Path: ...!local-2.nntp.ord.giganews.com!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 13:40:36 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: Optocoupler datasheets Date: Thu, 30 May 2024 06:40:36 -0700 Message-ID: <5c0h5j1925j8k9mipp7ph3pdqhijfep9ae@4ax.com> References: <66574685$0$2363143$882e4bbb@reader.netnews.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 51 X-Trace: sv3-78MlZHP0+zM1phZGeWOu9bOvuFUlJ8eDcRXyMcdbG3jK1YR32DAcwxQUNEf9KOMrj46vAJ7JJyKGKxb!BJqNcVPTZUO45Ti9Pfiv5/sZzSfzZkr6r3rMzWCp1Q/oEy3tzoY+cN0Wu9L21vjtYPSJs/WrbTUA!Nf8raQ== 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: 3134 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