Design of toroidal inductors with multiple parallel foil windings

This paper presents the design of toroidal inductors with multiple parallel foil windings. Compared to single-winding toroidal inductors, parallel-winding inductors have the same inductance and core loss, but can achieve higher voltage operation, reduced capacitance, reduced leakage flux, and reduced winding resistance if designed well. The parallel-winding design concept, optimization of an example, and detailed calculation of loss including a new analysis of circumferential-current associated loss are discussed in this paper. It is predicted that for a toroid with outer radius of 1 mm, inner radius of 0.6 mm, height of 0.3 mm, 4 turns, the ac winding loss can be decreased by 32% at 50 MHz with double windings, and can be decreased by 39% with five sections of windings in parallel.