Types of Capacitors

Capacitors are normally classified according to the type of dielectric material used. The most common types are mica, ceramic, plastic-film, and electrolytic (aluminum oxide, tantalum oxide) capacitors. Capacitors are also available as surface-mounted components. They are called chip capacitors.

Mica Capacitor

Ceramic Capacitor

Plastic-film Capacitor

Capacitor values are indicated on the capacitor body either by numerical or alphanumerical labels or sometimes by color code. Capacitor labels indicate various parameters such as capacitance, voltage rating, and tolerance.
The illustration shows the basic construction of mica, ceramic, and plastic-film capacitors.

Electrolytic Capacitors

Tantalum capacitors

  Aluminum Capacitor

Electrolytic capacitors offer much higher capacitance values than mica or ceramic capacitors and their voltage ratings are typically higher. Aluminum electrolytic capacitors are the most commonly used type. Tantalum capacitors have larger C, in smaller size, but they cost more than the aluminum type. Electrolytic capacitors are the only capacitors that require the observation of polarity when connecting to a circuit. Reversal of the voltage polarity can completely destroy a capacitor. The illustration shows typical electrolytic capacitors and a cut-away view of a teardrop-shaped tantalum capacitor.  

Variable Capacitors

Variable capacitors are used in a circuit where it is necessary to adjust the capacitance value, for example, in radio or TV tuners. The schematic symbol for a variable capacitor is shown above.

 

Adjustable capacitors that normally have slotted screw-type adjustments are called trimmers. They are used for very fine adjustments in a circuit. Ceramic or mica is a common dielectric in these capacitor types. Capacitance value is directly related to plate area A, and inversely related to plate separation d. For this reason, it is usually changed by adjusting one of these parameters.