JP3191537U - Light-emitting diode constant current drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a constant current drive of a light emitting diode which does not shorten the service life of the light emitting diode (LED) due to an overcurrent. SOLUTION: The structure is a constant current drive of a light emitting diode mainly composed of a rectifier circuit 1, a switching circuit 2 and a feedback circuit 3. The rectifier circuit 1 is connected to one AC power and outputs DC power. The switching circuit 2 is connected to the DC power of the rectifier circuit 1, is switched to the DC power by a pulse width modulation (PWM) method, and has one output terminal and is connected to the load 4. The feedback circuit 3 is connected between the output terminal of the switching circuit 2 and the switching circuit 2, and the duty cycle of the switching circuit 2 is controlled based on the amount of the current output by the output terminal to output the current to the load 4. Can be controlled constantly. [Selection diagram] Fig. 2

Description

  The present invention relates to a drive structure, and more particularly to a structure of an electronic drive that drives a light emission by providing a constant current source to a multi-circuit LED load provided in parallel.

  Light emitting diodes (LEDs) have features such as a long service life and excellent energy saving, and have already become the mainstream of many consumer electronic products or light sources in this era.

  To cause the LED to emit light, a forward current is generated through the drive and passes through the component. Generally, an LED cluster is used as a module to serve as a drive load. In actual application, the drive normally needs to drive a multi-circuit load (LED module) provided in parallel. Therefore, when designing a drive circuit, the same luminous intensity is applied to each LED load end. This role can be achieved via a constant voltage source or a constant current source.

  In general, a drive circuit that provides a constant voltage source is the lowest cost solution. A single current limiting resistor is connected in series to the tip of the LED load, and a constant voltage source is added to both ends of the circuit. However, this method has drawbacks. The current limiting resistor limits the current passing through, and the LED nonlinear VI curve at the load end is also very weak in stabilizing the current in this way. In addition, any change in the applied voltage or the forward voltage of the LED will change the current through the LED. If the rated forward voltage is 3.6 V, a current of 20 mA flows through the LED. If the voltage becomes 3V due to temperature or manufacturing process changes (still within the normal 3V to 4V tolerance), the forward current will drop to 14mA. That is, if the forward voltage changes only by 11%, the forward current fluctuates by 30%. Thus, when the current changes drastically, it directly affects the luminous intensity of the LED, which is unacceptable by many application facilities.

  In the conventional constant current source drive, the design of the circuit structure is complicated, there are many components, and if all the drives require similar duty characteristics, it is necessary to strictly watch the quality of these electronic components. is there. Not only is it difficult to increase the drive quality, but there are still many points to be improved, such as high manufacturing costs and disadvantages in volume reduction. In particular, when driving a multi-circuit LED load provided in parallel, if any one parallel load is removed or disconnected, the current supplied by the drive is directly distributed to the other loads. In view of the possibility that overcurrent could shorten the service life of the LED, further improvements were necessary.

JP 2007-82347 A

  In order to solve the drawbacks of the known structure, the present invention uses a simple electronic circuit design and completes driving of a constant current source of a multi-circuit load provided in parallel. Not only is the stability high, the manufacturing cost is low, which is advantageous for smaller applications. The most important thing is that even if one multi-circuit LED load provided in parallel is removed or disconnected, the circuit performs constant current control for other loads by comparing and detecting the feedback signal. Therefore, it is a main object to provide a constant current drive structure of a light emitting diode that does not shorten the service life of the LED.

  In order to solve the above problems, the present invention provides a structure of a constant current drive of a light emitting diode. Included in the present invention are a rectifier circuit, a switching circuit, and a feedback circuit. The rectifier circuit is connected to one AC power and outputs DC power. The switching circuit is connected to the DC power of the rectifier circuit and switched to the DC power using a pulse width modulation (PWM) method, and has one output terminal and one feedback control terminal connected to a load. . The feedback circuit is connected between the output terminal of the switching circuit and the feedback control terminal, and based on the amount of current output from the output terminal, the duty cycle of the switching circuit is controlled so that the output current is constant. Can be controlled.

