Problems getting CNY17-2 Optoisolator to work

Discussion in 'The Projects Forum' started by ak360, Oct 27, 2009.

  1. ak360

    Thread Starter Member

    Jan 18, 2009
    Hi guys,

    I am trying to use this CNY17-2 Opto Isolator. I need to be switching about 150mA on the "Output" side. Problem is, whenever I get anywhere near 100mA, the CNY17-2 becomes EXTREMELY hot and i hear a little sizzling inside of it and it fries. Are there any better, more durable opto isolators? Would using a BJT work just as well when it comes to isolating circuits?
  2. SgtWookie


    Jul 17, 2007
    Optoisolators are great for isolating circuits from each other.
    However, they're pretty limited in their current handling capabilities. 10mA is generally about the limit, unless you like to release the magic smoke as you've been doing. :eek:

    You can use a transistor to increase the current, like this:


    V1 is just a signal generator that outputs a 1kHz square wave, 5v p-p.
    R1 limits the current through the emitter to around 5mA.
    R2 limits the base current of Q1 to around 5mA.
    R3 helps to turn Q1 off when U1's output turns off.