An Adjustable Bobbin Design Method for Common‐Mode Chokes to Reduce Noise via Parasitic‐Capacitance Balancing

ABSTRACT

This paper proposes an adjustable bobbin design method for common‐mode chokes to reduce common‐mode noise through parasitic capacitance balancing. The proposed method employs a split‐bobbin structure with a common inner support region and a discrete outer control region so that branchwise winding‐spacing can be adjusted in a manufacturable and repeatable manner. A practical balancing concept and a design‐oriented interpretation are presented to relate bobbin geometry selection to the effective choke‐side capacitance condition under the implemented filter platform. Based on this interpretation, a stepwise bobbin selection workflow is established using discrete winding‐spacing candidates. Prototype chokes are fabricated and evaluated through component‐level impedance measurement and filter‐level conducted emission testing on a series resonant converter. Experimental results demonstrate that the proposed bobbin improves the average common‐mode conducted emission response in the selected low‐megahertz comparison band of the implemented platform compared to the conventional design. At 1.449 MHz, the proposed configurations reduce the average common‐mode conducted emission by 3.92 dB and 5.68 dB, respectively. The proposed method provides a practical platform‐level design approach for common‐mode noise reduction without additional passive components or unit‐by‐unit post‐assembly trimming.