LPH and HPF

Discussion in 'Homework Help' started by omerysmi, May 23, 2015.

  1. omerysmi

    Thread Starter Member

    Oct 10, 2014
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    0
    Hi, I have a question about LPF and HPF in RC circuit.
    I know that in LPF when τ>>t the capacitor is close to be a short.
    but what happens in HPF when τ>>t ? that capacitor is close to be a short also?

    Thanks for your help!
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,664
    634
    After T seconds very little current would be flowing through the capacitor, so it could be generalized as being open circuit.
     
  3. omerysmi

    Thread Starter Member

    Oct 10, 2014
    44
    0
    But in HPF when τ>>t the output signal is very similar to the input signal so it means that the capacitor is short and the input voltage pass to the output no?
    I talks about this circuit:
    [​IMG]
     
  4. MrAl

    Well-Known Member

    Jun 17, 2014
    2,440
    492
    Hi,

    In the HPF, for very short times the output equals the input so the cap looks more like a short.
    For very long times the output goes to zero so the cap looks like an open.

    Looking at it from a frequency perspective, for high frequencies the cap looks like a short, and for low frequencies the cap looks open.

    Since time is the inverse of frequency:
    T=1/f

    high frequency is similar to a short time period, where the period is relative to the RC time constant tau.
     
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