JP2007103232A - Led lighting circuit - Google Patents

Led lighting circuit Download PDF

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JP2007103232A
JP2007103232A JP2005293667A JP2005293667A JP2007103232A JP 2007103232 A JP2007103232 A JP 2007103232A JP 2005293667 A JP2005293667 A JP 2005293667A JP 2005293667 A JP2005293667 A JP 2005293667A JP 2007103232 A JP2007103232 A JP 2007103232A
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switch
led
current
coil
limit value
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JP4749110B2 (en
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Toshitaka Honda
年孝 本田
Shoji Dobashi
章二 土橋
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SHINKO DENSO CO Ltd
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SHINKO DENSO 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
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/30—Driver circuits
    • H05B45/37—Converter circuits
    • H05B45/3725—Switched mode power supply [SMPS]

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive LDE lighting circuit capable of lighting an LED with high efficiency, stably lighting an LDE in appearance even if a direct current power source with a certain voltage fluctuation is used. <P>SOLUTION: The LED lighting circuit is composed of a coil 13 excited by a current from a direct current power source 11 and accumulating energy; a current detecting resistor 15 connected to a current flowing position during both of driving period of the LED 12 lighted by an energy supplied at least from the direct current power source 11 or the coil 13, and exciting period of the coil 13; and a hysteresis comparator 17 having an upper limit value and lower limit value set in advance, turning off a switch 14 when the current detected by the current detecting resistor 15 exceeds the upper limit value, and turning on the switch 14 when the current detected by the current detecting resistor 15 becomes lower than the upper limit value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、直流電源からの電流で励磁されエネルギーを蓄積するコイルを有し、直流電源およびコイルの少なくともいずれか一方のエネルギーによりＬＥＤを点灯駆動するＬＥＤ点灯回路に関する。   The present invention relates to an LED lighting circuit that has a coil that is excited by a current from a DC power source and stores energy, and that drives the LED to be driven by the energy of at least one of the DC power source and the coil.

発光ダイオード（ＬＥＤ）は低抵抗特性であるので、ＬＥＤ点灯回路としては定電圧電源ではなく定電流電源で駆動されることが望ましい。一般に、定電圧電源は一般市販品も多く存在しその回路方式もほぼ確定しているが、定電流電源は測定器を除き一般市販品はほとんど存在しない。特にＬＥＤ点灯用としての定電流電源は、測定器並みの精度は必要としないので、高価な測定器用の定電流電源を用いることは好ましくない。   Since the light emitting diode (LED) has a low resistance characteristic, the LED lighting circuit is preferably driven by a constant current power supply instead of a constant voltage power supply. In general, many constant-voltage power supplies exist in general commercial products and their circuit systems are almost fixed. However, there are few constant-current power supplies except for measuring instruments. In particular, a constant current power source for lighting an LED does not require the same accuracy as a measuring instrument, and therefore it is not preferable to use an expensive constant current power source for a measuring instrument.

一方、ＬＥＤ点灯制御用として、携帯電話などの表示またはバックライト用としてのＬＥＤ点灯の電流制御用ＩＣが存在するが、これは３Ｖ程度の電池を使用した低電圧小電力の定電流電源であるので、数個のＬＥＤしか点灯することができない。このような電流制御用ＩＣを照明目的で、高電圧および大電力の制御に用いるには、多くの外付け部品を必要としあまり実用的ではない。   On the other hand, there is an LED lighting current control IC for LED lighting control, such as a display for a mobile phone or a backlight, which is a low voltage, low power constant current power source using a battery of about 3V. Therefore, only a few LEDs can be lit. In order to use such a current control IC for the purpose of lighting and control of a high voltage and a high power, many external parts are required and it is not very practical.

そのため、ＬＥＤを、照明用として利用する目的で、家庭用ＡＣ100Ｖまたは、自動車のバッテリーなどから、数個〜数百個のＬＥＤを一斉に高効率で、点灯するための定電流電源回路の実用化が必要である。   Therefore, for the purpose of using LEDs for lighting, practical application of constant current power supply circuit for lighting several to several hundred LEDs simultaneously and efficiently from household AC100V or automobile battery etc. is required.

ここで、直流電源にて高効率でＬＥＤを点灯させるものとして、スイッチが閉のときは直流電源からインダクタを励磁しつつインダクタに直列接続されたＬＥＤに直流電源を供給し、スイッチが開のときはインダクタとＬＥＤとの閉回路を形成してインダクタに蓄えられたエネルギーでＬＥＤを点灯するするように形成したものがある（例えば、特許文献１参照）。   Here, it is assumed that the LED is lit with high efficiency by the DC power source. When the switch is closed, the DC power source is supplied to the LED connected in series with the inductor while exciting the inductor from the DC power source, and the switch is opened. In some cases, a closed circuit of an inductor and an LED is formed so that the LED is turned on with energy stored in the inductor (see, for example, Patent Document 1).

また、点灯させるべきＬＥＤに半導体スイッチおよびシャントを直列に接続し、半導体スイッチ３のオンオフによりＬＥＤにパルス状の電流を供給し、一方、ＬＥＤへ電流が流れ始めて不完全積分器の出力がヒステリシスコンパレータの上限に達すると、半導体スイッチをオンからオフへ切り換え、不完全積分器の出力がヒステリシスコンパレータの下限まで下がると、半導体スイッチをオフからオンへ切り換えるようにしたものがある（例えば、特許文献２参照）。これにより、ＬＥＤ点灯回路における電力損失を少なくするとともに、ＬＥＤ点灯回路のＩＣ化を可能にしている。
特開２００２−１８４５８８号公報 特開平５−９４１５１号公報 Also, a semiconductor switch and a shunt are connected in series to the LED to be lit, and a pulsed current is supplied to the LED by turning on and off the semiconductor switch 3, while the current starts to flow to the LED and the output of the incomplete integrator is a hysteresis comparator. Is switched from on to off, and when the output of the incomplete integrator is lowered to the lower limit of the hysteresis comparator, the semiconductor switch is switched from off to on (for example, Patent Document 2). reference). Thereby, the power loss in the LED lighting circuit is reduced, and the LED lighting circuit can be made into an IC.
JP 2002-184588 A JP-A-5-94151

しかし、特許文献１のものでは、スイッチを閉じている時間によってＬＥＤに流れる電流値を制御することになるが、そのためにはスイッチを閉じている時間を調整することが必要となり、制御手段にスイッチのオフ期間を定めるタイマー回路が必要となる。また、ＬＥＤに流れる電流値を検出していないので、実際にＬＥＤに流れる電流値をフィードバック制御することができない。   However, in Patent Document 1, the value of the current flowing through the LED is controlled by the time during which the switch is closed. To this end, it is necessary to adjust the time during which the switch is closed, and the control means has a switch. A timer circuit for determining the off period is required. Further, since the current value flowing through the LED is not detected, the current value actually flowing through the LED cannot be feedback controlled.

