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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Sun, 09 Jun 2024 01:36:43 -0400
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On Sat, 08 Jun 2024 07:40:50 -0700, john larkin <jl@650pot.com> wrote:

>On Sat, 08 Jun 2024 00:29:20 -0400, legg <legg@nospam.magma.ca> wrote:
>
>>On Fri, 07 Jun 2024 15:19:50 -0700, john larkin <jl@650pot.com> wrote:
>>
>>>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.
>>
>>Tell it to the bandits. There are plenty of suckers out there and 
>>paper/internet bumph easily generated to suit them.
>
>You can buy Sony or cheap no-name Chinese junk. Your choice. Would you
>prefer to not have a choice?
>
>>>
>>>Communist thugs are the genocidal bandits. They have a captive market
>>>and no competition.
>>
>>Compared to the large-scale kleptocracies that replaced them? . . . 
>
>The US and Europe have antitrust laws that pretty well ensure multiple
>suppliers and competition. The real kleptocracy, in the USA or in
>Russia or in China, is the government.

In the US, the govt ensures that wall street is not inconvenienced.
Assets are stripped to pay dividends, labor juggled for a similar 
benefit. Industry in north america is just not delivering.
>
>If you don 't want to buy a car from Honda, GM, Ford, Toyota, Kia,
>Tesla, VW, or BMW, walk in the rain and snow like most of your
>ancestors did. Few of our ancestors could afford a horse.

You're forgetting BYD, Brilliance, Chery, Changfeng, Geely, Great Wall
or any of the european-name-brand subsidiaries in India.

I've only ever paid for one car - had to pay for the telephone pole it
was totalled against, as well (it was that long ago). 

Anyways - a bit of a non-sequitur , neh?

RL