time constant

Discussion in 'General Electronics Chat' started by gani, May 17, 2005.

  1. gani

    Thread Starter Active Member

    May 15, 2005
    46
    0
    hi
    oooooops! i posted my query in the wrong forum..
    sorry abt that.
    can some one help me?when lc is coontd across dc or ac there is energy transfer btn L and C,right?
    but this is only for the transient period.so how do we caluculate how long the transient period is?
    hoping to hear from u guys.Thanx!
     
  2. haditya

    Senior Member

    Jan 19, 2004
    220
    0
    when u caoonect a cap and inductor across dc the cap stores energy when given by .5*C*V^2
    and the inductor stores energy given by .5*L*i^2

    now while chargin V=Vo(1-e^(t/RC))
    and i=Vo(1-e^tRL)/R


    pluggin these values into the energy exp we get energy stored in the caps and inductors as a fn of time

    energy is continually stored in the reactive devices however a majority of it is done with a few time constants
     
  3. gani

    Thread Starter Active Member

    May 15, 2005
    46
    0

    thanx for the reply!
    yes i get that part abt the energy being stored in L and C.energy gets transferred btn l and C.but this is for only some period of time....the transient period.am i right?hmm... what i don get is how long is this transient period...?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Gani,

    Which case are you most interested in, under-damped, critically damped, or over-damped?

    hgmjr
     
  5. gani

    Thread Starter Active Member

    May 15, 2005
    46
    0
    THANX FOR THE REPLY HGMJR, IF U DON MIND....CUD U TELL ME ABT ALL. :)
    THANX!!!
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Gani,

    Take a look at this write-up and let me know if you have questions.

    You will see that I have described the general technique I used to get the decay time constant for the under-damped case (k<1).

    I thought I would give you a chance to work through the process for yourself before I go into greater detail. You should be able to find the time-domain expressions for all three cases in a textbook or on the Internet. With these expressions you can use the approach I have decribed to confirm my results for the decay time-constants for all three cases.

    Let me know if you need further assistance.

    hgmjr

    [attachmentid=648]
     
  7. gani

    Thread Starter Active Member

    May 15, 2005
    46
    0
    Thanx a lot for the help!!!
    Think i have got it okay!
    gani
     
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