一方、特許文献２のものではシャントによりＬＥＤに流れる電流を検出し不完全積分回路を介してヒステリシスコンパレータにフィードバックしているが、ヒステリシスコンパレータには半導体スイッチがオンして半導体スイッチに電流が流れるときのみの電流を検出するようにしているので、半導体スイッチのオフ期間を定めるタイマー回路が必要となる。また、ＬＥＤに直列に限流素子が接続されていないので、半導体スイッチのオンオフのデューティ比が小さくなったとき過大な電流が流れることがある。   On the other hand, in Patent Document 2, the current flowing through the LED is detected by a shunt and fed back to the hysteresis comparator via an incomplete integration circuit. When the semiconductor switch is turned on in the hysteresis comparator and the current flows through the semiconductor switch, Therefore, a timer circuit for determining the semiconductor switch OFF period is required. In addition, since the current limiting element is not connected in series with the LED, an excessive current may flow when the duty ratio of the on / off state of the semiconductor switch becomes small.

本発明の目的は、ある程度の電圧変動がある直流電源であっても目視上ＬＥＤの点灯が安定であり、安価でしかもＬＥＤを高効率に点灯できるＬＥＤ点灯回路を提供することである。   An object of the present invention is to provide an LED lighting circuit that can stably turn on an LED even with a direct current power supply having a certain voltage fluctuation, is inexpensive, and can light the LED with high efficiency.

請求項１の発明に係わるＬＥＤ点灯回路は、直流電源からの電流で励磁されエネルギーを蓄積するコイルと、前記直流電源および前記コイルの少なくともいずれか一方からのエネルギーにより点灯駆動されるＬＥＤの駆動期間および前記コイルの励磁期間の双方において電流の流れる位置に接続された電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とする。   According to a first aspect of the present invention, there is provided an LED lighting circuit including a coil that is excited by a current from a DC power source and stores energy, and a driving period of the LED that is driven to be driven by energy from at least one of the DC power source and the coil. And a current detection resistor connected to a position where current flows in both of the excitation periods of the coil and a current value detected by the current detection resistor having a predetermined upper limit value and lower limit value exceeding the upper limit value Comprises a hysteresis comparator that turns off the switch and turns on the switch when a current value detected by the current detection resistor becomes less than a lower limit value.

請求項２の発明に係わるＬＥＤ点灯回路は、直流電源とＬＥＤとの間に直列に接続されたコイルと、前記コイルと前記ＬＥＤとの接続点から分岐して前記ＬＥＤに並列接続されたスイッチと、前記スイッチがオンのときに前記直流電源から前記コイルおよび前記スイッチを通って形成される閉回路の電流を検出すると共に前記スイッチがオフのときに前記直流電源から前記コイルおよび前記ＬＥＤを通って形成される閉回路の電流を検出する電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とする。   An LED lighting circuit according to a second aspect of the present invention includes a coil connected in series between a DC power source and an LED, a switch branched from a connection point between the coil and the LED, and connected in parallel to the LED. Detecting a closed circuit current formed from the DC power source through the coil and the switch when the switch is on and from the DC power source through the coil and the LED when the switch is off. A current detection resistor for detecting the current of the closed circuit to be formed, and when the current value detected by the current detection resistor having an upper limit value and a lower limit value exceeds the upper limit value, the switch is turned off and the switch A hysteresis comparator is provided that turns on the switch when the current value detected by the current detection resistor becomes less than the lower limit value.

請求項３の発明に係わるＬＥＤ点灯回路は、請求項２の発明において、前記直流電源の極性に対して、ＬＥＤと電流検出抵抗との接続関係を鏡像的に接続したことを特徴とする。   The LED lighting circuit according to the invention of claim 3 is characterized in that, in the invention of claim 2, the connection relationship between the LED and the current detection resistor is mirror-connected to the polarity of the DC power supply.

請求項４の発明に係わるＬＥＤ点灯回路は、直流電源とＬＥＤとの間に直列に接続されたコイルと、直流電源とコイルとの接続点に直列に接続されたスイッチと、コイルとスイッチとの接続点から分岐して前記コイルとＬＥＤとの直列回路に並列に接続されたダイオードと、前記スイッチがオンのときに前記直流電源から前記スイッチ、前記コイルおよび前記ＬＥＤを通って形成される閉回路の電流を検出すると共に、前記スイッチがオフのときに前記コイル、前記ＬＥＤおよび前記ダイオードを通って形成される閉回路の電流を検出する電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし、前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とする。   According to a fourth aspect of the present invention, there is provided an LED lighting circuit comprising: a coil connected in series between a DC power source and the LED; a switch connected in series at a connection point between the DC power source and the coil; A diode branched from a connection point and connected in parallel to a series circuit of the coil and the LED, and a closed circuit formed from the DC power source through the switch, the coil, and the LED when the switch is on Current detection resistor for detecting a closed circuit current formed through the coil, the LED, and the diode when the switch is off, and a predetermined upper limit value and lower limit value. When the current value detected by the current detection resistor exceeds the upper limit value, the switch is turned off, and the current value detected by the current detection resistance value is less than the lower limit value. It can is characterized by comprising a hysteresis comparator which turns on the switch.

請求項５の発明に係わるＬＥＤ点灯回路は、請求項４の発明において、前記直流電源の極性に対して、ＬＥＤ、スイッチ、ダイオード、電流検出抵抗の接続関係を鏡像的に接続したことを特徴とする。   The LED lighting circuit according to the invention of claim 5 is characterized in that, in the invention of claim 4, the connection relationship of the LED, the switch, the diode, and the current detection resistor is mirror-connected to the polarity of the DC power supply. To do.

