A zero-current detection circuit with optimal ZVS/VS for boundary mode boost PFC converter

This paper presents a ZCD circuit that performs optimal zero-voltage switching or valley switching for boundary mode boost PFC converter. The proposed ZCD circuit monitors the demagnetization of the boost inductor via the auxiliary winding, and calculates the optimal switching timing utilizing the symmetrical characteristic of the resonant waveform. By this way, the delay caused by the gate driver circuit can be considered and eliminated. Soft-switching operation is feasible under any input voltage conditions since the switching mode will change between ZVS and VS automatically. The proposed circuit can also be applied to other resonant converters. A boundary mode PFC converter with the proposed ZCD circuit has been simulated using 0.5-um N-well process to verify the analyses.