ltspice, average power, again

Discussion in 'General Electronics Chat' started by bug13, Jun 24, 2014.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    [​IMG]

    Hi guys,

    I want to get the average power of a capacitor (C1) in this circuit, but I got positive and negative power here by Ctrl + Left Click.

    Is there a way to get absolute power like this?

    my circuit is attached.
     
    • zvs.asc
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  2. Billy4184

    Member

    Jun 20, 2014
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    Do you mean you want the cumulative total (integral)?
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    I was used the version 4.20j, but i can't open the file directly, when i running the LTspice IV, and open the file zvs.asc, it was lost two mosfets on the circuit.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That's what your pop-up box is showing! It reads 2.3049W.
     
  5. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    I am not sure what I want is the same thing you suggested. Let me try to explain it here: in my graph, image all the negative power is flipped over to positive along the zero line, and I want the average power of that(after negative power is flipped to positive)

    Edit:

    Assuming all power is positive, so I want the true power dissipation of the cap (c1), am I right here?
     
    Last edited: Jun 24, 2014
  6. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    I think my MOSFET is a third party lib, but what MOSFETs are used here is not important, you can add two compatible one and it should work.
     
  7. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    I think power is positive only? I just assume the negative power shows in my graph is for mathematics reason?

    I am sure the cap (c1) consume more power than 2.3W? Because the circuit I built blow up the cap (c1), due to over heat. And I am using a very BIG (size of a thumb) thin film cap.

    Or is there something i don't know?
     
    Last edited: Jun 24, 2014
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The polarity reflects whether the cap is a source or a sink for the power.
    Did you set the Equivalent Series Resistor (ESR) property of the cap model to a non-zero value? In a real cap it is the ESR which dissipates power and can cause over-heating.
     
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  9. crutschow

    Expert

    Mar 14, 2008
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    An ideal capacitor dissipates zero real power. If you don't have a series resistance in the capacitor model then the power you are seeing appears to be round-off error in the LTspice calculations. If you reduce the Maximum Timestep in the Transient Simulation Command to say 10ns (which increases the simulation time) you should see a reduction in the calculated Average Power.
     
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  10. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    Thanks again Alec_t and crustchow, now I understand, thanks a lot!
     
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