Self-Bootstrapping Isolated Power Converter

NASA’s Self-Bootstrapping IPC operates in either transition mode for bootstrapping or fixed frequency mode for a regulated output via closed feedback. The transition mode is initially turned on via the input (i.e., primary) voltage control of the main switch and acts as a bootstrap converter utilizing a Gallium Nitrate transistor to control peak primary inductor current. That peak current can be varied via the sensor gain and/or a precise artificially generated offset and controls the switching frequency together with the secondary load (i.e., output). The IPC operates in transition mode until the Pulse Width Modulator (PWM) Under Voltage Lockout threshold is reached and fixed frequency mode begins. Fixed frequency operation is controlled by the PWM and the normal operation mode of the converter maintains a frequency while varying the duty cycle as needed. The PWM is secondary ground referenced and controls primary switching via galvanic isolation. The peak current in transition mode is set higher than the peak current in fixed frequency operation to prevent interruption or instability while in fixed frequency operation after bootstrap is completed. However, the transition mode control can serve as the overall peak current limiter. This invention is applicable to both flyback and buck-derived topologies with similar efficiency and size advantages. While NASA originally developed the Self-Bootstrapping IPC for CubeSats and space-based electronics with strict SWaP requirements, it may also be useful for safety-critical industries (e.g., aerospace and defense) to allow for high reliability power supplies and more favorable SWaP than existing state-of-the-art high-power dc-dc converters. The reliability, efficiency, and SWaP advantages of this NASA invention could also benefit medium- and high-power commercial power supplies. Isolated power converters (IPCs) provide safety and performance benefits like noise reduction by separating current flow between a circuit’s input and output. Existing IPCs require bootstrapping the main converter on startup by using a dedicated converter to supply isolated power from the output to the input. The need for two converters decreases efficiency, increases size, weight, and power (SWaP) requirements, and adds complexity to the overall power converter. The bootstrapping problem is significant in space flight applications where SWaP considerations are critical. In response, engineers at NASA's Goddard Space Flight Center developed the Self-Bootstrapping IPC to eliminate the need for an isolated bootstrap converter by allowing bi-modal operation of a single converter. Specifically, the invention operates in transition mode for bootstrapping and then migrates to fixed frequency mode via closed feedback. This bi-modal converter allows users to benefit from reduced mass and volume, increased power density, and improved efficiency (91-94%).