Electronics > Beginners

Opto-coupler led driver protection circuit

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I think I get it now, am i right (see option G attached)? Thanks!

Yep, that's for encoders, you are right, a simple resistance will to the job, also the SN75ALS175 would be the perfect candidate for this... BUT, this could also works with some "custom" made +24V output from a board of my company. That's why I'm trying to be a "generic" input.

~ edited image after the post, D16 is now 1n4148 ~

Just throwing it out here, it may or may not be part of solution for your particular problem, but you also have bi-directional optocouplers.

Thanks @Ice-Tea for the proposal, I'll think about that.

For now I would like to test the "option G", I suppose it's right, but I'm waiting for @Kleinstein (or other expert) check :)

You write you are using old fashioned LS TTL.
Those LS TTL IC's are not very good for sourcing voltage and current (Drive voltage can be as low as 3.5V or so when "high").
Those LS TTL IC's are however quite good at sinking current to GND.

I've tested the "Option G" circuit on bench.
Led is working from almost 2V to 30V (my bench supply max is 30V).
Tested with reverse polarity no reverse current flow through the led and led driver, so it's ok.


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