Improving Power-Inductor Performance by Mixing Sub-micro Fe Powder with Amorphous Soft Magnetic Composites

Amorphous soft magnetic powder is one of the most favorable materials for power applications working in the MHz range. In order to induce high permeability, DC bias characteristics, and low core loss in the working frequency range, the core must achieve high packing density. Sub-micro-sized alpha-Fe powder has been applied to inductors because of its high saturation magnetization and low intra-particle eddy-current loss. In this study, we investigated the magnetic properties of amorphous Fe alloy/sub-micro-sized alpha-Fe powder composites. We prepared composites as a bimodal toroid core with various mixing ratios of amorphous Fe alloy and sub-micro alpha-Fe, whose average particle sizes are approximately 35 mu m and 3.3 mu m, respectively. As the amounts of sub-micro alpha-Fe contents increase, the packing ratio and density of the core maximize at the cores, which have a sub-micro alpha-Fe content of 30 wt.%. The measurement results of the magnetic relative permeability (mu) and quality (Q) at 1 MHz revealed similar behaviors with the packing ratio and density; both mu and Q are a maximum of 35.5 and 47 in the core with 30 wt.% sub-micro alpha-Fe contents. The total evaluated core-loss (P-cv) under a driven magnetic flux 200 mT in the MHz range gradually decreased as the sub-micro alpha-Fe content increased up to 30 wt.%, and the minimum core-loss was 562.2 mW/cm(3) at 1 MHz. Based on the experimental results, the improved magnetic performance of the core can be obtained not only by the intrinsic properties of material but also by the microstructure of the core body.