Quasi-Resonant Flyback Converter in 800 V System: Industrialization Aspects and Comparison to Active-Clamped Flyback Converter

This paper presents implementation and some industrialization aspects of the quasi-resonant flyback (QRF) dc-dc converter with valley switching. The QRF was used as an auxiliary power supply of an 800 V system and was supplied from the variable dc-link. The 57 W mock-up was built and tested. A comprehensive comparison of QRF and ACF (active-clamped flyback) dc-dc converters in this emerging application is provided. The both converters had similar specification, the same maximum switching frequency, majority of used parts, the same secondary sides and respective layout-which made comparisons plausible and unique in the literature. Aspects covered were: efficiency, no-load losses, FFT (fast Fourier transformation), EMI (electro-magnetic interference), supply chain, cooling, price, space, complexity, technical cleanliness, insulation coordination and functional safety. The QRF had higher efficiency than ACF in whole load and input voltage range-which was expected since an ACF has higher losses due to circulation energy. For the same reason, losses at no-load conditions were significantly lower with QRF. A comparison of measured drain-source voltages' FFT showed that the spectral content of QRF is a bit dependent on the input voltage and that amplitude of harmonics is a bit higher at 850 V than at 620 V input voltage. Those findings were different compared to the ones with ACF in sense that the spectral content of ACF was independent on the input voltage. So, it was clear that the QRF, in this application, is superior to ACF in every aspect except for FFT and EMI.