High Power Factor Bridgeless Critical Conduction Mode Buck–Flyback PFC Converter

ABSTRACT Buck power factor correction (PFC) converters are frequently employed in small and medium power applications due to the advantages of high efficiency and low output voltage. However, the converters operate only when the input voltage is higher than the output voltage, which results in the input current dead angles, deteriorating the power factor (PF) and input current harmonics ultimately. Aiming to improve the PF, a bridgeless critical conduction mode (CRM) Buck–Flyback PFC converter is proposed by paralleling the main CRM Buck converter and the auxiliary CRM Flyback converter in this paper. By utilizing the auxiliary Flyback circuit, the dead angles in the input current of the proposed circuit are eliminated so that the input current harmonics and PF can be improved significantly, particularly when the input voltage is low. The operational principle, control strategy, design considerations, and key characteristics of the proposed circuit are analyzed in detail. A 100 W experimental prototype is built and tested to verify the feasibility of the proposed converter. Experimental results demonstrate that the proposed bridgeless CRM Buck–Flyback PFC converter can realize greater than 0.96 PF, up to 93.2% efficiency, and low input current harmonic content.