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Capacitor Rated Voltage And Insulation Withstand Voltage
Aug 03, 2018

1. Insulation withstand voltage of capacitors The AD817AR circuit has a certain voltage applied between the two poles of the capacitor. If the voltage is too high, the capacitor will be broken down and burned. Therefore, in the manufacture and use of capacitors, in addition to considering the capacitance, it should also consider how high the capacitor can withstand. To understand this problem, we must also understand from the capacitor charging principle shown in Figure 2-4. When the power supply voltage is gradually increased from 1.5V, the positive and negative charges on the A and B plates become more and more, A The electric field between the B plates is getting larger and larger. When the electric field force is increased to a certain extent, the electric field force of the A plate can "force pull" the positive charge on the B plate. The electric field force of the B-plate also "forces the negative charge" on the A-plate. At this time, the electric charge can be transferred between the two plates of the capacitor to form a current, and the insulating medium can not be blocked. The two plates of the capacitor are equivalent to the interconnecting conductors, losing its original structure and function. This charge can penetrate the insulating medium between the plates, often referred to as capacitor breakdown. The current that is turned on after the capacitor is broken down is large, and a high temperature is generated to burn the material constituting the capacitor. In addition to breakdown of the internal insulating dielectric layer, the capacitor can also be broken through the insulating layer between the two poles. If the pressure resistance of the outer casing insulation layer is less than the inner dielectric layer, the breakdown first occurs on the outer casing insulation layer. In addition, capacitor breakdown is also related to the design structure and processing technology of the capacitor. If the surface of the capacitor plate is rough or has a tip, the tip will pierce the insulating medium to form a tip discharge, which creates conditions for capacitor breakdown. After the capacitor is made into a product, the withstand voltage of the insulating material becomes an inherent property of the capacitor. The maximum voltage that the capacitor can withstand is called the insulation withstand voltage of the capacitor. The insulation withstand voltage of a capacitor is generally 1.5 to 2 times its rated operating voltage. 2. Capacitor Rated Voltage Rated voltage is the rms value of the highest DC voltage and the highest AC voltage that the capacitor can withstand when operating at the lowest and highest ambient temperatures. There is room for the withstand voltage marked on each capacitor, which is generally 1.5 to 2 times higher than the rated voltage. This is because, in the application of the capacitor, not only the withstand voltage of the two poles but also the long-term comprehensive factors, such as the temperature rise and the withstand voltage will be reduced, and the applied voltage fluctuation will cause the actual voltage of the capacitor to be higher. Therefore, the capacitor does not exceed the rated voltage in the application to ensure application safety. The rated voltage and the insulation voltage are both related and different. Generally speaking, the rated voltage and the insulation voltage are related to the withstand voltage problem of the capacitor, but the insulation voltage refers to the voltage that the dielectric can withstand, and the rated voltage refers to the wide voltage. The voltage that the insulating medium can withstand, the withstand voltage of the plate and the housing, and the withstand voltage when the capacitor is in contact with the other components, the rated voltage is considered from all sides. The capacitor type is different, the rated voltage is also different. For example, the withstand voltage of a small mica capacitor is generally around 250V, the withstand voltage of a small ceramic dielectric capacitor is generally about 60V, and the withstand voltage of a polystyrene capacitor is 63V, 160V, 400V, 600V, etc. Kinds of electrolytic capacitors have various specifications such as 12V, 25V, 50V, 160V, and 400V. In practical applications, some capacitors are not marked with a rated voltage. They can only be used in voltage conditions below 100V, otherwise breakdown may occur, causing permanent damage to the capacitor. The rated voltage of the capacitor is determined by the inherent factors. When the ambient temperature is too high, the withstand voltage capability is reduced. When the ambient humidity is too high, the withstand voltage capability is also reduced. Therefore, these factors should also be considered when selecting capacitors. In principle, a capacitor with a low rated voltage can be replaced by a capacitor with a high rated voltage under the condition of equal capacitance