Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail
NNTP-Posting-Date: Mon, 03 Jun 2024 16:03:10 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: Operating temperature derating
Date: Mon, 03 Jun 2024 09:03:10 -0700
Message-ID: <ucpr5j58g5bfpcjt19lu3iej7pfok6rm9g@4ax.com>
References: <v3kld4$3uec9$1@dont-email.me>
User-Agent: ForteAgent/8.00.32.1272
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Lines: 37
X-Trace: sv3-y2WRYTjXOeFK2kcd6sTNK7+So8snVzl1+ohTEg0fj373lKax6tZhTQ7+Q7m9GEYtDQ4WxZLMu2FZXUK!drPLSlCgK4mRUyKkwYfgcdZeu/EjTo/ja7oh9XzIm8fbAEjGp8Decu1U8Pr0gllM+0vC/01XxMSc!Cf9+Hg==
X-Complaints-To: www.supernews.com/docs/abuse.html
X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly
X-Postfilter: 1.3.40
Bytes: 2428

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?

I don't think that there are any standards that manufacturers use to
make datasheet abs max specs. 

I like to test parts to destruction and estimate what they can
actually do. For example, max voltage ratings can sometimes be safely
exceeded, or a surface-mount resistor can dump a lot of power if it's
well heat sunk with copper pours.

Thermal imaging can quantify hot-spot temperatures.

Pushing parts past specs is only a good idea if there is a serious
performance upside.

RF parts are especially likely to be under-rated. Like a 2 volt rated
schottly detector diode that starts to leak at 7. Or RF amp parts that
actually run at 2x rated max voltage in normal use.

GaN fets are interesting. As are mosfets that avalanche at some
unspecified voltage.

A bit of air flow can really change things. I assume that most specs
are based on still air.

I've seen a few parts that were unreliable within their abs max specs
and needed to be derated from there.

Blow up some parts. It's fun.