How to use a general purpose optocoupler.

[windell747]

Aloha,

I would like to use an simple optocoupler to pull a pin to ground on a stepper motor driver. I have little electronics experience and I heard that there might be a need for pull up or pull down resistors when using an optocoupler.

Question 1:
I'm looking for simple typical application shematics for a general purpose optocoupler. Maybe a 4N25 or 4N28. Do any of your know of any on the web?

Question 2:
I was reviewing the data sheet for the 4N25 and 4N28 optocouplers and I can't seem to find the max current rating for the collector to emitter of the optocoupler. How do I find this out?

Mahalo Nui Loa

 

[itsmoked]

Really you should look on the web yourself...

I had the data sheet on the first returned link for 4n25.
About 4 seconds.

This took me about 3 minutes.

http://www.web-ee.com/primers/files/opto-couplers.pdf

Do you need a pull up or down? It depends totally on your circuit. If the stepper motor driver has an internal pullup then no you won't need more. Essentially the transistor in an opto will either conduct or not depending on the current thru the LED. Just remember optos are purely current devices.... current thru LED side, controls current thru transistor side.

You multiply the current thru the LED by the MINIMUM CURRENT TRANSFER RATIO. (CTR) For the transistor current.

This is true up to the max you can run thru the LED.

Just remember nothing comes free.. The higher the CTR the S L O W E R the transistor will respond to the LED..