Quasi-Constant Frequency Secondary Side Controlled Flyback Concept with Variable ON-Time

This paper introduces the novel Variable ON-time Secondary Side Controlled Flyback concept. The Flyback is controlled from the secondary side with communication to the primary side switch occurring through the coupled inductor itself, eliminating the need for any isolated signal coupling. Independently, simple primary side logic continuously adapts the primary ON-time to sustain constant switching frequency and automatically match energy transfer to the output load. Measurements of the proposed concept show near constant frequency with minimal output ripple during load changes and natural output current limiting in overload conditions.