Fully Soft-Switching Flying Capacitor Based Quasi-Resonant Buck Converter

A quasi-resonant converter and a complementary mixed-signal controller suitable for low-power step-down applications are introduced. The converter has the same structure as a 3-level flying capacitor buck converter but operates in a different manner. It has soft-switching on all transition edges, across the full load range, achieving flat and high efficiency curves. The advantages are obtained by fully charging and discharging the flying capacitor, as a resonant element, through a specific control technique ensuring proper timing. The operation is verified with an experimental prototype with input voltage of 12 V, output voltage regulated at 1 V, 1.8 V, 3.3 V and 5 V, supporting load currents from 5 mA to 1.5 A. The converter demonstrates high and practically flat efficiency curves. The measured efficiency reaches 89.5 % and, for a given conversion ratio, its variation is no larger than 3 %, over the full load range.