Electrolytic Capacitors

"Electrolytic" means any capacitor that requires a conductive layer between the dielectric and one electrode.  In the original electrolytic capacitor, the layer was an actual electrolyte, a conductive salt in a solvent.  Some electrolytic capacitors today don´t actually use an electrolyte, but the word is still commonly used, to the annoyance of some.  Electrolytic capacitors are made by growing a oxide film, the dielectric, on a metal, the anode, by electrochemical means.  The films are very thin with fairly high Ks (roughly 10-25) which make for a lot of capacitance in a small package.  The resulting devices pass current much better in one direction than the other, making a rectifier of a sort.  Because of this, the metals are sometimes called "valve" metals.  The metals presently used are aluminum, tantalum, and niobium, Above about the Electrolytic Capacitors information content.

Pros: Electrolytic capacitors are best used when you need a lot of capacitance in a small space and at a reasonable price, such as power supply filtering, or energy storage.  They are available in sizes far beyond that of other capacitors.  Aluminum electrolytics are presently available from 0.1 uF to several F.  I have no idea why someone would use a 0.1 uF electrolytic capacitor however.  Tantalum electrolytics are available from 0.1 uF to a few thousand uF, Above about the Electrolytic Capacitors information content.

Cons: Marginal electrical properties means that these capacitors must be applied with care.  The parameters to be watched include leakage, service life vs. temperature, ESR, ESL, and low-temperature performance.  Unlike other capacitors, electrolytic capacitors are not inherently non-polar, but non-polar types are available.  Electrolytics are widely available in SMD packages, at least in moderate sizes, but users complain of more reliability problems than with through-hole styles, Above about the Electrolytic Capacitors information content.

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