Cutting out a triac

Discussion in 'General Electronics Chat' started by Iodem_Asakura, May 26, 2005.

  1. Iodem_Asakura

    Thread Starter Senior Member

    Sep 14, 2004
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    Does somebody know how to turn off the conduction of a triac without open the line and don't wait until the line current reach 0?

    I think it can not be done, but i don't lose anything asking. Maybe you supprise me!

    Thanks for your answers.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    There is one way that it can be done. Simply place a normally-open switch in parallel with the TRIAC. You can then close the switch which will starve the triac of current thus turming it off.

    Of course this assumes that the trigger condition is not present.

    hgmjr
     
  3. Iodem_Asakura

    Thread Starter Senior Member

    Sep 14, 2004
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    Well, if there is not another way, i think i'll figure out i can't do it.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    I take it you are looking for something that allows you to use an electronic control signal to reset the traic to the non-conducting state.

    What about using a power mosfet device in parallel with the triac. Then you could drive the gate to turn on the mosfet and starve the traic of current.

    hgmjr
     
  5. Iodem_Asakura

    Thread Starter Senior Member

    Sep 14, 2004
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    That will work, but only in one direction of the current, i think.
     
  6. hgmjr

    Moderator

    Jan 28, 2005
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    You are correct.

    The mosfet will only turn off the triac in one direction.

    As I recall, if the voltage that is being switched by the triac is AC then the triac automatically turns off as the AC voltage across it passes through the zero crossing.

    Isn't this true?

    hgmjr(200)
     
  7. Iodem_Asakura

    Thread Starter Senior Member

    Sep 14, 2004
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    That's right. And that is the problem, in some cases i would like to shut down the triac before the ac current passes through zero.
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    I see. Interesting challenge. I'm going to need to think about that one. I'll get back to you in the next day or so.
     
  9. Iodem_Asakura

    Thread Starter Senior Member

    Sep 14, 2004
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    I think it's really hard to do that (to not say impossible).
     
  10. hgmjr

    Moderator

    Jan 28, 2005
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    Hi Iodem_Asakura,

    After giving your triac cutoff problem a good deal of thought, I think your assessment of the difficulty of a solution is correct.

    If you do find a solution, I hope you will post it here so that others can benefit from your success.

    hgmjr
     
  11. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    it's like trying to figure out how to stop an F1 racer running at 300kph without skidding and turning turnturtle or burning tire rubber :p :D :lol:

    but those are the kind of thoughts that sometimes starts the ball rolling ;)

    moz
     
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