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foil capacitor

Film capacitors, also known as film capacitors, belong to the group of non-polarized fixed capacitors. Their electrodes are thin metal foils separated by insulating films. They are constructed in wound form and are characterized by their compact design. In some embodiments, the electrodes are directly vapor deposited onto the insulating film that forms the dielectric.

As for plastic films, polyester( PET), polycarbonate( PC), polyphenylene sulfide( PPS), polytetrafluoroethylene(PTFE), polyethylene naphthalate (PEN), polystyrene( PS), and polypropylene( PP) are used.

If the dielectric is plastic, they are called plastic film capacitors, and if paper, they are paper capacitors. The dielectric strength of plastic film capacitors is very high, ranging from 500 V/µm to 700 V/µm, and the dielectric constants are between 2 and 3.5. An increase in dielectric strength is achieved by using a thicker plastic film or by using double-sided metallized films. In both designs - plastic and paper - the metal electrode can be vapor-deposited directly onto the plastic or paper film. In the case of very high dielectric strength, parts of the film are metallized and form a film capacitor in themselves. These individual partial capacitors are connected in series and thus have a higher dielectric strength. As far as the different designs are concerned, these are expressed in the type description.

Marking of film capacitors

Marking of film capacitors

For example, the "K" marking indicates that the electrode is a separate metal foil; in the case of metal plastic( MK), the metal electrode is vapor-deposited onto the plastic foil; in the case of metal paper( MP), it is a metal paper capacitor that uses an oil-impregnated paper foil as the dielectric onto which a metal layer is vapor-deposited as the electrode. And in the MKP marking, the dielectric is polypropylene with double-sided metallized paper on which the electrodes are vapor-deposited.

Structure of MKV capacitor

Structure of MKV capacitor

Capacitance values of film capacitors range from a few hundred picofarads to microfarads. Film and metal-paper capac itors differ from all other capacitors in that they are self-healing. When a voltage flashover occurs between the electrodes, the thin metal layer around the breakdown point evaporates, preventing a short circuit between the electrodes.

Informations:
Englisch: foil capacitor
Updated at: 17.05.2021
#Words: 351
Links: also known as (aka), indium (In), dielectric, arsenic (As), polyethylene terephthalate (PET)
Translations: DE
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