Variable on-Time Control Scheme for the Secondary-Side Controlled Flyback Converter

This paper presents an analysis of a novel control approach for the secondary side controlled flyback concept, along with improved drain-source voltage sensing for more precise gate signals and reduced losses. In contrast to the existing control scheme for this concept, the approach presented here sustains constant switching frequency throughout the load range without any additional hardware, boosting efficiency and simplifying coupled inductor design optimization. A 65-W demonstrator shows minimal output ripple during load changes, peak efficiency of 89.90%, natural output current limiting in overload conditions, and utilizes a novel lossless synchronous-rectification sensing subcircuit with minimal zero current crossing delay.