AC Copper Loss Reduction in Planar Inductors With Magnetic Building Blocks-Based Gapless Parallel Symmetrical Magnetoresistance Structure

Fringing and proximity effects are the main reasons for serious ac copper loss in high-frequency planar inductors. In this article, a novel air-gapless core structure based on magnetic building blocks (MBBs) with magnetoresistance parallel and symmetrically distributed relative to the windings is proposed, in which two magnetic building blocks parallel to the printed circuit board (PCB) windings are made of metal soft magnetic material with low relative permeability and three magnetic building blocks perpendicular to windings are made of ferrite with high relative permeability. Equivalent magnetic circuit models and theoretical analysis for the proposed core structure reveal that even if the interleaved winding structure fails in the inductor, a better distribution of magnetomotive force can be obtained by optimizing the distribution of magnetoresistance. Compared with the conventional inductors using stand airgaps, both the fringing and proximity effects can be weakened by the designed parallel symmetrical magnetoresistance core structure, which has been verified in 3-D finite-element analysis (FEA)-based simulations. The FEA calculated results show that the proposed optimized core structure can achieve a 46% reduction in ac resistance, and this advantage will extend with increasing frequency over a certain frequency range. On a boost converter operating in critical conduction mode, experimental verification including converter efficiency test and inductor loss test was carried out. The maximum efficiency improvement was 1.4%, and the reduction of inductor loss was also verified.