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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Fri, 07 Jun 2024 15:19:50 -0700
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On Fri, 07 Jun 2024 09:35:38 -0400, legg <legg@nospam.magma.ca> wrote:

>On Thu, 6 Jun 2024 14:01:04 -0700, Don Y <blockedofcourse@foo.invalid>
>wrote:
>
>>On 6/6/2024 10:45 AM, legg wrote:
>>> On Mon, 3 Jun 2024 07:52:58 -0700, Don Y <blockedofcourse@foo.invalid>
>>> wrote:
>>> 
>>>> Presumably, one should feel comfortable using a device at the
>>>> published operating temperature extremes "forever".
>>>>
>>>> But, what sort of derating likely went into that specification
>>>> in the first place?  Sad another way, how much *beyond* those
>>>> limits might want suspect you could operate the device?
>>> 
>>> There are two basic limits to operating environment temperatures.
>>> 
>>> Junction temperature limits are usually proscribed below book
>>> Tjmax for an agreed mtbf. Sometimes the environmental limits
>>> can be extended under reduced performance guidelines, without
>>> exceeding agreed Tj limits.
>>> 
>>> For a whole product, there's usually other component limiting factors
>>> that occur first - electrolytic and film capacitors, insulation system
>>> ratings and surface touch restrictions.
>>> 
>>> Performance is measured with these specified limits in mind.
>>> 
>>> or not.
>>
>>Yes, but is it (measured)?  Or, actively designed with as a target?
>>
>>Or, do you just use rules of thumb knowing that the typical *operating*
>>environment is likely to be X and chose components specified for Y > X
>>(but not necessarily Y >> X)?
>>
>>Note this iPhone claims a max operating of 93F and storage of 113F.
>>It is now 108F outside -- does that mean I can't use it outdoors?
>>And, when the temperature climbs to 115, I'll have to set it in an
>>ice bath?  (I'm being facetious, of course).
>>
>>I suspect there isn't a place in the lower 48 that doesn't
>>see ambient temperatures above 93F at least part of the year.
>>
>>And, Apple isn't a garage shop with few design/test resources at
>>its disposal.
>>
>>So, clearly there is margin in these specifications.  Whether it
>>is intended -- and to what extent -- is my point.
>>
>>When designing for industrial/commercial applications, we were always
>>extremely careful to *ensure* our products would operate in the temperature
>>ranges (and other environmental factors) that we specified.  A fisherman
>>out on the North Atlantic would be miffed if his kit stopped working
>>because it was too cold or too hot (or, too much salt spray).  A craftsman
>>would be annoyed if the tip of his screwdriver sheared off from "excessive"
>>torque.
>>
>>Similarly, a factory floor can't shut down because it's an unusually
>>warm day in the shop...
>>
>>Consumer kit *seems* to have a far more cavalier attitude towards
>>these things.  And, one that doesn't really hold up to close inspection
>>(e.g., the iPhone).
>>
>>
>The guidelines are derived from empirical data and accelerating 
>factors are determined. The arrhenius equation comes to mind.
>
>Predictors determine the design guidelines, but, yes, varying 
>degrees of physical testing is a standard element in design and 
>product verification.
>
>Commercial considerations of free enterprise have always pushed 
>human behaviour towards banditry, so what can I tell you?
>
>RL

That's entirely wrong. Whether you make spears or helicopters, you
need repeat business.

Communist thugs are the genocidal bandits. They have a captive market
and no competition.