Electronics Components: Sizes and Shapes of Capacitors
You’ll find one or more capacitors in almost every electronic circuit you build. And capacitors come in all sorts of shapes and sizes, influenced mostly by three things: the type of material used to create the plates, the type of material used for the dielectric, and the capacitance.
The most common types of capacitors are
Ceramic disk: The plates are made by coating both sides of a small ceramic or porcelain disk with silver solder. The ceramic or porcelain disk is the dielectric, and the silver solder forms the plates. Leads are soldered to the plates, and the entire thing is dipped in resin.
Ceramic disk capacitors are small and usually have low capacitance values, ranging from 1 pF to a few microfarads. Because they’re small, their values are usually printed using a three-digit shorthand notation.
Ceramic disk capacitors aren’t polarized, so you don’t have to worry about polarity when you use them.
Silver mica: The dielectric is made from mica, and this capacitor is sometimes referred to simply as a mica capacitor. As with ceramic capacitors, the plates in a silver mica capacitor are made from silver. Electrodes are joined to the plates, and then the capacitor is dipped in epoxy.
Silver mica capacitors come in about the same capacitance range as ceramic disk capacitors. However, they can be made to much higher tolerances — as close as 1% in some cases. Like ceramic disk capacitors, silver mica capacitors aren’t polarized.
Although ceramic disk and mica capacitors are constructed in a similar way, they’re easy to tell apart. Ceramic disk capacitors are thin, flat disks and are nearly always a dull, light-brown color. Silver mica capacitors are thicker, bulge at the ends where the leads are attached, and are shiny and sometimes colorful — red, blue, yellow, and green are common colors for silver mica capacitors.
Film: The dielectric is made from a thin film-like sheet of insulating material, and the plates are made from film-like sheets of metal foil. In some cases, the plates and the dielectric are then tightly rolled together and enclosed in a metal or plastic can. In other cases, the layers are stacked and then dipped in epoxy.
Depending on the materials used, capacitance for film capacitors can be as small as 1,000 pF or as large as 100 μF. Film capacitors aren’t polarized.
Electrolytic: One of the plates is made by coating a foil film with a highly conductive, semiliquid solution called electrolyte. The other plate is another foil film on which an extremely thin layer of oxide has been deposited; this thin layer serves as the dielectric. The two layers are then rolled up and enclosed in a metal can.
Electrolytic capacitors are polarized, so you must be sure to connect voltage to it in the proper direction. If you apply voltage in the wrong direction, the capacitor may be damaged and might even explode.
You find these two common types of electrolytic capacitors:
Aluminum: Can be quite large, with as much as a tenth of a farad or more (100,000 μF).
Tantalum: Are smaller, ranging up to about 1,000 μF.
Variable: A capacitor whose capacitance can be adjusted by turning a knob. One common use for a variable capacitor is to tune a radio circuit to a specific frequency.
In the most common type of variable capacitor, air is used as the dielectric, and the plates are made of rigid metal. Several pairs of plates are typically used in an intermeshed arrangement. One set of plates is fixed (not moveable), but the other set is attached to a rotating knob.
When you turn the knob, you change the amount of surface area on the plates that overlap. This, in turn, changes the capacitance of the device.
Variable capacitor Schematic symbol