Optimum design on the single-stage Forward-flyback PFC converter with two different QR controls

The single-stage Forward-flyback PFC converter is studied in this paper. This converter combines a flyback circuit with forward circuit through a common transformer. Only the flyback circuit works when the input voltage is lower than the reflected output voltage and both the flyback circuit and the forward circuit operate to share the output power in the rest region. The dead zones which exist in the AC input current of conventional forward converter are eliminated and high power factor can be achieved. Two quasi-resonant (QR) control schemes are proposed and compared. Optimum design considerations for the Forward-flyback PFC converter based on these two QR controls were presented. Detailed analysis and two experimental prototypes with 60W output power were built up to verify the theoretical analysis.