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

초록

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.

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