Path: ...!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 30 May 2024 19:01:15 +0000 From: boB Newsgroups: sci.electronics.design Subject: Re: Optocoupler datasheets Date: Thu, 30 May 2024 12:01:15 -0700 Message-ID: References: <66574685$0$2363143$882e4bbb@reader.netnews.com> <5c0h5j1925j8k9mipp7ph3pdqhijfep9ae@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 61 X-Trace: sv3-DUHQ0A4BXCqWHKi8FA95LMwm5ZSQ90S2q1reTnqaU7VuqUQ1J0OZ3mvIIswSMucGy9Tsl43RHEof3mc!XUajkS1Bu/OwTWQ/E8GF0/8Eiq40DHUIe3Jwqk9mQIFsbIHclqBt01h9vwTcep9zZjdpb9qpapYy!uRWEZ8MJ 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: 3445 On Thu, 30 May 2024 06:40:36 -0700, john larkin wrote: >On Thu, 30 May 2024 08:55:19 +0100, piglet >wrote: > >>On 30/05/2024 03:16, boB wrote: >>> On Wed, 29 May 2024 22:03:51 +0100, Clive Arthur >>> wrote: >>> >>>> On 29/05/2024 16:15, bitrex wrote: >>>>> Optocoupler datasheets seem like kind of a mess, I try not to use them >>>>> too often in situations where there's any kind of power budget because >>>>> other than "shove some relatively huge current through the LED like 5-10 >>>>> mA" it's hard to know what you can get away with. >>>>> >>>>> A light load on the transistor side will definitely reduce the forward >>>>> current required (and of course slow the speed to a crawl) but who can >>>>> say by how much while still ensuring the thing will turn on sufficiently >>>>> to saturate the output? >>>>> >>>>> The CTR varies widely from process variation, varies with temperature, >>>>> varies with collector emitter voltage, varies with forward current, and >>>>> the data sheets are full of caveats like "At I_f < 1 mA, note CTR >>>>> variation may increase" and "Graphs are representative, not indicative >>>>> of actual performance." ???? >>>>> >>>>> Any suggestions for how to approach methodically/mathematically >>>>> selecting drive current would be appreciated, thank you! ("Don't bother" >>>>> a valid option) >>>> >>>> Not really answering the question, but there's more than one way to skin >>>> a cat... >>>> >>>> https://www.nve.com/Isolators >>> >>> >>> You can also turn the LED off a bit faster and reduce off-time >>> interference/noise by pulling the anode low, activiely. >>> Not sure how much better it is though. >>> >>> boB >> >> >>I thought IREDs and LEDs are very fast, far faster than the >>phototransistor but someone has done as you suggest, see: >> >> >> >>piglet > > >https://www.dropbox.com/scl/fi/himnbhrq97vj6eplokek5/Faster_Opto_Totem.JPG?rlkey=ste2tfj8v3zpi45wh1wepyaov&raw=1 Interesting approach, John. Piglet, the first comment says where I first saw this which was from Avago/HP and their IGBT driver chips. boB