Controlled Auxiliary Circuit with Measured Response for Reduction of Output Voltage Overshoot in Buck Converters

In order to adhere to voltage regulation criteria, capacitor selection of a Buck converter must be based on the worst possible scenario. It is well known that, for a low duty cycle Buck converter, the output voltage deviation of a Buck converter undergoing an unloading transient will be significantly larger than that of a corresponding loading transient of equal magnitude. Therefore, in this paper, an auxiliary circuit and corresponding control method is presented to reduce the output voltage overshoot of a Buck converter undergoing an unloading transient. The proposed auxiliary circuit diverts a constant controlled current from the output of the converter to the input of the converter thereby significantly reducing the output voltage overshoot. In addition, the proposed auxiliary controller estimates the magnitude of the unloading transient and sets the auxiliary current to an appropriate level based on a pre-defined set of criteria. This allows for greater design flexibility and increases the auxiliary circuit efficiency for unloading transients of lesser magnitude. As demonstrated through simulation and experimental results, the proposed converter successfully estimates the unloading transient magnitude and diverts a proportional amount of current from the converter output.