Reduction of CM Noise by Minimizing Near-Field Effects in a DC/DC Converter

Enabled by the adoption of wide-bandgap power devices, converters in many applications continue to push switching frequency and power density. These trends have the unintentional effect of strengthening parasitic inductive and capacitive couplings between components, which may increase conducted electromagnetic interference (EMI). This paper investigates the impact of these near-field couplings on conducted common-mode (CM) noise in a buck converter with EMI filter. Magnetic and electric couplings are studied to identify the dominant near-field mechanism contributing to CM noise within the converter. A CM model with capacitive couplings is developed and demonstrated to accurately predict the CM noise spectrum under varying test conditions. Finally, the dominant noise path identified using the model is shielded to reduce CM noise up to 40 dB.