A High Precision PSR Constant Voltage Control Method for Active-Clamp Flyback Converter

Compared with traditional flyback converter, active-clamp (AC) flyback converters are highly attractive due to the reduced switching loss and small volume for adapters of notebook, mobile phones, and laptop, etc. To eliminate the opto-coupler and simplify the structure, primary-side regulation (PSR) AC flyback converter can be further used and the output voltage is always derived from the auxiliary winding voltage at knee-point. However, in high frequency AC flyback converter, the existing knee-point sampling method cannot achieve high accuracy due to the impact of parasitic parameters, resulting in an output deviation of about 5%. In this article, a high-precision PSR constant voltage (CV) control method with an error compensation strategy is proposed for AC flyback converter. This method samples the auxiliary winding voltage at the peak point of the secondary winding current when the voltage across the secondary parasitic inductance is almost negligible. By applying current prediction technology, the voltage error caused by the parasitic resistance can also be compensated. To verify the feasibility of the proposed PSR CV control method, a 60 W GaN-based AC flyback prototype has been built. Experimental results indicate that the output voltage precision is within 1.6%.