Parasitic values

[Guest]

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"John Popelish" wrote
> Not at all. If the inductor looks purely resistive, it is the
> inductance and capacitance that have canceled each other, leaving
> whatever series resistance the inductor had as the only remaining
> visible impedance. The value of that resistance really isn't involved
> in the calculation of that capacitance. If no inductance remains,
> then XC=XL.

==========================
Resistance values DO affect the effective values of L and C and of the
resonant frequency.

For example, a resistance in series with an inductance can be transformed to
an equivalent higher value parallel resistance and a higher value
inductance. With an associated capacitance this reduces the resonant
frequency.

And a resistance in series with a capacitor can be transformed to a parallel
combination of higher resistance and smaller capacitance which increases
resonant frequency.

The magnitude of the effects increases with lower values of Q = Series R /
X.

Pure values of resistance can be transformed to considerably different
purely resistive values by parasitic L and C.

In the extreme case, at the resonant frequency, effective Rp = L /C / Rs
where Rp and Rs are respectively the parallel and and series resistance
values.

But this is not magic. It's only elementary circuit behaviour.

Parasitic L and C are distributed values. A more exact analysis of the
effects is obtained by considering a lumped resistor to be a short
transmission line. But rarely is this necessary.
----
Reg.

 

[Guest]

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Terry Given" <the_domes@xtra.co.nz> writes:
> [...]
> When I was at University, in a fit of inspired stupidity I analysed a
> 2nd order LC filter with resistive Rs & Rl, using Maxwells equations.
> Unsurprisingly, it was a LOT of work, and gave me the exact same answer as
> the laplace approach.

Damned impressive anyway!
--
% Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven.
%% Fuquay-Varina, NC % She love the way Puccini lays down a tune, and
%%% 919-577-9882 % Verdi's always creepin' from her room."
%%%% <yates@ieee.org> % "Rockaria", *A New World Record*, ELO
http/home.earthlink.net/~yatescr

 

[Guest]

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Randy Yates" <yates@ieee.org> wrote in message
news:smdl2q5t.fsf@ieee.org...
> "Terry Given" <the_domes@xtra.co.nz> writes:
> > [...]
> > When I was at University, in a fit of inspired stupidity I analysed a
> > 2nd order LC filter with resistive Rs & Rl, using Maxwells equations.
> > Unsurprisingly, it was a LOT of work, and gave me the exact same answer
as
> > the laplace approach.
>
> Damned impressive anyway!
> % Randy Yates % "She's sweet on Wagner-I think she'd die
for

Nah, just handle-cranking. I was hell impressed when my (ex-) father-in-law
showed me a 16x16 matrix he inverted BY HAND (civil engineer). Lots of
cross-checking, and VERY big bits of paper. Now I see why Walter spent
$20,000 on his first HP calculator (alas I cant recall the model no. but it
was bigger than a typewriter)

I also discovered a not-too-dissimilar worked example (Kraus'
electromagnetics IIRC)

It provided an object lesson in the appropriate use of approximations though


Cheers
Terry

 

[Guest]

Archived from groups: rec.audio.tech,sci.electronics.design (More info?)

"Reg Edwards" <g4fgq.regp@ZZZbtinternet.com> wrote in message
news:c93sv1$kaj$1@titan.btinternet.com...
>
> "John Popelish" wrote
> > Not at all. If the inductor looks purely resistive, it is the
> > inductance and capacitance that have canceled each other, leaving
> > whatever series resistance the inductor had as the only remaining
> > visible impedance. The value of that resistance really isn't involved
> > in the calculation of that capacitance. If no inductance remains,
> > then XC=XL.
>
> ==========================
> Resistance values DO affect the effective values of L and C and of the
> resonant frequency.
>
> For example, a resistance in series with an inductance can be transformed
to
> an equivalent higher value parallel resistance and a higher value
> inductance. With an associated capacitance this reduces the resonant
> frequency.
>
> And a resistance in series with a capacitor can be transformed to a
parallel
> combination of higher resistance and smaller capacitance which increases
> resonant frequency.
>
> The magnitude of the effects increases with lower values of Q = Series R /
> X.
>
> Pure values of resistance can be transformed to considerably different
> purely resistive values by parasitic L and C.
>
> In the extreme case, at the resonant frequency, effective Rp = L /C / Rs
> where Rp and Rs are respectively the parallel and and series resistance
> values.
>
> But this is not magic. It's only elementary circuit behaviour.
>
> Parasitic L and C are distributed values. A more exact analysis of the
> effects is obtained by considering a lumped resistor to be a short
> transmission line. But rarely is this necessary.
> ----
> Reg.

Thankfully Reg is right. Imagine what a pain most circuit design would be
then. When I was at University, in a fit of inspired stupidity I analysed a
2nd order LC filter with resistive Rs & Rl, using Maxwells equations.
Unsurprisingly, it was a LOT of work, and gave me the exact same answer as
the laplace approach. The problem with approximations is when you dont
realise you are using them

Cheers
Terry