Reduction of CM Noise by Minimizing Near-Field Effects in a DCCDC 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 different areas of the power converter. If not properly addressed, these parasitic near-field couplings may increase the converter's conducted electromagnetic interference (EMI). This article investigates the impact of parasitic near-field couplings on conducted common-mode (CM) noise in a buck converter with the EMI filter. Magnetic and electric coupling mechanisms are studied using near-field measurements. A CM model with capacitive couplings is developed and shown to accurately predict the CM noise spectrum under two different test conditions. The model is analyzed and two critical capacitive couplings are identified. Finally, shielding techniques are demonstrated to reduce CM noise up to 35 dB, and a novel shielded-windings PCB inductor structure is proposed.