Design of PFC Converter with Flyback Converter 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 [W] experimental prototype.

Keywords: Bridgeless converter, boost-flyback converter, power factor correction (PFC), lossless snubber