The metallized film capacitor is a metal film deposited on the surface of the polyester film instead of the metal foil as an electrode. Since the thickness of the metallized film layer is much smaller than the thickness of the metal foil, the volume after winding is also much smaller than that of the metal foil type capacitor. The biggest advantage of metallized film capacitors is the "self-healing" property. The so-called self-healing property is that if the film medium is defective at a certain point and a breakdown short circuit occurs under the action of overvoltage, the metallization layer of the breakdown point can be melted and evaporated instantaneously under the action of the arc to form a small metal-free region. The two pole pieces of the capacitor are insulated from each other and continue to work. Therefore, the reliability of the capacitor operation is greatly improved. From the principle analysis, the metallized film capacitor should have no short-circuit failure mode, and the metal foil capacitor will have many short-circuit failure phenomena.
Metalized film capacitors have the above-mentioned great advantages, but they have the following two disadvantages compared with metal foil capacitors:
1. Capacity stability is not as good as foil capacitors. This is due to the fact that metallized capacitors are prone to loss of capacity and self-healing in long-term operating conditions. Therefore,if it is used in an oscillation circuit that requires high capacity stability,it is better to use a metal foil capacitor.
2. Poor tolerance to high currents. This is because the metallized film layer is much thinner than the metal foil, and the ability to carry large current is weak. In order to improve the shortcomings of metallized film capacitors, there are currently improved high current metallized film capacitor products in the manufacturing process. The main improvement methods are (1) using a double-sided metallized film as an electrode. (2) Increase the thickness of the metallization layer. (3) The end face metal welding process is improved to reduce the contact resistance.
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