A Control Method of Two-Switch Forward Converter for High efficiency Under Light Load Conditions

Two-switch forward converter is widely used topology in various applications. It operates in hard switching condition, causing low efficiency under light load conditions. To solve this problem, a new control method for reducing switching loss is proposed in this paper. Under light load conditions with discontinuous conduction mode, the drain-source voltages of switches resonate under light load conditions after two switches are turned off. There is minimum drain-source voltage due to the resonance. The proposed control method reduces turn-on switching loss by turning on the switches at the minimum drain-source voltage. The control method also decreases turn-off switching loss by turning off one switch with the reduced turn-off current. The effectiveness of the proposed control method is validated with 330-400V input and 48V/300W output prototype converter.