High frequency synchronous Buck converter using GaN-on-SiC HEMTs

GaN-on-SiC technology has been widely used in radiofrequency (RF) power amplifiers to achieve high power density at very high frequencies due to the enhanced power handling capabilities provided by the SiC substrate and very high transition frequencies of GaN High Electron Mobility Transistors (HEMTs). Along with other well-known advantages of GaN, such as high breakdown voltage and high temperature operation, these characteristics make GaN-on-SiC technology suitable for power electronics applications. This paper explores the use of GaN-on-SiC depletion-mode HEMTs in switched-mode power converters, targeting high efficiencies at switching frequencies in the tens of Megahertz range. The fundamental limits of the technology are analyzed, and design principles and guidelines are given to exploit the capabilities of the devices. Results are presented for a 10 W, 20 V synchronous Buck converter prototype operating at 10 to 40 MHz. Measured efficiency peaks above 96% at 10 MHz and remains above 90% over a wide range of operating conditions. To demonstrate the applicability of the technology, the Buck converter switching at 20 MHz is used as a supply modulator to track a 3 MHz envelope signal with greater than 90% average efficiency.