The new method of dc LED driver circuit

Introduction 0

although the high power LED is still cannot replace traditional light source on a large scale, but they has more and more widely used in outdoor lighting, LED by environmental protection, energy saving, high efficiency advantages, such as need for the LED driver to ensure that, this paper introduces a new method used for the design of dc system of constant current drive.

1 switch PWM constant current drive way LED driver only contributed a small portion of dc lighting system, but it is related to the reliability of the whole system. There are many kinds of, now in the market of the LED driver has a current limiting resistor type linear constant current, constant voltage type, type, PWM switch constant-current type, etc. , through contrast test, this circuit has chosen the PWM constant current drive mode switch. This way is to use the series in the power circuit of the switch tube and energy storage inductor, capacitor high efficiency constant current driver circuit, the output current is constant, the output of the dc voltage as the load resistance of different changes in a certain range, load resistance is small, low output voltage, the greater the load resistance, the higher the output voltage. This LED constant current drive mode to adapt to the current type characteristic, the temperature changes, or for other reasons in the LED PN junction voltage drop changes, can ensure the LED constant current light, will not damage the LED, and can delay the light failure. Principle

2 circuit design of this design is a kind of temperature protection LED constant current drive, including the high power LED light source, the dc power supply, the meter circuit, PWM control circuit, temperature detection circuit and current circuit. Dc power supply through the meter circuit connection PWM control circuit and temperature detection circuit, temperature detection circuit connected to the fly-wheel circuit respectively PWM control circuit, high power LED light source is connected to a PWM control circuit and temperature detection circuit. Among them, the dc power supply ( 12 v) The meter circuit to power a PWM control circuit and temperature detection circuit, PWM control circuit and fly-wheel circuit for high power LED light source is to provide a stable set of current, temperature detection circuit timely detect the working temperature of high power LED light source, feedback control of PWM control circuit, which makes high power LED light source working in a safe temperature range.

see figure 1, a kind of temperature protection LED constant current drive, including the high power LED light source 6, 1, 2 meter circuit dc power supply, PWM control circuit, temperature detection circuit 5 and 4 3 fly-wheel circuit. Dc power supply (1 12 v) The meter circuit 2 to PWM control circuit 4 5 power supply and temperature detection circuit, PWM control circuit 4 and 3 fly-wheel circuit for high power LED light source 6 provide stable set of current, temperature detection circuit 5 timely detect the working temperature of high power LED light source 6, 4 feedback control PWM control circuit, which makes high power LED light source 6 work in a safe temperature range. Figure 1

the composition of constant current drive

see figure 2, the circuit structure is as follows:

( 1) Dc power supply (1 Battery or solar photovoltaic (pv) power supply) :12 v。

　　( 2) 2 meter circuit composed of D1 and C1, its working principle is: the power supply by one-way conductive diode D1, filter capacitor C1 of PWM control circuit 4, 3 fly-wheel circuit and temperature detection circuit may provide power supply.

　　( 3) Constant current circuit composed of PWM control circuit 4, 5, stream temperature detection circuit circuit of 3, specific consists of U1, R1, L1, C2 and D2, LED1 ~ LED. The function test feedback loop current load resistor R1, L1, C2 and D2 3 fly-wheel circuit, U1 of PWM control circuit 4.

　　( 4) 5 by integrated circuit temperature detection circuit U2, RT resistance R2 and R3, temperature sensor, capacitance of C3, C4 and C5. U2, R3, RT, C4, C5 composition multivibrator circuit, the temperature sensor of RT resistance changes with the temperature change of the LED light source, which changes more harmonic oscillation circuit oscillation pulse duty ratio.

figure 2 drive circuit principle diagram of

U2 3 feet oscillation pulse output after the change, the R2, C3 filtering into PWM control circuit 4 ( Integrated block U1) 3 feet, to control the flow through the LED light source of current value, by the LED light source of current Io has the following formula can be calculated: Io = 0. 1 rt / R3 / R1。 Current through the LED light source controlled by temperature sensor RT, implements the limiting the temperature of the LED light source in a safe setting range.

described DC12V for dc power supply 1, described in the high power LED light source adopts two 6 1 wled series, also can use 1 wled 1 or 3 1 w leds in series form. Conclusion

3 through temperature protection and function of constant current, slows down the high temperature and strong current in this circuit design for the impact of the high power LED light source, so as to prolong the service life of the LED; It is particularly suited to dc lighting system with high power LED as light source.

edit: gather