Connect with us

SPICE simulation of finite Q inductors

Discussion in 'Electronic Design' started by Joel Kolstad, Jul 18, 2006.

Scroll to continue with content
  1. Joel Kolstad

    Joel Kolstad Guest

    Those of you who simulate things like passive LC filters... when you want a
    simulation that includes the finite Q effect of the inductor, do you tend to
    use a model that computes the equivalent parallel resistance, Rloss, based on
    the Q specified on a data sheet at a given frequency (and then use that at
    *all* frequencies of your simulation, effectively creating Q(freq) )? Or do
    you simply specify Q and then use that at all frequencies (creating
    Rloss(freq) )?

    For the following, assume you first calculated Rloss at a frequency f0:

    The actual Q of an inductor varies with sqrt(freq) until you start approaching
    self-resonance, so assuming Q is fixed, you underestimate Q above f0 and
    overestimate below f0. Using just Rloss, you overestimate below f0 and
    underestimate above f0.

    ---Joel
     
  2. Mark

    Mark Guest

    In most cases, the Q is important only near the resonant frequency. I
    use a single fixed value resistor in series with the L that sets the Q
    at the frequency corresponding to the circuit resonance frequency.

    Mark
     
  3. Jim Thompson

    Jim Thompson Guest

    In critical applications I'm inclined to use a multi-lump model to
    make sure I catch any "squirrels" ;-)

    ...Jim Thompson
     

  4. Too bad you can't make that work on Usenet. We're overrun with
    squirrels. :(


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  5. Jim Thompson

    Jim Thompson Guest

    I've suddenly acquired jack rabbits in my front yard. Can't figure
    out where they're nesting.

    ...Jim Thompson
     

  6. Be VERY careful, Jim. Eeyore sent them to spy on you!


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  7. Jim Thompson

    Jim Thompson Guest

    THAT explains it ;-)

    ...Jim Thompson
     

  8. You better oil up your Uzi, he wants them to build a roundabout in
    your yard.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  9. Jim Thompson

    Jim Thompson Guest

    I think the greeting sign (in Hebrew) out on the front patio will
    probably drive him back ;-)

    ...Jim Thompson
     

  10. Do you think that I should tell the little moron that I was trained
    to kill with the M16, the M60, and how to use the M72, yet I've never
    had to kill anyone?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  11. RRogers

    RRogers Guest

    I can't find the original message so I will continue here. The first
    order model should include the winding resistance as a series resistor,
    and then compute a parrallel resistor due to the core losses. Verify
    over the frequencies your interested in, materials vary a lot. In fact
    if a series resistance is sufficiently accurate, you can use
    pre-distortion (right term?), tilting the frequency axis, and design
    the filter having perfect (inf Q) components; and then undistort the
    results to get values. That sounds a little jumbled, but these days I
    presume that technique is obsolere. I reliably designed a 9 pole
    filter in the 70's this way; with both time and frequency requirements.


    Ray
     
  12. Leon

    Leon Guest

    Coilcraft has some nice SPICE models for their inductors. You could
    modify one of those.

    Leon
     
  13. Leon

    Leon Guest

    Coilcraft has some nice SPICE models for their inductors. You could
    modify one of those.

    Leon
     
  14. Well, you might as well just accept them, and hope your plants grow
    faster than they can eat them... :cool:

    Charlie
     
  15. Jim Thompson

    Jim Thompson Guest

    I don't think they eat cactus or mesquite ?:)

    If they do, I'll just get out the shotgun ;-)

    ...Jim Thompson
     

  16. If they eat cacti, ship them to Lake County Florida. There is enough
    there to feed millions of the willey wabbits down there. :(


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  17. Young mesquite, probably. Cacti, they usually use to cover their
    burrows. The problems are if you have any flowers or food plants
    growning. In Borrego, we had several families, but there was only one of
    the plants that they liked so well that it couldn't grow. But, once we
    planted some marigolds. Lasted two days...

    Charlie
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-