Isolated low-output-voltage PFC circuit with integrated magnetics: Design for low THD

This paper presents a detailed analysis of a Single-Stage Single-Switch Power Factor Corrector, S⁴PFC, with Integrated Magnetic, IM. The chosen topology for study for implementing S⁴PFC is based upon a Boost Converter operating in Discontinuous-Mode for Input Current Shaping, and a Forward Converter for output voltage regulation. Detailed are the modes of converter operation, as well as essential key design equations such as determining line/boost voltage ratio to determine dominant input current harmonics, maximum duty cycle design and Integrated Magnetic design calculations. The analysis presented is applicable to any Boost converter integrated with a Buck-derived converter and very good prediction accuracy is achieved. A 170W prototype has been built to experimentally verify the correspondence between predicted, simulated and measured results. Furthermore, a discussion of the performance data of the S⁴PFC is presented.