JP2007189819A - Light-emitting diode constant-current drive circuit - Google Patents

Light-emitting diode constant-current drive circuit Download PDF

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JP2007189819A
JP2007189819A JP2006005204A JP2006005204A JP2007189819A JP 2007189819 A JP2007189819 A JP 2007189819A JP 2006005204 A JP2006005204 A JP 2006005204A JP 2006005204 A JP2006005204 A JP 2006005204A JP 2007189819 A JP2007189819 A JP 2007189819A
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emitting diode
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JP4472640B2 (en
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Toshio Hiratsuka
利男 平塚
Yasuo Ohashi
靖生 大橋
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-efficiency light-emitting diode constant-current drive circuit capable of attaining significant reductions in cost, size and weight, as well as, restraining an increase in power consumption, even if there is dispersion in the power supply voltage or the forward voltage drop in the light-emitting diode is fluctuated, and adjusting the luminance, without having to change the emission wavelength of the light-emitting diode. <P>SOLUTION: The light-emitting diode constant-current drive circuit includes a transformer 4 having a primary and a secondary windings; a switching element 5 connected to the primary winding in series; an on/off control circuit 16 for on/off controlling the switching element 5; and a series connection circuit constituted of the diode 6, the constant-current element 15, and the light-emitting diode 12. A DC voltage (voltage of the capacitor 3) is added between the primary winding 4 and the switching element 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は発光ダイオード順方向電圧降下バラツキに関係なく電流駆動素子である発光ダイオードに定電流を供給しつつ、発光波長に影響を与えることなく、発光ダイオードの輝度を容易に調整できる低コストで、かつ小型・軽量、高効率な定電流駆動回路に関するものである。   The present invention supplies a constant current to a light emitting diode that is a current driving element regardless of variations in forward voltage drop of the light emitting diode, and at a low cost that can easily adjust the luminance of the light emitting diode without affecting the emission wavelength. Further, the present invention relates to a small-sized, light-weight and high-efficiency constant current driving circuit.

発光ダイオードは消費電力が少なく、長寿命、低温動作が可能などの特長を有しており、今後ますます種々の照明器具分野で採用されていくものと考えられる。（例えば、特許文献１参照）。
発光ダイオードは電流駆動素子であり、駆動電流は信頼性の観点から２０ｍＡ〜３０ｍＡが一般的である。これまでは発光ダイオードの電源としてはスイッチング電源を使用した定電圧ＡＣアダプタなどが用いられており、発光ダイオードと直列に抵抗を接続して発光ダイオードの駆動電流が２０ｍＡ〜２５ｍＡ（一般的に絶対最大定格は３０ｍＡ）となるように抵抗値を選定している。
特開２００３−１７３１６３号公報 Light-emitting diodes have features such as low power consumption, long life and low-temperature operation, and are expected to be increasingly used in various lighting equipment fields. (For example, refer to Patent Document 1).
The light emitting diode is a current driving element, and the driving current is generally 20 mA to 30 mA from the viewpoint of reliability. Up to now, a constant voltage AC adapter using a switching power supply has been used as the power source of the light emitting diode, and a resistance is connected in series with the light emitting diode, so that the driving current of the light emitting diode is 20 mA to 25 mA (generally an absolute maximum). The resistance value is selected so that the rating is 30 mA).
JP 2003-173163 A

図８は、従来の発光ダイオードの駆動回路を示している。
１は商用電源、２はブリッジダイオード、３はコンデンサ、４はトランス、５はスイッチング素子、６は整流ダイオード、７はフリーホイールダイオード、８はインダクタ、９はコンデンサ、１０はスイッチング素子５の制御回路、１１は抵抗、１２は発光ダイオードである。 FIG. 8 shows a conventional light emitting diode driving circuit.
1 is a commercial power supply, 2 is a bridge diode, 3 is a capacitor, 4 is a transformer, 5 is a switching element, 6 is a rectifier diode, 7 is a freewheeling diode, 8 is an inductor, 9 is a capacitor, and 10 is a control circuit for the switching element 5. , 11 are resistors, and 12 is a light emitting diode.

次に、図８に示す駆動回路の動作を説明する。
商用電源１の交流電圧をブリッジダイオード２で全波整流し、コンデンサ３で平滑し、ＭＯＳ−ＦＥＴなどのスイッチング素子５でコンデンサ３で平滑して得られた直流電圧Ｖ０を高周波で断続し、トランス４で直流的に絶縁された交流電圧に変換した後、ダイオード６、７で整流し、インダクタ８、コンデンサ９で構成される平滑フィルタ１−１で一定の直流電圧Ｖ１に変換する。直流電圧Ｖ１に抵抗１１と発光ダイオード１２の直列回路を接続し、発光ダイオード１２を発光させる。トランス４、スイッチング素子５、整流ダイオード６、フリーホイールダイオード７、インダクタ８、コンデンサ９、制御回路１０で構成される回路をＤＣ−ＤＣコンバータ１−２と称することとする。ＤＣ−ＤＣコンバータ１−２の出力電圧である直流電圧Ｖ１は商用電源の交流電圧が変動した場合や出力電流が変化しても制御回路１０によって一定に保たれる。 Next, the operation of the drive circuit shown in FIG. 8 will be described.
The AC voltage of the commercial power source 1 is full-wave rectified by the bridge diode 2, smoothed by the capacitor 3, and the DC voltage V0 obtained by smoothing the capacitor 3 by the switching element 5 such as a MOS-FET is intermittently transmitted at a high frequency. 4 is converted into an AC voltage that is galvanically isolated, then rectified by diodes 6 and 7, and converted to a constant DC voltage V1 by a smoothing filter 1-1 including an inductor 8 and a capacitor 9. A series circuit of the resistor 11 and the light emitting diode 12 is connected to the DC voltage V1 to cause the light emitting diode 12 to emit light. A circuit composed of the transformer 4, the switching element 5, the rectifier diode 6, the freewheel diode 7, the inductor 8, the capacitor 9, and the control circuit 10 is referred to as a DC-DC converter 1-2. The DC voltage V1, which is the output voltage of the DC-DC converter 1-2, is kept constant by the control circuit 10 when the AC voltage of the commercial power supply fluctuates or the output current changes.

