Abstract

Applications for AC/DC converters that require high input power factor has been traditionally implemented by two power stages. In order to provide a cost effective and high density solution for low power applications, this thesis proposes a single stage isolated converter topology designed to achieve a regulated dc output voltage having no low frequency components and a high input power factor. The topology is derived from the basic two switch forward converter, but incorporates an additional transformer winding, an inductor, and a few diodes. The proposed circuit inherently forces the input current to be discontinuous and ac modulated to achieve high input power factor. The converter's output is operated in discontinuous conduction mode to minimize the bulk capacitor's voltage variations with variations in the output load current. Analysis of the converter is presented and performance characteristics are given. Design guidelines to select critical components of the circuit are presented. Experimental results on a 150 W, 50 kHz, universal input (90-265 V), 54.75 V output AC/DC converter are given which confirm the predicted performance of the proposed topology.