Types of Capacitors & Their Uses

Capacitors come in a variety of sizes and dielectric types.

Capacitors serve as electrical reservoirs, storing and releasing electric charges. These fundamental components are used in all kinds of devices, from televisions and computers to radios and amplifiers. Almost every electronic circuit has several. As containers of charge, they have capacities and voltage ratings to cover a variety of needs and usage. Component manufacturers use different materials to manufacture capacitors, depending on the intended use.

Ceramic

Every capacitor is a "sandwich" of an insulator between two layers of metal. The material used for the insulator, called the dielectric, largely determines the capacitor's overall behavior. Capacitors with a ceramic dielectric tend to have small values, ranging from a few picofarads (trillionths of a farad, the unit of capacitance) up to 1,000 picofarads. They tend to have good capacitance stability over a wide temperature range. Quartz crystal oscillator circuits and radio-frequency electronic filters use ceramic capacitors.

Tantalum

Applications requiring a large capacitance value in a small space might use tantalum capacitors. These are polarized components; one lead prefers positive charges, and the other prefers negative ones. If a tantalum capacitor is wired backwards, the reverse polarity will probably destroy the part. A bad tantalum capacitor will "weep" a silvery fluid. Audio and analog signal equipment use tantalum capacitors, as do some power supplies.

Aluminum Electrolytic

Used mainly for power-supply filters and other applications less sensitive to capacitance value, aluminum electrolytic capacitors are inexpensive and rugged. Due to their manufacturing process, they are made with a tolerance of about 20 percent, so the actual value of the part may be 20 percent greater or less than the labeled value. Over decades, electrolytic capacitors can dry out, so technicians who restore vintage electronics routinely replace these capacitors.

Polyester Film

Capacitors with a polyester film dielectric come in a wide range of capacitance values and have good reliability. Their capacitance increases slightly with temperature, so these cannot be used for more sensitive circuits. Polyester film capacitors are inexpensive and widely available.

Silver Mica

Mica, a naturally occurring mineral that forms thin sheets, makes a good dielectric. Silver mica capacitors have accurate part values and good reliability, though they command higher prices than some other capacitors. These capacitors are used for frequency-sensitive parts of audio and radio circuits. Capacitance values start at a few picofarads and go up to low microfarads; voltage ratings range up to about 1,000 V.

References

• The Electronics Club; Capacitors; John Hewes; 2010
• Kemet: Application Notes for Tantalum Capacitors
• MusicSynthesizer.com; "Capacitors: A Field Guide to Types and Habitats"; Harry Bissell; 1999