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## Main Question or Discussion Point

How can I get the parasitic capacitance of a inductor? I have a scope, current probe, function generator.

Thank you.

Thank you.

- Thread starter learner1
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How can I get the parasitic capacitance of a inductor? I have a scope, current probe, function generator.

Thank you.

Thank you.

- #2

Averagesupernova

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What is the value of incuctance?

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You can do it manually by simply plotting a frequency/Impedance graph, and curve-fitting some sample values of capacitance based upon the 1/2piefc algebraic equation.

- #4

SGT

Varying the frequency of your sinusoid will change the amplitude of the signal. The amplitude will be minimal at the resonant frequency [tex]\omega_0[/tex].

Since [tex]\omega_0 = \frac{1}{\sqrt{LC}}[/tex] you can calculate the capacitance.

- #5

berkeman

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The easiest way will be from its datasheet. There should be a DCR (series resistance) and parallel capacitance listed. Depending on the L and C values, you may have a hard time measuring the resonance with your signal generator. Like if the sig gen only goes to 10MHz, and your inductor is 10uH with 10pF of capacitance, your resonant freq will be around 16MHz. Also keep in mind that your oscilloscope probe has capacitance (probably in the 10pF range), so that will alter your reading and needs to be accounted for.learner1 said:How can I get the parasitic capacitance of a inductor? I have a scope, current probe, function generator.

Thank you.

If you need higher frequencies for your tests, you can try adding a series diode and driving the inductor with a square wave. You would make a low-inductance measuring fixture similar to a Z-lead for your scope probe, and measure the ringout frequency of the inductor and parasitic capacitance (and then subtract the scope probe capacitance and any other fixture capacitance).

Let us know what you come up with, and maybe post a link to the inductor's datasheet so we can check it out. -Mike-

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I know the inductance is about 1.4mH. The inductor was directly connected to the signal generator. The voltage and current across the inductor are measured using scope. I increased the frequency of sinusoid until phase between V and I changed from 90 to –90 (impedance from inductive to capacitive). Then I use this frequency (420kHz) to calculate C based on . C is about 100pH.

Is this value reasonable?

I want to try something else to verify it.

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Averagesupernova

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I am thinking about another way to measure it. If the output impedance of the function generator is 50ohms, can I use Xc=50=1/2pifC and find this f? Am I looking for -45 phase shift? Thank you.

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Averagesupernova

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