A New GaN T-Type Three-Switch Bridge-Leg for Cryogenic HTS Magnet Power Supplies

Cryogenic step-down dc-dc converters for supplying high-temperature superconducting (HTS) magnets operate from low dc input voltages in the order of 1 V and provide high output/magnet currents. The proposed three-switch T-type (3STT) bridge-leg utilizes the (limited) reverse-blocking capability of standard GaN transistors to provide the same functionality (bipolar output voltage) as a conventional full-bridge (FB) topology. Advantageously, the 3STT features only a single transistor in the load current path (instead of two for the FB), reducing conduction losses by at least 50%. Loss measurements of a 25 A 3STT phase module demonstrator operating at 77 K (immersed in liquid nitrogen) verify the concept.