Comparison of transient states in step-down power converter (BUCK) in continuous and discontinuous conduction mode

Abstract

The object of this paper is a step-down (BUCK) power converter working in the continuous conduction mode (CCM) or discontinuous conduction mode (DCM). Two types of transient states in a converter have been analyzed and observed experimentally: slow transients, described by averaged models of a converter and fast transients, in the course of a single switching period. The averaged models of converter working in CCM, presented in various sources are similar, with some differences concerning only the description of parasitic effects. The averaged models for DCM depend on the adopted modeling method. Models obtained by the switch averaging approach are second-order models (containing two reactive elements in equivalent circuit representation). Models obtained by the separation of variables approach are first-order models. The experimental results given in this paper show the first-order type of transients. Another group of experiments concern fast transients in the course of a single switching period. The oscillations of inductor voltage in the part of a switching period are observed for DCM.