Auxiliary bridge arm–based switching control for optimal unloading transient performance of multiphase buck converters

For a low-conversion ratio buck converter, the step-down (unloading) transient lasts much longer than the step-up transient for the same change of the load. Regarding this issue, an auxiliary bridge arm (ABA) multiphase buck converter with switching control scheme is proposed for the optimal unloading transient performance. With the ABA, the input voltage is reversely connected into the inductor current freewheeling loop during the unloading transient. In this case, the fall slew rate of the inductor current increases, because of the voltage across the inductor increase. Meanwhile, the capacitor-charge balance theory is used to calculate the switching moment and achieve the minimum settling time and the voltage overshoots. Finally, a 12- to 3.3-V two-phase synchronous buck converter prototype is built. The experimental results show that the settling time and the voltage deviation are both improved over 50% compared with that of the average current sharing scheme and the time-optimal control scheme.