Ｆｅ‐Ｓｉ‐Ａｌ系圧粉磁芯の磁気特性に及ぼす噴霧粉形状の影響

Abstract

Powder cores made with Fe-Si-Al alloys, Mo-permalloy and so on are widely used for smoothing and boost choke coils of switching regulators and DC-DC converters. High permeability at DC bias magnetic field is required to be high performance and miniaturization of these magnetic cores. In this study effects of particle shapes on magnetic properties of compressed powder cores with Fe-Si-Al modified water-atomized powders were investigated. We concluded as follows. (1) Initial permeability and DC bias characteristics continuously change with particle shapes. Cores with elliptical shaped (large aspect ratio) powders exhibited high initial permeability but inferior DC bias characteristics. While with spherical shaped (small aspect ratio) powders, initial permeability was relatively low, but the permeability at high DC bias magnetic field was higher than that of elliptical shaped powders. (2) Differences of initial permeability with particle shapes can be explained by the differences of effective demagnetizing factors N of the particles through the analysis using Ollendorf 's equation. It is guessed that in case particles have large aspect ratios, they have small N, consequently initial permeability is high. Furthermore from the estimation of N, the core is magnetized connecting about four particles. (3) Permeability depends on not only particle shape of powder but also relative density of core. Using of spherical shaped particles rather than elliptical and higher density result in both high initial permeability and excellent DC bias characteristics.