About optical coupler

Discussion in 'The Projects Forum' started by alexchan1986, Dec 28, 2009.

  1. alexchan1986

    Thread Starter New Member

    Nov 4, 2009
    2
    0
    hi everybody!
    I would like to ask one thing:

    I am using an optical coupler(6N137) for isolation in my project.
    At the input I provide a square wave signal with GND reference and at the ouput I want to have the same square wave but with reference ground of 24V.

    Here's my problem:
    I can get the square wave output when the output ground is connected to GND. However when the output ground is connected to 24V, the output signal become constant 24V but not a square wave.

    I want to ask the reason of this and how to solve it.

    Thank you very much!

    datasheet of 6N137
    http://www.fairchildsemi.com/ds/6N/6N137.pdf
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You need to provide an accurate schematic of your circuit.

    Otherwise, we might go on for many pages and never resolve your problem.
     
  3. alexchan1986

    Thread Starter New Member

    Nov 4, 2009
    2
    0
  4. zhgart

    New Member

    Dec 28, 2009
    19
    1
    137 is a high speed optic coupler, I wonder why connect to power? if you do so, of cause no output.
     
  5. zhgart

    New Member

    Dec 28, 2009
    19
    1
    I can't access to your reference web site.

    I'm in China.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,179
    1,800
    The output of the 6N137 opto-coupler is an NPN transistor stage. The output can be hooked up in the common-emitter inverting configuration or the common-collector (emitter follower) non-inverting configuration.

    Either way involves a load resistor. If you want to use the common emitter configuration with the emitter at +24VDC then the collector must be connected to a load resistor with the other end at a HIGHER voltage than +24VDC.

    Lastly if the emitter is at +24VDC and the collector through a load resistor is at +24VDC what do you suppose the collector of the opto will do except sit at -- you guessed it -- +24VDC

    Taaa Daaahh!
     
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