JPH05129665A - Led drive circuit - Google Patents
Led drive circuitInfo
- Publication number
- JPH05129665A JPH05129665A JP29122491A JP29122491A JPH05129665A JP H05129665 A JPH05129665 A JP H05129665A JP 29122491 A JP29122491 A JP 29122491A JP 29122491 A JP29122491 A JP 29122491A JP H05129665 A JPH05129665 A JP H05129665A
- Authority
- JP
- Japan
- Prior art keywords
- led
- constant current
- leds
- current
- light emitting
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、操作パネル等に使用さ
れる発光ダイオード（ＬＥＤ）の光量を均一に表示する
ことができるＬＥＤ駆動回路に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED drive circuit capable of uniformly displaying the light quantity of a light emitting diode (LED) used in an operation panel or the like.
【０００２】[0002]
【従来の技術】図４は従来のＬＥＤ駆動回路を示す回路
図である。図に於いて、１ａ〜１ｎは各ＬＥＤ（各発光
ダイオード）、６は電源、７ａ〜７ｎは各電流制限抵抗
で、各ＬＥＤ１ａ〜１ｎのアノードが電源６に共通に接
続され、又、各ＬＥＤ１ａ〜１ｎのカソードが各ＬＥＤ
に対応して各電流制限抵抗７ａ〜７ｎの一端に接続され
ている。８ａ〜８ｎは各オープンコレクタ用ＩＣで、各
オープンコレクタ用ＩＣ８ａ〜８ｎの入力端子には制御
部（図示せず）から制御信号として出力されるＬＥＤオ
ン信号ａ〜ｎが各オープンコレクタ用ＩＣ８ａ〜８ｎに
対応して入力されている。又、各オープンコレクタ用Ｉ
Ｃ８ａ〜８ｎの出力は各電流制限抵抗７ａ〜７ｎの他端
に対応して接続されている。2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional LED drive circuit. In the figure, 1a to 1n are LEDs (light emitting diodes), 6 is a power source, 7a to 7n are current limiting resistors, the anodes of the LEDs 1a to 1n are commonly connected to the power source 6, and the LEDs 1a are also connected. ~ 1n cathode for each LED
Is connected to one end of each of the current limiting resistors 7a to 7n. 8a to 8n are ICs for open collectors, and LED ON signals a to n output as control signals from a control unit (not shown) are input to the input terminals of the ICs 8a to 8n for open collectors. It is input corresponding to 8n. I for each open collector
The outputs of C8a to 8n are connected to the other ends of the current limiting resistors 7a to 7n, respectively.
【０００３】従来のＬＥＤ駆動回路は上記のように構成
されており、図５はＬＥＤの負荷特性により動作点を求
める説明図であり、先ず、ＬＥＤの動作点の説明をす
る。The conventional LED drive circuit is constructed as described above, and FIG. 5 is an explanatory diagram for obtaining the operating point from the load characteristics of the LED. First, the operating point of the LED will be described.
【０００４】図に於いて、ＬＥＤに対して順方向に印加
する電圧に比例してＬＥＤの順方向電流が得られる順方
向電流−順方向電圧の特性曲線Ａと、電流制限抵抗７ａ
〜７ｎを電源６に接続した際の負荷特性Ｂとが交差する
交点ＰがＬＥＤの動作点Ｐであり、この動作点によりＬ
ＥＤの駆動電圧ＶF 及び駆動電流ＩF が得られる。In the figure, a forward current-forward voltage characteristic curve A for obtaining the forward current of the LED in proportion to the voltage applied to the LED in the forward direction and the current limiting resistor 7a.
The intersection point P at which the load characteristic B when 7n is connected to the power supply 6 intersects is the operating point P of the LED, and this operating point leads to L
The drive voltage VF and drive current IF of the ED can be obtained.
【０００５】次に、ＬＥＤ駆動回路の動作を説明する。
例えば、ＬＥＤ１ａだけを発光させる場合、上記制御部
から論理レベルＬのＬＥＤオン信号ａをオープンコレク
タ用ＩＣ８ａに出力し、オープンコレクタ用ＩＣ８ａの
出力はＬとなるので電源６から印加される電圧ＶF によ
りＬＥＤ１ａは駆動電流ＩF を流して発光する。又、発
光したＬＥＤ１ａを消灯させる場合、上記制御部から論
理レベルＨのＬＥＤオン信号ａをオープンコレクタ用Ｉ
Ｃ８ａに出力し、オープンコレクタ用ＩＣ８ａの出力は
Ｈとなるので電源６から印加される電圧に基づいてＬＥ
Ｄ１ａに駆動電流が流れず消灯する。Next, the operation of the LED drive circuit will be described.
