Multilevel switched-capacitor DC-DC converter with reduced capacitor bank

Capacitor-switching operations present in switched-capacitor (magnetic-less) DC-DC converters give rise to spiky capacitor and hence semiconductor devices currents. The magnitudes of these currents and hence semiconductor devices switching losses are proportional to instantaneous capacitor voltage unbalance. Capacitor switching power loss on the other hand is proportional to instantaneous voltage unbalance squared. For most switched-capacitor converter circuits, capacitor switching power loss varies in inverse proportion to both capacitance and switching frequency. Previous research has suggested that a given reduction in capacitor switching losses requires either a corresponding increase in one of these parameters or in the product of both. This paper will show that in the case of multilevel switched-capacitor DC-DC converters, the size of the clamping capacitor(s) has a dominant influence on the instantaneous voltage unbalance. Consequently, semiconductor device and capacitor switching losses can be lowered by increasing only the size of the clamping capacitor(s). Voltage-divider capacitors that are much smaller than clamping capacitors can be used to build multilevel switched-capacitor DC-DC converters, without significant performance degradation.