Isolation in Digital Power Supplies Using Micro-Transformers

Digital power supplies have gained traction as they provide programmability, ease of use, and higher performance. Powerful modern processors can be leveraged to implement complex control algorithms that lead to higher efficiency and faster transient response. One of the major barriers in adopting digital control for isolated power supplies is the need to send digital rather than analog information across the isolation barrier. Traditional opto-couplers are typically of analog interface, and they are very slow and difficult to integrate. Micro-transformer based isolators, on the other hand, are very fast and can easily be integrated with many circuit functions including digital interfaces. This paper describes the circuit architecture for a 200 MHz micro-transformer based isolator with 10 nS propagation delay. Low propagation delay is desired to achieve maximum dynamic response for a close loop power supply. The micro-transformers can be further leveraged to provide isolated power that can be used as initial bias for the controller at the secondary side before the power converter is started in a case where secondary controller is used. How a single package quad channel isolator with 500 mW isolated power can be used in a power converter with secondary controller will be discussed.