High-frequency losses in multiturn foil-wound air-cored inductors

The paper discusses a coupled-circuit model which can be used to calculate the effective resistance of a multilayer foil-wound inductor and describes a formal method of solution for the large set of describing equations. Alternative methods of calculating the self and mutual inductances required in the model are compared, and it is shown that care is needed in calculating the mutual inductance between coaxial circular coils with slightly different diameters. Measured and computed results are presented for two examples of inductors for the frequency range of 20¿¿100 kHz which is normally encountered in switched-mode power supplies. It is shown that a simplified model, which assumes that the current distribution is the same in all layers, is inadequate, even for inductors where the winding buildup is small compared to the mean diameter.