What is quasi-resonant converter?
Using the quasi-resonant phenomenon, the voltage or current on the device in the switching converter is changed by a quasi-sinusoidal law, thus creating a condition of ZVS or ZCS, which is called a quasi-resonant converter. In a single-ended, half-bridge or full-bridge converter, a quasi-resonant converter can be obtained using parasitic inductance and capacitance or externally coupled resonant inductance and capacitance. The resonance parameters can be more than two, for example three or more, which is also referred to as a multi-resonant converter. In order to keep the output voltage almost constant, both the resonant and quasi-resonant converters must use variable frequency control.