4N25 OPTOISOLATOR, NPN TRANSISTOR OUTPUT

Datasheet

The Vashay data sheet for this part is at:
http://www.vishay.com/docs/83725/4n25.pdf
This is also the datasheet for the 4N26 and 4N27, the differences are the 4N25 has a guaranteed isolation test voltage of 2500V, while the 4N26 and 4N27 are 1500V. The 4N27 is potentially faster than the 4N25 and 4N26, although the CTR for opto-isolators are notoriously variable, even from part to part from the same manufacturer, and even more between manufacturers. The CTR is is defined as a minimum and a typical value, with no maximum value.