Complementary Couple-Turns: An Effective Method for Reducing Common-Mode Noise in Full-Bridge LLC Resonant Converter With Split Primary Winding Transformer

In conventional full-bridge (FB) LLC resonant converters, the position of the resonant tank can affect the symmetry of the entire circuit, leading to different dv/dt values at the two winding terminals of the transformer. This results in noncancelable displacement currents generated in the parasitic interwinding capacitance of the transformer, leading to severe common-mode (CM) noise issues. In this article, a low CM noise FB LLC resonant converter with the split primary winding transformer (SPWT) configuration is proposed. The transformer primary winding is split into two windings and the resonant tank is connected between these two windings. With a symmetrical winding structure, the CM noise current generated in the transformer can be canceled completely. The concept of complementary couple-turns is proposed to ensure a symmetrical winding arrangement for the planar transformer in the printed circuit board (PCB) layout stage before it is fabricated physically. Practical considerations have been discussed when implementing the SPWT configuration, including leakage inductance, transformer winding loss, and voltage conversion ratio. A 360 W FB LLC converter with planar transformers is built to verify the proposed methods.