AC/DC flyback controller with UHV integrated startup current source in 180nm HVIC technology

This work demonstrates an AC/DC flyback converter controller fabricated in an 180nm HVIC technology that enables reduced layout size and increased digital content. It features a monolithically integrated ultra-high-voltage (UHV) start-up circuit. An integrated UHV depletion-mode transistor is used to draw current directly from the ~400V DC bus and charge up VDD to ~13V. Controlling the gate of this depletion transistor allows the start-up current to be completely cut off after the VDD is charged and the controller starts normal operation, which cannot be done using the resistor start-up approach. The start-up circuit includes built-in protection features and enables tight tolerances for key design parameters.