Led Constant Current Driver Switching Power Supply Developed

As a new concept of solid-state light source, LED has high light-emitting efficiency, almost pollution-free from the manufacture to use up and tens of times or more than usual light source. In recent years, LED has become the world's most promising high-tech, and the innovation of semiconductor lighting technology is changing the history of centuries-old tradition of lighting.LED needs constant-current drive, and there are three major ways in constant-current drive. First, output a constant-voltage and then limit the current with a resistor. Second, use a special constant-current LED Driver IC. Third, use the traditional constant-voltage power control chip to maintain constant-current. But there are some disadvantages like bad effect of constant-current, low efficiency, big volume and high cost in the first two ways. In this paper, a constant current feedback circuit is designed to help the traditional constant-voltage power control chip to achieve the function of constant-current, which then markedly enhances the cost-effective ratio of constant-current driven switching mode power supply.Based on the basic theory of switching mode power supply and research of main parameters of power convertor, the main work in this dissertation are listed as follows:1. The main circuit of Flyback switching mode power supply, clamp circuit, passive power factor correction circuit, EMI filter and feedback circuit have been analysed, designed and simulated. And then some of the circuits are qualitative and quantitative simulated by a program Pspice, which help to optimize the parameters of the circuit.2. By deriving from the formulas, calculating the magnetic flux density Bo as design reference, the disadvantage of using experience value of magnetic flux density is avoided.3. Development of two driven constant-current LED driver. By analysing and solving the problem of the special LED driver IC, the efficiency of constant-current circuit is enhanced up to 87.5%.4. Development of constant current LED driver whose constant-current is better and output current can be adjusted. The focuse is to develop a LED constant- current driver which contain EMI and PFC,with input voltage regulation less than 0.3% and wide operating voltage(86VAC~250VAC).