Optimum design of an RC snubber for a switching regulator by means of the root locus method

This paper presents the optimum design of an RC snubber to suppress the surge voltage across the transistor in a switching regulator with two-winding reactor. Analyzing the surge voltage across the transistor with an RC snubber by means of high-frequency equivalent circuits, we obtain the third-order characteristic equation. This third-order equation is analyzed by the aid of the root locus method. As a result, the region where the surge voltage can be suppressed is described in the R-C plane. The experimental confirmation of this analysis is shown. Considering the snubber loss, the optimum resistance and capacitance can be obtained. Further, the precise design procedure of RC snubbers is discussed by normalization and numerical calculation. This procedure is summarized in easy-to-use nomographs.