請求項６の発明に係わるＬＥＤ点灯回路は、直流電源とＬＥＤとの間に直列に接続されたスイッチと、スイッチとＬＥＤとの接続点に並列に接続されたコイルと、前記スイッチがオンのときに前記直流電源から前記スイッチおよび前記コイルを通って形成される閉回路の電流を検出すると共に、前記スイッチがオフのときに前記コイルおよび前記ＬＥＤを通って形成される閉回路の電流を検出する電流検出抵抗と、予め定めた上限値および下限値を有し、前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし、前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とする。   According to a sixth aspect of the present invention, there is provided an LED lighting circuit comprising: a switch connected in series between a DC power source and the LED; a coil connected in parallel to a connection point between the switch and the LED; and the switch being on. And detecting a closed circuit current formed through the switch and the coil from the DC power source and detecting a closed circuit current formed through the coil and the LED when the switch is off. A current detection resistor having a predetermined upper limit value and lower limit value, and when the current value detected by the current detection resistor exceeds the upper limit value, the switch is turned off, and the current detected by the current detection resistor A hysteresis comparator is provided that turns on the switch when the value becomes less than the lower limit value.

請求項７の発明に係わるＬＥＤ点灯回路は、請求項６の発明において、前記直流電源の極性に対して、ＬＥＤ、スイッチ、電流検出抵抗の接続関係を鏡像的に接続したことを特徴とする。   The LED lighting circuit according to a seventh aspect of the invention is characterized in that, in the sixth aspect of the invention, the connection relation of the LED, the switch, and the current detection resistor is mirror-connected to the polarity of the DC power supply.

本発明によれば、ＬＥＤの駆動期間およびコイルの励磁期間の双方において電流の流れる位置に電流検出抵抗を接続し、ヒステリシスコンパレータにより、この電流検出抵抗で検出された電流値が上限値を超えたときはスイッチをオフし、電流検出抵抗で検出された電流値が下限値未満となったときはスイッチをオンするので、上限値や下限値との比較だけでＬＥＤに流れる電流をほぼ定電流に制御できる。   According to the present invention, the current detection resistor is connected to a position where current flows in both the LED driving period and the coil excitation period, and the current value detected by the current detection resistor exceeds the upper limit value by the hysteresis comparator. When the current value detected by the current detection resistor becomes less than the lower limit value, the switch is turned on, so that the current flowing through the LED is almost constant by comparing with the upper limit value and the lower limit value. Can be controlled.

従って、定電流電源として家庭用単相交流１００Ｖを整流したもの、または、自動車のバッテリーからの直流電源など、ある程度の電圧変動する直流電源であっても、目視上ＬＥＤの点灯を安定に保つことができる。   Therefore, even if it is a DC power supply that rectifies a household single-phase AC 100V as a constant current power supply or a DC power supply from an automobile battery or the like, and the DC power supply fluctuates to some extent, the LED lighting can be kept stable visually. Can do.

（第１の実施の形態）
図１は本発明の第１の実施の形態に係わるＬＥＤ点灯回路の回路図である。直流電源１１からの直流で負荷であるＬＥＤ１２が点灯駆動される。直流電源１１とＬＥＤ１２との間にはコイル１３が直列に接続されている。コイル１３は直流電源１１からの電流で励磁され、発生する磁束によるエネルギーを蓄積する。コイル１３とＬＥＤ１２との接続点から分岐してＬＥＤ１２に並列にスイッチ１４が接続され、ＬＥＤ１２とスイッチ１４との並列回路に対して直列に電流検出抵抗１５が接続されている。 (First embodiment)
FIG. 1 is a circuit diagram of an LED lighting circuit according to the first embodiment of the present invention. The LED 12 that is a load is driven to be lit by a direct current from the direct current power source 11. A coil 13 is connected in series between the DC power supply 11 and the LED 12. The coil 13 is excited by a current from the DC power supply 11 and accumulates energy due to the generated magnetic flux. A switch 14 is branched from the connection point between the coil 13 and the LED 12 and connected in parallel to the LED 12, and a current detection resistor 15 is connected in series to the parallel circuit of the LED 12 and switch 14.

スイッチ１４がオンのときには、直流電源１１からコイル１３およびスイッチ１４を通り、さらに電流検出抵抗１５を通って直流電源１１に戻る閉回路が形成される。一方、スイッチがオフのときには、直流電源１１からコイル１３およびＬＥＤ１２を通り、さらに電流検出抵抗１５を通って直流電源１１に戻る閉回路が形成される。電流検出抵抗１５は、そのときに形成される閉回路の電流を検出する。   When the switch 14 is on, a closed circuit is formed from the DC power source 11 through the coil 13 and the switch 14 and further through the current detection resistor 15 to the DC power source 11. On the other hand, when the switch is off, a closed circuit is formed from the DC power source 11 through the coil 13 and the LED 12 and further through the current detection resistor 15 to the DC power source 11. The current detection resistor 15 detects a closed circuit current formed at that time.

また、直流電源１１を電源として所定の基準電圧を発生する基準電圧発生回路１６が設けられ、ヒステリシスコンパレータ１７にその基準電圧を供給している。ヒステリシスコンパレータ１７は、基準電圧をほぼ中心として±方向に動作値と復帰値とを有し、入力信号が動作値未満となると動作し、入力信号が復帰値を超えると復帰する。いま、入力信号を電流検出抵抗で検出された電流値とし、動作および復帰（出力信号）をスイッチ１４のオンオフとする。そして、動作値に電流の下限値を予め設定し、復帰値として電流の上限値を予め設定する。そうすると、電流検出抵抗１５で検出された電流が上限値を超えたときは、ヒステリシスコンパレータ１７はスイッチ１４をオフし、電流検出抵抗１５で検出された電流値が下限値未満となったときはスイッチ１４をオンすることになる。   Further, a reference voltage generation circuit 16 that generates a predetermined reference voltage using the DC power supply 11 as a power supply is provided, and the reference voltage is supplied to the hysteresis comparator 17. The hysteresis comparator 17 has an operation value and a return value in the ± direction around the reference voltage. The hysteresis comparator 17 operates when the input signal becomes less than the operation value, and returns when the input signal exceeds the return value. Now, the input signal is the current value detected by the current detection resistor, and the operation and recovery (output signal) are turned on and off. Then, a lower limit value of the current is set in advance as the operation value, and an upper limit value of the current is set in advance as the return value. Then, when the current detected by the current detection resistor 15 exceeds the upper limit value, the hysteresis comparator 17 turns off the switch 14, and when the current value detected by the current detection resistor 15 becomes less than the lower limit value, the switch 14 will be turned on.

