A New CCM/DCM Hybrid-Mode Synchronous Rectification Flyback Converter

A new continuous conduction mode (CCM)/discontinuous conduction mode (DCM) hybrid-mode synchronous rectification (SR) flyback converter is proposed in this paper. This converter is realized by adding a combined switch in parallel with the auxiliary winding of the flyback transformer. The added switch is controlled to conduct a short period before the primary switch turns on, which shorts the windings of the transformer. The drain-source voltage of SR arises rapidly to reach the turn-off threshold voltage inside SR controller and the SR is turned off before the primary switch conducts. In this way, the overlapped period existed in a conventional CCM SR flyback converter is eliminated. Meanwhile, the normal operation of SR flyback in DCM is not affected. Detailed theoretical analysis has been presented and verified by a 12 V/2.5 A CCM/DCM hybrid-mode flyback experimental prototype. The results prove that the efficiency of the proposed SR method in CCM can be improved compared with the conventional one.