Planar Litz Inductor Design for High-Frequency Soft-switched PWM Converter

The power density consideration of high-frequency soft-switched PWM converters demands highly efficient magnetic components. This paper presents a detailed procedure for designing a planar litz inductor carrying significant high-frequency AC current using a printed circuit board (PCB). The significance of the appropriate selection of copper thickness and trace width for planar windings is explained. Four different winding strategies based on the number of strands, routing, and placement of vias are evaluated. The impact of staggered and sandwiched traces in a multi-layer planar litz winding on inter-winding capacitances is highlighted. The core and copper losses are estimated using analytical models for a non-sinusoidal excitation condition. Analytical core loss is compared with SIMPLIS MDM simulation. The current density of different winding strategies is evaluated using Ansys Maxwell 2D. Inter-winding capacitances are extracted using Ansys Q3D. Five different inductors, one based on Litz winding and the other four based on PCB windings have been fabricated and tested in the laboratory. An estimation of the parasitic capacitance based on terminal measurements using a network analyzer is discussed.