Difference between polarized and non polarized capacitors

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SUMMARY

The discussion clarifies the differences between polarized and non-polarized capacitors, emphasizing that polarized capacitors, such as electrolytic capacitors, allow for higher capacitance in smaller sizes, albeit with a finite lifespan. Non-polarized capacitors are larger and more expensive to manufacture, making them less practical for high-capacitance applications. The construction differences stem from the materials used, with polarized capacitors utilizing a thin layer of aluminum oxide as a dielectric, which significantly reduces the distance factor in capacitance calculations. The discussion also highlights that connecting two electrolytic capacitors back-to-back can create a non-polarized effect but at a higher cost.

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hisham.i
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Hello,

I googled the difference between polarized and non polarized capacitors and all i found was differences in construction and the material that they are formed from.

I want to know why there is 2 types of capacitors, what are the differences (cost, technical, etc), why there is not only non polarized?

thanks
 
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Non-polarized capacitors (the ones we learn about in physics at first), at hard to manufacture at a small size compared to their capacitance (they become very big if we want a big capacitance). Also, they can be quite expensive when they become bigger.

Polarized capacitors give us a way to manufacture smaller capacitors, but with a high capacitance. The drawback however, is that they are polarized.

Some places with high requirements, it is not allowed to use polarized capacitors.
 
Electrolytic capacitors are a way to manufacture a high capacitance relatively cheaply and in a small sized package. They are definitely a compromise, and have a finite life.

You can connect two electrolytic capacitors back-to-back (electrically) so as to form a non-polarized electrolytic capacitor. Obviously, it will be about 4 times the cost of a single polarized capacitor giving the same capacitance.
 
The answer to your question is:
Electrolytic capacitors pack thousands of times more capacitance into a given volume than you can get with film dielectric types.
But - electrolytic capacitors are necessarily polarized because of how they're made..

capacitance= area / distance.

Area is the area of the foil

Etching an aluminum foil gives it more surface area per square inch. The microscopic hills and valleys have more surface area than would a mirror flat sheet. Remember the old saying "Colorado would be bigger than Texas if you ironed it flat" ?
Etching gives a large [STRIKE]denominator [/STRIKE] NUMERATOR (golly I'm doing everything backward today !)
Distance is the thickness of the dielectric.

In electrolytics the dielectric is not a plastic or paper film but a thin layer of aluminum oxide on one the aluminum sheets. It's only a few atoms thick so you have a very small denominator.
This little paper by Cornell-Dubelier explains it well.

http://electrochem.cwru.edu/encycl/misc/c04-appguide.pdf

old jim
 
Last edited:
Most likely this can only be answered by an "old timer". I am making measurements on an uA709 op amp (metal can). I would like to calculate the frequency rolloff curves (I can measure them). I assume the compensation is via the miller effect. To do the calculations I would need to know the gain of the transistors and the effective resistance seen at the compensation terminals, not including the values I put there. Anyone know those values?

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