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A real inductor, because of parasitic contributions, behaves differently with respect to an ideal inductor. In the following slide of a course I am studying the equivalent model of a real inductor is provided:

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Assuming negligibile some elements (as explained in the slide), we get the following simplified series configuration:

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Now I have problems: in the following slide, an alternative parallel configuration is given:

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Question: how does my professor find the values of this alternative parallel configuration? My idea is the following: I impose that the series impedance is equal to the parallel impedance, but as you can see from my computations, I still do not arrive to those formulas.

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Thank you

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2 Answers 2

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\$R_{p}^2 >>\omega^2 L_{p}^2\$

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The parallel RL inductor applies to ferrite chokes that are lossy only for EMI purposes to raise signal impedance and reduce RF current.

I could be wrong but I am pretty sure that...

It is not a transformation of a good inductor with some series resistance.

  • The parallel resistance must come from either hysteresis or eddy current losses and not series conductance of the wire.

So that page seems to be misleading or unclear how it follows the series RL model.

The series resistance may be “zero” for example as a ferrite bead around a wire or a flat strip over ribbon cable but it is the high inductance than the lower resistance in the 50 to 1k range that absorbs the Interfering RF. In this case the circuit behaves similar to a small 100 pF shunt cap in attenuation expect performed by raising the impedance shunted by specially formulated lossy ferrite.

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  • \$\begingroup\$ You can tell the Prof I said this and get a response. \$\endgroup\$ Jun 12, 2019 at 2:32

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