A magnetic structure integrating differential-mode and common-mode inductors with improved tolerance to DC saturation

The integration of differential-mode (DM) and common-mode (CM) inductors onto a single core has been expected to miniaturize EMC filters. On the other hand, this technique possibly leads to lower tolerance to magnetic saturation caused by the DC flux, hindering the miniaturization effect due to integration. Particularly, this problem seems to be exacerbated in the previously reported magnetic structure. The reason may lie in the fact that this conventional structure tends to induce a 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 this problem by proposing a novel structure that assigns more turns to the DM inductance to suppress the DC flux more effectively. A theoretical analysis and experiments verified that the proposed structure is equivalent to series-connected DM and CM inductors. Additionally, an analytical estimation revealed that the proposed structure reduced the core volume by 41% compared to the conventional structure for the same wire length. These results demonstrate effectiveness of the proposed structure for miniaturizing EMC filters.