Reduction of high-frequency conduction losses using a planar Litz structure

The new trend in power converters is to design planar magnetic components that aim at a low profile. However, at high frequencies, AC losses induced in the planar inductor and transformer windings become significant due to the skin and proximity effects. The planar litz structure had been proposed previously to reduce the AC resistance of the planar conductor. A planar litz conductor can be constructed by dividing the wide planar conductor up into multiple lengthwise strands and weaving these strands in much the same manner as one would use to construct a conventional round litz wire. Each strand is subjected to the magnetic field everywhere in the winding window, thereby equalizing the flux linkage. 3D finite element modeling (FEM) was performed for some simple models. The simulation results showed that the planar litz conductor can result in lower AC resistance than is achieved with a solid conductor in a specific frequency range. The performance of the planar litz winding was also verified with measurements on the experimental prototypes.