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 02:16:23 +0000
From: boB <boB@K7IQ.com>
Newsgroups: sci.electronics.design
Subject: Re: Optocoupler datasheets
Date: Wed, 29 May 2024 19:16:22 -0700
Message-ID: <g8of5j1vu7m597g7pb7c7de3131e2q1eoa@4ax.com>
References: <66574685$0$2363143$882e4bbb@reader.netnews.com> <v3857p$1a3te$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: 35
X-Trace: sv3-TWHxMZnaMOy3FvvEQdLaVnGu4dq27RiA9Z8TVdVDm2MO4rcFuKwAKLjWMpylMlR2tExtkZwp+5Amati!NItcSaln1lxyT8o1Pud45fHEbMgOEomuSljSIbkhKZ3VFxxpwgnYC7Z+P2AhM9IjP0Ac2IibZc2U!aqSBBL92
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: 2525

On Wed, 29 May 2024 22:03:51 +0100, Clive Arthur
<clive@nowaytoday.co.uk> 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