発光ダイオード１２を例えば白色発光ダイオードとすると、順方向電圧降下は３Ｖ〜４Ｖでありバラツキが比較的大きい。
一例としてＤＣ−ＤＣコンバータ１−２の出力電圧Ｖ１を２４±０．１２（±５％）Ｖ、発光ダイオード１２の直列接続数を５個、発光ダイオード１２の電流を２０ｍＡとした場合、直列接続された発光ダイオード１２の順方向電圧降下が全て４Ｖとすると、発光ダイオード１２の５個の電圧降下は２０Ｖとなる。
ＤＣ−ＤＣコンバータ１−２の出力電圧最低値Ｖ１＝２４−０．１２＝２３．８８Ｖで順方向電圧降下＝４Ｖの時でも輝度を確保するため２０ｍＡが必要とすると、必要な抵抗値は（２３．８８−２０）／０．０２＝１９４Ωとなる。
抵抗１１と発光ダイオード１２の消費電力の合計は２３．８８×０．０２＝０．４７８Ｗである。（電源電圧Ｖ１＝２４Ｖ一定である場合、（２４−２０）／０．０２＝２００Ω、消費電力＝２４×０．０２＝０．４８Ｗ）
発光ダイオード１２の順方向電圧降下が全て３Ｖの場合、発光ダイオード１２の５個の電圧降下は５×３＝１５Ｖとなる。 When the light emitting diode 12 is a white light emitting diode, for example, the forward voltage drop is 3 V to 4 V, and the variation is relatively large.
As an example, when the output voltage V1 of the DC-DC converter 1-2 is 24 ± 0.12 (± 5%) V, the number of series connection of the light emitting diodes 12 is 5, and the current of the light emitting diodes 12 is 20 mA, the series connection If the forward voltage drops of the light emitting diodes 12 are all 4V, the five voltage drops of the light emitting diodes 12 are 20V.
If the minimum output voltage of the DC-DC converter 1-2 is V1 = 24−0.12 = 23.88V and the forward voltage drop = 4V and 20 mA is required to secure the luminance, the necessary resistance value is ( 23.88-20) /0.02=194Ω.
The total power consumption of the resistor 11 and the light emitting diode 12 is 23.88 × 0.02 = 0.478 W. (When power supply voltage V1 = 24V is constant, (24-20) /0.02=200Ω, power consumption = 24 × 0.02 = 0.48 W)
When the forward voltage drops of the light emitting diodes 12 are all 3V, the five voltage drops of the light emitting diodes 12 are 5 × 3 = 15V.

したがって、発光ダイオード１２の駆動電流はＤＣ−ＤＣコンバータ１−２の出力電圧が最大値の場合、（２４．１２−１５）／１９４Ω＝０．０４７Ａ、すなわち、ＤＣ−ＤＣコンバータ１−２の出力電流は２０ｍＡから４７ｍＡに増加し、抵抗１１と発光ダイオード１２の消費電力の合計は０．４７８Ｗから２４．１２×０．０４７＝１．１３４Ｗに増加するばかりでなく、輝度が大きくなる。（電源電圧Ｖ１＝２４Ｖ一定である場合、（２４−１５）／２００Ω＝０．０４５Ａ、消費電力＝２４×０．０４５＝１．０８Ｗ）   Therefore, when the output voltage of the DC-DC converter 1-2 is the maximum value, the drive current of the light emitting diode 12 is (24.12-15) /194Ω=0.047A, that is, the output of the DC-DC converter 1-2. The current increases from 20 mA to 47 mA, and the total power consumption of the resistor 11 and the light emitting diode 12 increases not only from 0.478 W to 24.12 × 0.047 = 1.134 W, but also the luminance increases. (When power supply voltage V1 = 24V is constant, (24-15) /200Ω=0.045A, power consumption = 24 × 0.045 = 1.08 W)

以上のように、電源電圧の精度、発光ダイオードの順方向電圧降下バラツキを考慮すると、従来の駆動方法では発光ダイオードの駆動電流が大幅に変化するため、消費電力や輝度に大きな影響が出ることになる。また、駆動電流を絶対最大電流以下にすることができないことから信頼性上問題である。   As described above, in consideration of the accuracy of the power supply voltage and the forward voltage drop variation of the light emitting diode, the driving current of the light emitting diode greatly changes in the conventional driving method, which greatly affects power consumption and luminance. Become. In addition, the drive current cannot be reduced below the absolute maximum current, which is a problem in reliability.

一方、発光ダイオード１２の輝度を調整する場合はＤＣ−ＤＣコンバータ１−２の出力電圧を変化させて電流値を制御する方法が簡易であるが、発光ダイオード１２が発生する発光波長が変化する欠点がある。
この欠点を除去する為に、図９に示す回路が適用されている。１３はスイッチング素子、１４はスイッチング素子１３の制御回路である。ＤＣ−ＤＣコンバータ１−２の出力電圧を例えば２０ｋＨｚ以上の周波数でスイッチング素子１３を断続させてＤＣ−ＤＣコンバータ１−２の出力電圧をパルス電圧に変換する。この回路には動作周波数を一定にしスイッチング素子１３のオン・オフ時間を制御回路１４で制御しパルス電圧幅を変化させるパルス幅制御（Ｐｕｌｓｅ Ｗｉｄｔｈ Ｍｏｄｕｌａｔｉｏｎ；ＰＷＭ）技術が適用されることが多い。この結果、パルス電圧がある時は発光ダイオード１２には電流が流れ点灯するが、パルス電圧が無い時は消灯する。 On the other hand, when adjusting the luminance of the light emitting diode 12, a method of controlling the current value by changing the output voltage of the DC-DC converter 1-2 is simple, but the light emission wavelength generated by the light emitting diode 12 is changed. There is.
In order to eliminate this defect, the circuit shown in FIG. 9 is applied. Reference numeral 13 denotes a switching element, and reference numeral 14 denotes a control circuit for the switching element 13. For example, the output voltage of the DC-DC converter 1-2 is intermittently switched at a frequency of, for example, 20 kHz or more to convert the output voltage of the DC-DC converter 1-2 into a pulse voltage. In many cases, a pulse width modulation (PWM) technique in which the operating frequency is made constant and the on / off time of the switching element 13 is controlled by the control circuit 14 to change the pulse voltage width is applied. As a result, when there is a pulse voltage, a current flows through the light emitting diode 12 and it is turned on, but when there is no pulse voltage, it is turned off.

