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Capacitor industry knowledge
Jul 28, 2018

1. Introduction of common capacitor structure and features


It is well known that a capacitor is often referred to simply as a capacitor, represented by the letter C, which is a device that holds a charge. Capacitor is an energy storage component and is one of the most widely used electronic components in electronic equipment. It is widely used in the circuit of direct communication, coupling, bypass, filtering, tuning loop, energy conversion, control and so on. Generally, commonly used capacitors can be classified into electrolytic capacitors, mica capacitors, ceramic capacitors, glass glaze capacitors, etc. according to their dielectric materials.


1) Aluminum electrolytic capacitors. It is made of an aluminum cylinder as a negative electrode, which is filled with a liquid electrolyte, and is inserted into a curved aluminum strip to make a positive electrode. It also needs to be subjected to DC voltage treatment to form an oxide film on the positive electrode sheet as a medium. It is characterized by large capacity, but large leakage, large error, poor stability, often used as AC bypass and filtering, and also used for signal coupling when the requirements are not high. Electrolytic capacitors have positive and negative poles and cannot be reversed during use. Positive and negative polarity, when using, do not reverse the positive and negative.


2) Paper capacitor. Two pieces of metal foil are used as electrodes, sandwiched in extremely thin capacitor paper, rolled into a cylindrical or flat cylindrical core, and then sealed in a metal shell or an insulating material (such as lacquer, ceramic, glass glaze, etc.). It is characterized by a small size and a large capacity. However, the inherent inductance and loss are relatively large, and it is suitable for low frequency.


3) Metalized paper dielectric capacitor. The structure and paper dielectric capacitance are basically the same. It replaces the metal foil with a metal film on the capacitor paper. It is small in size and large in capacity, and is generally used in low frequency circuits.


4) Oil-impregnated paper capacitor. It immerses the paper capacitor in a specially treated oil to enhance its withstand voltage. It is characterized by large capacitance and high pressure resistance, but it is bulky.


5) Glass glaze capacitors. The glass glaze is used as a medium, which has the advantages of a ceramic capacitor, and has a smaller volume and high temperature resistance.


6) Ceramic capacitors. The ceramic capacitor is made of ceramic as a medium, and a silver layer is sprayed on both sides of the ceramic substrate, and then fired into a silver film to be a plate. It is characterized by small volume, good heat resistance, low loss, high insulation resistance, but small capacity, suitable for high frequency circuits.


7) Film capacitors. The structure is the same as the paper dielectric, and the medium is polyester or polystyrene. Polyester film capacitor, high dielectric constant, small volume, large capacity, good stability, suitable for bypass capacitors.


8) Mica capacitors. The electrode plate is sprayed with a metal foil or a silver layer on the mica plate, and the plate and the mica are laminated one by one, and then die-cast in the bakelite powder or sealed in an epoxy resin. It is characterized by low dielectric loss, large insulation resistance and small temperature coefficient, which is suitable for high frequency circuits.


9) 钽, 铌 electrolytic capacitors. It uses a metal crucible or crucible as a positive electrode, a dilute sulfuric acid or the like as a negative electrode, and an oxide film formed on the surface of a crucible or a crucible as a medium. It is characterized by small size, large capacity, stable performance, long life, large insulation resistance and good temperature characteristics. Used in devices with higher requirements.


10) Semi-variable capacitors. Also called a trimmer capacitor. It is made up of two or two small metal shrapnel sandwiched between media. Change the distance or area between the two pieces when adjusting. Its medium is air, ceramic, mica, film and so on.


11) Variable capacitance. It consists of a set of fixed pieces and a set of moving pieces, and its capacity can be continuously changed as the moving piece rotates. The two sets of variable capacitors are mounted together for coaxial rotation, called double connection. Variable capacitor media are available in both air and polystyrene. The air medium variable capacitor is bulky and has low loss and is often used in tube radios. The polystyrene dielectric variable capacitor is sealed and small in size, and is often used in transistor radios.

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