Common mode EMI noise reduction technique by noise path configuration of high frequency power transformer

It is known to all that parasitic capacitances in a transformer is very critical for EMI CM noise. Generally, Faraday shielding connected at primary minus is used in most transformers to shield the induced charge and block the CM noise path. Based on CM noise balance concept, a novel noise balance configuration by adding an extra capacitor between shielding foil and primary minus was proposed to reduce the CM noise by adjusting electrical potential in the shielding foil, so that to integrate the enhanced EMI filter function to the transformer. CM noise model had been built and analyzed in detail. The effect of the novel CM noise reduction technique had been verified by experiment.