  The present invention designs a simple electronic circuit and completes driving of a constant current source of a multi-circuit load provided in parallel. The most important thing is that even if one multi-circuit LED load provided in parallel is removed or disconnected, the circuit performs constant current control for other loads by comparing and detecting the feedback signal. Therefore, the service life of the LED is not shortened.

It is a circuit block diagram in the present invention. It is a detailed circuit diagram in the present invention.

Hereinafter, the structure, features, and effects of the present invention will be described in detail with reference to the best embodiments and drawings.

  FIG. 1 is a circuit block diagram of the present invention. The light emitting diode is driven by the constant current drive of the light emitting diode (LED) of the present invention to stably emit light. Included are a rectifier circuit 1, a switching circuit 2 and a feedback circuit 3. The rectifier circuit 1 is connected to one AC power and outputs DC power. The switching circuit 2 is connected to the DC power output from the rectifier circuit 1 and switches the DC power by a pulse width modulation (PWM) method. It has one output terminal 21 and one feedback control terminal 22, which is connected to one LED load 4. The feedback circuit 3 is connected between the output terminal 21 of the switching circuit 2 and the feedback control terminal 22 of the switching circuit, and controls the duty cycle of the switching circuit 2 based on the amount of current output from the output terminal 21. Thus, the output current is controlled to be constant.

  FIG. 2 is a detailed circuit diagram of the present invention. The drive of the present invention converts alternating current power into direct current power and drives light emission of the light emitting diode. A feedback circuit is provided to control the output current to be constant. The rectifier circuit 1 is mainly a single bridge type rectifier circuit, and the rectifier circuit 1 shown in the figure is composed of components such as a bridge rectifier BD1, capacitors CX1 and C1, and an electric resistance R1. Of course, other forms of rectifiers can be used.

  The rectifier circuit 1 converts AC power into DC power, and the output DC power is sent to the switching circuit 2. The switching circuit 2 is one high-frequency switching DC-DC converter (DC-to-DC converter), and is mainly composed of one high-frequency transformer TR1, one electronic switch Q1, and one pulse width modulation PWM controller U1. . The one-stage side of the high-frequency transformer TR1 is connected to the DC power output terminal of the rectifier circuit 1, and the switch terminal of the electronic switch Q1 is connected in series between the one-stage side of the high-frequency transformer TR1 and the ground, or between them. Electrical resistance R2 is connected in series. By connecting the control terminal of the electronic switch Q1 to the PWM controller U1, the electronic switch Q1 can change the switching frequency and the duty cycle under the control of the PWM controller. The electronic switch Q1 can be a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), or the like, but is not limited thereto. The feedback control terminal 22 of the PWM controller U1 can receive an input of a feedback signal, thereby changing the duty cycle of the electronic switch Q1.

  The DC power output from the output terminal 21 of the switching circuit 2 is connected to the load 4 and connected in parallel to the feedback circuit 3. The load 4 is an LED module, and one or multiple circuits are arranged in parallel. The figure shows a multi-circuit parallel configuration. In the best embodiment, one choke coil L1, L2,... LX is connected in series between the load 4 of each circuit and the output terminal 21 of the switching circuit 2, thereby driving the current more stably. can do.

