Choosing parts for SCR Dimmer?

Discussion in 'Homework Help' started by Zeppelin1007, Nov 13, 2012.

  1. Zeppelin1007

    Thread Starter New Member

    Mar 6, 2012
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    hey guys. SO i've been given the assignment of designing and building a dimmer for a 40watt 120v bulb using 2 SCRs. A triac would be nice, but no, must be SCRs.

    So i made the triac equivilant lol.

    Now in multisim, stuff works using the "virtual" parts. However, i can only get an output voltage on the meter of 0-65V

    So when i try to substitute in real parts in Multisim, i get about 20 minutes of convergence errors, followed by a circuit that sits at 66V across the light bulb and responds to no control. My guess is, i've picked the wrong parts, OR, i've wired something wrong. Can someone point me in the right direction?

    Ive found by varying the 2 capacitor values i can set my "start" voltage essentially. The bulb says 100W, but, i can't change it. Should be 40W. My sine wave phase shifts nicely.

    Thanks in advance guys.
     
  2. panic mode

    Senior Member

    Oct 10, 2011
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  3. Zeppelin1007

    Thread Starter New Member

    Mar 6, 2012
    10
    0
    Panic mode, no, i dont beleive there is no reason i cant use a bridge. Thanks for the resources! Ive got simulations to do.
     
  4. Zeppelin1007

    Thread Starter New Member

    Mar 6, 2012
    10
    0
    Panic Mode,
    I have simulated the given circuits and boy are the output wave forms messy! If i simply sub in a triac, life is well.

    Are these supposed to be full range? Ie 0-Full 120v?

    Im at the point to stop asking questions and start building and playing to see what happens.

    Thanks!
     
  5. panic mode

    Senior Member

    Oct 10, 2011
    1,320
    304
    it's just phase angle fired SCR. does not matter how delay is created as long as covers T/2. SCR works double duty here and runs each half-period rather than every other.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,984
    745
    Your circuit wont work , you cant connect both gates together, they have to be driven separately, as each thyristor will bias the other on, better with a triac.
     
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