Single-Stage Soft-Switching AC–DC Converter With Input-Current Shaping for Universal Line Applications

In this paper, a novel single-stage soft-switching ac-dc converter for universal line applications is presented. Unlike the conventional single-stage designs, the proposed input-current shaping scheme is intentionally arranged to be charged in the duty-off time. With this design, the switch current stress in the duty-on time is significantly reduced. Meanwhile, this design produces AC modulation effect on the charging time of the boost inductor so that the input i-nu curve drawn by the proposed converter has nearly linear relationship. Moreover, an active-clamp flyback-forward topology is used as the downstream DC-DC cell to alleviate voltage stress across the bulk capacitor. By deactivating the flyback subconverter and keeping the forward subconverter supplying the output power at light-load condition, the bulk-capacitor voltage can be alleviated effectively and guaranteed below 450 V in wide ranges of output load and line input (90-265 V_rms). Experimental results, obtained from a prototype circuit with 20-V/100-W output, have verified that three achievements can be obtained simultaneously, including the compliance with the line-current harmonic regulations, the reliable alleviation of the bulk-capacitor voltage stress, and the substantially promoted conversion efficiency.