Simple open collector circuit

Thread Starter

MBG

Joined Jan 30, 2022
23
I've always wanted to know if something as simple as this circuit has any issues. I forgot to show that on the opto side that it's 5 volts. I've done it many times and it works flawlessly and there are many devices that interface with other equipment (my drawing is 2 pieces of devices) that use an open collector output instead of a relay. I guess if the diode shorted that would be a problem but I can't see how it could. -- anyway, thanks.
 

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sghioto

Joined Dec 31, 2017
3,315
I don't see any isolation with the common grounds. Is that your intent?
Below is a version of isolating the 12 volt from the 5 volt supply using an opto.
1645386549275.png
 
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Thread Starter

MBG

Joined Jan 30, 2022
23
I don't see any isolation with the common grounds. Is that your intent?
Below is a version of isolating the 12 volt from the 5 volt supply using an opto.
View attachment 261161
well, the circuit to the left is built in to a lot of equipment that I want to connect to. my interface is on the right.
I have no control over the (typical) open collector circuit on the left. yes, concerned about common ground but it happens all the time and just always wondered about "issues".
maybe only problems if there are ground loops from more than one contact to ground?
 

AnalogKid

Joined Aug 1, 2013
10,098
That's where I was headed. If the emitter of the driver transistor on the left, and the emitter of the optocoupler output transistor on the right are connected together by chassis grounds / cable shields / whatever, then you do not need the opto.

To answer your question, no, no issues. If it works for you, fine. But with the information we have so far, there is no apparent need for the optoisolator at all.

ak
 

Thread Starter

MBG

Joined Jan 30, 2022
23
That's where I was headed. If the emitter of the driver transistor on the left, and the emitter of the optocoupler output transistor on the right are connected together by chassis grounds / cable shields / whatever, then you do not need the opto.

To answer your question, no, no issues. If it works for you, fine. But with the information we have so far, there is no apparent need for the optoisolator at all.

ak
Yes. Ok.
Just using the opto for added isolation and just have always been in the habit of using them for 2 pieces of equipment connected together. Not a product -- just hobbyist stuff I do. And often times my cable lengths can be quite long also.
Anyway, nice to know.
 
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