Advantages of 3-stage-DC/DC-converters for Server Switch Mode Power Supply (SMPS) applications

This contribution deals with the benefits and the challenges of 3-stage DC/DC converters in SMPS applications. They are compared to state of the art 2-stage DC/DC converters for high power and highest efficiency power supplies focusing on server, telecom AC/DC and battery charger applications as a major market for advanced system solutions. The main difference between a 3-stage SMPS and a conventional 2-stage topology is the existence of an extra stage to assume the output power regulation from the main stage. This publication points out the advantages, the problems and the limits of current-fed pre-regulated 3-stage topologies considering the demands. Further on a comparison of different approaches for a voltage-fed post-regulated 3-stage SMPS is presented. This paper also reconsiders the optimal operation frequency regarding the passive components in a resonant mode converter used in the post-regulated circuit. All presented results are extracted from calculations, simulations or practical measurements on the basis of different 800 W demonstrators with 12 V output.