I am really not sure how to use optoisolators, and I am trying to get an understanding on how to use them correctly. Which values on datasheets are the ones I am looking for on these to find the correct input current and forward voltage I'm looking for? How do I read the current transfer ratio graph when the lines are all different widths? What is the deal with current transfer ratios anyway; why does input current have any bearing on output side current?
I think I want to use a TLX9000, datasheet
here. I want to take a signal from a 13V source and output a logic level signal to a microcontroller.
I have been reading several things on the internet about calculating the resistors on the input and output side, but transferring that to what I see on datasheets isn't as obvious to me as I would like it to be.
The typical LED voltage drop on the datasheet is 1.25V, which I'm pretty certain on. On the other hand, I'm not sure what the current should be factored at. The recommended operating conditions say 10-15mA, the maximum says 30 mA, the electrical characteristics suggest at 1.25V it would be 10mA. Am I safe to assume 10mA, and use a 1.2K resistor on the input?
As for the output side, I'm pretty well lost. When I go to the graph on page 6, I'm not sure how to read the current transfer ratio, as the lines don't seem to be proportional to the position on the graph, so I don't know if each line is 100% or not. At 5Vce, is that appears to be somewhere around 375%, or am I reading it wrong? Beyond that, are we talking about 10mA in on the input side coming out as 37.5mA on the output side if I am correct? If so, would a 390Ohm resistor be appropriate on the output side?