For example, when only the LED 1a is caused to emit light, the LED ON signal a of logic level L is output from the control section to the open collector IC 8a, and the output of the open collector IC 8a becomes L, so that the voltage VF applied from the power source 6 The LED 1a emits light by passing a drive current IF. Further, when turning off the emitted LED 1a, the LED ON signal a of the logic level H is sent from the control unit to the open collector I.
It is output to C8a and the output of the open collector IC 8a becomes H. Therefore, based on the voltage applied from the power source 6, LE
The drive current does not flow to D1a and the light is turned off.
【０００６】[0006]
【発明が解決しようとする課題】上記のような従来のＬ
ＥＤ駆動回路では、各ＬＥＤの順方向電流−順方向電圧
の特性にばらつきがあるので動作点Ｐが変動して個々の
ＬＥＤに流れる電流が異なり各ＬＥＤの光量がばらつく
という問題があった。DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the ED drive circuit, there is a problem in that the characteristics of the forward current-forward voltage of each LED vary, so that the operating point P varies, the current flowing through each LED varies, and the light amount of each LED varies.
【０００７】又、上記各ＬＥＤの光量のばらつきをなく
す為に、ＬＥＤを選別したり電流制限抵抗を微調整して
ＬＥＤの駆動電流を一定にするように工夫するが、選別
ないし調整により時間がかかりコストが上がるという問
題があった。Further, in order to eliminate the variation in the light amount of each LED, the LED is selected or the current limiting resistance is finely adjusted to make the drive current of the LED constant. There was a problem that the cost would increase.
【０００８】本発明は、かかる課題を解決するためにな
されたもので、コストを低減すると共にＬＥＤの光量を
均一にすることができるＬＥＤ駆動回路を得ることを目
的とする。The present invention has been made to solve the above problems, and an object of the present invention is to obtain an LED drive circuit which can reduce the cost and make the light amount of the LED uniform.
【０００９】[0009]
【課題を解決するための手段】本発明に係るＬＥＤ駆動
回路は、順方向に直列接続された発光素子群と、その発
光素子群に定電流を供給する定電流電源と、上記発光素
子群の各発光素子に対してそれぞれ並列に接続され、外
部からの制御信号に基づいて対応する発光素子を点灯又
は消灯させるスイッチ素子群とを備えたものである。An LED drive circuit according to the present invention comprises a group of light emitting elements connected in series in the forward direction, a constant current power source for supplying a constant current to the group of light emitting elements, and a group of the above light emitting element groups. A switch element group that is connected in parallel to each light emitting element and that turns on or off the corresponding light emitting element based on a control signal from the outside is provided.
【００１０】[0010]
【作用】本発明に於いては、外部からの制御信号により
各発光素子にそれぞれ並列に接続されたスイッチ素子を
制御して定電流電源から供給される定電流により各発光
素子に流れて光量を均一にする。In the present invention, the switch element connected in parallel to each light emitting element is controlled by an external control signal, and the amount of light is supplied to each light emitting element by the constant current supplied from the constant current power source. Make it uniform.
【００１１】[0011]
【実施例】図１は本発明の一実施例を示すＬＥＤ駆動回
路図あり、ａ〜ｎ，１ａ〜１ｎは従来と同じのものであ
る。図に於いて、２は一端が直列に接続された各ＬＥＤ
１ａ〜１ｎの終端部（ＬＥＤ１ｎのアノード側）に接続
され、他端が定電流源（後述説明）に接続されたプルア
ップ抵抗で、各トランジスタ（後述説明）のベース電流
が安定して流れるように各トランジスタのコレクタ電圧
を補償するものである。３は定電流電源で、一端が直列
に接続された各ＬＥＤ１ａ〜１ｎの始端部（ＬＥＤ１ａ
のカソード側）に接続され、他端がプルアップ抵抗２に
接続され、一定値の電流を供給する。４ａ〜４ｎは各Ｐ
ＮＰ形トランジスタで、個々のＬＥＤ１ａ〜１ｎに対応
して並列接続され、コレクタがＬＥＤのカソードに接続
され、又、エミッタがＬＥＤのアノードに接続されてい
る。５ａ〜５ｎは各ベース抵抗で、各ベース抵抗５ａ〜
５ｎの一端が個々のトランジスタ４ａ〜４ｎに対応して
直列接続され、他端が上記制御部からのＬＥＤオン信号
ａ〜ｎに対応して直列接続されている。FIG. 1 is an LED drive circuit diagram showing an embodiment of the present invention, in which a to n and 1a to 1n are the same as the conventional one. In the figure, 2 is each LED whose one end is connected in series.
