Analysis and design of a push-pull single-stage flyback power factor corrector

A novel mixed-mode controlled push-pull single-stage flyback power factor corrector (PFC) composed of two flyback PFCs with a coupled inductor is proposed in this paper. The studied single-stage PFC consists of two power modules which have common secondary winding, output diode, output capacitor, and input filtering capacitor. Besides possessing the capability of sharing the input current and output current equally, integrating two input inductors into one magnetic core makes the operating frequency of the core double the switching frequency. In addition, a cut-in-half duty cycle can reduce the conduction losses of the switches and both the turns and diameters of the inductor windings. Both the continuous conduction mode (CCM) and the transition mode (TM) controls are fulfilled in the proposed single-stage PFC during one line frequency cycle. Under CCM operations, the smaller inductor current ripple reduces both the core loss of the coupled inductor and the conduction losses of the switches, which not only promotes the heavy-load efficiencies, but also alleviates the current stresses of the switches and the output diode. Under TM operations, quasi-resonant (QR) valley witching on the switches and zero-current switching (ZCS) of the output diode can reduce the switching losses. The light-load conversion efficiencies are thus improved. Detailed analysis of the proposed topology is given. The experiments are conducted on a prototype with a universal line voltage, a 19-V output DC voltage, and a 190-W output power to verify its feasibility.