what circuit is it?

Discussion in 'Homework Help' started by bug13, Aug 28, 2012.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    as seen in picture, what sort of circuit is it? does it have a name? what should I google for to find out more about it? and how do I do the calculation etc..

    this circuit is use to sense the voltage of a AC source, that all I know

    [​IMG]
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The intent is probably creating a DC offset AC signal. Looks very unsafe to me.
     
  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    How's that work?

     
  4. t_n_k

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    See the attachment - but don't try to build it as a real circuit. You could be electrocuted if something goes wrong or you make an error.
     
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  5. Jony130

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    Feb 17, 2009
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    The large capacitor you can treat as a voltage source as long as R*C (capacitor time constant) >> 1/f_ac_signal.
    So in your digram capacitor is charge to
    Vc = Vdd * R4/(R3+R4). So simply replace capacitor with Vc voltage source.
     
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  6. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    which resistor/s do I use to calculate the time constant?

     
  7. Jony130

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    Well I think that the time constant is equal to resistance seen from the capacitor terminal. t = R * C ---->R = R3||R4 + R1||R2
     
  8. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    ok, this confused me more, I simply don't understand why R3||R4 and R1||R2, if || here means parallel.

     
  9. Jony130

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    Simply you must find a equal resistance seeing from the capacitor terminal when the other remaining voltage source replace with a short-circuit.
     
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