An Accurate Output Current Prediction Scheme For Primary-Side Regulation Active-Clamp Flyback Converter

Active-clamp flyback converter is very popular as soft-switching technique is realized at very high frequency. In most conditions, opto-coupler, which suffers the non-linearity and temperature drift, is applied to realize feedback of the output signals. To eliminate the opto-coupler and simplify the control, an output current prediction scheme is proposed for primary-side regulation active-clamp (PSRAC) flyback converter in this paper. In this scheme, the integration of the auxiliary winding voltage is adopted to emulate the magnetizing current and the accurate output diode current can be acquired by subtracting the primary current from the magnetizing current. The proposed PSR control scheme, which contains the detailed output current prediction strategy and estimation circuit, is presented. Finally, a 21V/3A laboratory prototype has been built up and experimental results show that the flyback prototype can achieve±3% accuracy of output current.