This paper addresses the design of efficient switched-capacitor power converters, The discussion starts with a review of the fundamental limitation of switched-capacitor circuits which shows that the topology of such circuits and the ''forced'' step changes of capacitor voltages are the inherent attributes of power loss, Although the argument follows from a rather trivial result from basic circuit theory, it addresses an important issue on the maximum efficiency achievable in a switched-capacitor converter circuit, Based on the observed topological constraint of switched-capacitor converter circuits, the simplest lossless topology for AC/DC conversion is deduced, Also discussed is a simple version of lossless topology that achieves isolation between the source and the load, Finally, an experimental AC/DC switched-capacitor converter, based on the proposed idea, is presented which demonstrates an improved efficiency over other existing switched-capacitor converters, The proposed AC/DC converter contains no inductors and thus is suitable for custom IC implementation for very low power applications.
