Zichao Ye with adviser R. Pilawa-Podgurski
Flying-capacitor multi-level converters (FCMC) have received increased attention for medium- to low-power designs. Compared to conventional two-level converters, FCMCs have the advantages of lower device stress ratings, greatly reduced inductor values, increased effective ripple frequency and reduced dv/dt transients. Many examples show a higher conversion efficiency and higher power density than conventional two-level counterparts. However, a major challenge is to provide power to the gate-driving circuitry as the switch terminals are all floating. The existing method utilizes an isolated dc/dc converter, which is bulky and energy inefficient.

Two innovative circuitries are developed to power the floating switches without using isolated dc/dc converters. One method, cascaded bootstrap, can charge the switch floating-power supply from its low-side neighboring switch. The other, hybrid charge pump, utilizes internally available voltage nodes to deliver the required gate voltage. By combining these techniques, the FCMC can be powered by a single ground-referenced power supply. A prototype (Figure 26) has been built to show the functionality and simplicity of the circuit and demonstrate its compatibility with integrated circuit implementation. This research is supported by Texas Instruments.


Figure 26: A four-level buck converter with floating power-supply circuitry