Novel Magnetic Structure of Integrated Differential-Mode and Common-Mode Inductors to Suppress DC Saturation

Integrating differential-mode (DM) and common-mode (CM) inductors onto a single core has been expected to miniaturize EMI filters. However, the previously-reported magnetic structure often suffers from saturation by DC current, hindering miniaturization by integration. This problem seems exacerbated by the fact that this conventional structure tends to induce large DC flux because its equivalent number of turns for the DM inductance is restricted to only half of the total number of turns. This paper addresses the problem by proposing a novel structure that assigns more turns to the DM inductance to suppress the DC flux more effectively. This paper confirmed theoretically and experimentally that the proposed structure is equivalent to series-connected DM and CM inductors. Additionally, analytical estimation revealed that the proposed structure reduced core volume by 41% compared to the conventional structure under the same amount of copper. These results suggest effectiveness of the proposed structure for miniaturizing EMI filters.