Manufacturers like Maxim, Altera, and many more seem to adhere to a commonly defined range of temperatures for applications. For instance,

  • Full military (-55°C to +125°C)
  • Automotive (-40°C to +125°C)
  • AEC-Q100 Level 2 (-40°C to +105°C)
  • Extended industrial (-40°C to +85°C)
  • Industrial (-20°C to +85°C)

What is the rationale behind these ranges? Are they just an aggregate of temperatures that these applications usually operate in? Or are they calculated using a formula of some kind? Who came up with these?

  • \$\begingroup\$ The military(US) has a standard that specifies operating temp ratings for electronics, so I would expect companies use that when determining military specs. I would expect the same with automotive, auto companies probably have min/max specs and companies like Altera base their ratings to cover that range. Most likely not a secret formula so much as: military needs devices to operate up/down to set worst case temps, make standard/ask for those specs, companies make military rating to cover said standard/specs. Aka simple supply/demand. Would be interesting if I was wrong though. \$\endgroup\$ – I. Wolfe Feb 18 '15 at 16:39

All those Temperature Ranges are standards. Some defined by some authority, some just common consent. For example AEC-Q100 is the temperature range you have to expect in the internals (not motor room!) of a car. In Winter of Northern Countries you may have temperatures as low as -40°C. Your Car has to work without problems there. 105°C apply to a Car parked in a hot area in direct sunlight.

I expect that the 125°C max in many applications is also determined by material. 125°C is the maximum allowed temperature for most semiconductors.

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