A High Input Voltage Auxiliary Power Supply Utilizing Automatic Balanced MOSFET Stack

In order to deal with the challenges in establishing a high input voltage high step-down auxiliary power supply (APS) for modular converters, a flyback converter utilizing series-connected silicon carbide (SiC) MOSFETs is proposed in this article. With the aid of a novel snubber circuit structure, the used series-connected SiC MOSFETs can switch with nearly perfect dynamic voltage sharing. Besides, the snubber circuit acts as voltage clamping circuit for the flyback converter, so voltage overshoot caused by transformer leakage inductance can be effectively controlled. Furthermore, the snubber circuit helps to power the control, gate driver, and startup circuits of the APS, leading to a reduction in system complexity and improvement in efficiency. Detailed circuit analysis and design considerations of the APS are presented. Finally, hardware of a 4 kV/120 W APS is established and experimentally verified.