Leveraging Ultra-High Efficiency in High Power Open Frame Flyback Applications

Abstract:
Efficiency improvements in flyback converters, driven by advancements in wide-bandgap (WBG) switches, synchronous rectification (SR), and adaptive control, are making them suitable for applications that previously relied on resonant topologies. With improved efficiency, the role of flyback converters in mid-power applications – especially open-frame chargers for eBikes and power tools – is expanding. A 300 W implementation using a 750 V GaN primary switch and variable off-time PWM control achieves 93% efficiency without added complexity or significant cost increase. Design considerations for SR, ZVS, and WBG devices are examined. This paper introduces a hybrid switching control approach that maintains high efficiency across a wide load range. Results suggest that, when selectively enhanced, flyback topologies can effectively replace resonant converters in mid-power applications up to 400 W, offering a practical balance between performance and cost.