Passive Lossless Snubber for Boost PFC With Minimum Voltage and Current Stress

A passive lossless snubber for boost power-factor corrector (PFC) is presented. It has a number of advantages over the prior art. First, it does not introduce extra voltage and current stress on the main switch. Second, it provides soft-switching conditions for the main switch over wide input and load range. Third, it limits the turn- on current of the main switch resulting from the reverse recovery current of the output diode. The operating principle of the proposed snubber and procedure of designing the component values are given. A comparative study into the performance characteristics between the prior-art passive lossless snubbers and the proposed snubber will be performed. The performance of the proposed snubber has been evaluated experimentally on a 750-W PFC with universal input. The boost converter is operated in continuous conduction mode and its input current is shaped by using average current-mode control. Experimental results show that soft switching of the main switch is maintained over 88% with an input of 110 V, 60 Hz, and 91.8% an the input of 220 V, 50 Hz, over one line cycle, and from full load to 20% load. The efficiencies of the PFC with unsnubbered hard switching, conventional resistor-capacitor-diode snubber, and proposed snubber will be compared. Results show that the proposed snubber can significantly improve the efficiency over the designed operating range.