Compressed cores made with soft magnetic alloy powders are widely used for smoothing and boost choke coils of switching regulators and DC-PC converters. Low core loss is required to be high performance of these compressed cores. In this study effects of particle size and crystal grain size on core loss of compressed cores with Fe-Si-Al atomized powders were investigated. Particle size and crystal grain size of powders were changed by water-atomization and heat treatment conditions. Compressed cores were made with these powders and obtained following results. (1) Eddy current loss decreased with decreasing of the particle size, and hysteresis loss decreased with increasing of the crystal grain size of powders; the compressed core with small particle size and large crystal size showed low core loss. (2) The compressed core with heat-treated fine powder (mean diameter = about 10 mu m) showed very low core loss (about 300kW/m~3, at B=0.1T and f=100kHz).
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