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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Sue Hedrick
Date posted: Mon Mar 5 16:01:08 US/Eastern 2007
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: Mon Mar 5 17:48:33 US/Eastern 2007
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 resistive 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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