Controller and control method for an asymmetric half-bridge power supply

A controller for an asymmetric half-bridge power supply, the asymmetric half-bridge power supply comprising a first arm switch and a second arm switch forming a half-bridge for controlling a resonant circuit, the resonant circuit comprising a transformer and an oscillating capacitor, the controller being used to control the first arm switch and the second arm switch, the controller comprising:

• a first arm controller configured to provide a first control signal to turn on the first arm switch for a first turn-on time;
• and
• a second arm controller configured to provide a second control signal to turn on the second arm switch for a second turn-on time, and comprising:
• a ZVS (zero voltage switching) detection circuit configured to provide a duration parameter stored from an earlier switching cycle, the duration parameter indicating a length of a previous second turn-on time of the second arm switch in the earlier switching cycle, detect whether the first arm switch has performed ZVS when a signal edge of the first control signal turns on the first arm switch, and adjust the duration parameter accordingly;
• and
• a turn-on time controller configured to determine an updated second turn-on time for a next switching cycle based on the adjusted duration parameter and to turn on the second arm switch for the updated second turn-on time in the next switching cycle, the next switching cycle being immediately following the earlier switching cycle.