New Digital Control Method for Improving Dynamic Response of Synchronous Rectified PSR Flyback Converter With CCM and DCM Modes

In order to improve the dynamic response of synchronous rectified primary-side regulation (PSR) flyback converter with CCM and DCM modes, a novel digital control method is proposed. In a dynamic process, when output voltage is detected to fluctuate greatly, two special working modes called light-to-heavy mode and heavy-to-light mode are introduced. The output capacitor will be quickly charged and discharged by an optimized control scheme to make the output voltage's dynamic fluctuation smaller. On the other hand, during the dynamic process control, for eliminating overshoot and oscillation when the output voltage returns to the reference voltage, the load is detected by the output voltage slope to determine the appropriate operating mode. With the proposed control method, the dynamic performance can be greatly improved. An field programmable gate array (FPGA)-controlled 20-V/5-A synchronous rectified PSR flyback converter is established to verify the proposed control scheme. In the prototype test, compared to the traditional multimode control, the undershoot voltage and overshoot voltage of the proposed control scheme are improved from 5.02 to 1.63 V and 3.15 to 1.73 V, respectively. The undershoot and overshoot recovery times are reduced from 83.43 to 1.79 ms and 40.32 to 1.85 ms, respectively.