このように、高周波で点灯、消灯を繰り返すと、人間の目には点灯し続けているように見え、点灯する時間と消灯する時間の比を調整することで発光ダイオード１２の発光波長を変化させることなく発光ダイオード１２の輝度を調整することができる。
しかし、ＰＷＭを用いた発光ダイオードの輝度調整では、ＤＣ−ＤＣコンバータ１−２の出力にＰＷＭ用のスイッチング素子１３と制御回路１４が必要になるので、電源のコストダウンや小型化が困難になるとともに、ＤＣ−ＤＣコンバータ１−２とパルス幅制御回路を駆動回路とすれば、電源効率が低下することになる。 As described above, when the light is turned on and off at a high frequency, it appears to be continuously lit by human eyes, and the light emission wavelength of the light emitting diode 12 is changed by adjusting the ratio of the time for turning on and turning off. The brightness of the light emitting diode 12 can be adjusted without any problem.
However, in the brightness adjustment of the light emitting diode using PWM, the PWM switching element 13 and the control circuit 14 are required for the output of the DC-DC converter 1-2, which makes it difficult to reduce the power supply cost and reduce the size. At the same time, if the DC-DC converter 1-2 and the pulse width control circuit are drive circuits, the power supply efficiency is lowered.

従来の定電圧電源と抵抗を用いる発光ダイオード駆動方式では電源電圧の精度、発光ダイオードの順方向電圧降下バラツキを考慮すると、駆動電流が大幅に変化するため、消費電力の増加や発光ダイオードの輝度が変化する問題があった。
また、抵抗で発光ダイオードの電流を規定値内に抑えることが困難であり、駆動電流を絶対最大電流以下にすることができないことから信頼性を考慮した設計が困難になる問題があった。
また、発光ダイオードの発光波長を変化させずに輝度調整を行う場合は、パルス幅制御回路を追加する必要があるが、電源コストの上昇や小型化の阻害要因になるばかりでなく、電源効率の低下をもたらす原因になる問題があった。
そこで、本発明の目的は、発光ダイオードの駆動電流を一定にし、電源電圧の変化や発光ダイオードの順方向電圧降下バラツキがあったとしても、消費電力の増加を抑制し、発光ダイオードの輝度の変化を防止することができ、かつ発光ダイオードの発光波長を変化させずに輝度調整を行うことが可能な低コスト、小型・軽量、高効率発光ダイオード定電流駆動回路を提供することにある。 In the conventional LED driving method using a constant voltage power supply and a resistor, considering the accuracy of the power supply voltage and variations in the forward voltage drop of the LED, the driving current changes greatly, increasing the power consumption and the brightness of the LED. There was a changing problem.
In addition, it is difficult to suppress the current of the light emitting diode within a specified value with a resistor, and the drive current cannot be made equal to or lower than the absolute maximum current.
In addition, when adjusting the brightness without changing the emission wavelength of the light emitting diode, it is necessary to add a pulse width control circuit, which not only hinders the increase in power supply cost and downsizing, but also improves the power efficiency. There was a problem that caused a drop.
Therefore, an object of the present invention is to keep the driving current of the light emitting diode constant, and suppress the increase in power consumption and change the luminance of the light emitting diode even if there is a change in power supply voltage or a forward voltage drop variation of the light emitting diode. It is an object of the present invention to provide a low-cost, small-sized, lightweight, high-efficiency light-emitting diode constant current driving circuit that can prevent luminance and can adjust luminance without changing the light emission wavelength of the light-emitting diode.

上記課題を解決するために、請求項１記載の発明は、発光ダイオード定電流駆動回路に係り、一次巻線と二次巻線を有するトランスと、前記一次巻線に直列接続されるスイッチング素子と、前記スイッチング素子をオン・オフ制御するオン・オフ制御回路と、前記二次巻線間に接続される、ダイオードと発光ダイオードとの直列接続回路と、を有する発光ダイオード駆動回路における前記ダイオードと発光ダイオードとの直列接続回路中に定電流素子を設けたことを特徴としている。
請求項２記載の発明は、請求項１記載の発光ダイオード定電流駆動回路において、前記一次巻線と前記スイッチング素子間に直流電圧を加えることを特徴としている。 In order to solve the above problems, an invention according to claim 1 relates to a light-emitting diode constant current driving circuit, a transformer having a primary winding and a secondary winding, and a switching element connected in series to the primary winding; A light emitting diode drive circuit comprising: an on / off control circuit for controlling on / off of the switching element; and a series connection circuit of a diode and a light emitting diode connected between the secondary windings. A constant current element is provided in a series connection circuit with a diode.
According to a second aspect of the present invention, in the light-emitting diode constant current driving circuit according to the first aspect, a DC voltage is applied between the primary winding and the switching element.

また、請求項３記載の発明は、発光ダイオード定電流駆動回路に係り、二個のコンデンサの直列接続回路と二個のスイッチング素子の直列接続回路とを並列接続して成るブリッジ回路と、前記スイッチング素子をオン・オフ制御するオン・オフ制御回路と、一次巻線と中間タップ付二次巻線とを有するトランスとを有し、前記一次巻線を前記ブリッジ回路の各中間接続点間に挿入し、前記二次巻線の両端をそれぞれダイオードを介して接続（二次巻線接続点）し、前記二次巻線接続点と前記中間タップとの間に発光ダイオードを接続して成る発光ダイオード駆動回路における前記発光ダイオードに直列に定電流素子を接続したことを特徴としている。
そして、請求項４記載の発明は、請求項３記載の発光ダイオード定電流駆動回路において、前記ブリッジ回路の入力側に直流電圧を加えることを特徴としている。 According to a third aspect of the present invention, there is provided a constant current driving circuit for a light emitting diode, a bridge circuit formed by connecting a series connection circuit of two capacitors and a series connection circuit of two switching elements in parallel, and the switching circuit. An on / off control circuit for controlling on / off of the element, and a transformer having a primary winding and a secondary winding with an intermediate tap, and the primary winding is inserted between each intermediate connection point of the bridge circuit And a light emitting diode formed by connecting both ends of the secondary winding via a diode (secondary winding connection point), and connecting a light emitting diode between the secondary winding connection point and the intermediate tap. A constant current element is connected in series to the light emitting diode in the drive circuit.
According to a fourth aspect of the present invention, in the light emitting diode constant current driving circuit according to the third aspect, a DC voltage is applied to the input side of the bridge circuit.

