Voltage‐extrapolative charge balance controller with charge compensation for flyback converter operating in DCM

Abstract

This study presents a voltage-extrapolative charge balance (VECB) controller with charge compensation for flyback converter operating in discontinuous conduction mode (DCM). Compared with conventional charge balance controller, the VECB controller benefits from voltage extrapolation, which improves the transient response to load disturbance. Based on the output voltage differential value, a voltage extrapolator calculates the output voltage after two switching cycles under the influence of discharge. Furthermore, the extrapolated voltage is used to calculate the reference charge for the next switching cycle. The VECB controller eliminates the lag in calculating the reference charge, which improves the transient response to load disturbance. Closed-loop small signal models under VECB and conventional charge balance controls are derived and compared to prove the improvement. Furthermore, charge damping and its influence to the output voltage are intensely studied. To minimise the influence, a constant factor is adopted to carry out charge compensation, which is proved to be adequate. Finally, the effectiveness of VECB controller is verified on a flyback converter prototype.