The auxiliary submodule power supply is a vital component of a modular multilevel converter submodule or any multi-submodule converter. Considering the high isolation requirements and difficulties to provide power from the ground potential, the auxiliary submodule power supply must be simple, work reliably and not compromise the submodule’s reliability. A flyback supply from the submodule’s dc link with multiple sets of isolated secondary windings solves at once the low-voltage generation and the required voltage isolation for semiconductor gate circuits and protection without need for an externally supplied low-voltage input to the submodule(high-isolation connection). This paper presents an isolated, flyback-based auxiliary submodule power supply with planar magnetic, printed circuit board integrated windings and multiple isolated outputs for a medium voltage modular multilevel converter as well as detailed electrical and magnetic mathematical modelling, technological integration challenges description and proper experimental test considerations.