PRISM Forum - Message Replies

Topic: PRISM Questions and Answers
Topic Posted by: SRC ( )
Organization: SRC
Date Posted: Wed Jan 12 8:33:33 US/Eastern 2000
Topic Description: Welcome to the PRISM forum! Please feel free to post your questions and comments about the PRISM assessment software here.

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Original Message:

Posted by: Sue Hedrick ( )
Date posted: Wed May 3 16:43:04 US/Eastern 2006
Subject: Resistor calculation
With regard to resistor calculations, how can I determine theta EC. I had thought that it was calculated using (storage temp - max operating temp) / resistor power rating. This gives me huge numbers, greater than 600 deg C / W. What should I be doing? Thanks, Sue

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Subject: Resistor calculation
Reply Posted by: Sue Hedrick
Date Posted: Thu May 4 10:28:39 US/Eastern 2006
Hi David, Thanks for your reply. Perhaps you could help me to pick which method to use. We have considered them all and each has its own difficulties in this application. The default rise of 30 degrees C is too high. The power stress on these parts is under 10%. We have no way of measuring the actual temperature rise of these parts. We have contacted the manufacturer and they do not have Thermal resistance data for these parts, neither theta EA or theta EC. To calculate Delta T of the parts, I need to know the thickness of the layers of resitive material and substrate material along with the thermal characteristics of each. Perhaps there are easier ways to calculate these parameters that I am not aware of. Any help would be appreciated. Thanks, Sue

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