Hi. Why does this sort of octocoupler modules have 3 kOhm resistor in series with output? Like, foolproofing in case of a user wires the output in series with the load which draws more than 50 mA?
I'd think it's the input side.
Please give a link to the data sheet.
yes, seems so, probably too many customers destroying optoisolator and want money back
No, it's the output.
I don't have a datasheet, unfortunately.
It's not a matter of fortune. Crossing your fingers or knocking on wood or other woodoo is not a replacement for a data sheet before a buy.
I didn't buy it, actually. Nor am I going to buy it. I'm just looking into how other folks use optocouplers.
It's also possible the wrong value resistor was substituted - it's possible this was supposed to be an inline current limiter, maybe a few hundred ohms, but... China.
No one will ever know, unless you find the original design in a drawing somewhere. If it's a scavenged piece of electronics(maybe, thrown out because it was realized that an assembly error had happened?), just chalk it up to "Huh?" and move on.
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Circuit designed by ChatGPT?
You can see also a jumper - I think you can by-pass the resistor, if you sure that your schematic don;t need it
No, this jumper allows you to (dis)connect grounds of the interfacing circuits.
Board information
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Yes, I have found a schematic already:
A very weird connections...
The review of the module and discussion about it, including the purpose of 3k resistor:
Looks like
We already have the solution,
now let's find a matching problem!
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Very conclusive, thanks a lot. I thought that maybe output of this module was designed to be placed between base/gate and VCC, but it looked a bit narrow purpose. Now I see that I'm not alone.
My wish was to find out whether the module is weird or I'm missing something, and now I'm fully satisfied.
My vote. If one fell into my lap, and I was in a hurry to put an isolator into a project, I might consider changing resistances appropriately, otherwise, into the round can it goes.
If really wished to use one of these, I would:
- solder a bridge/jumper in place of or around the output resistor (limiting the output current is my job, but it's about the outer circuit, not the module).
- lower input resistance to 220 Ohms;
- (optionally) add an extra resistor in series to input, then cut traces and rewire conductors so that indicator LED and original series resistor would end up being in parallel to the (optocouple's input + new resistor).
If one fell in my lap I would strip it for parts and roll my own.
And yes, the gate resistor is incorrectly placed in this video.
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