GaN Based Switched Capacitor Three-Level Buck Converter with Cascaded Synchronous Bootstrap Gate Drive Scheme

With the power architecture transition from a 12 V to 48 V rack in modern data centers there is an increased interest in improving 48 V power conversion efficiency and power density. A three-level GaN based converter provides a high density and high efficiency solution. In this paper, we will introduce a high performance GaN based switched capacitor three level buck converter for 48 V applications. To fully utilize GaN technology in multilevel topologies, an improved cascaded synchronous bootstrapping technique is also proposed. The proposed gate driving technique is smaller and simpler than the previous gate driving techniques employed in GaN based multilevel topologies and offers tight gate voltage regulation. For experimental verification, a three-level switched capacitor buck converter with the improved gate drive scheme and closed loop flying capacitor balancing is compared against a traditional buck converter. In order to demonstrate a possible further application of the gate-drive scheme, a higher voltage (400 V) prototype is built, with improved experimental results over a regular half-bridge prototype. A simple startup protection scheme using Zener diodes is also verified, which removes the need for full voltage rated switches altogether. Finally, an improved 48 V to 12 V three-level prototype is discussed which combines the benefit of using lower rated GaN devices along with inductor size reduction.