Single-stage a.c.-d.c. converters employing boost-type input current shapers (ICS) usually suffer from relatively high switch current stress and line current waveform distortion caused by the voltage-follower control. To remedy these drawbacks, this paper presents a novel single-stage soft-switching a.c.-d.c. converter. Unlike the conventional single-stage designs, the proposed ICS 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 greatly reduced. Moreover, this design produces a.c. modulation effect on the charging time of the ICS so that the waveforms of the average charging current and discharging current of the boost inductor can compensate each other automatically. Consequently, the input i-v curve has nearly linear relationship. In the proposed topology, an auxiliary transformer winding is employed to achieve the above functions. By programming the turns ratio between the auxiliary and secondary windings, the proposed converter can be guaranteed to comply with the IEC 1000-3-2 Class D specifications at as high efficiency as possible. Experimental results, obtained from a prototype circuit with universal line input and 48 V/100 W output, are given to confirm the predicted performance.
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