Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Don Y Newsgroups: sci.electronics.design Subject: Re: Operating temperature derating Date: Thu, 6 Jun 2024 14:01:04 -0700 Organization: A noiseless patient Spider Lines: 63 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Thu, 06 Jun 2024 23:01:38 +0200 (CEST) Injection-Info: dont-email.me; posting-host="7be623c0363dffc6819743a805623c50"; logging-data="1763208"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19YLmzk6i4G2bz8D3nfV5Dh" User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Cancel-Lock: sha1:C1NV9E2JiB4/65dittOljSxJLGI= In-Reply-To: Content-Language: en-US Bytes: 3719 On 6/6/2024 10:45 AM, legg wrote: > On Mon, 3 Jun 2024 07:52:58 -0700, 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? > > 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).