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# Equivalent circuit of electrolytic capacitor

#### cupoftea

Hi,
Bottom of page 10 of this gives an equivalent circuit model of an Aluminium electrolytic capacitor...

They identify "Co" and "Ce". They say Ce=0.01 x Co

Page 1 of this...
...gives a totally different circuit model for an Alu electrolytic cap.

Both articles speak of the "LC" resonant frequency of the El cap, and show it as the "valley"
of the "impednance vs frequency" graph.

The Kemet article says the valley is at w = 1 [SQRT(L x Ce)]

The Wuerth article says the valley is at w = 1/[SQRT(L x Cs)]

These are totally different frequencies. Why is it that Kemet dont appreciate that the ESR pretty well shorts out the Ce?

If you were using each one to determine the ESL, you would come up with different values.

The Kemet equivalent circuit is unusual, I didn't yet see it in other literature. But it's still a simplified circuit and you shouldn't read too much into it. Better measure the real complex impedance curve. And if it's important for you to have an exact model, see which model can be fitted best to the empirical impedance curve.

Also - the equiv ckt varies a lot with temp !

Thanks, and the C, ESL and ESR of a surface mount 'lytic cap are all variable with frequency, so its impossible to measure say, the ESL at 450kHz

Thanks, and the C, ESL and ESR of a surface mount 'lytic cap are all variable with frequency, so its impossible to measure say, the ESL at 450kHz
The fact that ESL varies with frequency doesn't make it impossible to measure. It just means that a value you measure at some particular time, under one set of conditions, will be different from the value you measure at another time under different conditions.

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