A pull-up resistor connected to the terminal ends of 1a to 1n (the anode side of the LED 1n) and the other end connected to a constant current source (described later) so that the base current of each transistor (described later) flows stably. In addition, the collector voltage of each transistor is compensated. Reference numeral 3 denotes a constant current power supply, and one end of each of the LEDs 1a to 1n connected in series has a starting end (LED 1a).
The cathode side) and the other end is connected to the pull-up resistor 2 to supply a constant current. 4a to 4n are each P
The NP type transistor is connected in parallel to each of the LEDs 1a to 1n, the collector is connected to the cathode of the LED, and the emitter is connected to the anode of the LED. 5a to 5n are base resistors, and the base resistors 5a to 5n are
One end of 5n is connected in series corresponding to each of the transistors 4a to 4n, and the other end is connected in series corresponding to the LED on signals a to n from the control unit.
【００１２】本発明のＬＥＤ駆動回路は上記のように構
成されており、図２は図１のＬＥＤを全て点灯したとき
の等価回路図、図３は図１のＬＥＤ１ａを消灯して他の
ＬＥＤを点灯したときの説明図であり、本回路の動作を
説明する。The LED drive circuit of the present invention is constructed as described above, FIG. 2 is an equivalent circuit diagram when all the LEDs of FIG. 1 are turned on, and FIG. 3 is an LED of FIG. It is an explanatory view when is turned on, and the operation of this circuit will be described.
【００１３】図１及び図２に於いて、全てのＬＥＤ１ａ
〜１ｎを点灯させる場合、上記制御部から出力されるＬ
ＥＤオン信号ａ〜ｎを全てオープン状態（オープンコレ
クタ用ＩＣ出力のＨレベル或いはエミッタ接地されたＮ
ＰＮ形トランジスタがオフしたときのコレクタ出力に相
当）して各ＰＮＰ形トランジスタ４ａ〜４ｎのベースに
接続された各ベース５ａ〜５ｎに出力する。すると、各
ＰＮＰ形トランジスタ４ａ〜４ｎはオフ状態になり、そ
の結果、図２に示すような等価回路が得られ、全てのＬ
ＥＤ１ａ〜１ｎは定電流電源３から供給される定電流に
より一定に流れる。その為、個々のＬＥＤ１ａ〜１ｎに
流れる電流値がばらつくことなく、よって、個々のＬＥ
Ｄ１ａ〜１ｎの光量を安定させることができる。In FIG. 1 and FIG. 2, all LEDs 1a
When lighting up to 1n, L output from the control unit
ED on signals a to n are all in open state (H level of IC output for open collector or N grounded emitter)
It corresponds to the collector output when the PN type transistor is turned off) and outputs to each base 5a to 5n connected to the base of each PNP type transistor 4a to 4n. Then, the PNP transistors 4a to 4n are turned off, and as a result, an equivalent circuit as shown in FIG.
The EDs 1a to 1n flow constantly due to the constant current supplied from the constant current power supply 3. Therefore, the values of the currents flowing through the individual LEDs 1a to 1n do not fluctuate, so that
The light amount of D1a to 1n can be stabilized.
