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From: piglet <erichpwagner@hotmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Optocoupler datasheets
Date: Thu, 30 May 2024 08:55:19 +0100
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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