  In the circuit formed by the switching circuit 2 and the load 4 of each circuit, one conversion resistor RT1, RT2,... RTX is connected in series, and the electric resistance values of the conversion resistors are all the same. Both ends of the conversion resistors RT1, RT2,... RTX are connected to input terminals of one comparator U2 constituted by operational amplifiers. Since the conversion resistors RT1, RT2,... RTX and the load 4 are connected in series, the flowing current can be converted into a voltage signal. Since the current flowing through the conversion resistors RT1, RT2,... RTX is the output current flowing through the load 4, the comparator U2 can compare the amount of current of the load. The output terminal of the comparator U2 is connected to the input terminal (that is, the light emitting diode side) of one photocoupler PC1, and the output terminal of the photocoupler PC1 is connected to the feedback control terminal 22 of the PWM controller U1, thereby providing feedback. The signal is output to the PWM controller U1. Since the electrical resistance values of the conversion resistors RT1, RT2,... RTX in each circuit are all the same, if any one LED load is removed or disconnected, the conversion to which the load of another circuit is connected When the voltage applied to the resistors RT1, RT2,. Since the output current is adjusted by changing the conduction time of the electronic switch Q1, the load of each circuit reaches the purpose of providing a constant current. In addition, since the circuit current of the disconnected load is zero and the voltage at the conversion resistor connected in series with the disconnected load is always zero, the normal operation of the comparator U2 is not disturbed or adversely affected.

  The detailed description of the present invention according to the above embodiments does not limit the scope of the present invention. Even if a person familiar with the present technology makes changes or adjustments within the scope of the present invention, the important significance of the present invention is not lost and is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Rectifier circuit 2 Switching circuit 21 Output terminal 22 of switching circuit Feedback control terminal 3 of switching circuit Feedback circuit 4 Load Q1 Electronic switch U1 PWM controller TR1 High frequency transformer L1, L2 ... LX ... Choke coil RT1, RT2 ... RTX ... Conversion resistance U2 Comparator PC1 Photocoupler

Claims (6)

Including a rectifier circuit, a switching circuit and a feedback circuit,
The rectifier circuit is connected to one AC power and outputs DC power,
The switching circuit connects to the DC power of the rectifier circuit and switches to the DC power using a pulse width modulation (PWM) method, which has one output terminal connected to the load and one feedback control terminal. And the feedback circuit is connected between the output terminal of the switching circuit and the switching circuit, and controls the duty cycle of the switching circuit based on the amount of current output from the output terminal, thereby making the output current constant. The constant current drive structure of the light emitting diode, characterized in that it can be controlled to   The switching circuit includes one electronic switch, one high-frequency transformer, and one PWM controller. One stage of the high-frequency transformer is connected to the DC power output terminal of the rectifier circuit, and the switch terminal of the electronic switch Is connected in series between one stage of the high-frequency transformer and the ground, and the control terminal of the electronic switch is connected to the PWM controller, and the electronic switch receives the control of the PWM controller to change the switching frequency and the duty cycle. The structure of the constant current drive of the emitting diode according to claim 1, characterized in that it is varied.   3. The light emitting diode constant current drive structure according to claim 2, wherein the electronic switch is a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT), an insulated gate bipolar transistor (IGBT), or the like. . The feedback circuit includes one conversion resistor, one comparator, and one photocoupler,
In the circuit formed by the switching circuit and the load, the conversion resistors are connected in series, and both ends of the conversion resistors are connected to the input terminals of the comparators, respectively.
Connect the output terminal of the comparator to the input terminal of the photocoupler,
The output terminal of the photocoupler is connected to the feedback control terminal of the switching circuit, so that the feedback signal is output to the switching circuit. When the voltage of the conversion resistor is abnormal, the comparator controls the photocoupler and performs the shutdown operation. The structure of the constant current drive of the light emitting diode according to claim 2, wherein:   5. The light-emitting diode constant current drive structure according to claim 4, wherein the comparator comprises an operational amplifier.   When the output terminal of the switching circuit is connected in parallel with a multi-circuit load, each circuit load has one conversion resistor connected in series, and the electric resistance value of each one conversion resistor is all the same. When the load of one circuit is removed or disconnected, when the voltage applied to the conversion resistor to which the load of the other circuit is connected is greater than a predetermined value (that is, when an abnormality occurs), the comparator, that is, the photocoupler, performs a shutdown operation. The load of each circuit can provide a constant current because the output current is adjusted by changing the conduction time of the electronic switch by changing the duty cycle of the PWM controller by changing the feedback signal immediately. 4. The structure of the constant current drive of the light emitting diode according to 4.

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