Critical Conduction Mode Pfc Chip Analysis And Design

As the development of power electronics, the desire towards higher performance of electrical equipments is becoming more and more these years. Between those performance parameters, power factor is an important one which judges whether the equipment is using electricity well or not. Higher power factor means less harmonics pollution and better efficiency. And one important way to increase power factor is to do power factor correction. In the mass, power factor correction can be divided into passive power factor correction and active power factor correction. The former has the drawbacks of high weight and big size, and does not accord with the development of power electronics. So it is only used in those fields where do not care weight and size and are sensitive to price. On the other side, active power factor correction combines power factor technology and switching power supply skills and overcome those above-mentioned drawbacks. It is a hot spot which is now being widely studied and has been used in a lot of situations.This paper mainly studies the critical conduction mode control in the active power factor correction. It firstly introduces some basic theory of power factor correction and several switching power supply converters which are widely used in the active power factor correction. Then some math derivation is done to prove that both ways can make the conduction time constant, no matter it contains multiplier or not. They are equal in mathematics. Two design schemes are given in details. One is based on the framework of L6561, and the other one is based on the framework of UC3852. Using ordinary CMOS technology, circuit modules are analyzed and designed. The system simulation results are given and compared with each other. In the last, some layouts are given and several fabricated circuits are tested.