Mapping the Interdependence of Parasitic Capacitances in Isolated Phase-Shifted Full-Bridge DC/DC Converter

Common mode (CM) noise emitted by power electronics heavily depend on parasitic effects which define the CM impedance specific to the circuit. The main concern in terms of CM noise regarding switched-mode power supplies is capacitive coupling. In isolated DC/DC converters, this includes the parasitic switch-node capacitances and the primary-secondary interwinding capacitance of the transformer. Although their determination and mitigation have been extensively addressed, the relationship between them has not yet been mapped. In this paper, a CM impedance measurement is presented to explore this interdependence in a phase-shifted full-bridge converter. The findings show how the switch-node capacitance and the interwinding capacitance depend on and transform into each other in isolated topologies by identifying a frequency dependent CM current path distribution.