また、請求項５記載の発明は、発光ダイオード定電流駆動回路に係り、スイッチング素子と発光ダイオードとの直列接続回路と、前記スイッチング素子をオン・オフ制御するオン・オフ制御回路とを有して成る発光ダイオード駆動回路の前記直列接続回路に定電流素子を挿入したことを特徴している。
また、請求項６記載の発明は、請求項５記載の発光ダイオード定電流駆動回路において、前記前記直列接続回路の両端に直流電圧を加えることを特徴としている。 The invention according to claim 5 relates to a light emitting diode constant current driving circuit, comprising a series connection circuit of a switching element and a light emitting diode, and an on / off control circuit for controlling on / off of the switching element. A constant current element is inserted into the series connection circuit of the light emitting diode driving circuit.
According to a sixth aspect of the present invention, in the light-emitting diode constant current driving circuit according to the fifth aspect, a DC voltage is applied to both ends of the series connection circuit.

そして、請求項７記載の発明は、請求項１〜６のいずれか１項記載の発光ダイオード定電流駆動回路において、前記オン・オフ制御回路が前記スイッチング素子のオン時間とオフ時間の比を制御するパルス幅制御を行うことを特徴している。   According to a seventh aspect of the present invention, in the light-emitting diode constant current drive circuit according to any one of the first to sixth aspects, the on / off control circuit controls a ratio of an on time to an off time of the switching element. It is characterized by performing pulse width control.

上記のように、本発明によれば、電源部とＰＷＭ制御部が統合できるので、図８で示した従来回路必要としたインダクタ、コンデンサで構成されるフィルタ１−１と発光ダイオードの輝度を調整するＰＷＭ制御専用のスイッチング素子と制御回路が不要となる。
したがって、電源の構成が極めて簡易になり、発光ダイオード駆動回路の低コスト化、小型・軽量化、高効率化が実現できる。また、発光ダイオードの電流を抵抗で規定する方式から定電流素子を用いた定電流駆動方式に変えることにより、発光ダイオードの順方向電圧降下バラツキによる消費電力の増加を防止できるので発熱が抑えられ、発光ダイオードの駆動電流を規格内に抑えることができるので信頼性向上を図ることができる。 As described above, according to the present invention, since the power supply unit and the PWM control unit can be integrated, the brightness of the light-emitting diode and the filter 1-1 including the inductor and the capacitor required for the conventional circuit shown in FIG. 8 is adjusted. This eliminates the need for a switching element and control circuit dedicated to PWM control.
Therefore, the configuration of the power supply becomes extremely simple, and it is possible to reduce the cost, size, weight, and efficiency of the light emitting diode driving circuit. In addition, by changing the current of the light emitting diode from a method that regulates the resistance to a constant current driving method using a constant current element, an increase in power consumption due to variations in the forward voltage drop of the light emitting diode can be prevented, so heat generation can be suppressed, Since the driving current of the light emitting diode can be kept within the standard, the reliability can be improved.

＜実施例１＞
本発明に関わる発光ダイオードの定電流駆動回路の実施例１を図１に示す。
図において、１は商用電源、２ブリッジダイオード、３はコンデンサ、４はトランスで１次巻線４ａと２次巻線４ｂを備えている。５はスイッチング素子、６は整流ダイオード、１２は発光ダイオード、１５は定電流素子、１６はスイッチング素子５の制御回路である。 <Example 1>
FIG. 1 shows a first embodiment of a constant current driving circuit for a light emitting diode according to the present invention.
In the figure, 1 is a commercial power source, 2 bridge diode, 3 is a capacitor, 4 is a transformer, and includes a primary winding 4a and a secondary winding 4b. Reference numeral 5 denotes a switching element, 6 denotes a rectifier diode, 12 denotes a light emitting diode, 15 denotes a constant current element, and 16 denotes a control circuit for the switching element 5.

次に、図１に示す回路の動作を説明する。
商用電源１の交流電圧をブリッジダイオード２で整流し、コンデンサ３で平滑し、トランス４、ＭＯＳ−ＦＥＴなどのスイッチング素子５で高周波矩形波交流電圧（パルス電圧）に変換し、整流ダイオード６で整流して得られたパルス電圧に定電流素子１５、発光ダイオード１２の直列回路を接続する。スイッチング素子５は制御回路１６によって制御される。 Next, the operation of the circuit shown in FIG. 1 will be described.
The AC voltage of the commercial power source 1 is rectified by the bridge diode 2, smoothed by the capacitor 3, converted to a high-frequency rectangular wave AC voltage (pulse voltage) by the switching element 5 such as the transformer 4 and MOS-FET, and rectified by the rectifier diode 6. A series circuit of the constant current element 15 and the light emitting diode 12 is connected to the obtained pulse voltage. The switching element 5 is controlled by the control circuit 16.

