circuit component parasitics

The resistance of any given inductor is usually given as such in the manufacturer's data sheet. The parallel capacitance has to be deduced from the self-resonant frequency of the inductor, which is often given on the data sheet as well.

For a single layer winding, the parallel capacitance often turns out to be of the order of one picofarad. It's much higher with multi-layer windings.

Modelling an inductor as a single perfect inductance in parallel with a single perfect capacitance and in series with a single perfect resistor is often good enough, but it isn't all that realistic.

--------- Bill Sloman, Nijmegen

I'd kind of like to foment a discussion of the difference between "good enough" and "realistic." ;-)

Cheers! Rich

Realistic is/was a Radio Shack brand name, and it's hardly good enough.

Best regards, Spehro Pefhany

The "Realistic" brand name has been around for a VERY long time.

When we went to the minister's house to be married 45 years ago, he had a Realistic brand "HiFi".

I wanted to go find another minister ;-)

...Jim Thompson

with a

resistor

"good

Good enough, in that it captures the behaviour that we need to model.

Unrealistic, in that it doesn't give you a clue about changing the inductor to change the parallel capacitance - which you can do, for a multilayer winding, by making the coil as a stack of thin multilayer coils, rather than winding the coil as a series of cylindrical layers.

--------- Bill Sloman. Nijmegen

Yes, Pie-wound, which I think really is "pie", and not the Greek letter "pi". ;-)

But if the operative word here is "model," then wouldn't a lower-C coil just be modeled with a smaller C in the model?

Or is your point that determining that C value is the hard part?

Thanks, Rich

I read in sci.electronics.design that Rich Grise wrote (in ) about 'circuit component parasitics', on Mon, 11 Apr 2005:

There isn't just one stray C, even for a solenoid. For a pie-wound coil, each pie has a self-capacitance and there is also an 'end-to-end' capacitance.

I suspect that in the ARRL Handbook you can read that a pie-wound choke can resonate in several modes, with some pies being net inductive and others net capacitive. Especially if you used the trick of making the pies of different numbers of turns in an effort to get a high impedance over a wide range of frequencies. Fun!

Come on, Mr. Speff - most of us can tell "Polish" from "polish". ;-)

... and reading from Reading.

...but from just up the road a bit, can you tell "slough" from the "Slough of Despond"?

Regards Ian

;-)

letter

coil

Yes, but my point is that you want to be able to change that capacitance, and for that you need a model that gives you some idea idea of how the lumped capacitance is built up.

I'm interested in the difference between predicting what a circuit will do, and understanding what is going on.

There's nothing hard about measuring the capacitance after you've wound the coil. The trick is in predicting what sort of capacitance you will get if you wind the coil in a different way.

coil,

And this would be what you would have to capture in a quasi-realistic model.

choke

impedance

More fun than I've yet contemplated - but I've added it to my list of projects to be attempted when I can find the right customer.

------- Bill Sloman,Nijmegen

I read in sci.electronics.design that Ian wrote (in ) about 'circuit component parasitics', on Tue, 12 Apr 2005:

Not according to John Betjeman, anyway.