optocoupled output circuit

Discussion in 'The Projects Forum' started by www111, Apr 14, 2016.

  1. www111

    Thread Starter New Member

    Apr 19, 2013
    Dear All,

    I came across this schematic for opto-coupled output: Attachment

    We have FPGA out 1.8V and resistor 100Ohm to regulate the current for diode from MOCD207-M.

    I'm not sure how the other side works.

    1. How works this circuit?
    2. What is the purpose of the diode CDSU4148-HF?
    3. What will happen if we put a series resistor with the diode?
    4. What will happen if we remove the diode?
    5. Does some one have experience with opto-coupled darlington output and can the darlington substitute the proposed circuit?

    Best Regards.
  2. #12


    Nov 30, 2010
    It looks like a high frequency switcher.
    To keep the transistor from saturating, which slows it down.
    It won't work as well.
    The transistor will saturate and slow down.
    I have included a datasheet for a photodarlington.