図２にトランス二次側電圧Ｖ４と整流ダイオード６で整流して得られたパルス電圧波形Ｖ６を示す。発光ダイオード１２を流れる電流はパルス電圧Ｖ６がある時だけ定電流素子１５で規定された定電流が流れ点灯する。
定電流素子１５の特性例を図３に示す。横軸は印加電圧Ｖ１４、縦軸は電流Ｉ１４である。定電流素子１５にある電圧Ｖ140以上の電圧を印加すると、印加電圧に関係なく一定の電流Ｉ140が流れる。電源電圧の変動、発光ダイオードの順方向電圧のバラツキは定電流素子に印加される電圧が電圧変動と順方向電圧のバラツキを吸収するように変化し、流れる電流はＩ140と一定に保たれる。したがって、消費電力は電源電圧の変動分だけ増減するが、発光ダイオードの輝度は変化しない。
図１に示す回路ではパルス電圧Ｖ６が無いときは発光ダイオード１２は消灯するが、パルス電圧Ｖ６が数ｋＨｚ以上の高周波であれば、消灯していることは人間の目では認知できないので発光ダイオード１２は点灯し続けているように見える。図２に示すパルス電圧Ｖ６の一周期Ｔに対するパルス電圧Ｖ６の割合（ｔ０／Ｔ）を減少させると発光ダイオード１２の輝度が低下し、割合を増加させると輝度が上昇しているように見える。パルス電圧Ｖ６の割合（ｔ０／Ｔ）は制御回路１６で調整できる。 FIG. 2 shows a pulse voltage waveform V6 obtained by rectification using the transformer secondary voltage V4 and the rectifier diode 6. The current flowing through the light emitting diode 12 is lit by the constant current defined by the constant current element 15 only when there is a pulse voltage V6.
A characteristic example of the constant current element 15 is shown in FIG. The horizontal axis represents the applied voltage V14, and the vertical axis represents the current I14. When a voltage V 140 or higher is applied to the constant current element 15, a constant current I 140 flows regardless of the applied voltage. Variation in power supply voltage, variation of the forward voltage of the light-emitting diode changes as the voltage applied to the constant current element absorbs the variation of the voltage change and the forward voltage, current flows is kept constant and I 140 . Therefore, the power consumption increases or decreases by the fluctuation of the power supply voltage, but the luminance of the light emitting diode does not change.
In the circuit shown in FIG. 1, the light emitting diode 12 is turned off when there is no pulse voltage V6. However, if the pulse voltage V6 is a high frequency of several kHz or more, the light emitting diode 12 cannot be recognized by the human eye. Seems to keep lit. When the ratio (t0 / T) of the pulse voltage V6 to one period T of the pulse voltage V6 shown in FIG. 2 is decreased, the luminance of the light emitting diode 12 is decreased, and when the ratio is increased, it appears that the luminance is increased. The ratio (t0 / T) of the pulse voltage V6 can be adjusted by the control circuit 16.

＜実施例２＞
図４に本発明に関わる発光ダイオード定電流駆動回路の実施例２を示す。
高周波矩形波交流電圧に変換する回路にはハーフブリッジコンバータで使用する回路を適用している以外は図１で示した構成と基本的には同じである。１は商用電源、２ブリッジダイオード、３ａ、３ｂ はコンデンサ、４はトランスで１次巻線４ａと２次巻線４ｂと２次巻線に中間タップ４ｃを備えている。５ａ、５ｂ はスイッチング素子、６ａ、６ｂ はダイオード、１２は発光ダイオード、１５は定電流素子、１６は制御回路である。 <Example 2>
FIG. 4 shows a second embodiment of a light-emitting diode constant current driving circuit according to the present invention.
The circuit for converting to a high-frequency rectangular wave AC voltage is basically the same as the configuration shown in FIG. 1 except that the circuit used in the half-bridge converter is applied. Reference numeral 1 denotes a commercial power source, 2 bridge diodes, 3a and 3b capacitors, and 4 a transformer, which includes a primary winding 4a, a secondary winding 4b, and an intermediate tap 4c in the secondary winding. 5a and 5b are switching elements, 6a and 6b are diodes, 12 is a light emitting diode, 15 is a constant current element, and 16 is a control circuit.

次に図４に示す回路の動作を説明する。
商用電源１の交流電圧をブリッジダイオード２で整流し、コンデンサ３ａ、３ｂ で平滑するとともに、電源電圧を分圧する。コンデンサ３ａ、３ｂ の接続点電圧は電源電圧の１／２である。トランス４、ＭＯＳ−ＦＥＴなどのスイッチング素子５ａ、５ｂ を交互にオン・オフさせることで高周波矩形波交流電圧に変換し、トランス４にセンタータップトランスを使用すればダイオード６ａ、６ｂ で整流、センタータップトランスでなければダイオード６ａ、６ｂ はブリッジダイオードに変更して整流する。 Next, the operation of the circuit shown in FIG. 4 will be described.
The AC voltage of the commercial power supply 1 is rectified by the bridge diode 2, smoothed by the capacitors 3a and 3b, and the power supply voltage is divided. The connection point voltage of the capacitors 3a and 3b is ½ of the power supply voltage. Transformer 4 and switching elements 5a and 5b such as MOS-FETs are alternately turned on and off to convert to a high frequency rectangular wave AC voltage. If a center tap transformer is used for transformer 4, rectification and center tap are performed by diodes 6a and 6b. If it is not a transformer, the diodes 6a and 6b are changed to bridge diodes for rectification.

図５にトランス４の２次側電圧Ｖ６、ダイオード６ａ、６ｂで整流して得られるパルス電圧波形Ｖ６ａ＋Ｖ６ｂを示す。整流して得られたパルス電圧Ｖ６ａ＋Ｖ６ｂに、定電流素子１５、発光ダイオード１２の直列回路を接続する。スイッチング素子５ａ、５ｂ は制御回路１６によって制御される。図１の回路ではパルス電圧の割合（ｔ０／Ｔ）は０〜０．７程度であるが、図５のパルス電圧波形Ｖ６ａ＋Ｖ６ｂは、（２ｔ０／Ｔ）となるので０〜１と大きくでき、１の場合は一定の直流電圧と見做すことができる。発光ダイオード１２を流れる電流はパルス電圧がある時だけ定電流素子１５で規定した定電流が流れ点灯する。   FIG. 5 shows a pulse voltage waveform V6a + V6b obtained by rectifying the secondary side voltage V6 of the transformer 4 and the diodes 6a and 6b. A series circuit of the constant current element 15 and the light emitting diode 12 is connected to the pulse voltage V6a + V6b obtained by rectification. The switching elements 5a and 5b are controlled by the control circuit 16. In the circuit of FIG. 1, the pulse voltage ratio (t0 / T) is about 0 to 0.7, but the pulse voltage waveform V6a + V6b of FIG. 5 is (2t0 / T) and can be increased to 0 to 1. In this case, it can be regarded as a constant DC voltage. The current flowing through the light emitting diode 12 is lit by a constant current defined by the constant current element 15 only when there is a pulse voltage.

