ltspice, average power, again

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

  1. bug13

    Thread Starter Senior 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 Senior 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 Senior 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 Senior 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 Senior Member

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