An efficient quasi-active power factor correction scheme

This paper presents a novel input current shaper based on a quasi-active power factor correction (PFC) scheme. The power factor is improved by adding two auxiliary windings coupled to the transformer of a cascade dc/dc flyback converter. The auxiliary windings are placed between the input rectifier and the low-frequency filter capacitor to serve as a magnetic switch to drive an input inductor. Since the dc/dc converter is operated at high switching frequency, the auxiliary windings produce a high frequency pulsating source such that the input current conduction angle is significantly lengthened and the input current harmonics is reduced. It eliminates the use of active switch and control circuit for PFC. The input inductor can be designed to operate in discontinuous current mode (DCM) with lower harmonic content or continuous conduction mode (CCM) with higher efficiency. However, a trade-off between efficiency and harmonic content must be made. Operating principles, analysis, simulation and practical results of the proposed method are presented.