光するＬＥＤ列１２（第２又は第６ＬＥＤ列）及びＬＥＤ列１３（第３又は第７ＬＥＤ列）と、スイッチ４６、４７と、電圧検出回路６０と、制御回路７０とを備えている。(Fourth embodiment)
FIG. 7 is a circuit diagram of still another LED driving circuit 40. As shown in FIG. 7, the LED drive circuit 40 replaces the bypass circuits 16 and 17 of the LED drive circuit 10 shown in FIG. 1 with a switch 46 (first current limiting unit, first or fourth switch) and a switch 47 (first switch). (2 current limiter, second or fifth switch) and the constant current circuit 18 of the LED drive circuit 10 is removed. The LED drive circuit 40 includes a rectifier circuit 15, an LED array 11 (first or fifth LED array) and LED array 14 (fourth or eighth LED array) that emit light at a low color temperature, and an LED array that emits light at a high color temperature. 12 (second or sixth LED string) and LED string 13 (third or seventh LED string), switches 46 and 47, voltage detection circuit 60, and control circuit 70.

電圧検出回路６０は、整流回路１５に並列に接続され、全波整流電圧Ｖ０の値を検出する。制御回路７０は、電圧検出回路６０が検出した全波整流電圧Ｖ０の値に応じて、スイッチ４６、４７の導通を制御する。スイッチ４６、４７は、アナログスイッチでもカットオフできる電流制限回路でも良く、制御回路７０によりそのオンオフが切り換えられる。   The voltage detection circuit 60 is connected in parallel to the rectifier circuit 15 and detects the value of the full-wave rectified voltage V0. The control circuit 70 controls conduction of the switches 46 and 47 in accordance with the value of the full-wave rectified voltage V0 detected by the voltage detection circuit 60. The switches 46 and 47 may be analog switches or current limiting circuits that can be cut off, and are turned on and off by the control circuit 70.

図２、７を参照しながらＬＥＤ駆動回路４０の動作を説明する。ＬＥＤ列１２、１４の閾値電圧の和となる電圧Ｖ２よりも低い電圧を「低い電圧」、電圧Ｖ２以上でＬＥＤ列１２、１３の閾値電圧の和である電圧Ｖ３よりも低い電圧を「中間の電圧」とする。スイッチ４６は整流回路１５が低い電圧を出力しているときに導通し、スイッチ４７は整流回路１５が中間の電圧を出力しているときに導通する。   The operation of the LED drive circuit 40 will be described with reference to FIGS. A voltage lower than the voltage V2 that is the sum of the threshold voltages of the LED strings 12 and 14 is “low voltage”, and a voltage that is higher than the voltage V2 and lower than the voltage V3 that is the sum of the threshold voltages of the LED strings 12 and 13 is “intermediate” "Voltage". The switch 46 becomes conductive when the rectifier circuit 15 outputs a low voltage, and the switch 47 becomes conductive when the rectifier circuit 15 outputs an intermediate voltage.

整流回路１５が全波整流電圧Ｖ０を出力する場合、全波整流電圧Ｖ０がＬＥＤ列１１の閾値電圧（電圧Ｖ１）未満である位相ｔ１では、スイッチ４６を導通させておいても電流Ｉ４１は流れない。全波整流電圧Ｖ０が電圧Ｖ１以上で電圧Ｖ２未満となる位相ｔ２では、ＬＥＤ列１１及びスイッチ４６を電流Ｉ４１が流れ、ＬＥＤ列１１が低い色温度で発光する。全波整流電圧Ｖ０が電圧Ｖ２以上で電圧Ｖ３未満となる位相ｔ３では、スイッチ４６がオフしスイッチ４７がオンする。このときＬＥＤ列１２、１４及びスイッチ４７に電流Ｉ４２が流れ、ＬＥＤ列１２、１４が中間の色温度で発光する。全波整流電圧Ｖ０が電圧Ｖ３以上となる位相では、スイッチ４７がオフし、ＬＥＤ列１２、１３に電流Ｉ４３が流れ、ＬＥＤ列１２、１３が高い色温度で発光する。   When the rectifier circuit 15 outputs the full-wave rectified voltage V0, the current I41 flows even in the phase t1 where the full-wave rectified voltage V0 is less than the threshold voltage (voltage V1) of the LED array 11 even when the switch 46 is turned on. Absent. In the phase t2 where the full-wave rectified voltage V0 is equal to or higher than the voltage V1 and lower than the voltage V2, the current I41 flows through the LED array 11 and the switch 46, and the LED array 11 emits light at a low color temperature. At phase t3 when full-wave rectified voltage V0 is equal to or higher than voltage V2 and lower than voltage V3, switch 46 is turned off and switch 47 is turned on. At this time, a current I42 flows through the LED strings 12, 14 and the switch 47, and the LED strings 12, 14 emit light at an intermediate color temperature. In a phase where the full-wave rectified voltage V0 is equal to or higher than the voltage V3, the switch 47 is turned off, the current I43 flows through the LED strings 12 and 13, and the LED strings 12 and 13 emit light at a high color temperature.

