OptoCouplers

Discussion in 'General Electronics Chat' started by crobertsbmw, Sep 7, 2011.

  1. crobertsbmw

    Thread Starter New Member

    Sep 7, 2011
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    So I have been trying to figure out how I can switch 220Vac on and off with a microcontroller. I learned that I need a triac or relay and then need to isolate it with an optocoupler. So I bought some parts off digikey and breadboarded this thing up. The odd thing is that I can't get the lightbulb (what I am currently using as the load) to turn off. No-matter the input on terminal two of the opto-coupler (right now I just have it running off of a external power suppply). I even tried disconnecting the gate of the triac (for a floating voltage) and the bulb was still on. Any ideas for how I can get this thing to switch on and off? I kind of wonder if these optocouplers even work.



    [​IMG]
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    It is possible that you have the A1 & A2 connections to the TRIAC reversed.

    See the following image for correct connection.

    [​IMG]
     
    Last edited: Sep 7, 2011
  3. crobertsbmw

    Thread Starter New Member

    Sep 7, 2011
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    I checked the leads of the triac, and they are correctly oriented. I may just have to buy a new pieces. Maybe somehow I ruined the three optocouplers and triac switches that I have.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    ??? 3 of them? If you disconnect the gate and it still conducts, then yes it may have burnt. However, I wonder how you did this with 3 of them? Are you sure there is nothing wrong with how you mounted the circuit?

    Btw, Rin is to big. It should be calculated for 5mA through the LED (for the 3063). It'll now give you a bit more than 3mA, but this has nothing to do with your problem.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Are you powering the load (light bulb) with DC or AC?
    Triacs and SCR's won't turn off until the current flowing through them drops below a certain value. If you're using a light bulb for a load and trying to switch DC power, that's the problem. If you would like to stay with DC power during testing, try using a brushed motor for a load. The brushes on the commutator will keep breaking the current flow every fraction of a rotation, allowing the thyristor to turn off.
     
  6. crobertsbmw

    Thread Starter New Member

    Sep 7, 2011
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    No, I am using AC power. I am pretty sure that I connected everything up correctly. I am going to go order some more optocouplers and triacs in case that I did screw something up. I will re-breadboard the circuit and see if I get the same results.. (cross your fingers)
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
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    Yes, agree.

    The "LED trigger current, max - Ift" parameter given in the data sheet is the value of current that the device will trigger reliably and is not the current that will destroy the device. Therefore, it is required to operate the LED current to EXCEED(or at least equal to) this current value. The operating range is somewhere between Ift & Imax, with the latter equals to 60mA, beyond which the device will be damaged.

    For the MOC3063M, Ift is given as 5mA max. so LED current of 5mA or more will do. I would choose a value of 7.5mA to have a bit of margin.

    To calculate Rin, subtracts the 1.3V forward voltage of the LED from the supply voltage and then use Ohm's law.

    Rin = (3.3-1.3)/7.5mA = 266.66Ω so one can use a 270Ω 1/4W resistor for Rin.
     
  8. crobertsbmw

    Thread Starter New Member

    Sep 7, 2011
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    I don't know how I did it but I must have blown three of these triacs. I got new parts, bread-boarded it up and now it works wonderfully.
     
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