Tips And Tricks For High-Speed, High-Current Measurement

by Grant Smith, Texas Instruments, Santa Clara, Calif. , How2Power Today, Jan 15 2016

Focus:
Accurate high-speed, high-current measurement is a key requirement for power supply design. Today’s 1200-V, high-current SiC FETs are capable of switching on and off in as little as 5 ns. Di/dt values can exceed 10 A/ns, and peak currents can exceed 100 A. Complicating matters further are space restrictions that stem from use of the higher switching frequencies supported by SiC transistors. So, current measurement circuits embedded in SiC-based power converters need to be as small as possible. This article describes requirements for measuring current in SiC-based power converters, discusses two measurement options—current transformers and current-sense resistors—and gives tips for applying them. Finally, it presents two high-speed, high-current current measurement circuits using current-sense resistors and wideband differential amplifiers. Prior to the main discussion, the article discusses trends in the adoption of SiC Schottky diodes and MOSFETs, the impact of falling SiC device prices, and reductions in application costs enabled by SiC. It also looks at gate-drive requirements for SiC MOSFETs and the performance of a SiC-compatible driver IC, the UCC27531.

What you’ll learn:

• How to measure current accurately in SiC-based power converters
• How to build circuits for measuring high-speed, high-current SMPS waveforms

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