全波整流電圧Ｖ０が低下する位相では、全波整流電圧が上昇する位相とは逆の過程を辿る。整流回路１５が脈流電圧Ｖ０ａを出力する場合、調光度に応じて脈流電圧Ｖ０ａに含まれる前述の位相の割合が変化し発光色が変化する。この結果、ＬＥＤ駆動回路４０も、ＬＥＤ駆動回路１０と同様に、回路構成が簡単でありながら調光に応じて発光色を滑らかに変化させることができる。   The phase in which the full-wave rectified voltage V0 decreases follows the reverse process of the phase in which the full-wave rectified voltage increases. When the rectifier circuit 15 outputs the pulsating voltage V0a, the ratio of the phase included in the pulsating voltage V0a changes according to the dimming degree, and the emission color changes. As a result, the LED drive circuit 40 can change the emission color smoothly in accordance with the light control while the circuit configuration is simple, as with the LED drive circuit 10.

図１に示したＬＥＤ駆動回路１０では、ＬＥＤ列１２を流れる電流Ｉ２が、バイパス回路１６に含まれるＦＥＴ１６ａをカットオフし、ＬＥＤ列１３を流れる電流Ｉ３が、バイパス回路１７に含まれるＦＥＴ１７ａをカットオフする。これと同様に、ＬＥＤ駆動回路４０でも、制御回路７０が、ＬＥＤ列１２を流れる電流Ｉ４２に応じてスイッチ４６をオフし、ＬＥＤ列１３を流れる電流Ｉ４３に応じてスイッチ４７をオフしても良い。   In the LED drive circuit 10 shown in FIG. 1, the current I2 flowing through the LED string 12 cuts off the FET 16a included in the bypass circuit 16, and the current I3 flowing through the LED string 13 cuts the FET 17a included in the bypass circuit 17. Turn off. Similarly, in the LED drive circuit 40, the control circuit 70 may turn off the switch 46 according to the current I 42 flowing through the LED string 12 and turn off the switch 47 according to the current I 43 flowing through the LED string 13. .

Claims (9)

