ELECTRICAL CHARACTERISTICS OF SPIRAL COIL PLANAR INDUCTORS USING AMORPHOUS ALLOY RIBBONS AS MAGNETIC LAYERS

Various types of planar inductors have been proposed for reducing the volume of switching converters. Planar inductors using amorphous alloy ribbons as magnetic layers are also studied. The purpose of this study is to clarify the relation between the electrical performance of the inductor, and the properties and composition of amorphous ribbon. The experimental results show that superimposed dc current, 80, increases linearly with the product of B(m) and ribbon thickness t, where I80 is defined as the dc current corresponding to an inductance which decreases to 80% of an initial value. In the case of stacking amorphous alloy ribbons, 80 increases with gradual approach to saturation, as the stack thickness increases regardless of ribbon thickness. However, the saturation value of I80 depends on ribbon thickness. The saturation value increases with increasing ribbon thickness. The above results suggest that from a practical viewpoint the use of thick ribbons is preferable. With respect to alloy composition, the Fe-based alloy is more favorable compared with the Co-based alloy because of its higher stored magnetic energy.