Film capacitors are among the most widely used capacitor types today alongside electrolytic and ceramic capacitors. This is due to their unique construction and properties, which give them an advantage over other capacitor types in pulse and current-carrying applications, among others. In this article, the basics of operation, different categories, and cross-referencing process for film capacitors will be discussed.
Characteristics of Film Capacitors
The distinguishing characteristic of a film capacitor is the dielectric material, which is made of plastic film, sometimes combined with paper. They are not polarized, meaning that they can be used in both AC and DC applications. When comparing ceramic vs. film capacitors, while both are non-polarized, the latter are preferred in applications where temperature and frequency stability are required. When comparing electrolytic vs. film capacitors for decoupling applications, film capacitors provide lower parasitic inductance and resistance. Another advantage of film capacitors is their lifetime, which is comparatively longer than for electrolytic and ceramic capacitors.
Types of Film Capacitors and Applications
There are two distinguishing factors to consider when selecting a film capacitor. The first is the dielectric type. Different plastics can be used as dielectrics in order to adjust the thermal and electrical properties of the capacitor. For example, high voltage film capacitors can be constructed with the right choice of the dielectric.
Polypropylene capacitors, or polypropylene film capacitors, use the dielectric material of the same name, sometimes abbreviated to PP. One advantage of this dielectric is high temperature and frequency stability. Because of this, polypropylene capacitors are often used in high-frequency applications, such as oscillators and power supplies. They can be bought in three stability classes, with a lower number designating tighter temperature stability requirements.
Polyester capacitors, or polyester film capacitors, feature a dielectric material of the polymer polyethylene terephthalate (PET). These capacitors are also known by their trade names, such as Mylar film capacitors or Hostaphan film capacitors. One advantage of the PET dielectric is its higher temperature rating, which allows SMT film capacitors to be manufactured and withstand soldering process temperatures. It also features a high capacitance per unit volume due to high relative permittivity, though this also results in more temperature instability than other film capacitor types. Thus polyester capacitors are typically used in general purpose, non-critical applications.
The third type of film capacitors is polyphenylene sulfide film capacitors or PPS film capacitors. These have excellent temperature and stability characteristics and are SMD capable, but come at a higher cost than equivalent polypropylene film capacitors. In addition to these three popular dielectrics, there are other plastics used with varying electrical and physical characteristics.
The second distinguishing factor for film capacitors is the manufacturing process. There are two distinct ways to make a film capacitor. The first is by applying the electrodes directly to the dielectric. These are known as metalized film capacitors. The second is to use a metal film as the electrode, which is a cheaper process but produces a larger and less stable capacitor. These are known as metal film capacitors or metal foil capacitors.
Using SourcingBot to Find the Right Film Capacitor
SourcingBot is a great engineering resource for finding the right film capacitor for new designs, as well as finding replacement options for existing designs. The film capacitor database, which can be searched at, features over eighty thousand film capacitors. The parametric search features make it easy to filter by circuit requirements and find the largest number of eligible parts for a new design.
In addition, SourcingBot calculates cross-references for every film capacitor. Simply visit a part page, such as this example from Vishay: https://sourcingbot.com/passive-components/capacitors/film-capacitors/vishay/mkt1817410066w. At the bottom of the page, a list of the most similar parts has been calculated to help engineers find relevant replacement parts for their designs. In addition, filters can be used on similar parts, allowing the user to focus on specific mechanical and electrical properties.