RLC Balance Technique of Transformer to Reduce CM EMI for Isolated DC-DC Converters

The capacitance balance technique to reduce CM EMI noise in isolated converters will fail due to the resonance of the CM impedance of the transformer. This paper identifies the unbalanced CM impedances of the transformer will lead to spikes in the CM EMI spectrum. Two RLC branches are used to represent the CM impedances of the transformer. An RLC balance technique is proposed to achieve impedance balance at the capacitive region, the resonant point, and the inductive region. Then, the proposed method is extended to several isolated converters. Finally, the effectiveness of the proposed method and the correctness of the parameters design are verified by experiment results.