Theoretical performance limits of twophase switched-capacitor (SC) dc-dc converters are discussed in this paper. For a given number of capacitors k, the complete set of attainable dc conversion ratios is found. The maximum step-up or stepdown ratio is given by the kth Fibonacci number, while the bound on the number of switches required in any SC circuit is 3k -2. Practical implications, illustrated by several SC converter examples, include savings in the number of components required for a given application, and the ability to construct SC converters that can maintain the output voltage regulation and high conversion efficiency over a wide range of input voltage variations. Limits found for the output resistance and efflciency can be used for selection and comparison of S C converters.

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The realization of line and load regulation in switchedcapacitor (SC)-based converters is discussed. A duty-cycle control is based on partial charging of the capacitors in the circuit. The influence on the efficiency is pointed out. The use of inductors in SC-based converters is discussed.

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