Active clamp flyback converter and circuit diagram

The flyback converter using active clamping technology is shown in Figure 1. The flyback converter is characterized by a simple main circuit. The application of active clamping circuit can make the transformer leakage magnetic energy feedback. The junction capacitance Cr of the main switch tube resonates with the transformer leakage inductance Lr, and ZVS of the main switch tube and clamping MOS tube can be achieved in both DCM and CCM working modes , minimizing the voltage stress at shutdown. The active clamping circuit can also limit the di/dt of the output rectifier diode when it is turned off, thereby reducing the switching loss and output switching noise caused by reverse recovery. The conditions for the active clamp flyback converter to achieve ZVS are (Wastiom, 1994, APEC):

Where Iv max is the peak current of the main switch tube, which is also the peak current of the load current converted to the primary of the transformer.

Two flyback converters can form an active clamp flyback converter with staggered outputs as shown in Figure 2, sharing a clamping capacitor Co. The two flyback converters can also share an active clamping circuit. Staggered parallel connection doubles the input and output circuits and greatly reduces the ripple, as shown in Figure 3, so the input and output capacitors can be reduced.