Improved digital control scheme of synchronous rectification for resonant converter at light load conditions

This paper proposes a synchronous rectification (SR) control scheme for LLC resonant converter by digital controller. In the proposed SR control scheme, conduction detector circuit senses the drain-source voltage of secondary SR switches to detect the state of paralleled body diode. Digital controller tunes the turn-on and turn-off time of SR switches depending on conduction detector circuit output. Proposed SR control scheme can properly achieve SR at full load condition a simple implementation. Furthermore, it is capable of suppressing circulating current from output to input than conventional SR control scheme in light load condition. Thus, proposed SR control scheme can improve efficiency rather than conventional SR control scheme.