Triac RC Calculation

Discussion in 'Electronics Resources' started by gr13, Feb 20, 2012.

  1. gr13

    Thread Starter New Member

    Nov 16, 2009
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  2. gr13

    Thread Starter New Member

    Nov 16, 2009
    3
    0
    [​IMG]

    In this circuit, a series resistor-capacitor network creates a phase-shifted voltage for the "gate" terminal of a power-control device known as a TRIAC. All portions of the circuit except for the RC network are ßhaded" for de-emphasis:

    Calculate how many degrees of phase shift the capacitor's voltage is, compared to the total voltage across the series RC network, assuming a frequency of 60 Hz, and a 50% potentiometer setting.

    Answer :EC phase shift = -76.7 degree

    Please let me know involved steps; I am not from electronics - tried 1/2∏fC, but answer was something different than provided in hints!

    Thanks
     
  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    gr13 likes this.
  4. gr13

    Thread Starter New Member

    Nov 16, 2009
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    Thanks :)
    should we simply put a negative sign for capacitive reactance?

    Just one more clarification please!

    books simply say that it's 90 degree phase shift - is that statement wrongly interpreted by most of us? Or it's only me who is confused :(
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Yes we should.

    Yes you are right the books say 90 degree phase for capacitor alone.
    So we have 90° phase shift between capacitor current and capacitor voltage. The capacitor current leads the voltage in capacitor.
    http://forum.allaboutcircuits.com/showthread.php?p=407090#post407090
    But in this Triac circuit we're talking about phase shift between input voltage and voltage across the capacitor.
    http://forum.allaboutcircuits.com/showpost.php?p=312218&postcount=7
     
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