There are various types of capacitors on the market, each with its own characteristics and applications. Available capacitor types include precision trimmer capacitors for oscillators or radio circuits, and high-power metal can-type capacitors for high-voltage power correction and smoothing circuits.
Comparisons between different types of capacitors are usually made with regard to the dielectrics used between the boards. Like resistors, there are variable types of capacitors that allow us to change their capacitance value for use in radio or “frequency tuned” type circuits.
Commercial types of capacitors are made of metal foil that is interwoven with a thin sheet of paraffin-impregnated paper or polyester film as a dielectric material. Some capacitors look like tubes because the metal foil is rolled into a cylinder to form a small package with an insulating dielectric material sandwiched between them. Small capacitors are usually made of ceramic material and then dipped in epoxy to seal them.
Either way, capacitors play an important role in electronic circuits, so here are some of the more “common” capacitor types.
Dielectric capacitors are usually of variable type, and continuous changes in capacitors are necessary to tune transmitters, receivers, and transistor radios. The variable dielectric capacitor is a multi-plate air-spaced type having a set of fixed plates (stator blades) and a set of movable plates (rotor blades) moving between the fixed plates. The position of the moving plate relative to the fixed plate determines the total capacitance value. When the two sets of plates are fully engaged, the capacitance is usually the largest. High-voltage type tuning capacitors have a relatively large gap or air gap between the plates, and their breakdown voltage reaches thousands of volts.
In addition to the continuous variable type, a preset type variable capacitor called a trimmer can also be used. These are usually small devices that can be adjusted or “preset” to specific capacitance values with the help of a small screwdriver, and can provide very small capacitances of 500 pF or less and are non-polarized. (read more variable capacitor)
Film capacitor type
Film capacitors are the most commonly used capacitors of all types and consist of a relatively large series of capacitors, with the difference in their dielectric properties. These include polyester (polyester film), polystyrene, polypropylene, polycarbonate, metalized paper, Teflon, etc. Film capacitors range in capacitance from 5pF to 100uF, depending on the actual type of capacitor and its rated voltage. Film capacitors are also available in various shapes and housing types, including:
§ Wrap and Fill (Oval and Round)-Capacitors are wrapped with tight plastic tape and the ends are filled with epoxy to seal them.
§ Epoxy case (rectangular and round)-The capacitor is enclosed in a molded plastic case and then filled with epoxy.
§ Hermetically sealed metal (rectangular and round)-Capacitors are enclosed in metal tubes or can be sealed with epoxy resin.
Film capacitors using polystyrene, polycarbonate, or polytetrafluoroethylene as their dielectric are sometimes referred to as “plastic capacitors.” The structure of a plastic film capacitor is similar to that of a paper film capacitor, but a plastic film is used instead of paper. Compared with impregnated paper types, the main advantages of plastic film capacitors are that they work well at high temperatures, have smaller tolerances, very long service life, and high reliability. Examples of film capacitors are rectangular metalized film and cylindrical film and sheet types as shown below.
Ceramic capacitors or disc capacitors are made by coating both sides of small porcelain or ceramic disc with silver and then stacking them together to make a capacitor. For very low capacitance values, using a single ceramic disc of about 3-6mm. Ceramic capacitors have a high dielectric constant (High-K) and are available, so relatively high capacitance can be obtained in a small physical size.
They exhibit large non-linear changes in capacitance to temperature and are therefore used as decoupling or bypass capacitors because they are also non-polarized devices. Ceramic capacitors range in value from a few picofarads to one microfarad or two microfarads (μF), but their rated voltages are usually very low.
Ceramic type capacitors usually have a 3-digit code printed on their body to identify their capacitance value in picofarads. Generally, the first two digits represent the capacitor value and the third digit represents the number of zeros to be added. For example, a ceramic disc capacitor with the label 103 will represent 10 and 3 in a pico-stopwatch, which is equal to 10,000 pF or 10 nF.
When very large capacitance values are needed, electrolytic capacitors are usually used. Instead of using a very thin metal film layer for one of the electrodes, a semi-liquid electrolyte solution in the form of jelly or paste is used, which is used as the second electrode (usually the cathode).
Dielectrics are very thin oxide layers that grow electrochemically during production, and the thickness of the film is less than 10 microns. This insulating layer is very thin, and since the distance d between the plates is very small, a capacitor having a large capacitance value can be manufactured for a small physical size.
Most electrolytic type capacitors are polarized, that is, the DC voltage applied to the capacitor terminals must have the correct polarity, that is, positive terminal positive, negative terminal negative, because incorrect polarization can destroy the insulating oxide layer and may cause permanent damage.