Re: Optocoupler datasheets

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