Characteristics of Film Capacitors
Film capacitors are electrical capacitors with an insulating plastic film and generally called power film capacitors. Insulating plastic film is used as dielectric in film capacitors. You can find a wide variety of film capacitors in the market such as polymer film capacitors, plastic film capacitors, metallized polypropylene film capacitors, film dielectric capacitors etc. Film capacitors are used in many AC and DC microelectronics and electronic circuits like electrolytic capacitors. The electrodes of film capacitors may be metallized aluminium or zinc applied directly to the surface of plastic film. Both conductive layers are wound into a cylindrical shaped winding.
Polypropylene film capacitors have the lowest dielectric absorption which makes them suitable such as VCO timing, sample-and-hold applications and audio circuits. These kinds of capacitors are widely used for EMI suppression. Polypropylene film capacitors are also used as CRT-Scan deflection circuits and in IGBT applications. Polyester film capacitor is another type in this category. Thermoplastic polymer material is used to make dielectric. These capacitors come in two forms; metallized winding and stacked versions. These capacitors are famous with name of PET due to polyethylene terephthalate material. These are cheap in cost and have high capacitance values. These capacitors are mainly used in DC applications and maximum temperature rating is 125 degree celsius.
Polyethylene Naphthalate Film Capacitors are another type of metallized film capacitors and widely used for high temperature applications. Dielectric used in these types of film capacitors is made of thermoplastic biaxial polymer material polyethylene naphthalene and these are also known as PEN. These are similar to PET in capacitance, temperature and frequency dependence. PEN capacitors are mainly used for non-critical filtering, coupling and decoupling in electronic circuits, when the temperature dependencies do not matter.
Polyphenylene sulfide film capacitors are film capacitors with dielectric made of the thermoplastic, organic, and partially crystalline polymer material Poly Phenylene Sulfide and that’s why these capacitors are also called as PPS, trade name Torelina. They are only produced as metallized types.
The temperature dependence of the capacitance of PPS film capacitors over the entire temperature range is very small (± 1.5%) compared with other film capacitors. Also the frequency dependence in the range from 100 Hz to 100 kHz of the capacitance of the PPS film capacitors is ± 0.5%, very low compared with other film capacitors. The dissipation factor of PPS film capacitors is quite small, and the temperature and frequency dependence of the dissipation factor over a wide range is very stable. Only at temperatures above 100 °C does the dissipation factor increase to larger values. The dielectric absorption performance is excellent, behind only PTFE and PS dielectric capacitors. Polyphenylene sulfide film capacitors are well-suited for applications in frequency-determining circuits and for high-temperature applications. Because of their good electrical properties, PPS film capacitors are an ideal replacement for polycarbonate film capacitors.
