An Optimized, Variable-Gain Switched-Capacitor DC-DC Converter

Abstract

A novel, variable-gain switched-capacitor DC-DC converter is designed, constructed and tested. The proposed converter minimizes many of the problems which have traditionally hindered switched-capacitor DC-DC converters. The converter has high efficiency, strong regulation and low output voltage ripple across a wide variation in the line and load. The converter utilizes an optimized switching configuration that contains the maximum number of ideal conversion ratios for the given number of capacitors driven by a two-phase clock. The switched-capacitor converter is controlled by a gain-hopping feedforward control scheme in conjunction with duty-cycle, pulse-width modulation feedback control. The proposed control technique enhances the efficiency and regulation capability of switched-capacitor DC-DC converters, which are typically limited when there is a large variation in the line. Because the converter is optimized, programmable and capable of providing buck and/or boost operation (stepping-up and/or stepping-down the input voltage), the new switched-capacitor DC-DC converter is well-suited for a variety of applications and operating conditions. In addition, a novel algorithm based on graph theory and network analysis is developed which enumerates all possible ideal conversion ratios for a given switched-capacitor DC-DC converter structure. In particular, this algorithm can be used as a design tool to greatly improve the operation of multi-gain switched-capacitor converters, where the aim is to maximize the number of ideal conversion ratios while minimizing the number of switches and capacitors. Furthermore, the structure of all attainable positive, ideal conversion ratios of a two-phase switched-capacitor DC-DC converter, utilizing up to five capacitors, is enumerated. As a result, the design process for switched-capacitor converters is greatly simplified and a suitable converter structure can be more easily selected for a given application.