What Are The Film Capacitors And The Different Types Of Dielectric Used In Them?

By Author: Deki Electronics
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Film capacitors refer to those types of capacitors that use a thin plastic film as a dielectric i.e. as a medium to transmit electric force without conduction. The film capacitors are used for various electronic devices. While the high power film capacitors are used in X-ray flashes, pulsed lasers, phase shifters etc, the low power film capacitors are used in analog-digital converters or A/D converters, and as decoupling capacitors. The film capacitors are also used in other applications such as filters, fluorescent light ballasts, audio crossovers etc. They are also used for storing energy and releasing it in high-current pulse used for generating lighting discharges.

The most common materials used as a dielectric are polyester and polypropylene. Other materials used as a dielectric are polyphenylene sulfide, polystyrene, polycarbonate, polytetrafluoroethylene, and polyimide.

Polypropylene film capacitors:

Polypropylene film capacitors are used in high voltage AC and DC applications. Some of the prominent characteristics of this type of capacitors are high insulation resistance, high breakdown strength, ...
... low dissipation factor, and low dielectric absorption. All these characteristics help this capacitor to be used in a wide range of applications such as high-frequency AC system, snubber circuits etc.

Polyester film capacitors:

As the name suggests, the polyester film capacitors use polyester as a dielectric. They are available in leaded version and offers high dielectric strength. This type of dielectric helps in the construction of high voltage capacitors in small physical sizes. They have self-healing properties and they come at cheaper prices. They have a low tolerance of about 5% to 10% and hence can be used in filtering applications. Their level of equivalent series resistance is low. They are mostly used in DC blocking and general coupling and decoupling applications. They are also used in audio applications and in circuits with a capacitor that can handle high peak current levels.

They are available in two different forms - the metalized film capacitor and the foil capacitor. The foil capacitors are larger in size than the metalized capacitor. In foil capacitor, two plates of aluminum foils are used as electrodes and they are separated by a dielectric film. The foil capacitor provides various benefits in comparison to the metalized capacitor. Generally, polyester capacitors cannot be used for high frequency or high current applications. However, the foil capacitor offers a higher current for pulse application in comparison to the metalized version. Since the aluminum foil electrodes in this type of capacitor act as a heat sink, they are used in high voltage applications. This extended foil design also helps in operating at high peak current levels.

Mixed dielectric film capacitors:

Mixed dielectric film capacitors are produced with a combination of a layer of paper and a layer of polypropylene films. Many major manufacturers of film capacitors used different combinations of mixed film materials in producing these types of capacitors. These types of capacitors are produced in such a way that it can withstand high current discharge.

Different film capacitors vary in terms of materials used for making dielectric films and they are used in different types of electronic applications.

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