Design considerations and performance evaluations of synchronous rectification in flyback converters

Design trade-offs and performance comparisons of various implementations of the flyback power converter with a synchronous rectifier are presented. Specifically, the merits and limitations of the constant-frequency (CF) continuous-conduction-mode, CF discontinuous-conduction-mode (DCM), variable-frequency DCM, and zero-voltage-switched DCM flyback power converters with synchronous rectifiers 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, offline, 15 V/36 W flyback prototype.