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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Tue, 4 Jun 2024 06:22:15 -0700
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On 6/3/2024 7:52 AM, Don Y 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?

Well, a quick canvas of colleagues suggests derating isn't
even a consideration!  Rather, that the operating environment
is used to drive the design, with no real effort to quantify
actual device operating limits:
   "We know the characteristics of the components that we
    use and the general characteristics of the enclosure
    to convince ourselves that we can meet the expected
    operating temperature range"

And, what exactly *is* that range?
    "<mumble>"

Amusingly, for consumer devices, you rarely even see these
limits published.  Or, KNOW that they are bogus;
- TVs claiming 5-35C
- cordless phones 25C +- 10
- HiFi kit with NO environmental constraints
- laptops?
- cell phones (95F with storage to 113 means "not here"!)

So, all of the TVs mounted (here) in garages or on back porches
have been inoperable once the outdoor temperature exceeded 100F?

And, don't dare walk outdoors with your cordless phone or $1000
cell phone lest it stop working mid call!

HiFi?  Will it quit at 76F? or 62F?

It's amusing that folks don't seem to know the constraints of
the devices they are producing!