Analysis and design of a mixed-mode controlled push-pull boost power factor corrector

A novel mixed-mode controlled push-pull power factor corrector (PFC) composed of two boost-type PFCs with a coupled inductor is proposed in this paper. Besides possessing the capability of sharing the input current and output current equally, integrating two boost inductors into one magnetic core makes the operating frequency of the core double the switching frequency. The circuit volume and the current ripple can be thus reduced under the same inductance. Therefore, both the power factor (PF) value and the power density are increased. 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 PFC during one line frequency cycle. The durations of these two modes depend on both the line voltage and the output load due to the pre-set fixed off-time (FOT). 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 diodes. Under TM operations, quasi-resonant (QR) valley-switching on the switches and zero-current-switching (ZCS) of the output diodes can reduce the switching losses. The light-load conversion efficiencies are thus improved. Detailed analysis and design procedures of the proposed topology are given. Simulations and experiments are conducted on a prototype with a universal line voltage, a 380 V output DC voltage, and a 300-W output power to verify its feasibility.