Design and Implementation of oaxial Winding Transformers for Isolated DC-DC Converters

High power isolated DC/DC converters have been extensively used in various applications. Significant research efforts have been devoted to increase the operating efficiency and power density of the converter. Soft switching full bridge converter has been proposed to meet these goals by establishing zero voltage switching condition across the power transistors. However, a significant inductor is required to facilitate the resonance condition, and results in increased loss and reduced power density of the converter. In this article, a full bridge converter with limited soft switching capability (Bendre, 2003), (Bendre, 2002) and a coaxially-wound transformer are presented to improve the power density. With the coaxial winding structure, the coupling coefficient the transformer will be much higher than conventional transformer, and result in small leakage inductance. The duty cycle loss of the converter is also reduced thanks to the low leakage inductance of the coaxial transformer. Various coaxial structures are presented in this paper Detailed simulations using Ansoft are conducted to observe their magnetic characteristics. These coaxial transformers are constructed in the laboratory and tested with the full bridge converter under soft switching conditions to evaluate the performance of the entire system.