Film capacitor

Film capacitors, plastic film capacitors, film dielectric capacitors, or polymer film capacitors, generically called “film caps” as well as power film capacitors, are electrical capacitors with an insulating plastic film as the dielectric, sometimes combined with paper as carrier of the electrodes.Schematic picture comparison of film/foil vs. metallized film capacitor internalsCross-section of a plastic film capacitorFlattened winding of a 'naked' film capacitor before encasement, with a view of collateral metal contact layers ('schoopage') and attached terminalsMetallized polycarbonate film capacitor with double sided metallized filmsHigh voltage capacitor with two capacitors internally series-connectedHigh voltage capacitor with four capacitors internally series-connectedAxial style for point-to-point and through-hole mountingRadial style (single ended) for through-hole solder mounting on printed circuit boardsRadial style with heavy-duty solder terminals for snubber applications and high surge pulse loadsHeavy-duty snubber capacitor with screw terminalsSMD style for printed circuit board surface mounting, with metallized contacts on two opposite edgesMP capacitor, single-sided metallized paper (additional layer of paper to cover pinhole defects), windings impregnated with insulating oilMKP power capacitor, single-sided metallized paper and polypropylene film, (mixed dielectric), windings impregnated with insulating oilMKV power capacitor, double-sided metallized paper (field-free mechanical carrier of the electrodes), polypropylene film (dielectric), windings impregnated with insulating oilDissipation factor of different film materials as a function of temperatureDissipation factor of different film materials as a function of frequencyMetallized paper RFI suppression capacitors (MP3) with safety marks for “X2” safety standardMetallized polypropylene RFI suppression capacitor (MKP) for 'X2' safety standardCombined XY-RFI suppression capacitorAppliance Class I capacitor connectionAppliance Class II capacitor connectionRC snubbers, a simple RC circuit with a small resistor (R) in series with a small film capacitor (C) in a common caseSnubber film capacitors with heavy-duty terminals for higher-power electronic applicationsPower film capacitor for AC power factor correction (PFC), packaged in a cylindrical metal canPower film capacitor in rectangular housing Film capacitors, plastic film capacitors, film dielectric capacitors, or polymer film capacitors, generically called “film caps” as well as power film capacitors, are electrical capacitors with an insulating plastic film as the dielectric, sometimes combined with paper as carrier of the electrodes. The dielectric films, depending on the desired dielectric strength, are drawn in a special process to an extremely thin thickness, and are then provided with electrodes. The electrodes of film capacitors may be metallized aluminum or zinc applied directly to the surface of the plastic film, or a separate metallic foil. Two of these conductive layers are wound into a cylinder shaped winding, usually flattened to reduce mounting space requirements on a printed circuit board, or layered as multiple single layers stacked together, to form a capacitor body. Film capacitors, together with ceramic capacitors and electrolytic capacitors, are the most common capacitor types for use in electronic equipment, and are used in many AC and DC microelectronics and electronics circuits. A related component type is the power (film) capacitor. Although the materials and construction techniques used for large power film capacitors are very similar to those used for ordinary film capacitors, capacitors with high to very high power ratings for applications in power systems and electrical installations are often classified separately, for historical reasons. As modern electronic equipment gained the capacity to handle power levels that were previously the exclusive domain of 'electrical power' components, the distinction between the 'electronic' and 'electrical' power ratings has become less distinct. In the past, the boundary between these two families was approximately at a reactive power of 200 volt-amperes, but modern power electronics can handle increasing power levels. Film capacitors are made out of two pieces of plastic film covered with metallic electrodes, wound into a cylindrical shaped winding, with terminals attached, and then encapsulated. In general, film capacitors are not polarized, so the two terminals are interchangeable. There are two different types of plastic film capacitors, made with two different electrode configurations: A key advantage of modern film capacitor internal construction is direct contact to the electrodes on both ends of the winding. This contact keeps all current paths to the entire electrode very short. The setup behaves like a large number of individual capacitors connected in parallel, thus reducing the internal ohmic losses (ESR) and the parasitic inductance (ESL). The inherent geometry of film capacitor structure results in very low ohmic losses and a very low parasitic inductance, which makes them especially suitable for applications with very high surge currents (snubbers) and for AC power applications, or for applications at higher frequencies. Another feature of film capacitors is the possibility of choosing different film materials for the dielectric layer to select for desirable electrical characteristics, such as stability, wide temperature range, or ability to withstand very high voltages. Polypropylene film capacitors are specified because of their low electrical losses and their nearly linear behavior over a very wide frequency range, for stability Class 1 applications in resonant circuits, comparable only with ceramic capacitors. For simple high frequency filter circuits, polyester capacitors offer low-cost solutions with excellent long-term stability, allowing replacement of more expensive tantalum electrolytic capacitors. The film/foil variants of plastic film capacitors are especially capable of handling high and very high current surges.