調光に連動して出力が変化する電源に接続された整流回路と、
前記整流回路に接続され、かつ複数のＬＥＤが直列に接続された第１ＬＥＤ列と、
前記整流回路に対して前記第１ＬＥＤ列と並列に接続され、かつ複数のＬＥＤが直列に接続された第２ＬＥＤ列と、
前記第２ＬＥＤ列と直列に接続され、かつ複数のＬＥＤが直列に接続された第３ＬＥＤ列と、
前記第２ＬＥＤ列と前記第３ＬＥＤ列との間に一端が接続され、かつ複数のＬＥＤが直列に接続された第４ＬＥＤ列と、
前記第１ＬＥＤ列を流れる電流を制限する第１電流制限部と、
前記第２及び第４ＬＥＤ列を流れる電流を制限する第２電流制限部と、を備え、
前記第１ＬＥＤ列に含まれる前記複数のＬＥＤは、前記第２及び第３ＬＥＤ列に含まれる前記複数のＬＥＤよりも低い色温度で発光し、
前記第１ＬＥＤ列が発光するための第１閾値電圧は、前記第２及び第４ＬＥＤ列が発光するための第２閾値電圧よりも小さく、
前記第２閾値電圧は、前記第２及び第３ＬＥＤ列が発光するための第３閾値電圧よりも小さい、
ことを特徴とするＬＥＤ駆動回路。A rectifier circuit connected to a power supply whose output changes in conjunction with dimming,
A first LED row connected to the rectifier circuit and having a plurality of LEDs connected in series;
A second LED string connected in parallel to the first LED string to the rectifier circuit, and a plurality of LEDs connected in series;
A third LED row connected in series with the second LED row, and a plurality of LEDs connected in series;
A fourth LED row in which one end is connected between the second LED row and the third LED row, and a plurality of LEDs are connected in series;
A first current limiting unit that limits a current flowing through the first LED string;
A second current limiting unit that limits a current flowing through the second and fourth LED strings,
The plurality of LEDs included in the first LED row emit light at a lower color temperature than the plurality of LEDs included in the second and third LED rows,
The first threshold voltage for the first LED array to emit light is smaller than the second threshold voltage for the second and fourth LED arrays to emit light,
The second threshold voltage is smaller than a third threshold voltage for the second and third LED arrays to emit light,
An LED drive circuit characterized by that. 前記第１電流制限部は、前記整流回路の出力電圧が第１範囲内にあるときに、前記第１ＬＥＤ列を流れる電流を制限し、
前記第２電流制限部は、前記出力電圧が前記第１範囲よりも高い第２範囲内にあるときに、前記第２及び第４ＬＥＤ列を流れる電流を制限し、
前記整流回路の電流出力端子は、前記第１及び第２ＬＥＤ列のアノードに接続し、
前記第１ＬＥＤ列のカソードは、前記第１電流制限部の電流入力端子に接続し、
前記第２ＬＥＤ列のカソードは、前記第３及び第４ＬＥＤ列のアノードに接続し、
前記第３ＬＥＤ列のカソード並びに前記第１及び第２電流制限部の電流出力端子は、直接又は回路素子を介して前記整流回路の電流が戻る端子に接続し、
前記第４ＬＥＤ列のカソードは、前記第２電流制限部の電流入力端子に接続している、請求項１に記載のＬＥＤ駆動回路。The first current limiting unit limits a current flowing through the first LED string when an output voltage of the rectifier circuit is within a first range,
The second current limiting unit limits a current flowing through the second and fourth LED strings when the output voltage is in a second range higher than the first range,
A current output terminal of the rectifier circuit is connected to anodes of the first and second LED strings;
The cathode of the first LED row is connected to the current input terminal of the first current limiting unit,
A cathode of the second LED string is connected to an anode of the third and fourth LED strings;
The cathode of the third LED row and the current output terminals of the first and second current limiting units are connected to a terminal to which the current of the rectifier circuit returns directly or via a circuit element,
2. The LED drive circuit according to claim 1, wherein a cathode of the fourth LED row is connected to a current input terminal of the second current limiting unit. 前記第１電流制限部は、第１スイッチ素子及び第１電流検出素子を有し、
前記第２電流制限部は、第２スイッチ素子及び第２電流検出素子を有し、
前記第３ＬＥＤ列のカソードは、直接又は回路素子を介して前記第２電流検出素子に接続し、
前記第２電流制限部の電流出力端子は、前記第１電流検出素子に接続し、
前記第１電流制限部の電流出力端子は、前記整流回路の電流が戻る端子に接続している、請求項２に記載のＬＥＤ駆動回路。The first current limiting unit includes a first switch element and a first current detection element,
The second current limiting unit includes a second switch element and a second current detection element,
The cathode of the third LED row is connected to the second current detection element directly or via a circuit element;
A current output terminal of the second current limiting unit is connected to the first current detection element;
The LED drive circuit according to claim 2, wherein a current output terminal of the first current limiting unit is connected to a terminal to which a current of the rectifier circuit returns. 前記第３ＬＥＤ列のカソードは、第３スイッチ素子及び第３電流検出素子を有する第３電流制限回路を介して前記第２電流検出素子に接続している、請求項３に記載のＬＥＤ駆動回路。   4. The LED drive circuit according to claim 3, wherein a cathode of the third LED row is connected to the second current detection element via a third current limiting circuit having a third switch element and a third current detection element. 前記整流回路の電流出力端子と前記第２ＬＥＤ列のアノードの間に挿入された逆流防止用ダイオードと、
前記第２ＬＥＤ列と並列接続されたコンデンサと、
をさらに備える、請求項３又は４に記載のＬＥＤ駆動回路。A backflow prevention diode inserted between the current output terminal of the rectifier circuit and the anode of the second LED array;
A capacitor connected in parallel with the second LED string;
The LED drive circuit according to claim 3 or 4, further comprising: 前記第１スイッチ素子と前記第１電流検出素子の間又は前記第２スイッチ素子と前記第２電流検出素子の間に接続された抵抗をさらに有する、請求項３〜５のいずれか一項に記載のＬＥＤ駆動回路。   6. The device according to claim 3, further comprising a resistor connected between the first switch element and the first current detection element or between the second switch element and the second current detection element. LED drive circuit. 前記第２ＬＥＤ列を流れる電流が前記第１スイッチ素子をカットオフし、前記第３ＬＥＤ列を流れる電流が前記第２スイッチ素子をカットオフする、請求項３〜６のいずれか一項に記載のＬＥＤ駆動回路。   The LED according to any one of claims 3 to 6, wherein a current flowing through the second LED array cuts off the first switch element, and a current flowing through the third LED array cuts off the second switch element. Driving circuit. 前記第１電流制限部は、前記出力電圧が前記第１範囲内にあるときに導通する第１スイッチであり、
前記第２電流制限部は、前記出力電圧が前記第２範囲内にあるときに導通する第２スイッチである、請求項２に記載のＬＥＤ駆動回路。The first current limiting unit is a first switch that conducts when the output voltage is within the first range;
The LED driving circuit according to claim 2, wherein the second current limiting unit is a second switch that is turned on when the output voltage is within the second range. 前記第４ＬＥＤ列に含まれる前記複数のＬＥＤは、前記第２及び第３ＬＥＤ列に含まれる前記複数のＬＥＤよりも低い色温度で発光する、請求項１〜８のいずれか一項に記載のＬＥＤ駆動回路。   9. The LED according to claim 1, wherein the plurality of LEDs included in the fourth LED array emit light at a color temperature lower than that of the plurality of LEDs included in the second and third LED arrays. Driving circuit.
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