Metal film capacitor is a layer of metal film directly evaporated on the paper as an electrode, also known as metalized paper dielectric capacitor. The electrode is a thinner metal film than the aluminum foil. This capacitor is characterized by its self-healing effect. If the voltage is too high, the dielectric inside the capacitor is broken at a certain point, the short-circuit current will evaporate the metal film where the dielectric is damaged, thereby avoiding a short circuit between the two pole pieces, so that the capacitor continues to work. Of course, the range of breakdown should not be too large, otherwise it will affect the capacitance of the capacitor. Metal film paper capacitors are usually encapsulated with epoxy resin, so they have good moisture resistance.
In principle, there is no short-circuit failure mode for metal film capacitors, and many short-circuit failure phenomena occur for metal foil capacitors. Although metal film capacitors have the above-mentioned great advantages, they also have disadvantages compared to metal foil capacitors:
1. The capacity stability is not as good as the foil capacitor. This is because metallized capacitors are prone to capacity loss in long-term operating conditions and can reduce capacity after self-healing. Therefore, if it is used in an oscillation circuit that requires high capacity stability, a metal foil capacitor should be selected.
2, poor ability to withstand large currents. This is because the metallized film layer is much thinner than the metal foil, and the ability to carry large currents is weak. In order to change the shortcoming of metallized film capacitors, there are currently improved high-current metal film capacitor products in the manufacturing process. Because the resistance of the metal film capacitor is more excellent, and is also satisfactory in terms of solderability and self-recovering properties, this greatly saves size space.
Advantages of metal film capacitors
1. Stability and reliability.
2. The non-inductive structure minimizes the loss factor.
3. Excellent environmental performance.
4. ESR is low.
5. Metal film capacitor is non-inductive, using polyester film as the medium and aluminum foil as the electrode winding, tinned copper-clad steel wire, with epoxy resin encapsulation.
6, good heat resistance, the rated operating temperature is 70 ℃, the maximum working temperature can reach 155 ℃.
7. Good voltage stability and small temperature coefficient.
8. It is widely used in AC, DC and pulse circuits.
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