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General capacitors are commonly used at Level I, II and III, and Electrolytic capacitor are used at Level IV, V and VI, which are selected according to the purpose.
The effective value of the highest DC voltage that can be continuously applied to the capacitor at the lowest and rated ambient temperatures, usually directly marked on the capacitor casing. If the working voltage exceeds the capacitor's withstand voltage, the capacitor will break down, causing irreparable permanent damage.
The DC voltage is applied to the capacitor and generates leakage current, and the ratio of the two is called insulation resistance.
When the capacitance is small, it mainly depends on the Surface states of the capacitance. When the capacitance is>0.1uf, it mainly depends on the performance of the medium. The greater the insulation resistance, the better.
Time constant of capacitance: To properly evaluate the insulation condition of large capacity capacitors, a time constant was introduced, which is equal to the product of the insulation resistance and capacity of the capacitor.
The energy consumed by a capacitor due to heating per unit time under the action of an electric field is called loss. All types of capacitors have specified allowable loss values within a certain frequency range. The loss of capacitors is mainly caused by dielectric loss, conductivity loss, and the resistance of all metal parts of the capacitor.
Under the action of a direct current electric field, the loss of a capacitor exists in the form of leakage conduction loss, which is generally small. Under the action of an alternating electric field, the loss of a capacitor is not only related to leakage conduction, but also to the periodic polarization establishment process.
As the frequency increases, the capacitance of a general capacitor shows a decreasing pattern.
Aluminum Electrolytic capacitorStructural characteristics of the device:
The aluminum shell and plastic cover are sealed together to form a Electrolytic capacitor. Compared with other types of capacitors, aluminum Electrolytic capacitor show the following obvious characteristics in structure:
(1) The working medium of the aluminum Electrolytic capacitor is to generate a very thin layer of aluminum oxide (Al2O3) on the surface of the aluminum foil by anodic oxidation. This oxide dielectric layer and the anode of the capacitor combine to form a complete system. They are interdependent and cannot be independent of each other; The electrode and dielectric of a capacitor, as we usually refer to it, are independent of each other.
The core of aluminum Electrolytic capacitor is formed by overlapping and winding four layers of anode aluminum foil, electrolytic paper, cathode aluminum foil, electrolytic paper, etc; After the core is immersed in electrolyte, use
(2) The anode of aluminum Electrolytic capacitor is an aluminum foil with Al2O3 dielectric layer on the surface. The cathode is not the negative foil we are accustomed to think of, but the electrolyte of the capacitor.
(3) The negative foil plays the role of electrical lead in the Electrolytic capacitor, because the electrolyte as the cathode of the Electrolytic capacitor cannot be directly connected to the external circuit, and must form an electrical path through another metal electrode and other parts of the circuit.
(4) The anode aluminum foil and cathode aluminum foil of aluminum Electrolytic capacitor are usually corrosion aluminum foil, and the actual surface area is far greater than its apparent surface area, which is one of the reasons why aluminum Electrolytic capacitor usually has large capacitance. Due to the use of aluminum foil with numerous micro etched pores, liquid electrolytes are usually required to more effectively utilize its actual electrode area.
(5) Since the dielectric oxide film of aluminum Electrolytic capacitor is obtained by anodic oxidation, and its thickness is proportional to the voltage applied by anodic oxidation, in principle, the dielectric layer thickness of aluminum Electrolytic capacitor can be accurately controlled artificially.