A Digital Pulse-Width Modulator for Phase-Shift Operation of Full-Bridge Isolated DC-DC Converters

This paper presents the concept, implementation and testing of a digital pulse-width modulator for phase-shift driving of full-bridge isolated DC-DC converters. The proposed phase-shift digital modulator employs a hybrid counter/delay line structure in order to achieve a 1.25 ns phase-shift resolution with a switching frequency of about 400 kHz on the secondary side, using a clock frequency of 25 MHz. Provisions for programmable dead times for switching of the bridge legs are included. The modulator is tested as a part of a digital controller for a full-bridge DC-DC isolated converter supplied from a 320 V DC bus with a 20 V-180 V, 2 A programmable output.