The Design Of LED Drive Circuit With Stepless Dimming Based On PWM

Light Emitting Diode,which is known as the 21 st century "green light",has the advantages of low power consumption, high brightness, energy saving, small size, long life,can emit polychromatic,etc.Because LED has so many advantages there is growing LED-related technology development and research attention. Today, LED has been used in many applications.Related technologies, especially about the LED driver technology and dimming technology will continuously develop innovative and have a big impact in the field of lighting, it has far-reaching significance for reducing energy consumption.No matter what kind of power can not supply the LED directly, there must be the front-end drive circuit.Incandescent lamp I-V characteristic curve is linear,so it can be driven by voltage source.LED is different from purely resistive ordinary incandescent,its I-V characteristic curve is exponential,it means that its I-V characteristic curve is nonlinear,and when the voltage has a small change,the current will produce great changes.If used a voltage source to supply the LED,when the voltage rises a little,the current would increase dramatically,which makes the LED temperature increase and damages to the LED. So it can not use a voltage source to supply the LED,Using a constant current source will reduce the influence of the temperature problem,it needs to design a dedicated driver circuit for LED to make the current be constant.Maintain current constancy is the best way to protect the LED,So the LED driver usually use constant current source.Based on the principles and characteristics of the LED,I design a constant current drive circuit based on PWM,it aims to output constant current for LED,it can not only make the LED load work safely and stably,but it can also control the current accurately based on the PWM technology.Firstly,thesis analyzes the LED driving basic principle, the principle and the advantages and disadvantages of different LED constant current drive converter program and briefly describes the different occasions selection of these programs; then analyzes the principle and the advantages and disadvantages of three methods of dimming.Considering from the LED constant current drive application,points out that the PWM dimming control scheme is the best choice;then this paper describes the design of constant-current drive circuit, the circuit structure of PFC,the working principle of the dimming systems circuits andthe communication circuits.I carry on the manufacture of welded and the entire lamp assembly of PCB,then I do the test of the LED illumination under the different PWM duty cycle,the designed LED stepless dimming drive circuit and LED lamp proved reliable and fruitful.