A Practical Look At Current Ratings

by Sanjay Havanur, Principal Applications Engineer, Sunnyvale, Calif., How2Power Today, Dec 15 2009

Focus:
System designers are often faced with the task of selecting the most suitable power device from a wide array of products from different manufacturers with very similar ratings. While a detailed parameter-by-parameter comparison is technically the most correct way of selection, it is not the most practical and designers typically resort to making their first cut based on three or four simple parameters such as package type, voltage and current ratings, and RDS(ON). This article examines current ratings and explains why they are not generally helpful, and can even be misleading, when selecting power devices. It also explains why the proper way to evaluate a power device is to calculate how much power it will dissipate in your application. The focus here is on MOSFETs in low- and medium-power packages, but this discussion applies to other semiconductor devices as well.

What you’ll learn:

• How to determine the true current rating (i.e. usable current) of a semiconductor device in your application
• How to select power MOSFETs and other semiconductor devices for power supply applications

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