このように、ＬＥＤ１２の一端を通常の電源回路のように直流電源１１のグランド側ではなく、電流検出抵抗１５とスイッチ１４との接続点に接続する。これにより、電流がスイッチ１４側を流れるとき、および負荷であるＬＥＤ１２側を流れるときの双方において、電流検出抵抗１５に電流が流れる回路構成としている。従って、スイッチ１４のオフ期間を定めるタイマー回路を使用しなくても、ヒステリシスコンパレータ１７のみで定電流の制御が可能となる。   In this manner, one end of the LED 12 is connected to the connection point between the current detection resistor 15 and the switch 14 instead of the ground side of the DC power supply 11 as in a normal power supply circuit. Thus, the circuit configuration is such that the current flows through the current detection resistor 15 both when the current flows on the switch 14 side and when the current flows on the LED 12 side as a load. Therefore, the constant current can be controlled only by the hysteresis comparator 17 without using a timer circuit that determines the OFF period of the switch 14.

次に動作を説明する。いま、スイッチ１４がオンとなったとする。スイッチ１４がオンとなると直流電源１１からスイッチ１４と電流検出抵抗１５とを通り直流電源１１に戻る閉回路が形成されるので、コイル１３に電流が流れる。このとき、コイル１３のインダクタンスにより、電流は急激には増加せずに徐々に増加する。この状態はコイル１３の励磁状態であり、コイル１３にエネルギーが蓄積されつつある状態である。   Next, the operation will be described. Now, assume that the switch 14 is turned on. When the switch 14 is turned on, a closed circuit is formed from the DC power supply 11 through the switch 14 and the current detection resistor 15 to return to the DC power supply 11, so that a current flows through the coil 13. At this time, due to the inductance of the coil 13, the current does not increase rapidly but increases gradually. This state is an excitation state of the coil 13, and energy is being accumulated in the coil 13.

そして、このときに流れる電流は電流検出抵抗１５で検出されてヒステリシスコンパレータ１７に入力される。ヒステリシスコンパレータ１７では入力した電流の値が予め定められた上限値を超えたかまたは下限値未満となったかを判定する。この電流の値がヒステリシスコンパレータ１７の上限値に達したとすると、ヒステリシスコンパレータ１７は動作状態から復帰状態に反転しスイッチ１４をオフする。スイッチ１４がオフとなると、直流電源１１からコイル１３を経由してＬＥＤ１２側に電流が流れ電流検出抵抗１５を通り直流電源１１に戻る閉回路が形成される。この閉回路に流れる電流は、コイル１３のインダクタンスにより急激には減少せずに徐々に減少する。この状態は、直流電源１１からのエネルギーに重畳してコイル１３に蓄積されたエネルギーを放出している状態である。   The current flowing at this time is detected by the current detection resistor 15 and input to the hysteresis comparator 17. The hysteresis comparator 17 determines whether the input current value exceeds a predetermined upper limit value or less than a lower limit value. If the current value reaches the upper limit value of the hysteresis comparator 17, the hysteresis comparator 17 is inverted from the operating state to the return state, and the switch 14 is turned off. When the switch 14 is turned off, a closed circuit is formed in which a current flows from the DC power supply 11 to the LED 12 via the coil 13 and returns to the DC power supply 11 through the current detection resistor 15. The current flowing through the closed circuit gradually decreases without being rapidly decreased due to the inductance of the coil 13. This state is a state in which the energy accumulated in the coil 13 is released while being superimposed on the energy from the DC power supply 11.

このとき、直流電源１１およびコイル１３からのエネルギーでＬＥＤ１２を点灯する。コイル１３からのエネルギーが減少することに伴い、閉回路を流れる電流が徐々に減少して、その電流の値がヒステリシスコンパレータ１７の下限値に達したとすると、ヒステリシスコンパレータ１７が復帰状態から動作状態に反転し、ヒステリシスコンパレータ１７はスイッチ１４をオンする。   At this time, the LED 12 is turned on with energy from the DC power supply 11 and the coil 13. As the energy from the coil 13 decreases, the current flowing through the closed circuit gradually decreases and the value of the current reaches the lower limit value of the hysteresis comparator 17. And the hysteresis comparator 17 turns on the switch 14.

この動作を繰り返すことにより、電流検出抵抗１５を流れる電流値は、ヒステリシスコンパレータ１７の上限値と下限値との間に制限され、その平均値はほぼ一定となる。   By repeating this operation, the value of the current flowing through the current detection resistor 15 is limited between the upper limit value and the lower limit value of the hysteresis comparator 17, and the average value thereof is substantially constant.

図１では、直流電源１１とＬＥＤ１２との間にコイル１３を直列に接続し、ＬＥＤ１２とスイッチ１４との並列回路に対して直列に電流検出抵抗１５を接続した場合を示したが、図２に示すように、コイル１３と電流検出抵抗１５とを直流電源１１の極性に対して、鏡像的に接続することも可能である。図１の場合は、スイッチ１４がＮＰＮ形トランジスタ（Ｎ形ＦＥＴ）である場合に有効な回路であり、図２はスイッチ１４がＰＮＰ形トランジスタ（Ｐ形ＦＥＴ）である場合に有効な回路である。 第１の実施の形態によれば、ＬＥＤの駆動期間およびコイルの励磁期間の双方において流れる電流を電流検出抵抗１５で検出し、ヒステリシスコンパレータ１７により、この電流検出抵抗１５で検出された電流値が上限値を超えたときはスイッチ１４をオフし、電流検出抵抗１５で検出された電流値が下限値未満となったときはスイッチ１４をオンするので、上限値や下限値との比較だけでＬＥＤ１２に流れる電流をほぼ定電流に制御できる。すなわち、ＬＥＤ１２に流れる電流は上限値と下限値との範囲で変動するだけであり、ほぼ定電流に制御できる。従って、スイッチ１４のオフ期間を定める発振周波数決定用のタイマー回路が不要となる。   FIG. 1 shows a case where the coil 13 is connected in series between the DC power source 11 and the LED 12, and the current detection resistor 15 is connected in series to the parallel circuit of the LED 12 and the switch 14. FIG. As shown, it is possible to connect the coil 13 and the current detection resistor 15 in a mirror image with respect to the polarity of the DC power supply 11. 1 is an effective circuit when the switch 14 is an NPN transistor (N-type FET), and FIG. 2 is an effective circuit when the switch 14 is a PNP-type transistor (P-type FET). . According to the first embodiment, the current flowing through both the LED drive period and the coil excitation period is detected by the current detection resistor 15, and the current value detected by the current detection resistor 15 is detected by the hysteresis comparator 17. When the upper limit value is exceeded, the switch 14 is turned off, and when the current value detected by the current detection resistor 15 is less than the lower limit value, the switch 14 is turned on. Can be controlled to a substantially constant current. That is, the current flowing through the LED 12 only fluctuates in the range between the upper limit value and the lower limit value, and can be controlled to a substantially constant current. Therefore, a timer circuit for determining the oscillation frequency that determines the OFF period of the switch 14 is not necessary.

