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Capacitor circuit and current flow

Discussion in 'General Electronics Chat' started by nicksydney, Feb 20, 2012.

  1. ljcox

    ljcox Well-Known Member

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    You're welcome.

    I just noticed that my post was badly worded.

    I should read:-

    I have simulated 2 situations where an inductance of 1H has a resistance of 10 Ohm with a 10 Ohm resistor acrsoos it in Case 1 & 20 Ohm in Case 2.
     
  2. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again,

    Len:
    Thanks for the schematic upload. I was able to repeat your simulations with that.
    I wasnt saying that it was bad to show the true back emf, i think it was a good idea. I even mentioned back in this thread that there will always be some back emf whether it bothers the circuit or not :)

    I attached a simulation run of the 'theoretical' cap and resistor and inductor and also another run of the 'actual' circuit WITHOUT the clamp diode. In both runs the cap voltage is clearly shown to be going negative. The inductance value used was 50mH. As mentioned previously, with inductance values less than 50mH the undershoot will be less, and with inductance values over 50mH it will be more (in other words the undershoot is highly dependent on the inductance value when not using a clamp diode).
     
    Last edited: Feb 27, 2012
  3. ljcox

    ljcox Well-Known Member

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    Thanks Mr Al,
    Yes, the traces show good agreement up to the point where the diode conducts in the lower one.

    Incidentally, how did you produce the traces?

    Is this a function of LTSPICE that I don't know about?

    Or did you use another method?
     
  4. dave

    Dave New Member

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  5. ljcox

    ljcox Well-Known Member

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    Inspired by Mr Al's traces & after my previous post, I looked at the LTSPICE options & found a better way to reproduce the traces.

    In Tools, there is a "Write to a .wmf file" option.

    I found that this file can be opened in Paint & thus modified & saved as a .gif, etc.

    So the attachment is a trace from our favourite circuit for L1 = 2H.
     
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Len,

    I hate to see what would happen with a 2H inductor and no clamp diode :)

    To copy the trace to the clipboard, go to the main menu bar "Tools", then "Copy bitmap to clipboard", making sure you have the the focus set to the output trace window (not the schematic window).
    To copy the schematic instead, have the schematic window in focus instead and not the output trace window.
    You can then paste it into something like Paint and make the canvas larger then paste another trace if you like, or the schematic, etc.
     
  7. ljcox

    ljcox Well-Known Member

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    Thanks Mr Al,
    I used clipboard as you described, but your traces look different & much better than mine.
    What am I missing?
     
  8. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hi Len,

    Oh sorry i thought you meant how to copy the traces, not how to improve the quality of the trace itself. So that's what you meant by "produce" :)

    Go to "Control Panel", then on the "Waveforms" tab, check "Plot data with thick lines".
     
  9. ljcox

    ljcox Well-Known Member

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    Thanks Mr Al,
    I did the sim for the 5 mH case as a test.

    I used the Tools\Write to a .wmf file option.

    Then opened it in Paint typed the annotations on it & saved as a .gif.

    This is an over damped case.
     
    Last edited: Feb 28, 2012
  10. alec_t

    alec_t Well-Known Member Most Helpful Member

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    No need to use Paint to add annotations. Just make the plot pane the active window, go to Plot Settings >> Notes & Annotations.
    You can then add text, arrows etc.
     
  11. ljcox

    ljcox Well-Known Member

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    Thanks alec_t, I tried that and then saved the result as a .wmf.

    It is better than doing the annotations in Paint.

    I find Paint is a bit tedious to use.
     

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