＜実施例３＞
図６に本発明に関わる発光ダイオード定電流電源駆動の実施例３を示す。
１は商用電源、２ブリッジダイオード、３はコンデンサ、５はスイッチング素子、１２は発光ダイオード、１５は定電流素子、１６は制御回路である。
次に図６に示す回路の動作を説明する。商用電源１の交流電圧をブリッジダイオード２で整流し、コンデンサ３で平滑する。ＭＯＳ−ＦＥＴなどのスイッチング素子５をオン・オフさせることで高周波矩形波電圧に変換し、得られたパルス電圧に定電流素子１５、発光ダイオード１２の直列回路を接続する。スイッチング素子５は制御回路１６によって制御される。図７に得られる矩形波パルス電圧波形Ｖ７を示す。図６の回路ではパルス電圧の割合（ｔ０／Ｔ）は０〜１と大きくでき、１の場合は一定の直流電圧と見做すことができる。発光ダイオード１２を流れる電流はパルス電圧がある時だけ定電流素子１５で規定した定電流が流れ点灯する。 <Example 3>
FIG. 6 shows a third embodiment of light-emitting diode constant current power supply driving according to the present invention.
1 is a commercial power supply, 2 bridge diode, 3 is a capacitor, 5 is a switching element, 12 is a light emitting diode, 15 is a constant current element, and 16 is a control circuit.
Next, the operation of the circuit shown in FIG. 6 will be described. The AC voltage of the commercial power source 1 is rectified by the bridge diode 2 and smoothed by the capacitor 3. The switching element 5 such as a MOS-FET is turned on / off to convert it to a high-frequency rectangular wave voltage, and the series circuit of the constant current element 15 and the light emitting diode 12 is connected to the obtained pulse voltage. The switching element 5 is controlled by the control circuit 16. FIG. 7 shows a rectangular pulse voltage waveform V7 obtained. In the circuit of FIG. 6, the pulse voltage ratio (t0 / T) can be as large as 0 to 1, and in the case of 1, it can be regarded as a constant DC voltage. The current flowing through the light emitting diode 12 is lit by a constant current defined by the constant current element 15 only when there is a pulse voltage.

以上、本発明によれば電源部とＰＷＭ制御部が統合できるので、図８で示した従来回路必要としたインダクタ、コンデンサで構成されるフィルタ１−１と発光ダイオードの輝度を調整するＰＷＭ制御専用のスイッチング素子と制御回路が不要となる。したがって、電源の構成が極めて簡易になり、発光ダイオード駆動回路の低コスト化、小型・軽量化、高効率化が実現できる。また、発光ダイオードの電流を抵抗で規定する方式から定電流素子を用いた定電流駆動方式に変えることにより、発光ダイオードの順方向電圧降下バラツキによる消費電力の増加を防止できるので発熱が抑えられ、発光ダイオードの駆動電流を規格内に抑えることができるので信頼性向上を図ることができる。   As described above, according to the present invention, the power supply unit and the PWM control unit can be integrated. Therefore, the filter 1-1 for the conventional circuit shown in FIG. The switching element and the control circuit are not required. Therefore, the configuration of the power supply becomes extremely simple, and it is possible to reduce the cost, size, weight, and efficiency of the light emitting diode driving circuit. In addition, by changing the current of the light emitting diode from a method that regulates the resistance to a constant current driving method using a constant current element, an increase in power consumption due to variations in the forward voltage drop of the light emitting diode can be prevented, so heat generation can be suppressed, Since the driving current of the light emitting diode can be kept within the standard, the reliability can be improved.

本発明の実施例１に係る発光ダイオード定電流駆動回路である。1 is a light-emitting diode constant current driving circuit according to Example 1 of the present invention. 図１の発光ダイオード輝度調整回路の動作波形である。It is an operation | movement waveform of the light emitting diode brightness | luminance adjustment circuit of FIG. 定電流素子の特性例であるIt is a characteristic example of a constant current element 本発明の実施例２に係る発光ダイオード定電流駆動回路である。4 is a light-emitting diode constant current drive circuit according to Example 2 of the present invention. 図４の発光ダイオード輝度調整回路の動作波形である。5 is an operation waveform of the light-emitting diode luminance adjustment circuit of FIG. 4. 本発明の実施例３に係る発光ダイオード定電流駆動回路である。6 is a light-emitting diode constant current drive circuit according to Example 3 of the present invention. 図６の発光ダイオード輝度調整回路の動作波形である。FIG. 7 is an operation waveform of the light emitting diode luminance adjustment circuit of FIG. 6. FIG. 従来の発光ダイオード駆動回路と輝度調整回路を組合せた発光ダイオード定電流駆動回路である。This is a light emitting diode constant current driving circuit in which a conventional light emitting diode driving circuit and a brightness adjusting circuit are combined. 発光ダイオード輝度調整回路である。It is a light emitting diode brightness adjustment circuit.

符号の説明Explanation of symbols

１ 商用電源
２ ブリッジダイオード
３、３ａ、３ｂ コンデンサ
４ トランス
５、５ａ、５ｂ スイッチング素子
６、６ａ、６ｂ ダイオード
１２ 発光ダイオード
１５ 定電流素子
１６ スイッチング素子制御回路 DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Bridge diode 3, 3a, 3b Capacitor 4 Transformer 5, 5a, 5b Switching element 6, 6a, 6b Diode 12 Light emitting diode 15 Constant current element 16 Switching element control circuit

上記課題を解決するために、請求項１記載の発明は、発光ダイオード定電流駆動回路に係り、一次巻線と二次巻線を有するトランスと、前記一次巻線に直列接続されるスイッチング素子と、前記スイッチング素子を高周波でオン・オフ制御するオン・オフ制御回路と、前記二次巻線間に接続される、ダイオードと発光ダイオードとの直列接続回路と、を有する発光ダイオード駆動回路であって、前記ダイオードと発光ダイオードとの直列接続回路中に定電流素子を設け、かつ、前記一次巻線と前記スイッチング素子間に直流電圧を加えることで、高周波矩形波電圧を前記発光ダイオードに印加することを特徴としている。 In order to solve the above problems, an invention according to claim 1 relates to a light-emitting diode constant current driving circuit, a transformer having a primary winding and a secondary winding, and a switching element connected in series to the primary winding; the on-off control circuit for controlling on and off the switching element at a high frequency, the connected between the secondary winding, a light emitting diode driving circuit having a series circuit, a diode and a light emitting diode , a constant current element is provided in the series circuit of the diode and a light emitting diode, and wherein by adding a DC voltage between the primary winding and the switching element, applying a high-frequency square wave voltage to the light emitting diode It is characterized by.