【００１４】又、図１及び図３に於いて、ＬＥＤ１ａの
みを消灯して他のＬＥＤ１ｂ〜１ｎを点灯させる場合、
上記制御部から出力されるＬＥＤオン信号ａをＬレベル
にし、他のＬＥＤオン信号ｂ〜ｎをオープン状態にして
各ＰＮＰ形トランジスタ４ａ〜４ｎに接続された各ベー
ス抵抗５ａ〜５ｎに出力する。すると、ＰＮＰ形トラン
ジスタ４ａのみにベース電流が流れてオン状態になると
共に他のＰＮＰ形トランジスタ４ｂ〜４ｎはオフ状態に
なり、その結果として図３に示すような回路が得られ
る。尚、ＰＮＰ形トランジスタ４ａのベース電流は定電
流電源３から発生する電圧とベース抵抗５ｂとから決定
され、この両者を適宜に選択しておくことによりＰＮＰ
形トランジスタ４ａを飽和領域でオンさせることができ
る。Further, in FIGS. 1 and 3, when only the LED 1a is turned off and the other LEDs 1b to 1n are turned on,
The LED on signal a output from the control unit is set to L level, and the other LED on signals b to n are opened and output to the base resistors 5a to 5n connected to the PNP transistors 4a to 4n. Then, the base current flows only in the PNP type transistor 4a to be turned on, and the other PNP type transistors 4b to 4n are turned off, and as a result, a circuit as shown in FIG. 3 is obtained. The base current of the PNP transistor 4a is determined by the voltage generated from the constant current power source 3 and the base resistor 5b, and the PNP can be selected by appropriately selecting both of them.
Transistor 4a can be turned on in the saturation region.
【００１５】即ち、ＬＥＤ１ａのアノード−カソード間
電圧は、ＰＮＰ形トランジスタ４ａのオン電圧Ｖｃｓａ
ｔ（一般に、この値はＬＥＤが十分な発光に必要な電流
を流す時に発生するアノード−カソード間電圧に比べて
十分に小さな値である）に抑えられてＬＥＤ１ａは不点
灯になると共に他のＬＥＤ１ｂ〜１ｎはＰＮＰ形トラン
ジスタ５ａを介して定電流電源３から供給される定電流
により一定に流れ個々のＬＥＤ１ｂ〜１ｎの光量を安定
させることができる。That is, the voltage between the anode and the cathode of the LED 1a is the ON voltage Vcsa of the PNP transistor 4a.
t (generally, this value is sufficiently smaller than the voltage between the anode and the cathode generated when the LED supplies a current necessary for sufficient light emission), the LED 1a becomes unlit, and the other LEDs 1b ˜1n constantly flow by the constant current supplied from the constant current power source 3 through the PNP transistor 5a, and can stabilize the light amount of each of the LEDs 1b to 1n.
【００１６】尚、定電流電源３を電源として直列接続さ
れた任意の位置のＬＥＤに対応したＰＮＰ形トランジス
タをオンさせると、即ち、任意のＰＮＰ形トランジスタ
のベース電流を流すと、その分岐された電流が次段以降
のＬＥＤに流れる電流が減少し、結果として、全て点灯
させるＬＥＤに流れる電流と等しくなるのでＬＥＤの光
量にばらつきを生じる可能性があるが、これには、ＰＮ
Ｐ形トランジスタの直流電流増幅率ｈfe（ｈfe＝コレク
タ電流÷ベース電流）の値の大きいものを選び、定電流
電源３からの定電流を分岐する（ベース電流）電流分を
できるだけ小さくすることにより上記の問題を解決する
ことができる。例えば、ｈfeが１００以上の値を有する
トランジスタは現在数多く存在しており、ｈfe＝１００
のトランジスタを用いた時、そのトランジスタに分岐し
ていくベース電流値はコレクタに流れる定電流電源から
の定電流値と比較して非常小さく（コレクタ電流の１／
１００）、ＬＥＤの光量に対するばらつきを無視するこ
とができる。When the PNP transistor corresponding to the LED at an arbitrary position connected in series with the constant current power source 3 as a power source is turned on, that is, when the base current of the arbitrary PNP transistor is passed, the branch is made. The current flowing through the LEDs of the next and subsequent stages decreases, and as a result, the current becomes equal to the current flowing through all the LEDs to be turned on, which may cause variations in the light amount of the LEDs.
By selecting a P-type transistor with a large value of DC current amplification factor hfe (hfe = collector current ÷ base current), the constant current from the constant current power source 3 is branched (base current) to make it as small as possible. Can solve the problem. For example, there are many transistors in which hfe has a value of 100 or more, and hfe = 100.
When the transistor of is used, the base current value branching to the transistor is very small compared to the constant current value from the constant current power source flowing to the collector (1 / the collector current).
100), the variation with respect to the light amount of the LED can be ignored.
【００１７】又、上記の説明では各ＬＥＤの点灯／不点
灯を制御するトランジスタとしてＰＮＰ形を上げたがＮ
ＰＮ形又は他の能動素子を用いて構わない。Further, in the above description, the PNP type is used as the transistor for controlling lighting / non-lighting of each LED.
A PN type or other active device may be used.
