Primary side control circuit of a flyback converter

Abstract

Voltage feedback in flyback converters is typically done with the assistance of opto-couplers, to preserve electrical isolation. However the output voltage also exists (in part) across the primary side switch when in its off state. This paper investigates the extraction of the output voltage within one switching cycle. Good results are obtained from a flyback converter with a novel control circuit using cycle by cycle control. The converter works in both continuous and discontinuous mode of operation.