Resonant half-bridge flyback power converter and primary controller circuit and control method thereof

Abstract

A resonant half-bridge flyback power converter includes: a power transformer and a resonant capacitor which are coupled in series between a half-bridge power stage and an output power; and a primary controller circuit controlling a high side power switch and a low side power switch of the half-bridge power stage. When the high side switch is OFF, the control signal of the low side power switch includes a resonant switching pulse for achieving resonant switching of the low side switch and a soft switching pulse for achieving ZVS of the high side switch. When the output power is lower than a delay threshold, the primary controller circuit determines a delay period which is between the resonant switching pulse and the soft switching pulse to control both the high side power switch and the low side power switch to be OFF. The delay period is negatively correlated with the output power.