Asymmetrical half bridge (AHB) is a Flyback-based resonant PWM converter which offers higher power density and higher efficiency compared with other Flyback-based converter because of the zero-voltage switching (ZVS) capability, it’s well applied to voltage step-down and wide output voltage operating range applications. However, the most efficient ZVS control during such wide operating range and dynamic conditions has been a critical challenge. This digest gives a fast PWM on-time calculation approach for boundary ZVS operation, a zero-voltage detection approach and overall control architecture of this effect. The controller is implemented digitally. The proposed approach has been validated on a 252W digital AHB prototype with 97.3% peak efficiency point in full load 28V/9A output condition.
