Single-Stage Bridgeless AC–DC PFC Converter Using a Lossless Passive Snubber and Valley Switching

Abstract

A single-stage bridgeless ac–dc PFC converter using a lossless passive snubber and valley switching is proposed. The proposed converter is based on a two-stage bridgeless boost-flyback converter. In the proposed converter, the conduction losses are reduced by removing an input full-bridge diode rectifier. The boost inductor is designed to be operated in the discontinuous–conduction mode for achieving high power factor. In the flyback module, the couple inductor that provides input–output electrical isolation for safety is designed to be operated in the critical-conduction mode for low RMS current and low turn-on switching loss by using valley-switching operation. Because of the lossless snubber circuit, the voltage spike of switch is clamped, and the leakage inductor energy is recycled. The snubber capacitor is used as a dc-bus capacitor, which is divided into two capacitors. In addition, some input power is directly conducted to the output, and the remaining power is stored in dc-bus capacitor. So, low-voltage rating capacitors can be used as the dc-bus capacitor and power transfer efficiency is improved. The presented theoretical analysis is verified on an output 48-V and 60-Wexperimental prototype.