Need help understanding optoisolator

Discussion in 'The Projects Forum' started by Netwaves, Feb 12, 2015.

  1. Netwaves

    Thread Starter Member

    Feb 9, 2015
    I need help understanding how an optoisolator is seen by a circuit. The one I am working with is the NEC PS2501-4. My questions are:

    How can I calculate it's resistance and amperage?
    Will it been seen by my circuit as a resistor? So can I calculate it's resistance in series and parallel to other true resistors?
    I've tried to glean this information from the data sheet that is available but it's very confusing.

  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    The input side is a LED. It needs to be driven from a constant current at about 10mA. Just like as with a visible LED, in most cases, a resistor needs to be placed in series with the LED.

    The output side is a NPN transistor. It is used as a switch, usually with its emitter connected to 0V, and its collector pulled up to a positive voltage of a few Volts using a load resistor. Or it can we wired as an emitter-follower, with the load resistor between emitter and 0V.

    The Current Transfer Ratio is stated on the data sheet and is a minimum of 80%, meaning that 10mA into the LED makes 8mA at the collector of the NPN.

    Here is a lab demo of how to use an optoisolator.
    Netwaves likes this.