Digital controller chip set for isolated DC power supplies

This paper describes a digital controller chip set for high-frequency DC-DC power converters with galvanic isolation. The secondary-side controller includes an A/D converter and a transmitter that sends a digital error signal as serial data through an opto-coupler. The primary-side controller includes a serial-data receiver, a programmable digital PID regulator, and a high-resolution (10-bit) digital pulse-width modulator. The digital error signal transmission through the isolation boundary eliminates the problem of gain variation when the opto-coupler is used in linear mode. The chip set is tested as a replacement for a conventional analog current-mode controller in a 3.3 V, 20 A, 400 KHz DC power supply. Experimental results with the digital controller show improved dynamic responses compared to the responses obtained with the analog controller.