Capacitors are one of the most common components in an electronic device, there are a large variety of types available today. The capacitor is a great device that can store electrical energy in an electric field. Today you’ll get to know the various types of capacitors, and their set of characteristics. They employ applications base on their properties, that is, their voltage rating.
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Types of capacitors
Below are the various type of capacitors and their properties.
The dielectric capacitors are the most common variable types, where a continuous variation of capacitance is needed for tuning transmitters, receivers, and transistor radios. These types of capacitors are multi-plate air-spaced types, having a set of fixed plates (the stator vanes) and a set of movable plates (the rotor vanes). It moves in between the fixed plates.
The overall capacitance value is determined by the position of the moving plates with respect to the fixed plates. When two sets of plates fully mesh together, the capacitance is said to be at maximum. The high voltage type tuning capacitors have relatively large spacings or air gaps between the plates with breakdown voltages reaching many thousands of volts.
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The continuously variable capacitors and preset type variable capacitors are available. They are known as Trimmers. They are generally small devices that can be adjusted or pre-set to a particular capacitance value with the aid of a small screwdriver. Also, they have a very small capacitance value of about 500 pF or less and they are non-polarized.
This is one of the most available types of capacitors, consisting of a relatively large family of capacitors. Their difference is in their dielectric properties including polyester (Mylar), polystyrene, polypropylene, polycarbonate, metalized paper, Teflon, etc. Film capacitors are available in capacitance ranges from as small as 5pF to as large as 100uF depending on the actual types of capacitors and their voltage rating. They also come in an assortment of shapes and case styles which include wrap and fill (oval & round), epoxy case (rectangular & round), metal hermetically sealed (rectangular & round).
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Film capacitor that employs polystyrene, polycarbonate, or Teflon as their dielectrics are sometimes called “plastic capacitors”. Although the construction of plastic film capacitors is similar to that of paper film, the plastic film serves better than paper. The major benefit of plastic film capacitors compare to the impregnated-paper types is that they perform better under high temperatures, have smaller tolerances, serve longer, and are highly reliable. Examples of film capacitors are the rectangular metalized film and cylindrical film & foil types. See diagram below:
Radial Lead Type
Axial Lead Type
These types of capacitors are made from long thin strips of thin metal foil. The dielectric material is sandwiched together and is wound into a tight roll and then sealed in the paper of metal tubes. The film capacitors require a much thicker dielectric film to reduce the risk of tears or punctures in the film. This is why it is more suited to lower capacitance values and larger case sizes.
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The metalized foil capacitors have the conductive film metalized sprayed directly onto each side of the dielectric. This gives the capacitor self-healing properties which is why it can use much thinner dielectric films. Therefore, higher capacitance values and smaller case sizes for a given capacitance. Film and foil capacitors are generally applicable to a higher power and more precise applications.
Ceramic capacitors are generally called DISC capacitors. They are made by coated two sides of small porcelain or ceramic disc with silver, stacked together to form a capacitor. A single ceramic disc of about 3-6mm is used for a capacitor with a low capacitance value. Ceramic types of capacitors are designed to have a high dielectric constant (High-K). They are used on applications that require relatively high capacitance with a small physical size.
Furthermore, they exhibit large non-linear changes in capacitance against temperature. This is why they are used as de-coupling or by-pass capacitors and they are also non-polarized components. These types of capacitors have values ranging from a few picofarads to one or two microfarads, μF, despite the fact their voltage rating is quite low.
Ceramic capacitors have a 3-digit code printed to their body showing their capacitance value in picofarads. The first two digits indicate the capacitors value and the third digit indicates 10 and 3 zeros’ in picofarads which is equivalent to 10,000 pF or 10nF. Also, the 104 indicate 10 and 4 zeros in pico-farads which is equivalent to 100,000 pF or 100nF and so on. So, if a ceramic capacitor has above the number 154 just like the image below, it indicates 15 and 4 zeros in picofarads equivalent to 150,000 pF or 150nF or 0.15 μF. Sometimes, latter codes are used to indicate their tolerance value i.e., J = 5%, K = 10% or M = 20% etc.
Read more: Understanding the dielectric of a capacitor
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Electrolytic types of capacitors are generally used when very large capacitance values are required. In this design, instead of a very thin metallic film layer for one of the electrodes, a semi-liquid electrolyte solution in form of jelly or paste is used as the second electrode (usually the cathode). The dielectric is a very thin layer of oxide acting as an insulating layer and making it possible to make the capacitor with a large value of capacitance for small physical size as the distance between the plates, d is very small.
Most electrolytic capacitors are polarized, that is, the DC voltage applied to the capacitor terminals must be of the correct polarity. For example, positive to the positive terminal and negative to the negative terminal as an incorrect polarization. This will break down the insulating oxide layer and permanent damage may occur. Well, all polarized electrolytic capacitors have their polarity clearly marked with a negative sign indicating their negative terminal and the polarity must be followed.
Generally, electrolytic types of capacitors are used in DC power supply circuits because of their large capacitance and small size. The small size helps to reduce the ripple voltage or for coupling and decoupling applications. One main limitation of these capacitors is that their relatively low voltage rating and the polarization of electrolytic capacitors. Also, that they must be used on AC supplies. Electrolytic capacitors are available in two basic forms; Aluminum and Tantalum electrolytic capacitors.
Aluminum electrolytic capacitors
The aluminum electrolytic capacitors also come in two types; the plain foil type and the etched foil type. The thickness of the aluminum oxide film and high breakdown voltage give these capacitors very high capacitance values for their size. The foil plates of the capacitor are anodized with a DC current. This process set up the polarity of the plate material and determines the positive and negative side of the plate.
The etched foil type of aluminum electrolytic capacitors differs from the plain foil type in that the aluminum oxide on the anode and cathode foils has been chemically etched to increase its surface area and permittivity. With this, as smaller sized capacitor equivalent value than a plain foil type, but cannot withstand DC currents compared to the plain type. Also, its tolerance range is quite large at up to 20%. Typically, the capacitance value for an aluminum electrolytic capacitor ranges from 1uF up to 47,000uF.
Tantalum electrolytic capacitors
These types of electrolytic capacitors are available in both wet (foil) and dry (solid) electrolytic, but the dry or solid tantalum are common. Solid tantalum capacitors use manganese dioxide as their second terminal and are physically smaller than the equivalent aluminum capacitors. The dielectric properties of tantalum oxide are also much good than that of aluminum oxide due to its lower leakage current and better capacitance stability. This makes it suitable for blocking, by-passing, decoupling, filtering, and timing applications.
Furthermore, Tantalum capacitors can tolerate reverse voltage much easily even though they are polarized. But are rated at much lower working voltages. Solid tantalum capacitors are usually used in circuits where the AC voltage is small compared to the DC voltage. Some tantalum capacitor contains two capacitors in one; connected negative-to-negative to form a “non-polarized” capacitor for use in low voltage AC circuits as a non-polarized device. Generally, the positive lead is noted on the capacitor body by the polarity mark, with the body of a tantalum bead capacitor being an oval geometrical shape.
Watch the video below to learn more about the various types of capacitors:
That is all for this section where the various types of capacitors are being discussed. I hope you get enough of the reading, if so, kindly share with other students. Thanks for reading, see you next time!