The Austin SuperMOS is an intelligent 7.2kV/60A SiC power switch integrated with a gate driver and an isolated auxiliary power supply. Design considerations for the auxiliary power supply in a 5kV Austin SuperMOS based full bridge power electronic building block (PEBB), in terms of electrical performance and insulation against high voltages, are presented in this paper. In the presented auxiliary power supply an LLC resonant converter along with 4 individual floated voltage sources containing high frequency and high-voltage isolation transformers are employed. The design of individual floating sources is based on circuit and FEM simulations. Partial discharge measurements are also shown for the proposed high voltage transformer design. Last but not the least, electrical measurements performed on the fabricated full bridge PEBB reveal stable and proper operation of the system.