Common-Mode noise Reduction Using a Parasitic-Capacitance-Adjustable Bobbin with an Impedance-Balancing Structure

This paper presents a novel common-mode(CM) choke structure that achieves impedance balancing by controlling Equivalent Parallel Capacitance(EPC) through an adjustable bobbin design. High-speed power converters generate significant high-frequency CM noise during rapid switching, requiring effective suppression for Electromagnetic Compatibility(EMC) and reliability. While conventional CM filters can attenuate CM noise, their high-frequency performance is strongly affected by the EPC of the inductors and tolerances of Y-capacitors. To address this limitation, a bobbin structure is proposed that enables precise adjustment of the inter-winding distance, thereby allowing control of the EPC without additional passive components. The proposed structure satisfies the Wheatstone bridge-based impedance balancing condition. The validation is performed using a 3.7 kW resonant inverter system, demonstrating up to 9.3 dBµV of CM noise reduction in the 1 MHz to 5 MHz frequency band.