A Cryogenic 3-kW GaN E-HEMT Synchronous Buck Converter

Superconductivity is a technology with the potential to enable new and exciting fields, from transportation to energy production. Cryogenic power supplies are useful components for applications involving superconductivity. This article focuses on the design of a cryogenic gallium nitride (GaN) enhancement mode high-electron-mobility transistor (E-HEMT) synchronous buck converter, which achieves an efficiency of 99.2% at 3 kW, and uses a nanocrystalline filter inductor within the cryogenic environment. An air-core inductor-based method is used to separate the switch and inductor losses of the converter, and film boiling in liquid nitrogen is used to set the safe operating range of the converter. The selection of magnetic materials and litz wire at cryogenic temperatures are evaluated, where a nanocrystalline inductor is designed, which shows reduced losses in liquid nitrogen compared to at room temperature. It is shown that by cryogenically cooling the GaN switches their losses are halved compared to when operating at room temperature under the same conditions.