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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: Shanta
Date posted: Thu Jun 5 16:12:04 US/Eastern 2003
Subject: Default temperature rise for diodes in PRISM model
In the PRISM model, the default temperature rise for diodes is 60C. If the system is operating at 40C (average room temperature), the diodes in the system operate at 100C (40+60). Why is the default temperature rise so high? Seems hard to believe that standard, off the shelf diodes, can operate/withstand 100C temperatures. Since the overall system temperature is 40C, won't the diodes operate at a temperature slightly higher than that? Is the temperature rise only due to internal heating (thermal resistance*power)?


Subject: PRISM Default Parameters
Reply Posted by: B.W.Dudley ( )
Organization: RAC
Date Posted: Tue Jul 22 13:06:53 US/Eastern 2003
The default value for semiconductor devices in the PRISM program is 60 degrees C. You are correct in that some devices do not have the specified temperature extremes values to meet ambients of 30 or 40 degrees C. The rationale for the very high default value is the fact that high powered semiconductor devices do have temperature rise of 60 or more degrees C so a worst case senerio was used. Default parameters are not required to perform an analysis with PRISM. The best analysis is the one that uses values that are actually expected based on the device selected and the operating parameters applied.

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