また、請求項２記載の発明は、発光ダイオード定電流駆動回路に係り、二個のコンデンサの直列接続回路と二個のスイッチング素子の直列接続回路とを並列接続して成るブリッジ回路と、前記スイッチング素子を高周波でオン・オフ制御するオン・オフ制御回路と、一次巻線と中間タップ付二次巻線とを有するトランスとを有し、前記一次巻線を前記ブリッジ回路の各中間接続点間に挿入し、前記二次巻線の両端をそれぞれダイオードを介して接続（二次巻線接続点）し、前記二次巻線接続点と前記中間タップとの間に発光ダイオードを接続して成る発光ダイオード駆動回路における前記発光ダイオードに直列に定電流素子を接続し、かつ前記ブリッジ回路の入力側に直流電圧を加えることで、高周波矩形波電圧を前記発光ダイオードに印加することを特徴としている。 According to a second aspect of the present invention, there is provided a light-emitting diode constant current driving circuit, a bridge circuit comprising a parallel connection of a series connection circuit of two capacitors and a series connection circuit of two switching elements, and the switching circuit. An on / off control circuit for controlling on / off of the element at a high frequency ; and a transformer having a primary winding and a secondary winding with an intermediate tap, and the primary winding is connected between each intermediate connection point of the bridge circuit. And connecting both ends of the secondary winding via a diode (secondary winding connection point), and connecting a light emitting diode between the secondary winding connection point and the intermediate tap. connect the constant current element in series with the light emitting diodes in the LED driving circuit, and by adding a DC voltage to the input side of the bridge circuit, applying a high-frequency square wave voltage to the light emitting diode It is characterized in that that.

また、請求項３記載の発明は、発光ダイオード定電流駆動回路に係り、スイッチング素子と発光ダイオードとの直列接続回路と、前記スイッチング素子を高周波でオン・オフ制御するオン・オフ制御回路とを有して成る発光ダイオード駆動回路の前記直列接続回路に定電流素子を挿入し、かつ前記直列接続回路の両端に直流電圧を加えることで、高周波矩形波電圧を前記発光ダイオードに印加することを特徴としている。 The invention described in claim 3 relates to a light emitting diode constant current driving circuit, comprising a series connection circuit of a switching element and a light emitting diode, and an on / off control circuit for on / off controlling the switching element at a high frequency. A high-frequency rectangular wave voltage is applied to the light emitting diode by inserting a constant current element into the series connected circuit of the light emitting diode driving circuit and applying a DC voltage to both ends of the series connected circuit. Yes.

そして、請求項４記載の発明は、請求項１〜３のいずれか１項記載の発光ダイオード定電流駆動回路において、前記オン・オフ制御回路が前記スイッチング素子のオン時間とオフ時間の比を制御するパルス幅制御を行うことを特徴としている。
According to a fourth aspect of the present invention, in the light-emitting diode constant current drive circuit according to any one of the first to third aspects, the on / off control circuit controls a ratio of an on time to an off time of the switching element. It is characterized by performing pulse width control.

上記課題を解決するために、請求項１記載の発明は、発光ダイオード定電流駆動回路に係り、一次巻線と二次巻線を有するトランスと、前記一次巻線に直列接続されるスイッチング素子と、前記スイッチング素子を高周波でオン・オフ制御するオン・オフ制御回路と、前記二次巻線間に接続される、ダイオードと発光ダイオードとの直列接続回路と、を有する発光ダイオード駆動回路であって、前記ダイオードと発光ダイオードとの直列接続回路中に定電流素子を設け、かつ、前記一次巻線と前記スイッチング素子間に直流電圧を加え、前記オン・オフ制御回路により前記スイッチング素子のオン時間だけ高周波矩形波電圧を前記発光ダイオードに印加し、前記スイッチング素子のオン時間とオフ時間の比を変えることで前記発光ダイオードの輝度を変えることを特徴としている。 In order to solve the above problems, an invention according to claim 1 relates to a light-emitting diode constant current driving circuit, a transformer having a primary winding and a secondary winding, and a switching element connected in series to the primary winding; A light emitting diode driving circuit comprising: an on / off control circuit for controlling on / off of the switching element at a high frequency; and a series connection circuit of a diode and a light emitting diode connected between the secondary windings. A constant current element is provided in a series connection circuit of the diode and the light emitting diode, and a DC voltage is applied between the primary winding and the switching element, and only the ON time of the switching element is applied by the ON / OFF control circuit. Applying a high-frequency rectangular wave voltage to the light emitting diode, and changing the ratio between the on time and the off time of the switching element, the light emitting diode It is characterized by changing the brightness.

