Adding active clamping and soft switching to boost-flyback single-stage isolated power-factor-corrected power supplies

Single-stage isolated power-factor-corrected power supplies (SSIPP) have the attractive features of fast regulation and a single control loop. However, SSIPP circuits also have higher voltage stress and heavier loss (when compared with a normal DC-DC power converter), which severely limit their practical applications. In this paper, the authors propose to add active clamping to SSIPP to recycle the energy trapped in the leakage inductance of their transformer (to keep the switch voltage stress low) and to achieve soft switching of their electronic devices (to further reduce the loss). This arrangement significantly improves the viability of SSIPP for practical applications. The auxiliary active-clamping transistor in the proposed circuit uses the same control/driver circuit as the main switching transistor. Simulations and experimental works verifying the operation of the converter are reported.