Single-stage, single-switch input-current-shaping technique with reduced switching loss

In this paper, a new single-stage, single-switch input-current-shaping (S/sup 4/ICS) technique which features substantially reduced turn-on switching loss of the switch in a S/sup 4/ICS flyback topology is described. In the proposed technique, the turn-on switching loss due to the discharging of the output capacitance of the switch is reduced by turning on the switch when its voltage is minimum. To achieve the turn-on loss reduction for a wide range of line and load conditions, the flyback transformer is continuously operated at the boundary of the continuous conduction mode (CCM) and discontinuous conduction mode (DCM) by employing a variable-frequency control. The performance of the new S/sup 4/ICS flyback technique was evaluated on a 70-W (20-V/3.5-A) experimental prototype.