High Step-Down Ratio Buck Converters With eGaN Devices

Focus:

Some companies using a +48 V system power distribution bus with on-board bus converters and point-of-load regulators (POLs) are wondering if they can simplify their systems. For them, a single POL that converts the +48 V bus directly to the load voltages is an intriguing idea. Until now, the limitations of silicon MOSFETs have made it impractical to design and manufacture such a POL. This article discusses how new gallium-nitride (GaN) power transistors from EPC have overcome these hurdles, making it feasible to build POLs with the high step-down ratios needed to generate 1 V or less directly from a 48 V bus. Experimental results are presented for two 48 V to 1 V buck converters--one built with silicon MOSFETs and another with GaN transistors. The test setup used in these experiments is described; data is given for the devices under test; and test results for the two buck converters are given at switching frequencies of 200 kHz and 500 kHz. Deadtime considerations and test results are discussed. Other issues discussed include the on-time limitations of 60-V to 100-V rated Si MOSFETs versus those of the new GaN transistors, the impact of these limitations on step-down ratios; and design issues surrounding the currently used power system architectures. An appendix describes the "Evolution Of The Intermediate Bus Architecture (IBA)."

What you’ll learn:

• How to design high step-down ratio buck converters such as 48 V to 1 V while achieving reasonable efficiency and other performance goals
• How to compare silicon MOSFET versus GaN power transistor performance in buck converter applications
• How to understand the evolution of the intermediate bus architecture

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Author & Publication:

Johan Strydom, Efficient Power Conversion, El Segundo, Calif. and Bob White, Embedded Power Labs, Highlands Ranch, Colo., How2Power Today, Nov 23 2010

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