Multiturn high-frequency coaxial winding power transformers

Previous papers on coaxial winding transformers have focused on designs that use a copper tube to form a single-turn outer winding, and litz wire for a multiple-turn inner winding. In high-power applications, the increased resistance of a solid outer winding due to skin effects can be a limiting factor in achieving good performance, especially at frequencies above several hundred kilohertz. A single-turn outer winding leads to large core cross section areas at lower frequencies and the turns ratio is limited to a ratio of n:1, where n is an integer. This paper demonstrates several methods for achieving multiturn outer windings to improve design flexibility for the coaxial winding power transformer. Experimental measurements on transformers that have multiturn outer windings are included to confirm analytical results and demonstrate the modified designs