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.