Analysis and Implementation of a cm-Scale Switched Capacitor Converter for Low Power, Kilovolt-Range Applications

Abstract

This paper explores the design and implementation of a cm-scale switched capacitor (SC) converter with a kilovolt range output, such as could be used for driving electrostatic, piezoelectric, or dielectric elastomer electromechanical transducers. The design uses a two-stage power conversion approach: a first stage, two-channel series parallel (SP) converter boosts a low-voltage input (e.g. stacked Li-ion cells) by 16x; a second stage symmetric ladder converter boosts the differential series-parallel output by ~10x, providing capabilities to reach voltages in the kV range. The first stage uses a pseudo-soft-charging switching scheme to reduce charge sharing loss and recover energy in parasitic (e.g. bottom-plate) capacitances without the use of an inductor. The implementation optimizes the use of discrete components and represents a scalable design while maintaining a small form factor. The first stage integrated circuit is implemented in 650V SOI CMOS with a die area of 10 mm2; the second stage printed circuit board design uses discrete components with board area < 50 mm2. The converter provides conversion ratio VCR up to 150, peak efficiency ~ 80%, and output power up to 50 mW. Efficient regulation is demonstrated by using a mixture of frequency and digital adjustment of the first stage switching sequence.