How to measure the world's fastest power switch

by Steve Sandler, Picotest, EDN, Nov 13 2014

Focus:
In this article, the author measures the switching speed of 3rd and 4th generation enhancement-mode GaN (eGaN) FETs from Efficient Power Conversion (EPC). These discrete and monolithic half bridge devices are mounted to EPC eval boards—one configured as a half-bridge circuit, another as a full dc-dc converter. The article explains the minimum requirements for the probe and test instrument; introduces the oscilloscope, cable and transmission-line probe used here; measures the rise time of the test set-up; and calculates the smallest rise times that can be measured with high accuracy. It then presents the switch-node rise time measurements for the half bridge and dc-dc converter and discusses how these results compare with silicon MOSFETs. The article concludes by discussing the design limitations that influence GaN switching speeds in an actual application, the impact of GaN switching speeds on converter switching frequencies, and what switching frequencies the author believes will be achievable with GaN power switches in the future.

What you’ll learn:

• How to accurately measure the switching speeds of GaN power switches
• How to understand test setup requirements for measuring very fast power transistors

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