また、スイッチ１４のオフ期間中のコイル１３の逆起電力は、直流電源１１の直流電圧に積み増しされる方向となるので、複数個のＬＥＤ１２を直列接続とし、ＬＥＤ１２の順方向電圧の和が直流電源１１の電源電圧より高い場合に有効である。   Further, since the back electromotive force of the coil 13 during the OFF period of the switch 14 is accumulated in the DC voltage of the DC power supply 11, a plurality of LEDs 12 are connected in series, and the sum of the forward voltages of the LEDs 12 is DC. This is effective when the power supply voltage is higher than the power supply 11.

（第２の実施の形態）
図３は本発明の第２の実施の形態に係わるＬＥＤ点灯回路の回路図である。この第２の実施の形態は、図１に示した第１の実施の形態に対し、ＬＥＤ１２にスイッチ１４を並列接続することに代えて、ＬＥＤ１２にスイッチ１４を直列接続し、ダイオード１８を設けて、スイッチ１４がオフのときにコイル１３とＬＥＤ１２とダイオード１８とで閉回路を形成するようにしたものである。また、電流検出抵抗１５は、その閉回路のＬＥＤ１２とダイオード１８との接続点間に接続され、ＬＥＤ１２の駆動期間およびコイル１３の励磁期間の双方において流れる電流を検出する。図１と同一要素には同一符号を付し重複する説明は省略する。 (Second Embodiment)
FIG. 3 is a circuit diagram of an LED lighting circuit according to the second embodiment of the present invention. This second embodiment is different from the first embodiment shown in FIG. 1 in that instead of connecting the switch 14 to the LED 12 in parallel, the switch 14 is connected in series to the LED 12 and a diode 18 is provided. When the switch 14 is off, the coil 13, the LED 12, and the diode 18 form a closed circuit. The current detection resistor 15 is connected between the connection points of the LED 12 and the diode 18 in the closed circuit, and detects a current flowing in both the drive period of the LED 12 and the excitation period of the coil 13. The same elements as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

図３に示すように、直流電源１１とＬＥＤ１２との間には直列にスイッチ１４とコイル１３とが接続されている。そして、コイル１３とスイッチ１４との接続点から分岐して、コイル１３とＬＥＤ１２との直列回路に並列にダイオード１８が接続されている。また、ＬＥＤ１２とダイオード１８との接続点間に接続されている。   As shown in FIG. 3, a switch 14 and a coil 13 are connected in series between the DC power supply 11 and the LED 12. A diode 18 is branched from a connection point between the coil 13 and the switch 14 and connected in parallel to the series circuit of the coil 13 and the LED 12. Further, it is connected between connection points of the LED 12 and the diode 18.

次に動作を説明する。いま、スイッチ１４がオンとなったとする。スイッチ１４がオンとなると直流電源１１からスイッチ１４とコイル１３とを通り、さらにＬＥＤ１２と電流検出抵抗１５とを通って直流電源１１に戻る閉回路が形成されるので、コイル１３に電流が流れる。このとき、コイル１３のインダクタンスにより、電流は急激には増加せずに徐々に増加する。この状態はコイル１３の励磁状態であり、コイル１３にエネルギーが蓄積されつつある状態であるとともに、負荷であるＬＥＤ１２を点灯駆動している状態である。   Next, the operation will be described. Now, assume that the switch 14 is turned on. When the switch 14 is turned on, a closed circuit is formed that passes from the DC power source 11 through the switch 14 and the coil 13, and further returns to the DC power source 11 through the LED 12 and the current detection resistor 15. At this time, due to the inductance of the coil 13, the current does not increase rapidly but increases gradually. This state is an excitation state of the coil 13, a state in which energy is being accumulated in the coil 13, and a state in which the LED 12, which is a load, is driven to be lit.

そして、このときに流れる電流は電流検出抵抗１５で検出されてヒステリシスコンパレータ１７に入力される。ヒステリシスコンパレータ１７では入力した電流の値が予め定められた上限値を超えたかまたは下限値未満となったかを判定する。電流の値が徐々に上昇し上限値に達したとすると、ヒステリシスコンパレータ１７は動作状態から復帰状態に反転しスイッチ１４をオフする。   The current flowing at this time is detected by the current detection resistor 15 and input to the hysteresis comparator 17. The hysteresis comparator 17 determines whether the input current value exceeds a predetermined upper limit value or less than a lower limit value. If the current value gradually increases and reaches the upper limit value, the hysteresis comparator 17 reverses from the operating state to the return state and turns off the switch 14.

スイッチ１４がオフとなると、コイル１３からＬＥＤ１２と電流検出抵抗１５とを通り、さらにダイオード１８を通ってコイル１３に戻る閉回路が形成される。この閉回路に流れる電流は、コイル１３のインダクタンスにより急激には減少せずに徐々に減少する。この状態はコイル１３に蓄積されたエネルギーを放出している状態である。   When the switch 14 is turned off, a closed circuit is formed from the coil 13 through the LED 12 and the current detection resistor 15, and further through the diode 18 to the coil 13. The current flowing through the closed circuit gradually decreases without being rapidly decreased due to the inductance of the coil 13. This state is a state in which the energy accumulated in the coil 13 is released.

このとき、コイル１３からのエネルギーでＬＥＤ１２を点灯する。コイル１３からのエネルギーが減少することに伴い、閉回路を流れる電流が徐々に減少して、その電流の値がヒステリシスコンパレータ１７の下限値に達したとすると、ヒステリシスコンパレータ１７が復帰状態から動作状態に反転し、ヒステリシスコンパレータ１７はスイッチ１４をオンする。   At this time, the LED 12 is turned on with the energy from the coil 13. As the energy from the coil 13 decreases, the current flowing through the closed circuit gradually decreases and the value of the current reaches the lower limit value of the hysteresis comparator 17. And the hysteresis comparator 17 turns on the switch 14.

