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Parasitic capacitance in inductors

Discussion in 'Electronic Design' started by Paul Burridge, Nov 17, 2003.

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  1. John Larkin

    John Larkin Guest

    If Bowick thinks that the distributed capacitance of a coil is caused
    by its resistance, then he is a lumped element.

  2. How about 'impedance', instead of resistance?

    "Thus if any wire _impedance_ at all exists, a voltage drop (even
    though very minute) will occur between the windings, ..."
  3. I read in that John Larkin <[email protected]> wrote (in <[email protected]>) about 'Parasitic capacitance in inductors', on Thu, 20 Nov
    He doesn't say that. What he effectively says is that even at
    arbitrarily low frequencies the resistance of each turn produces a
    voltage across the inter-turn capacitance. This is true, but it is far
    from the whole story, which is what I commented initially.
  4. Ben Bradley

    Ben Bradley Guest

    In, pat dot lawler att verizon dott nneett
    And since its an inductor conducting an AC current, such impedance
    DOES exist (or more correctly it always exists, the inductive
    reactance part is greater than zero for ac and is zero for DC).
    For an alternating current, inductance is an impedance (a general
    term) or a reactance (a more specific term) - there will be a voltage
    drop between adjacent windings, even if the resistance is zero. In
    practical inductors, at the usual frequencies of interest, the
    inductive reactance accounts for much more of the voltage difference
    between windings than does the resistance.
  5. It's not though, is it? The propagation velocity in wire is somewhat
    slower than that in air. That's why one has to multiply it by the
    'free space correction factor' - something in the region of 97% of
    light speed, IIRC.
  6. Bowick actually refers to this parasitic capacitance between turns as
    "distributed". I'm still waiting for the Panel to come to a definitive
    conclusion as to whether Bowick's explantation, which I have
    reproduced here verbatim, is accurate or not. Is the quote given from
    his book correct or not?
  7. And well worth it, I'm sure. Reg, do you have any programs in your
    remarkable collection that tackle the problems of maximising radiated
    power of (far from) non-ideal antennas for clandestine operation?
  8. It is not close enough to right to be useful.
  9. Reg Edwards

    Reg Edwards Guest


    You don't need a program. Just turn up the wick.


    Winny was disappointed, eh?

    Reg, G4FGQ ;o)
  10. I read in that Paul Burridge
    >) about 'Parasitic capacitance in inductors', on Fri, 21 Nov
    I repeat that it's true, but it's not the WHOLE truth. The per-turn
    resistance DOES create a voltage across the inter-turn capacitance, but
    in the frequency range where the per-turn inductive reactance is
    comparable with or far exceeds the per-turn resistance, the voltage due
    to the inductive reactance also appears across the inter-turn

    The inter-turn capacitance is there whether there is any current in the
    inductor or not. So where the voltage across it comes from is a question
    quite separate from that about the existence of the capacitance.
  11. Fred Bloggs

    Fred Bloggs Guest

    We're not talking about that kind of "distributed." The distributed
    component I'm talking about dimensionally spans a significant fraction
    of a wavelength of the operating frequency.
  12. Yeah, but then the final trannie goes 'pop' due to the appalling
    mismatch caused by a (necessarily) folded-up ariel.
  13. Rich Grise

    Rich Grise Guest

    The resistance doesn't have anyhting to do with the capacitance,
    except when they're interacting. The capacitance is because
    there are two conductors separated by an insulator. It just
    sits there, so to speak. :)

  14. So are you saying there doesn't need to be any potential difference to
    arise between the turns for there to be an inter-turn capacitance?
  15. I read in that Paul Burridge
    >) about 'Parasitic capacitance in inductors', on Wed, 26 Nov
    Indeed. An uncharged capacitor doesn't cease to exist.
  16. I think that's a metaphysical question that more properly belongs to
    the realm of philosophy, John. :)
  17. I read in that Paul Burridge
    >) about 'Parasitic capacitance in inductors', on Thu, 27 Nov
    I checked before making such a controversial statement. I short-
    circuited some of the capacitors in my stock, and they didn't disappear.
  18. Ah, but shorted them at what frequency?
  19. I read in that Paul Burridge
    >) about 'Parasitic capacitance in inductors', on Thu, 27 Nov
    About one every 20 seconds, I think.
  20. Very good. :) It obviously took you a while to think that one up.
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