A double closed-loop control method for quasi-resonant converter

To achieve the soft-switching condition and stabilize the output voltage of quasi-resonant converters, the paper proposes a double closed-loop control method (DCCM). In the inner loop, soft-switching is guaranteed with the off-time of the switch determined by the zero-crossing signal of the switching voltage. In the outer loop, the output voltage is regulated to be constant against load variations by controlling the on-time of the switch according to the error between the output voltage and the reference voltage. The operation principle and implementation of the proposed method have been investigated in detail on an example BUCK zero-voltage-switching quasi-resonant converter. Both simulation and experiment results have verified the validation of the proposed method.