A Winding Structure of Air-Core Planar Inductors for Reducing High-Frequency Eddy Currents

Abstract

High-frequency converters with high power density have shown promise in recent years. Air-core planar inductors built with printed circuit boards can eliminate problems associated with the use of magnetic materials, such as iron loss and magnetic saturation. However, conventional air-core planar inductors suffer from eddy current loss. Eddy currents affect the resistance and inductance of the inductor. This article proposes a stranded wire structure to reduce eddy currents more than that in the conventional spiral wire structure. Eddy currents can be reduced by splitting the windings as well as currents of each split winding are balanced in the proposed structure. Seven types of air-core planar inductors were built, and their resistances, inductances, and impedances were measured to evaluate the effects of different structures on eddy currents. Furthermore, the temperature distribution of the planar inductors was measured while supplying a sinusoidal voltage with a power amplifier. The experimental results demonstrate the usefulness of the proposed stranded wire structure. Furthermore, the experimental result shows that the stray capacitance of the inductor can be reduced as a by-product of the proposed stranded wire structure.