また、請求項２記載の発明は、発光ダイオード定電流駆動回路に係り、二個のコンデンサの直列接続回路と二個のスイッチング素子の直列接続回路とを並列接続して成るブリッジ回路と、前記スイッチング素子を高周波でオン・オフ制御するオン・オフ制御回路と、一次巻線と中間タップ付二次巻線とを有するトランスとを有し、前記一次巻線を前記ブリッジ回路の各中間接続点間に挿入し、前記二次巻線の両端をそれぞれダイオードを介して接続（二次巻線接続点）し、前記二次巻線接続点と前記中間タップとの間に発光ダイオードを接続して成る発光ダイオード駆動回路における前記発光ダイオードに直列に定電流素子を接続し、かつ前記ブリッジ回路の入力側に直流電圧を加え、前記オン・オフ制御回路により前記スイッチング素子のオン時間だけ高周波矩形波電圧を前記発光ダイオードに印加し、前記スイッチング素子のオン時間とオフ時間の比を変えることで前記発光ダイオードの輝度を変えることを特徴としている。 According to a second aspect of the present invention, there is provided a constant current driving circuit for a light emitting diode, a bridge circuit formed by connecting in parallel a series connection circuit of two capacitors and a series connection circuit of two switching elements, and the switching circuit. An on / off control circuit for controlling on / off of the element at a high frequency; and a transformer having a primary winding and a secondary winding with an intermediate tap, and the primary winding is connected between each intermediate connection point of the bridge circuit. The secondary winding is connected to both ends of the secondary winding via diodes (secondary winding connection point), and a light emitting diode is connected between the secondary winding connection point and the intermediate tap. emitting diode to connect the constant current element in series with the light emitting diodes in the drive circuit, and a DC voltage to the input side of the bridge circuit in addition, of the switching element by the on-off control circuit Only down time by applying a high frequency square wave voltage to the light emitting diode is characterized by changing the brightness of the light emitting diode by changing the ratio of on and off times of the switching element.

Claims (7)

一次巻線と二次巻線を有するトランスと、前記一次巻線に直列接続されるスイッチング素子と、前記スイッチング素子をオン・オフ制御するオン・オフ制御回路と、前記二次巻線間に接続される、ダイオードと発光ダイオードとの直列接続回路と、を有する発光ダイオード駆動回路における前記ダイオードと発光ダイオードとの直列接続回路中に定電流素子を設けたことを特徴とする発光ダイオード定電流駆動回路。   A transformer having a primary winding and a secondary winding, a switching element connected in series to the primary winding, an on / off control circuit for controlling on / off of the switching element, and a connection between the secondary windings A light emitting diode constant current driving circuit comprising a constant current element provided in a series connection circuit of the diode and the light emitting diode in the light emitting diode driving circuit having a diode and a light emitting diode connected in series . 前記一次巻線と前記スイッチング素子間に直流電圧を加えることを特徴とする請求項１記載の発光ダイオード定電流駆動回路。   2. The light emitting diode constant current drive circuit according to claim 1, wherein a DC voltage is applied between the primary winding and the switching element. 二個のコンデンサの直列接続回路と二個のスイッチング素子の直列接続回路とを並列接続して成るブリッジ回路と、前記スイッチング素子をオン・オフ制御するオン・オフ制御回路と、一次巻線と中間タップ付二次巻線とを有するトランスとを有し、前記一次巻線を前記ブリッジ回路の各中間接続点間に挿入し、前記二次巻線の両端をそれぞれダイオードを介して接続（二次巻線接続点）し、前記二次巻線接続点と前記中間タップとの間に発光ダイオードを接続して成る発光ダイオード駆動回路における前記発光ダイオードに直列に定電流素子を接続したことを特徴する発光ダイオード定電流駆動回路。   A bridge circuit formed by connecting a series connection circuit of two capacitors and a series connection circuit of two switching elements in parallel, an on / off control circuit for controlling on / off of the switching elements, a primary winding and an intermediate A transformer having a tapped secondary winding, the primary winding is inserted between each intermediate connection point of the bridge circuit, and both ends of the secondary winding are connected via diodes (secondary winding). And a constant current element connected in series to the light emitting diode in a light emitting diode driving circuit comprising a light emitting diode connected between the secondary winding connecting point and the intermediate tap. Light-emitting diode constant current drive circuit. 前記ブリッジ回路の入力側に直流電圧を加えることを特徴とする請求項３記載の発光ダイオード定電流駆動回路。   4. The light-emitting diode constant current drive circuit according to claim 3, wherein a DC voltage is applied to an input side of the bridge circuit. スイッチング素子と発光ダイオードとの直列接続回路と、前記スイッチング素子をオン・オフ制御するオン・オフ制御回路とを有して成る発光ダイオード駆動回路の前記直列接続回路に定電流素子を挿入したことを特徴する発光ダイオード定電流駆動回路。   A constant current element is inserted into the series connection circuit of the light emitting diode driving circuit having a series connection circuit of a switching element and a light emitting diode and an on / off control circuit for controlling on / off of the switching element. Characteristic light-emitting diode constant current drive circuit. 前記前記直列接続回路の両端に直流電圧を加えることを特徴とする請求項５記載の発光ダイオード定電流駆動回路。   6. The light emitting diode constant current driving circuit according to claim 5, wherein a DC voltage is applied to both ends of the series connection circuit. 前記オン・オフ制御回路が前記スイッチング素子のオン時間とオフ時間の比を制御するパルス幅制御を行うことを特徴する請求項１〜６のいずれか１項記載の発光ダイオード定電流駆動回路。   The light-emitting diode constant current drive circuit according to claim 1, wherein the on / off control circuit performs pulse width control for controlling a ratio between an on time and an off time of the switching element.
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Cited By (5)

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JP2011249771A (en) * 2010-05-24 2011-12-08 Taida Electronic Ind Co Ltd Light source module
KR101092218B1 (en) * 2009-10-06 2011-12-12 한국전기연구원 LED Driving Circuit using Sumple Current Source
JP2012018842A (en) * 2010-07-08 2012-01-26 Sharp Corp Led lighting device
JP2012029535A (en) * 2010-07-27 2012-02-09 Panasonic Electric Works Co Ltd Power supply device, and illumination device having the same
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Publication number Priority date Publication date Assignee Title
KR101092218B1 (en) * 2009-10-06 2011-12-12 한국전기연구원 LED Driving Circuit using Sumple Current Source
JP2011249771A (en) * 2010-05-24 2011-12-08 Taida Electronic Ind Co Ltd Light source module
JP2012018842A (en) * 2010-07-08 2012-01-26 Sharp Corp Led lighting device
JP2012029535A (en) * 2010-07-27 2012-02-09 Panasonic Electric Works Co Ltd Power supply device, and illumination device having the same
KR101267957B1 (en) 2012-02-28 2013-05-27 주응택 Apparatus for control of led lamp

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