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NNTP-Posting-Date: Thu, 30 May 2024 13:40:36 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: Optocoupler datasheets
Date: Thu, 30 May 2024 06:40:36 -0700
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On Thu, 30 May 2024 08:55:19 +0100, piglet <erichpwagner@hotmail.com>
wrote:

>On 30/05/2024 03:16, boB wrote:
>> 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
>
>
>I thought IREDs and LEDs are very fast, far faster than the 
>phototransistor but someone has done as you suggest, see:
>
><https://www.edn.com/optocoupler-speed-up-also-reduces-power-consumption/>
>
>piglet


https://www.dropbox.com/scl/fi/himnbhrq97vj6eplokek5/Faster_Opto_Totem.JPG?rlkey=ste2tfj8v3zpi45wh1wepyaov&raw=1