One of the most important passive electrical components found in a wide range of circuits are capacitors. Capacitors can be divided into two broad categories: polarized and nonpolarized. As a result of their flexibility and low price points, film capacitors are the most common types.
Belonging to the category of non-polarized capacitors, film capacitors utilize thin plastic films to produce their dielectric. These films are often metalized and can be purchased under the name of “metalized condenser.” Also called plastic capacitors or metalized capacitors, there are numerous types that fall under these umbrella terms.
Thin film capacitors, in particular, are composed of a plastic film with bipolar capacitors as their dielectric. To create a roll or candy-like rectangular shape, these films can be metalized or stacked in layers. Other dielectrics that are commonly used include polypropylene (PP), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), and polyphenylene sulfide (PPS).
The major advantage of using a film capacitor is the very low distortion factor and incredible frequency features it offers. Moreover, the type of plastic film used for many film condensers provides additional flexibility, and these capacitors generally do not wear out easily, meaning that they are perfect for various applications, including coupling/decoupling circuits, high voltage and high-frequency applications, and more.
Different Types of Film Capacitors
There are several types of film capacitors, all of which vary according to the type of dielectric plastic materials used. Despite the available options, polyester condensers and polypropylene condensers are the most used. For example, polyester film capacitors have a dielectric material made of polyethylene terephthalate (PET), which is why they are often referred to as PET film capacitors.
The second type, polypropylene film capacitors or PP film capacitors, have a dielectric material made of polypropylene. As such, it is obvious that capacitors are defined by the type of polymer used for the dielectric, and in the next section, we will outline two other popular types and their applications. It is worth noting that capacitors are categorized based on construction as well; thus, they can be grouped into two groups: film/foil capacitors and metalized film capacitors.
Film/foil capacitors use plastic films as their dielectric and are usually mounted between two layers of aluminum foil electrodes. Additionally, these capacitors are either non-inductive or inductive, and their layers are organized in such a way that they do not come in direct contact with the metallic layers. Instead, the aluminum foils are situated in the middle of the two films in such a way that the inductive film foil capacitor is easily wound.
In a non-inductive film/foil capacitor, the aluminum foils are configured so that each foil is positioned to a certain degree out of the films. For coupling, decoupling capacitors, and bypass applications, PET film/foil capacitors are ideal, while PP film/foil capacitors are good choices for high frequency applications like resonant and oscillator circuits. In terms of benefits, these capacitors offer high insulation resistance, good capacitance stability, and high efficiency at high frequencies.
Metalized Film Capacitors
The main difference between a film/foil capacitor and a metalized capacitor lies in the fact that the metallic electrodes are fused into either side of the dielectric plastic in metalized capacitors instead of being stacked in layers. However, it raises the cost and adds an extra step in the production process, but is more reliable and compact. To acquire the desired capacitance value, the thickness of the plastic film can be as small as 0.6μm.
One of the primary benefits of these capacitors is their self-healing property which helps them repair themselves if the electrodes have been exposed to each other instead of being short-circuited, thus, increasing the capacitor reliability. In addition, they are small in size and form, making them perfect for compact applications. In electronic control circuits, metalized film capacitors are go-to choices.
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