この動作を繰り返すことにより、電流検出抵抗１５を流れる電流値は、ヒステリシスコンパレータ１７の上限値と下限値との間に制限され、その平均値はほぼ一定となる。   By repeating this operation, the value of the current flowing through the current detection resistor 15 is limited between the upper limit value and the lower limit value of the hysteresis comparator 17, and the average value thereof is substantially constant.

このように、動作原理の基本は、図１に示した第１の実施の形態と概ね同様であるが、ＬＥＤ１２に印加される電圧はコイル１３の逆起電力となるため、直流電源１１の直流電圧より低い値となる。また、ＬＥＤ１２を流れる電流は、コイル１３の励磁期間中およびスイッチ１４のオフ期間中の双方となるため、第１の実施の形態と異なりデューティー比は１００％となる。   As described above, the basic principle of the operation is substantially the same as that of the first embodiment shown in FIG. 1, but the voltage applied to the LED 12 becomes the counter electromotive force of the coil 13, and therefore the DC power of the DC power supply 11. The value is lower than the voltage. Further, since the current flowing through the LED 12 is both during the excitation period of the coil 13 and during the OFF period of the switch 14, the duty ratio is 100% unlike the first embodiment.

図３では、直流電源１１とＬＥＤ１２との間にスイッチ１４およびコイル１３を直列に接続し、コイル１３とＬＥＤ１２との直列回路に電流検出抵抗１５を接続するともにコイル１３とスイッチ１４との接続点から分岐してダイオード１８を接続したが、図４に示すように、ＬＥＤ１２、スイッチ１４、ダイオード１８、電流検出抵抗１５の接続関係を直流電源１１の極性に対して、鏡像的に接続することも可能である。図３の場合は、スイッチ１４がＮＰＮ形トランジスタ（Ｎ形ＦＥＴ）である場合に有効な回路であり、図４はスイッチ１４がＰＮＰ形トランジスタ（Ｐ形ＦＥＴ）である場合に有効な回路である。 第２の実施の形態によれば、ヒステリシスコンパレータ１７の上限値や下限値との比較だけでＬＥＤ１２に流れる電流をほぼ定電流に制御できるので、スイッチ１４のオフ期間を定める発振周波数決定用のタイマー回路が不要となる。   In FIG. 3, the switch 14 and the coil 13 are connected in series between the DC power supply 11 and the LED 12, the current detection resistor 15 is connected to the series circuit of the coil 13 and the LED 12, and the connection point between the coil 13 and the switch 14. As shown in FIG. 4, the connection relationship of the LED 12, the switch 14, the diode 18, and the current detection resistor 15 may be mirror-connected to the polarity of the DC power source 11. Is possible. 3 is an effective circuit when the switch 14 is an NPN transistor (N-type FET), and FIG. 4 is an effective circuit when the switch 14 is a PNP-type transistor (P-type FET). . According to the second embodiment, since the current flowing through the LED 12 can be controlled to a substantially constant current only by comparing the upper limit value and the lower limit value of the hysteresis comparator 17, the timer for determining the oscillation frequency that determines the OFF period of the switch 14 is used. A circuit becomes unnecessary.

また、ＬＥＤ１２に印加される電圧はコイル１３の逆起電力となるため、直流電源１１の直流電圧より低い値となり、直列に接続されたＬＥＤ１２の順方向電圧の和が直流電源１１の電源電圧より低い場合に有効である。   Further, since the voltage applied to the LED 12 is a counter electromotive force of the coil 13, the voltage is lower than the DC voltage of the DC power supply 11, and the sum of the forward voltages of the LEDs 12 connected in series is greater than the power supply voltage of the DC power supply 11. Effective when low.

（第３の実施の形態）
図５は本発明の第３の実施の形態に係わるＬＥＤ点灯回路の回路図である。この第３の実施の形態は、図１に示した第１の実施の形態に対し、ＬＥＤ１２にスイッチ１４を並列接続することに代えて、ＬＥＤ１２とコイル１３との並列回路にスイッチ１４を直列接続し、スイッチ１４がオフのときにコイル１３とＬＥＤ１２とで閉回路を形成するようにしたものである。また、電流検出抵抗１５は、その閉回路に接続され、ＬＥＤ１２の駆動期間およびコイル１３の励磁期間の双方において流れる電流を検出する。図１と同一要素には同一符号を付し重複する説明は省略する。 (Third embodiment)
FIG. 5 is a circuit diagram of an LED lighting circuit according to the third embodiment of the present invention. In the third embodiment, instead of connecting the switch 14 to the LED 12 in parallel to the first embodiment shown in FIG. 1, the switch 14 is connected in series to the parallel circuit of the LED 12 and the coil 13. When the switch 14 is off, the coil 13 and the LED 12 form a closed circuit. The current detection resistor 15 is connected to the closed circuit, and detects a current flowing in both the drive period of the LED 12 and the excitation period of the coil 13. The same elements as those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.

図５に示すように、コイル１３と電流検出抵抗１５とを直列に接続し、さらに、その直列回路とＬＥＤ１２とを並列接続して、その並列回路と直流電源１１との間に直列にスイッチ１４が接続されている。   As shown in FIG. 5, the coil 13 and the current detection resistor 15 are connected in series, the series circuit and the LED 12 are connected in parallel, and the switch 14 is connected in series between the parallel circuit and the DC power supply 11. Is connected.

次に動作を説明する。いま、スイッチ１４がオンとなったとする。スイッチ１４がオンとなると直流電源１１からスイッチ１４とコイル１３とを通り、さらに電流検出抵抗１５とを通って直流電源１１に戻る閉回路が形成される。これにより、コイル１３には電流が流れるがＬＥＤ１２には電流は流れない。これは、図５に示すようにＬＥＤ１２の極性が直流電源１１に対し逆極性に接続されているからである。   Next, the operation will be described. Now, assume that the switch 14 is turned on. When the switch 14 is turned on, a closed circuit is formed from the DC power source 11 through the switch 14 and the coil 13, and further through the current detection resistor 15 to return to the DC power source 11. As a result, a current flows through the coil 13, but no current flows through the LED 12. This is because the polarity of the LED 12 is connected to the reverse polarity with respect to the DC power supply 11 as shown in FIG.

