How to get 500W in an eighth-brick converter with GaN, part 1

November 30, 2015 // By John Glaser
John Glaser of Efficient Power Conversion Corporation considers how to achieve 500 W in an eighth-brick converter using GaN technology.

DC-DC “brick” converters are familiar to many engineers, and have wide usage in telecommunications, networking, data centers, and many other applications. This is due in large part to adoption of a common footprint defined by the Distributed-power Open Standards Alliance (DOSA) and generally accepted input/output voltage ranges [1]. These converters provide isolation and voltage step-down, and have become increasingly sophisticated, with features that enable advanced system optimization and control. They often reside on motherboards where they drive point-of-load converters for processors and memory. Increasing data processing throughput requires more power, more board real estate, or both. Power processing is considered a cost, and information processing a source of profit. Hence, there is continuous pressure to increase power density. However, as the technology has matured, improvements in basic power conversion capability, that is, power density and efficiency, have slowed down to a crawl.

All is not lost, however, as GaN power semiconductors give basic power converter technology a much-needed shot in the arm. GaN transistors already show large improvements over similarly rated silicon devices [2]. This article shows that these improvements are more than good looking datasheets via a design example that demonstrates a complete eight-brick converter design with eGaN FETs and real test results. This converter can deliver more than 500 W using a conventional transformer-isolated, hard-switched, PWM regulated design. It represents a new starting point that can be achieved with GaN – and with room to grow.

This article will appear in two parts. Part 1 covers brick technology, a comparison of eGaN FETs to silicon MOSFETS, a basic overview of the GaN-based eighth-brick design, and experimental results. Part 2 gives a detailed design overview to show how to get the most out of eGaN FETs, along with a number of ways that the design could be improved.

Introduction

At the 100 W to 1 kW level, quarter-brick (Q-brick) and eighth-brick (E-brick) DOSA-compliant converters are commonly used to convert

Design category: