Controlled current source circuit (CCSC) for Reduction of output voltage overshoot in Buck converters

In this paper, an auxiliary circuit is presented to improve the dynamic response of a buck converter. Since it is well established that for typical voltage regulator applications, voltage overshoots (due to step-down load transients) are much larger than voltage undershoots (due to step-up load transients), the goal of the proposed method is to reduce the former. The circuit only functions during step-down load transients and operates by rapidly transferring excess load current from the output of the buck converter to its input. Unlike previous unloading auxiliary circuits, the proposed method uses a controlled current source circuit (CCSC) to remove a constant regulated current from the output. The CCSC has the following advantages over previous circuits: a) predictable behavior allowing for simplified design, b) inherent over-current protection, c) low peak current to average current ratio allowing for use of smaller components. Through selection of the auxiliary current, it is possible to obtain a balanced overshoot/undershoot response for a buck converter, significantly reducing the required output capacitance. In this paper, it is shown through analysis, simulation and experimental results that for a modest increase in component cost, a large reduction of voltage overshoot and output capacitor requirement can be realized.