Design considerations and performance evaluations of synchronous rectification in flyback converters

Design tradeoffs and performance comparisons of various implementations of the flyback converter with a synchronous rectifier (SR) are presented. Specifically, the merits and limitations of the constant-frequency (CF) continuous-conduction mode (CCM), CF discontinuous-conduction mode (DCM), variable-frequency (VF) DCM, and zero-voltage-switched (ZVS) DCM flyback converters with SRs are discussed. The theoretical efficiency improvements of the discussed synchronous rectification approaches relative to Schottky diode implementations are derived. Finally, theoretical results are verified on an experimental universal-input off-line 15 V/36 W flyback prototype.