Influence Analysis of Thermally Conductive Epoxy Resin on the Electrical Design of a Compact AC/DC Converter

The design of a compact AC/DC converter for a wide output voltage range imposes stringent challenges regarding electrical and thermal performance. To match these requirements this paper presents the design approach and measurements of a Totem-Pole Power Factor Correction (PFC) and a resonant LLC converter stage, optimized for a maximum average efficiency over a wide operating range. The work deals with the design process itself, which is subdivided into the derivation of the necessary efficiency due to the thermal and geometrical boundary conditions. Further it details the influence of the high packing density and the thermal management on the electrical behavior. A thermally conductive epoxy resin which is designed to meet increasing demands for efficient thermal dissipation has significant unintentional influence on the electrical behavior of the LLC resonant circuit. The root causes are analyzed and verified by measurements.