Current Self-balance Mechanism in Multiphase Buck Converter

Abstract

Some of the recent applications in the field of the power supplies use multiphase converters to achieve fast dynamic response, smaller input/output filters or better packaging. Typically, these converters have several paralleled power stages with a current loop in each phase and an unique voltage loop. The presence of the current loops is necessary to increase dynamic response (by using current mode control) and to avoid current unbalance among phases. The purpose of this paper is to demonstrate that in CCM, with a proper design, there is an intrinsic mechanism of self-balance that helps a lot in avoiding the current unbalance. Thus, in the buck converter, if natural ZVS is achieved in both transitions, the instantaneous inductor current compensates partially the different dc current through the phases. The need for using n current-loops will be finally determined by the application but not by the converter itself. Using the buck converter as a base, a multiphase converter has been developed. Several tests have been carried out in the lab and the results show clearly that, when the conditions are met, the phase currents are very good balanced even during transient conditions.