Experimental Demonstration of the Transformer Interwinding Capacitance Voltage Waveform in an Isolated Full-Bridge Forward Converter

A thorough analysis of the transformer interwinding capacitance voltage waveform is presented when an isolated full-bridge forward converter is operated as hard-switched and phase-shifted. A large voltage variation is observed during steady-state, especially in scenarios with a large transformer turns-ratio. It is presented that a split inductor theoretically eliminates the voltage variation when the converter is hard-switched. When the converter is phase-shifted, the voltage variation is reduced while making it independent on the transformer turns-ratio. Measurements of the transformer interwinding capacitance voltage is carried out in four operation scenarios. The measured and calculated waveforms matches with offsets of only 1.3% when the converter is hard-switched, while the maximum off-set is 4.2 V when phase-shifted. A second-order resonance is present in the measured voltage waveform. It is experimentally demonstrated that the amplitude of the second-order resonance is reduced when using a split inductor by a factor of 2.7 and 1.8 when hard-switched or phase-shifted, respectively.