Mixed Mode control (Fixed off Time & Quasi Resonant) for flyback converter

A standard flyback converter that automatically selects the best control strategy, between two different control ones, according to the operating condition (Converter Input Voltage and Load), in order to optimize the efficiency, is presented. The control strategies are: Quasi-Resonant Control and Fixed Off Time Control. Quasi resonant control takes place at medium-high converter input voltage or / and light load and helps to keep the switching losses low. Fixed Off time control takes place at low converter input voltage and high load and allows the converter to operate in Continuous Conduction Mode helping to keep the conduction losses low, reducing RMS currents. Steady state equations are discovered and a comparison with pure QR converter is done with the purpose of highlighting the advantage of the double control schemes especially in wide input range converter.