Solving The Valley Jumping Issue in Quasi-Square Wave Resonant Power Supplies

摘要

Quasi-square wave resonant converters, also known as quasi-resonant (QR) converters, allow the design of flyback Switched-Mode Power Supplies (SMPS] with a reduced Electro-Magnetic Interference (EMI] signature and an improved efficiency at full load. However, as the switching frequency increases when the load decreases, the frequency excursion must be limited to avoid additional switching losses. Traditional QR controllers feature a frequency clamp to limit the frequency excursion. When the switching frequency of the system reaches the frequency clamp limit, valley jumping occurs: the controller hesitates between two possible valley choices, resulting in an instable operation and noise in the transformer.