What are the Types of Electrolytic Capacitor?
Electrolytic capacitors are capacitors made of an oxide film formed by electrolysis as a medium. The aluminum electrolytic capacitor uses high-purity aluminum as the anode, and a paste composed of ethylene glycol, glycerol, boron and ammonia water as the electrolyte, and electrolysis in the electrolyte produces a very thin layer on the surface of the aluminum. A capacitor made of aluminum oxide film as a dielectric.
Depending on the material used to construct the dielectric, general electrolytic capacitors can be divided into three types:
- Aluminum Electrolytic Capacitor
- Tantalum Electrolytic Capacitor
- Niobium Electrolytic Capacitor
All types of electrolytic capacitors work in a similar way. However, the electrodes are made of different types of materials.
Aluminum electrolytic capacitor
An aluminum capacitor is an electrolytic capacitor whose anode (+) is made of pure aluminum foil with an etched surface. Aluminum is anodized to form an extremely thin insulating layer of aluminum oxide that acts as a capacitor dielectric. In principle, the oxide layer is the second electrode (cation) (-) of the capacitor, which is covered by a non-solid electrolyte. The negative electrode of the capacitor is connected to the electrolyte through a second aluminum foil called the "cathode foil". Aluminum electrolytic capacitors have the advantages of large capacitance, moderate volume, and relatively cheap price. They are also the most widely used electrolytic capacitors. This electrolytic capacitor is composed of two aluminum strips and two layers of insulating films stacked on each other. made of electrolyte.
The common capacitor needs to be processed by a DC voltage device before leaving the factory, so that an oxide film is formed on the positive plate as a medium. Under the continuous influence of the DC voltage, the aluminum oxide film of the aluminum electrolytic capacitor will gradually thicken, and the electrolyte will gradually thicken or even dry out due to the evaporation of water due to continuous operation, resulting in failure. The electrolyte gradually becomes thinner under the weak dissolving power, so the insulation resistance becomes smaller, the leakage current increases, and the withstand voltage decreases. Therefore, aluminum electrolytic capacitors that have been stored for a long time cannot be used immediately, and must be activated and re-energized to gradually restore the oxide film. The main features are positive and negative polarity, small size, large capacity, large loss, and large leakage. It is often used in power supply filtering, low-frequency coupling, decoupling, bypass or low-frequency circuits.
Internal Structure of Aluminum Electrolytic Capacitor
The principle of anodization of aluminum electrolytic capacitors makes them polarized capacitors. The operation of these devices requires correct DC voltage polarity. Short circuits can occur when capacitors are operated with AC voltage or the wrong polarity. The only exception is bipolar aluminum electrolytic capacitors, which have two anodes arranged back-to-back in a single housing that can be used for AC purposes.
Tantalum Electrolytic Capacitor
Tantalum electrolytic capacitors are passive components of electronic circuits. This type of electrolytic capacitor has an anode composed of porous tantalum metal particles, which is covered by an insulating oxide layer and surrounded by a liquid or solid electrolyte as a cathode. Unlike conventional capacitors and electrolytic capacitors, tantalum capacitors have a relatively thin and high dielectric constant dielectric layer, enabling them to have very high capacitance per unit volume (high volume efficiency) and are relatively light. Compared with aluminum electrolytic capacitors, tantalum electrolytic capacitors are much more expensive.
The standard tantalum capacitors are essentially polarized components. Reverse voltage can damage capacitors. A non-polar tantalum capacitor is made by effectively connecting two polarized capacitors in series, with the anodes facing in opposite directions.
Liquid tantalum electrolytic capacitors are made of metal tantalum as the positive electrode, dilute sulfuric acid as the negative electrode, and the oxide film formed on the surface of tantalum as the medium. Solid tantalum electrolytic capacitors are made of high-purity metal tantalum powder pressed into a positive electrode and sintered in a vacuum, and then a tantalum oxide dielectric film is formed on the tantalum sheet by electrochemical corrosion, and then a layer of solid manganese dioxide is deposited on the dielectric film as the electrolyte, the metal is sprayed outside to form a negative electrode, and the package is added.
Tantalum electrolytic capacitors have the advantages of small size, large capacity, stable performance, long life, large insulation resistance, good temperature characteristics, loss and leakage less than aluminum electrolytic capacitors. Used in circuits with higher requirements, instead of aluminum electrolytic capacitors. Pay attention to its performance characteristics in application, and correct use will help to give full play to its functions, such as considering the working environment of the product and its heating temperature, and taking measures such as derating, if it is used improperly, it will affect the working life of the product.
Niobium Electrolytic Capacitor
In niobium electrolytic capacitors, polarized capacitors, the anode consists of passivated niobium metal or niobium monoxide, on which an insulating niobium pentoxide layer is used as the dielectric of the niobium capacitor. As the second electrode (cathode), the oxide layer has a solid electrolyte on the surface
Capacitors made of niobium are polarized elements by design, so they can only receive DC voltages in the correct direction. As with the other two types of electrolytic capacitors, reverse voltage or ripple current above a certain value can damage the dielectric, thereby damaging the capacitor. In order to ensure the safe operation of niobium capacitors, manufacturers specify specific circuit design rules.
Niobium electrolytic capacitors are similar in structure to tantalum electrolytic capacitors, and the dielectric is niobium oxide. The dielectric constant of niobium oxide is much larger than that of tantalum oxide. Niobium electrolytic capacitors will be smaller in size, and other properties are slightly worse than tantalum electrolytic capacitors.
The physical and chemical properties of niobium are similar to tantalum. People are trying to develop niobium capacitors. Because the dielectric oxide film of niobium is sensitive to temperature rise, the leakage current of niobium capacitors changes greatly. Therefore, niobium has not been accepted in the capacitor market.
