Planar transformer winding technique for reduced capacitance in LLC power converters

Abstract

Planar transformers (PTs) offer advantages over traditional wire-wound transformers including low-height, low leakage inductance, excellent thermal characteristics, Exceptional reproducibility and manufacturing simplicity. Despite these features, PTs have very high parasitic capacitance due to the large overlapping area and the small distance between consecutive layers. These parasitic capacitances can severely affect the performance of power converters and limit the application of PTs in high frequencies. In this paper, a new PT with very low parasitic capacitance is introduced to mitigate the problems that arise from the parasitic capacitances. The superiority of the proposed PT is confirmed through finite element analysis (FEA) and the experimental measurements and it is shown that the proposed transformer has 21.2 times less intra and 16.6 times less inter-winding capacitance than traditional spiral PT. This significant capacitance reduction has a tangible effect on the performance of power converter and the experimental results of employing the proposed transformer in 1.2 kW LLC resonant converter shows considerable performance improvement of the converter in terms of common mode (CM) noise and light-loading voltage regulation.