Capacitor Transient Response

Discussion in 'Programmer's Corner' started by silv3r.m00n, Apr 15, 2010.

  1. silv3r.m00n

    Thread Starter New Member

    Apr 15, 2010
    14
    0
    Hello

    This chapter >> http://www.allaboutcircuits.com/vol_1/chpt_16/2.html
    on Capacitor Transient Response has a spice program at the end as follows :

    capacitor charging
    v1 1 0 dc 15
    r1 1 2 10k
    c1 2 0 100u ic=0
    .tran .5 10 uic
    .plot tran v(2,0) v(1,2)
    .end

    When I run the program in spice i get the correct plot.
    I want to see the current also.
    so I added
    .plot tran v(2,0) v(1,2) i(v1)

    but the current graph is flat i.e. near zero values right from the beginning.

    Current is supposed to start from v/r and then slowly become zero. But I cant see that in the plot.

    Is my program wrong ?

    Please help
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Instead of i(v1), try i(r1) or i(c1).
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    Or try plotting the current only, it might only a problem in Y-axis scale of the V and I.
     
  4. silv3r.m00n

    Thread Starter New Member

    Apr 15, 2010
    14
    0
    i(r1) or i(c1) gives error : Error: no such vector r1#branch

    I guess current can only be measured across a voltage source in spice.
    To measure it across a particular resistance branch a false voltage source = 0V has to be added.

    Silver
     
  5. silv3r.m00n

    Thread Starter New Member

    Apr 15, 2010
    14
    0
    Worked.

    But the current is mirror image. It starts from -V/R and slowly moves to 0.

    I see this everywhere. Currents are always reversed.

    Code ( (Unknown Language)):
    1.  
    2. AC Source connected to a resistor
    3. v1 1 0 ac sin(0 100 60 0 0)
    4. rload 1 0 2
    5. .tran 1m 30m
    6. .plot tran v(1) i(v1)
    7. .end
    8.  
    The above simple program shows the plot of voltage and current. And they are out of phase by 180 degree. Why does this happen ? Is the program wrong somewhere. The current is supposed to be in phase with voltage.
     
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