Flyback converter having an active snubber

A flyback converter having an active snubber comprising a primary winding to receive an input power, a primary switch to control a current period of the primary winding and a pulse-width modulation (PWM) unit to output a periodic signal which includes an ON period and an OFF period to drive the primary switch, the active snubber being coupled in parallel with two ends of the primary winding, the active snubber including:

• a first circumferential circuit which is coupled in parallel with the primary winding and has a damping capacitor and a first diode which has an anode bridging the primary winding and the primary switch;
• a second circumferential circuit which is coupled in parallel with two ends of the first diode and has a damping control switch and an inductor which has one end bridging the primary winding and the primary switch;
• and
• a zero voltage switch unit which is synchronous with the PWM unit and receives a detection voltage between the first diode and the damping capacitor and sets a base value to be compared with the detection voltage;
• wherein a damping control signal is generated through a sync clock of the PWM unit and by judging that the detection voltage is lower than a base value to drive and turn ON the damping control switch and set ON the second circumferential circuit.