Tantalum electrolytic capacitors use a sintered pellet (“slug”) of high-purity tantalum powder with tantalum pentoxide as dielectric.Aluminum electrolytic capacitors use a high-purity etched aluminium foil with aluminium oxide as dielectric. There are three different anode metals in use for electrolytic capacitors: This and the storage principle distinguish them from electrochemical capacitors or supercapacitors, in which the electrolyte generally is the ionic conductive connection between two electrodes and the storage occurs with statically double-layer capacitance and electrochemical pseudocapacitance.īasic materials and construction Basic principle of anodic oxidation (forming), in which, by applying a voltage with a current source, an oxide layer is formed on a metallic anodeĮlectrolytic capacitors use a chemical feature of some special metals, previously called "valve metals", which on contact with a particular electrolyte form a very thin insulating oxide layer on their surface by anodic oxidation which can function as a dielectric. The non-solid or solid electrolyte in principle is the cathode, which thus forms the second electrode of the capacitor. Like other conventional capacitors, electrolytic capacitors store the electric energy statically by charge separation in an electric field in the dielectric oxide layer between two electrodes. 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.ĭepending on the nature of the anode metal used and the electrolyte used, there is a wide variety of electrolytic capacitors Charge principle General information Electrolytic capacitors family tree Īs to the basic construction principles of electrolytic capacitors, there are three different types: aluminum, tantalum, and niobium capacitors. A bipolar electrolytic capacitor can also be made by connecting two normal electrolytic capacitors in series, anode to anode or cathode to cathode. Bipolar electrolytic capacitors which may be operated with either polarity are also made, using special constructions with two anodes connected in series. The failure of electrolytic capacitors can be hazardous, resulting in an explosion or fire. Applying a reverse polarity voltage, or a voltage exceeding the maximum rated working voltage of as little as 1 or 1.5 volts, can destroy the dielectric and thus the capacitor. For this reason the polarity is marked on the device housing. 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.Įlectrolytic capacitors are polarized components because of their asymmetrical construction and must be operated with a higher potential (i.e., more positive) on the anode than on the cathode at all times. The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals, and for storing large amounts of energy. There are three families of electrolytic capacitor: aluminium electrolytic capacitors, tantalum electrolytic capacitors, and niobium electrolytic capacitors. Because of their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a much higher capacitance- voltage (CV) product per unit volume than ceramic capacitors or film capacitors, and so can have large capacitance values. A solid, liquid, or gel electrolyte covers the surface of this oxide layer, serving as the cathode or negative plate of the capacitor. This oxide layer acts as the dielectric of the capacitor. For other types of polarized capacitors, see Supercapacitor.Īn electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization.
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