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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Sat, 8 Jun 2024 04:17:40 -0700
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On 6/7/2024 9:25 PM, legg wrote:
>> [Given that using ANYTHING beyond its operating limits leaves you
>> without a leg to stand on, it would be nice to have some idea as to
>> what a reasonable expectation for those limits might be, despite
>> the "fluff" on the spec sheet.  E.g., I would be really pressing my
>> luck to use something at 80C in that most components would likely
>> not be specified at those extremes.  But, 55C for a 50C-specified
>> device?  60C?]
> 
> Given that you expect to get what's promised when you pay for it,
> outside of banditry, I only expect performance and a reasonable
> service life.

But performance is only formally defined within the "operating conditions".
And, many bits of consumer kit don't even specify these!

> I often kick mysellf in the head when I realize that shortcomings
> in product performance were actually predicted in the written
> specification - that the performance that I was expecting was not
> only outside published spec, but might not be physically
> possible, using current materials and techniques.

Would you expect a cell phone to operate in the same nominal environments
that a human being would encounter in their normal living?  If it FAILED
to operate "above 93F" (which is likely most of the lower 48, at some
portion of the day, lately), you'd likely be looking for another device
as you would always have to be in an air conditioned environment to make
that guarantee.

[And, if *storage* above 113 was contraindicated, how many could leave
it in an unattended/garaged car?  You KNOW that you can't store *ice*
above 0C and, thus, don't!]

So, what value writing those limits on the formal product specification?
Obviously (as we haven't seen class-action lawsuits from folks claiming
their thousand dollar phones don't work in the Summer months) the devices
work beyond their stated operational limits.

Is the limit published solely to give the manufacturer a legal "out"
if large numbers of units suddenly DO start failing?  While that may avoid
a lawsuit, today, how likely would it be to endear future purchasers to
a product if such a constraint became well-known?

Said another way, why not just *say* "25C" and hope customers are just
as oblivious of the actual declaration?

*Or*, say 42.1C after a careful analysis of the design and its actual
operating temperature limits?

[I just don't see value in these numbers as they stand, currently]