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In Reply to: RE: "self resonant frequency" of an inductor posted by Lew on November 25, 2014 at 07:09:53
The self resonant freq. DOES matter. Your instinct is correct.
The turns of wire that make up the choke cause a capacitance to be in parallel with the inductance. Remember, at the resonant freq., a parallel LC setup presents an "infinite" impedance.
Eli D.
Follow Ups:
The inherent capacitance of an inductor, would it be in parallel with any external added capacitance, in an LC or CLC filter, for example? If so, and since the external capacitance is likely to be many orders of magnitude higher than the self-capacitance of the inductor, would that not alter the actual resonant frequency, greatly? (But I can see that the capacitance of an inductor may not be considered in parallel with external C.)
Edits: 11/25/14
The internal capacitance of an inductor isn't influenced by external capacitance to any great extent. Also, above the self resonant freq. the inductor begins to behave as if it's a capacitor which could be a factor in overall filter performance.
So, above 1kHz, the one inductor I found on Mouser with 1 kHz self-resonant frequency would begin to behave as a capacitor that does not block DC. It's capacitative in that its impedance goes down with increasing frequency above 1 kHz, rather than up, as one would expect from an inductor. (This is well described in Morgan Jones' books; I must have banked the knowledge in some shady area of my brain.)
Actually, to a simple approximation, it is capacitance in parallel with the series resistance of the inductor, thus the ability conduct DC. Also take note of comments above regarding that 1KHz spec. 1KHz isn't really plausible for a 100mH inductor so must be a typo. Certainly bears further investigation.
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