Electrolytic capacitor

Electrolytic capacitor is the generic term for three different capacitor family members:

All electrolytic capacitors (e-caps) are polarized capacitors whose anode (+) is made of a particular metal on which an insulating oxide layer forms by anodization, acting as the dielectric of the electrolytic capacitor. A non-solid or solid electrolyte which covers the surface of the oxide layer in principle serves as the second electrode (cathode) (-) of the capacitor.

Due to their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have—based on the volume—a much higher capacitance-voltage (CV) product compared to ceramic capacitors or film capacitors, but a much smaller CV value than electrochemical supercapacitors.

The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals up to some mega-hertz and for storing large amounts of energy. They are widely used for decoupling or noise filtering in power supplies and DC link circuits for variable-frequency drives, for coupling signals between amplifier stages, and storing energy as in a flashlamp.

Standard electrolytic capacitors are polarized components due to their asymmetrical construction, and may only be operated with a higher voltage (ie, more positive) on the anode than on the cathode at all times. Voltages with reverse polarity, or voltage or ripple current higher than specified (as little as 1 or 1.5 volts may suffice), can destroy the dielectric and thus the capacitor. The destruction of electrolytic capacitors can have catastrophic consequences (explosion, fire).

Bipolar electrolytic (aka non-polarized) capacitors which may be operated with either polarity are special constructions with two anodes connected in series.

As to the basic construction principles of electrolytic capacitors, there are three different types: aluminum, tantalum, and niobium capacitors. Each of these three capacitor families uses non-solid and solid manganese dioxide or solid polymer electrolytes, so a great spread of different combinations of anode material and solid or non-solid electrolytes is available.

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