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Concept
Aluminum electrolytic capacitor
Summary
Aluminum electrolytic capacitors are polarized electrolytic capacitors whose anode electrode (+) is made of a pure aluminum foil with an etched surface. The aluminum forms a very thin insulating layer of aluminum oxide by anodization that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer, serving in principle as the second electrode (cathode) (-) of the capacitor. A second aluminum foil called “cathode foil” contacts the electrolyte and serves as the electrical connection to the negative terminal of the capacitor.
Aluminum electrolytic capacitors are divided into three subfamilies by electrolyte type:
non-solid (liquid, wet) aluminum electrolytic capacitors,
solid manganese dioxide aluminum electrolytic capacitors, and
solid polymer aluminum electrolytic capacitors.
The least priced and type of aluminum electrolytic capacitors with non-solid electrolyte also have the broadest range of sizes, capacitance, and voltage values. They are made with capacitance values from 0.1 μF up to 2,700,000 μF (2.7 F), and voltage ratings ranging from 4 V up to 630 V. The liquid electrolyte provides oxygen for re-forming or "self-healing" of the dielectric oxide layer. However, it can evaporate through a temperature-dependent drying-out process, which causes electrical parameters to drift, limiting the service life time of the capacitors.
Due to their relatively high capacitance values aluminum electrolytic capacitors have low impedance values even at lower frequencies like mains frequency. They are typically used in power supplies, switched-mode power supplies and DC-DC converters for smoothing and buffering rectified DC voltages in many electronic devices as well as in industrial power supplies and frequency converters as DC link capacitors for drives, inverters for photovoltaic, and converters in wind power plants. Special types are used for energy storage, for example in photoflash or strobe applications or for signal coupling in audio applications.
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