コイル１３に流れる電流は、コイル１３のインダクタンスにより急激には増加せずに徐々に増加する。この状態はコイル１３の励磁状態であり、コイル１３にエネルギーが蓄積されつつある状態である。   The current flowing through the coil 13 does not increase rapidly but increases gradually due to the inductance of the coil 13. This state is an excitation state of the coil 13, and energy is being accumulated in the coil 13.

そして、このときに流れる電流は電流検出抵抗１５で検出されてヒステリシスコンパレータ１７に入力される。ヒステリシスコンパレータ１７では入力した電流の値が予め定められた上限値を超えたかまたは下限値未満となったかを判定する。電流の値が徐々に上昇し上限値に達したとすると、ヒステリシスコンパレータ１７は動作状態から復帰状態に反転しスイッチ１４をオフする。   The current flowing at this time is detected by the current detection resistor 15 and input to the hysteresis comparator 17. The hysteresis comparator 17 determines whether the input current value exceeds a predetermined upper limit value or less than a lower limit value. If the current value gradually increases and reaches the upper limit value, the hysteresis comparator 17 reverses from the operating state to the return state and turns off the switch 14.

スイッチ１４がオフとなると、コイル１３から電流検出抵抗１５とＬＥＤ１２とを通ってコイル１３に戻る閉回路が形成される。この閉回路に流れる電流は、コイル１３のインダクタンスにより急激には減少せずに徐々に減少する。この状態はコイル１３に蓄積されたエネルギーを放出している状態である。   When the switch 14 is turned off, a closed circuit is formed that returns from the coil 13 to the coil 13 through the current detection resistor 15 and the LED 12. The current flowing through the closed circuit gradually decreases without being rapidly decreased due to the inductance of the coil 13. This state is a state in which the energy accumulated in the coil 13 is released.

このとき、コイル１３からのエネルギーでＬＥＤ１２を点灯する。コイル１３からのエネルギーが減少することに伴い、閉回路を流れる電流が徐々に減少して、その電流の値がヒステリシスコンパレータ１７の下限値に達したとすると、ヒステリシスコンパレータ１７が復帰状態から動作状態に反転し、ヒステリシスコンパレータ１７はスイッチ１４をオンする。   At this time, the LED 12 is turned on with the energy from the coil 13. As the energy from the coil 13 decreases, the current flowing through the closed circuit gradually decreases and the value of the current reaches the lower limit value of the hysteresis comparator 17. And the hysteresis comparator 17 turns on the switch 14.

この動作を繰り返すことにより、電流検出抵抗１５を流れる電流値は、ヒステリシスコンパレータ１７の上限値と下限値との間に制限され、その平均値はほぼ一定となる。   By repeating this operation, the value of the current flowing through the current detection resistor 15 is limited between the upper limit value and the lower limit value of the hysteresis comparator 17, and the average value thereof is substantially constant.

このように、第３の実施の形態のＬＥＤ点灯回路は、スイッチ１４のオフ期間中のみ負荷であるＬＥＤ１２に電流を流す点で、第２の実施の形態と異なり、この場合のＬＥＤ１２を流れる電流は、第１の実施の形態と同様にデューティー比が約５０％となる。   Thus, unlike the second embodiment, the LED lighting circuit of the third embodiment is different from the second embodiment in that a current flows through the LED 12 that is a load only during the OFF period of the switch 14. As in the first embodiment, the duty ratio is about 50%.

図５では、直流電源とＬＥＤとの間に直列にスイッチを接続し、スイッチとＬＥＤとの接続点に並列にコイルおよび電流検出抵抗を接続したが、図６に示すように、ＬＥＤ１２、スイッチ１４、電流検出抵抗１５の接続関係を直流電源１１の極性に対して、鏡像的に接続することも可能である。図５の場合は、スイッチ１４がＮＰＮ形トランジスタ（Ｎ形ＦＥＴ）である場合に有効な回路であり、図６はスイッチ１４がＰＮＰ形トランジスタ（Ｐ形ＦＥＴ）である場合に有効な回路である。 第３の実施の形態によれば、第２の実施の形態と同様に、ヒステリシスコンパレータ１７の上限値や下限値との比較だけでＬＥＤ１２に流れる電流をほぼ定電流に制御できるので、スイッチ１４のオフ期間を定める発振周波数決定用のタイマー回路が不要となる。   In FIG. 5, a switch is connected in series between the DC power source and the LED, and a coil and a current detection resistor are connected in parallel to the connection point between the switch and the LED. However, as shown in FIG. The connection relationship of the current detection resistor 15 can be mirror-imaged with respect to the polarity of the DC power supply 11. 5 is an effective circuit when the switch 14 is an NPN transistor (N-type FET), and FIG. 6 is an effective circuit when the switch 14 is a PNP-type transistor (P-type FET). . According to the third embodiment, as in the second embodiment, the current flowing through the LED 12 can be controlled to a substantially constant current only by comparison with the upper limit value and the lower limit value of the hysteresis comparator 17. A timer circuit for determining the oscillation frequency for determining the off period is not necessary.

また、ＬＥＤ１２に印加される電圧はコイル１３の逆起電力となるため、直流電源１１の直流電圧より低い値となり、直列に接続されたＬＥＤ１２の順方向電圧の和が直流電源１１の電源電圧より低い場合に有効である。   Further, since the voltage applied to the LED 12 is a counter electromotive force of the coil 13, the voltage is lower than the DC voltage of the DC power supply 11, and the sum of the forward voltages of the LEDs 12 connected in series is greater than the power supply voltage of the DC power supply 11. Effective when low.

本発明の第１の実施の形態に係わるＬＥＤ点灯回路の回路図。The circuit diagram of the LED lighting circuit concerning the 1st Embodiment of this invention. 本発明の第１の実施の形態に係わるＬＥＤ点灯回路の他の一例を示す回路図。The circuit diagram which shows another example of the LED lighting circuit concerning the 1st Embodiment of this invention. 本発明の第２の実施の形態に係わるＬＥＤ点灯回路の回路図。The circuit diagram of the LED lighting circuit concerning the 2nd Embodiment of this invention. 本発明の第２の実施の形態に係わるＬＥＤ点灯回路の他の一例を示す回路図。The circuit diagram which shows another example of the LED lighting circuit concerning the 2nd Embodiment of this invention. 本発明の第３の実施の形態に係わるＬＥＤ点灯回路の回路図。The circuit diagram of the LED lighting circuit concerning the 3rd Embodiment of this invention. 本発明の第３の実施の形態に係わるＬＥＤ点灯回路の他の一例を示す回路図。The circuit diagram which shows another example of the LED lighting circuit concerning the 3rd Embodiment of this invention.

