A critical conduction mode bridgeless flyback converter

This paper proposes a new isolated bridgeless AC-DC power factor correction (PFC) converter. The proposed circuit consists of dual flyback converters which provide high power factor (PF). By eliminating input bridge diodes, the number of conducting components is reduced. Therefore, conduction losses are decreased and efficiency can be further improved. Critical conduction mode (CRM) operation decreases the switching losses of switch components. Thus, operational modes of CRM are analyzed and sensing configurations are also presented to address some of the challenge points such as zero crossing detection (ZCD) circuit and sensing circuits of the bridgeless converter. Using a transformer allows for more flexible voltage gain design and, thus, a single-stage isolated PFC. The proposed circuit is verified with a 75 W (12 V/6.4 A) experimental prototype in discontinuous conduction mode (DCM) and CRM.