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.

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.

Overview of construction and features

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.