Re: [TCML] Primary selfC

[Ed Phillips <evp@xxxxxxxxxxx>]

Hi Bart,

Until Paul can speak to my earlier question, I think you're subscribing to the same false intuition that I and many, many others apparently do.

For a secondary coil (where we are more accustomed to discussing Cself), the value of Cself is not affected by the number or turns, the spacing of the turns, the diameter of the wire, or the dielectric between the turns.  All that matters is the geometry of the overall cylinder that contains the coil.  Try it with your favorite simulator!  No doubt the same is true for a primary coil as well.  This is why Paul was suggesting modeling the primary as a free-standing disk - the shape of the flat spiral primary.

I whole-heartedly agree - it sure does seem that the relationship between turns would be a dominant factor in Cself, but apparently it is not.

Regards, Gary Lau
MA, USA

	Remember that, while there is capacitance between turns, if affects mostly the adjacent turns and appears across the inductance of a single turn - in effect a little LC circuit.  In a multi-turn coil you have a whole bunch of these little circuits in SERIES so the capacitance due to this effect is almost negligible.  Look up Medhurst's experimental work on the subject.  

	I can't imagine the self-capacitance of any low inductance primary of any geometry being of significance.

Ed


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