How do I calculate LC circuit time-constant?

Discussion in 'General Electronics Chat' started by Rajan_1993, Sep 13, 2017.

  1. Rajan_1993

    Thread Starter New Member

    Dec 24, 2014
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    Is that correct thing to say that LC circuit also has time-constant as RC circuit and if so how do I find the time constant for LC circuit? If possible can anybody explain by some sort of example. I would really appreciate that. Please guide me on this.
     
  2. OBW0549

    Well-Known Member

    Mar 2, 2015
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    No.

    An LC circuit (either series or parallel) has a resonant frequency, equal to f = 1/(2⋅π⋅√(LC)), where f is in Hz, L is in Henries, and C is in Farads.
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  4. crutschow

    Expert

    Mar 14, 2008
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    But an LR circuit does have a time-constant equal to L/R.
     
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  5. DickCappels

    Moderator

    Aug 21, 2008
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    Are you interested in the risetime of a high or low pass filter?

    Edit: Can you draw a picture to illustrate your question?
     
    Last edited: Sep 14, 2017
  6. MrAl

    Distinguished Member

    Jun 17, 2014
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    Hi,

    The time constant in a series RC circuit is R*C.
    The time constant in a series RL circuit is L/R.
    So they are a little different, but represent the time it takes to change by A*(1-e^(-1)) which is about 0.632 times the maximum change. So for a circuit that changes by 2 from start time to some long time period, for one time constant we'd see a change of about 1.264 in whatever units.
    Often approximated to 63 percent of max.
    Also often approximated to be a straight line rather then the slight curve it really has.
     
  7. Lyonspride

    Member

    Jan 6, 2014
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    Don't forget that the capacitors ESR plays a part too. This is where theory can get screwed over by reality, as theory tends to assume perfect component properties.
     
  8. Rajan_1993

    Thread Starter New Member

    Dec 24, 2014
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    We have designed a schematic and we are trying to determine an impedance of the circuit. That circuit contains some switches and R, L, C and an MCU.
     
  9. MrAl

    Distinguished Member

    Jun 17, 2014
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    Hi,

    Great, let's celebrate :)

    Now how about showing the circuit so we can calculate the impedance.
     
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