符号の説明Explanation of symbols

１１…直流電源、１２…ＬＥＤ、１３…コイル、１４…スイッチ、１５…電流検出抵抗、１６…基準電圧発生回路、１７…ヒステリシスコンパレータ、１８…ダイオード
DESCRIPTION OF SYMBOLS 11 ... DC power supply, 12 ... LED, 13 ... Coil, 14 ... Switch, 15 ... Current detection resistor, 16 ... Reference voltage generation circuit, 17 ... Hysteresis comparator, 18 ... Diode

Claims (7)

直流電源からの電流で励磁されエネルギーを蓄積するコイルと、前記直流電源および前記コイルの少なくともいずれか一方からのエネルギーにより点灯駆動されるＬＥＤの駆動期間および前記コイルの励磁期間の双方において電流の流れる位置に接続された電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とするＬＥＤ点灯回路。   Current flows in both the drive period of the coil that is excited by the current from the DC power source and accumulates energy, the driving period of the LED that is lit and driven by the energy from at least one of the DC power source and the coil, and the excitation period of the coil A current detection resistor connected to the position and a predetermined upper limit value and lower limit value, and when the current value detected by the current detection resistor exceeds the upper limit value, the switch is turned off and detected by the current detection resistor An LED lighting circuit comprising: a hysteresis comparator that turns on the switch when the measured current value becomes less than a lower limit value. 直流電源とＬＥＤとの間に直列に接続されたコイルと、前記コイルと前記ＬＥＤとの接続点から分岐して前記ＬＥＤに並列接続されたスイッチと、前記スイッチがオンのときに前記直流電源から前記コイルおよび前記スイッチを通って形成される閉回路の電流を検出すると共に前記スイッチがオフのときに前記直流電源から前記コイルおよび前記ＬＥＤを通って形成される閉回路の電流を検出する電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とするＬＥＤ点灯回路。   A coil connected in series between the DC power supply and the LED, a switch branched from a connection point between the coil and the LED and connected in parallel to the LED, and from the DC power supply when the switch is on Detecting a closed circuit current formed through the coil and the switch and detecting a closed circuit current formed through the coil and the LED from the DC power source when the switch is off When the current value detected by the current detection resistor exceeds the upper limit value, the switch is turned off and the current value detected by the current detection resistor is the lower limit value. An LED lighting circuit comprising: a hysteresis comparator that turns on the switch when it becomes less than 前記直流電源の極性に対して、ＬＥＤと電流検出抵抗との接続関係を鏡像的に接続したことを特徴とする請求項２記載のＬＥＤ点灯回路。   The LED lighting circuit according to claim 2, wherein the connection relationship between the LED and the current detection resistor is mirror-connected to the polarity of the DC power supply. 直流電源とＬＥＤとの間に直列に接続されたコイルと、直流電源とコイルとの接続点に直列に接続されたスイッチと、コイルとスイッチとの接続点から分岐して前記コイルとＬＥＤとの直列回路に並列に接続されたダイオードと、前記スイッチがオンのときに前記直流電源から前記スイッチ、前記コイルおよび前記ＬＥＤを通って形成される閉回路の電流を検出すると共に、前記スイッチがオフのときに前記コイル、前記ＬＥＤおよび前記ダイオードを通って形成される閉回路の電流を検出する電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし、前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とするＬＥＤ点灯回路。   A coil connected in series between the DC power supply and the LED, a switch connected in series at the connection point between the DC power supply and the coil, and a branch from the connection point between the coil and the switch, A diode connected in parallel to a series circuit and a closed circuit current formed through the switch, the coil, and the LED from the DC power source when the switch is on, and the switch is off Sometimes a current detection resistor for detecting a closed circuit current formed through the coil, the LED and the diode, and a current value detected by the current detection resistor having a predetermined upper limit value and a lower limit value. Hysteresis that turns off the switch when the upper limit is exceeded, and turns on the switch when the current value detected by the current detection resistor is less than the lower limit. LED lighting circuit, characterized by comprising a comparator. 前記直流電源の極性に対して、ＬＥＤ、スイッチ、ダイオード、電流検出抵抗の接続関係を鏡像的に接続したことを特徴とする請求項４記載のＬＥＤ点灯回路。   The LED lighting circuit according to claim 4, wherein the connection relationship of the LED, the switch, the diode, and the current detection resistor is mirror-connected to the polarity of the DC power supply. 直流電源とＬＥＤとの間に直列に接続されたスイッチと、スイッチとＬＥＤとの接続点に並列に接続されたコイルと、前記スイッチがオンのときに前記直流電源から前記スイッチおよび前記コイルを通って形成される閉回路の電流を検出すると共に前記スイッチがオフのときに前記コイルおよび前記ＬＥＤを通って形成される閉回路の電流を検出する電流検出抵抗と、予め定めた上限値および下限値を有し前記電流検出抵抗で検出された電流値が上限値を超えたときは前記スイッチをオフし前記電流検出抵抗で検出された電流値が下限値未満となったときは前記スイッチをオンするヒステリシスコンパレータとを具備したことを特徴とするＬＥＤ点灯回路。   A switch connected in series between the DC power supply and the LED, a coil connected in parallel to the connection point between the switch and the LED, and when the switch is on, the DC power supply passes through the switch and the coil. A current detection resistor for detecting a closed circuit current formed and detecting a closed circuit current formed through the coil and the LED when the switch is off, and a predetermined upper limit value and lower limit value. The switch is turned off when the current value detected by the current detection resistor exceeds the upper limit value, and the switch is turned on when the current value detected by the current detection resistor becomes less than the lower limit value. An LED lighting circuit comprising a hysteresis comparator. 前記直流電源の極性に対して、ＬＥＤ、スイッチ、電流検出抵抗の接続関係を鏡像的に接続したことを特徴とする請求項６記載のＬＥＤ点灯回路。
The LED lighting circuit according to claim 6, wherein the connection relationship of the LED, the switch, and the current detection resistor is mirror-connected to the polarity of the DC power supply.
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