Comparison of Common-Mode EMI Noise in a Phase-Shifted and Hard-Switched Full-Bridge Forward Converters

This paper presents the comparison of the common-mode (CM) noise in widely-used phase-shifted (PSFC) and hard-switched (HSFC) full-bridge forward converters. The CM noise voltages across the interleaved transformers' coupling capacitances-one of the significant parasitic coupling capacitances in the isolated converters-are analyzed for both types of switching schemes. Experimental prototypes are built for both switching techniques to verify the CM noise models and their analyses. In contrast to the state-of-the-art belief, the comparison reveals that PSFC generates far more CM noise than its counterpart for the same operating parameters.