A single-stage ac-dc forward converter with input power factor correction and reduced dc bus voltage

Single-stage converters are simpler and less expensive than conventional two-stage converters. It can be a challenge, however, to design single-stage converters to satisfy certain key criteria such as input power factor, primary-side dc bus voltage, and output voltage ripple. This is especially true for higher power single-stage converters such as the single-stage ac-dc two-switch forward converter. In the paper, a technique that involves the use of an auxiliary bypass switch is proposed to increase the flexibility in design and performance of the two-switch forward converter. The technique is presented, and the operation of the bypass switch with various PWM techniques is explained. Experimental results obtained from a lab prototype demonstrate and confirm the concepts discussed in the paper.