1. Dhananjay Katavate

    Thread Starter New Member

    Jun 22, 2016
    1
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    Why the DAC is not used to drive the optocoupler .
    My application is to dimming of AC load using Optocoupler.
     
  2. Picbuster

    Member

    Dec 2, 2013
    376
    50
    study the opto performance versus dc input.
    After this study you know why.
     
  3. dannyf

    Well-Known Member

    Sep 13, 2015
    1,826
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    Why do you think DACs are not used to drive optocouplers?
     
  4. dk007

    New Member

    Jun 22, 2016
    6
    0
    I saw that many of peoples uses pwm to control the optocoupler driving
     
  5. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    You have phase shift a AC load pwm will not give a even dimming of power.
     
  6. grahamed

    Member

    Jul 23, 2012
    99
    11
    Why not?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    See Fairchild app note AN-3006.
    Max.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    The IRLED in the opto isn't linear - a couple of the big name manufacturers have published appnotes for linear opto drive.

    Basically; your signal source would drive two opto IRLEDs in series - the transistor in one of them is included in a nfb loop on the IRLED drive circuit, while the other opto transistor drives your target load.

    I'm guessing the AC load means you're using an opto triac, that's probably a bit more tricky but it should be possible to work out some sort of compromise.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,564
    2,379
    For AC load the Fairchild app shows both phase angle switching and zero cross switching via opto triac driver.
    Max.
     
  10. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    If read the appnotes to pwm the Phototriac you have to get timing right which is what I found 6 years ago when I tried pwm to dim lights that was on 120 AC if you got the pwm right you could dim the lights some what but it was never as good as Zero–Crossing

     
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