An isolated, quasi-resonant flying capacitor-based flyback converter topology, and a complementary mixed-signal controller, suitable for low-power applications (ranging from fraction of a watt to tens of watts) are introduced. The solution demonstrates high conversion ratio, approaching 60x, and operating condition independent soft-switching of all components, on all transition edges (thus a high efficiency). These features are achieved by utilizing two resonant circuits and operating the flyback transformer in an unconventional manner. The first resonant circuit comprises of a small primary side flying capacitor, that is fully charged/discharged, and the second circuit has a resonant series capacitor, and both are being connected to the transformer inductances through a specific control scheme. The solution also allows for a significant transformer size reduction by operating at high switching frequency, owing to soft-switching. The effectiveness of the topology and control scheme are experimentally verified with a custom-built 400 V to 3.3 V/ 5 V/ 6 V, 20A, discrete prototype, achieving peak power processing efficiency of 95.5%.