【００１８】この様に、各ＬＥＤに一定した電流を供給
するようにしたので、各ＬＥＤの光量のばらつきがなく
安定して駆動することができる。As described above, since a constant current is supplied to each LED, there is no variation in the light amount of each LED and stable driving is possible.
【００１９】[0019]
【発明の効果】以上のように本発明によれば、各発光素
子を点灯又は消灯させても発光素子に定電流を供給でき
るようにしたので、発光素子の順方向電流−順方向電圧
特性のばらつきに影響されず光量を均一にすることがで
きる。As described above, according to the present invention, a constant current can be supplied to a light emitting element even if each light emitting element is turned on or off. Therefore, the forward current-forward voltage characteristic of the light emitting element can be improved. The amount of light can be made uniform without being affected by variations.
【図１】本発明の一実施例を示す回路図である。FIG. 1 is a circuit diagram showing an embodiment of the present invention.
【図２】図１のＬＥＤを全て点灯した時の等価回路であ
る。FIG. 2 is an equivalent circuit when all the LEDs in FIG. 1 are turned on.
【図３】図１の１個のＬＥＤを消灯し他のＬＥＤを点灯
した時の説明図である。FIG. 3 is an explanatory diagram when one LED of FIG. 1 is turned off and the other LEDs are turned on.
【図４】従来のＬＥＤ駆動回路を示す回路図である。FIG. 4 is a circuit diagram showing a conventional LED drive circuit.
【図５】ＬＥＤの負荷特性により動作点を求める説明図
である。FIG. 5 is an explanatory diagram for obtaining an operating point based on a load characteristic of an LED.
１ａ〜１ｎ ＬＥＤ ２ プルアップ抵抗 ３ 定電流電源 ４ａ〜４ｎ ＰＮＰ形トランジスタ ５ａ〜５ｎ ベース抵抗 1a to 1n LED 2 Pull-up resistor 3 Constant current power source 4a to 4n PNP transistor 5a to 5n Base resistor
Claims (1)
続され、外部からの制御信号に基づいて対応する発光素
子を点灯又は消灯させるスイッチ素子群とを備えたこと
を特徴とするＬＥＤ駆動回路。1. A light emitting element group connected in series in a forward direction, a constant current power supply for supplying a constant current to the light emitting element group, and each of the light emitting elements of the light emitting element group are connected in parallel to each other and externally connected. And a switch element group for turning on or off a corresponding light emitting element based on a control signal from the LED drive circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29122491A JPH05129665A (en) | 1991-11-07 | 1991-11-07 | Led drive circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP29122491A JPH05129665A (en) | 1991-11-07 | 1991-11-07 | Led drive circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH05129665A true JPH05129665A (en) | 1993-05-25 |
Family
ID=17766083
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP29122491A Pending JPH05129665A (en) | 1991-11-07 | 1991-11-07 | Led drive circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH05129665A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008058367A (en) * | 2006-08-29 | 2008-03-13 | Hitachi Lighting Ltd | Light emitting diode blink controller and lighting device |
| JP2008277496A (en) * | 2007-04-27 | 2008-11-13 | Sharp Corp | Led drive circuit and light-emitting device |
| JP2010153566A (en) * | 2008-12-25 | 2010-07-08 | Fuji Electric Holdings Co Ltd | Led driving method |
| US8044898B2 (en) | 2007-04-16 | 2011-10-25 | Nagano Keiki Co., Ltd. | LED display apparatus having a column and row controller |
| JP2012033514A (en) * | 2011-11-17 | 2012-02-16 | Mitsubishi Electric Corp | Planar light source device |
-
1991
- 1991-11-07 JP JP29122491A patent/JPH05129665A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008058367A (en) * | 2006-08-29 | 2008-03-13 | Hitachi Lighting Ltd | Light emitting diode blink controller and lighting device |
| US8044898B2 (en) | 2007-04-16 | 2011-10-25 | Nagano Keiki Co., Ltd. | LED display apparatus having a column and row controller |
| JP2008277496A (en) * | 2007-04-27 | 2008-11-13 | Sharp Corp | Led drive circuit and light-emitting device |
| JP2010153566A (en) * | 2008-12-25 | 2010-07-08 | Fuji Electric Holdings Co Ltd | Led driving method |
| JP2012033514A (en) * | 2011-11-17 | 2012-02-16 | Mitsubishi Electric Corp | Planar light source device |
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