New digital control method for improving dynamic performance of a quasi-resonant flyback converter

To improve the dynamic performance of a quasiresonant flyback converter, a new digital control method is proposed. When the output voltage is below the lower limit, continuous conduction modulation (CCM) mode with high magnetizing current is applied to increase the input power which pulls up the output voltage very fast. When the output voltage is higher than the upper limit, a proportional iterative of switching period (PISP) is firstly applied to detect the stable control parameters of the changed load. After PISP, the switch is then kept off. The output voltage returns to the reference voltage at its maximum speed. When the output voltage returns to the reference voltage, the stable control parameters are used as starting control parameters of nominal control which automatically eliminates the following voltage resonance. Based on the proposed control method, the dynamic performance is greatly improved. In a 12V/3A prototype, compared to nominal control, the maximum undershoot and overshoot voltages are reduced from 11.60V to 1.02V and 1.44V to 0.88V. The maximum undershoot and overshoot recovery times are reduced from 654.0us to 59.8us and 47.4ms to 2.92ms, respectively.