Interleaved common mode transformer with common mode capacitors

Abstract

The interleaved common mode transformer is a transformer particularly well suited for providing low voltage, high current dc outputs. Improving the efficiency of low voltage, high current transformer circuits requires a multi-faceted approach. Ac terminations and ac currents in connecting circuitry are particularly troublesome, so the input and output terminations of the transformer are dc. To utilize the winding fully, a common-mode push-pull configuration with common mode capacitors is used. Stray capacitance is less of a concern than leakage inductance at low voltages, so the windings are highly interleaved. Separate parallel secondary windings are used, an ac winding primarily for the ac currents, and a dc winding primarily for dc currents and heat sinking. The ac windings are thin; approximately two times the penetration depth. The dc windings are substantial, for low voltage drop and good heat sinking. For economical construction with minimum height, plated circuit board fabrication methods and materials are used for the windings. 100 percent duty-ratio switching is preferred to minimize core losses and reduce filtering requirements, as the filters are lossy.