A new winding structure with low common‐mode current in input series output parallel planar transformer LLC converter

MHz switches and integrated magnetic planar transformers (PT) promote the high density and miniaturization of DC/DC converters. The parasitic parameters of the PT at high frequency significantly affect the performance of converters, resulting in severe electromagnetic interference (EMI) problems. Firstly, this paper proposes a new common‐mode (CM)‐suppression winding structure for the input series output parallel (ISOP) matrix transformer LLC converter. The sources and conduction principle of CM noise are analyzed. Furthermore, this optimization based on winding shape and position is simple and feasible, suppressing the CM noise significantly. Compared with conventional multilayer winding structure, this optimization increases the current‐carrying area by 2.8%–5.9%, effectively improving the primary current distribution. In addition, the proposed structure makes the best planar windings in footprint with expanded windings, bringing the simplest layout in the primary winding. Finally, a 1 MHz 400 V/12 V 300 W LLC converter is constructed to verify the effect of this winding structure. The results show that a 40% reduction in CM current can be achieved while maintaining the current balance.