# 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!

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

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

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7. ### gani Thread Starter Active Member

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