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Modelling Capacitor

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kaosad

New Member
How do I model non-ideal capacitor. Do I put inductor and resistor in series or in parallel, or both?

How about non-ideal inductor?
 

dknguyen

Well-Known Member
Most Helpful Member
AN ideal inductor has parasitic interwinding capacitance in parallel with it (the capacitance between the coils of the inductor all sitting beside each other), and the wire resistance is in series with it.

A capacitor has an inductance in series with it and a resistance in series with it (the lead resistance and inductance).
 

Speakerguy

Active Member
If you want to get very detailed, you need to know what type of capacitor you are modeling. I've seen equivalent circuit diagrams for electrolytics that are quite complex. Even with 'simple' caps like film and ceramics, ESL and ESR are functions of frequency.
 
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mneary

New Member
'ceramic' is a term which encompasses dozens of materials. Dielectric absorption is one forgotten factor; in some materials it models as a parallel capacitance of up to C/10 in series with maybe 10e9 ohms. (Makes sample and hold circuits very interesting.)

In many ceramics, even C is a function of voltage.
 

Speakerguy

Active Member
I had never heard of voltage coefficient of capacitance until I read about Y5V types and barium titanate/Class II ceramics in general.

I've even heard a ceramic capacitor *chirp*. Honest to god make sound. It was an 0603 X7R in a PLL loop filter for a chip that was malfunctioning. If anyone doubts me, I've got 2 other engineers and a manager at my old employer (medium sized specialty IC manufacturer) that saw/heard it too.
 

dknguyen

Well-Known Member
Most Helpful Member
Yup, a lot of those ceramic dielectrics are piezoelectric materials. Not good for certain parts of audio circuits.
 

kaosad

New Member
One more question: Electrolytic capacitor has some current leakage, so does modelling such non-ideal capacitor by including high resistor in parallel to it valid?
 

dknguyen

Well-Known Member
Most Helpful Member
I don't know about modelling capacitors that far, but it sounds valid for a first order approximation. THen there is dielectric absorption and all that other stuff.
 
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