# Glossary of Capacitor Terms

#### Illinois Capacitor provides this list of capacitor terminology to assist our customers, students and educators alike. If you have a comment on a definition, or have a suggestion for additions, please let us know.

#### Aluminum Electrolytic Capacitor

A capacitor made up of two aluminum electrodes seperated by paper saturated with an electrolyte. The dielectric is the oxide of the anode.

#### Anode

The positive electrode of an electrolytic capacitor.

#### Blocking

A situation where Direct Current (DC) is kept from a circuit element due to the high series impedence of a capacitor.

#### By-passing (De-Coupling)

A situation where the AC portion of a signal is kept from a circuit element via a low impedence path in parallel with the circuit element.

#### Capacitance

A measure of the energy storage capability of a capacitor at a given voltage usually expressed in farads, microfarads, nanofarads, or picofarads.

#### Capacitive Reactance (Xc)

The opposition to the flow of alternating or pulsating current by a capacitor measured in ohms. The imaginery component of the impedence of a capacitor.

#### Capacitor

A passive circuit element capable of storing electrical energy and releasing it at a predetermined time and at a predetermined rate.

#### Cathode

The negative electrode of a capacitor.

#### Charge

The quantity of electrical charge measured in coulombs.

#### Coupling

Situation where two circuits are connected together where only the AC voltage is passed.

#### Current

The amount of charge moving past a given reference point over time.

#### Dielectric

An insulating or non-conductive medium between the plates of a capacitor.

#### Dielectric Absorption

A measure of the reluctance of a capacitor's dielectric to discharge completely - usually measured in percent of original charge.

#### Dielectric Constant

The ratio of a capacitor's capacitance with a given dielectric to the same capacitor having a vacuum as a dielectric.

#### Dissipation Factor (D.F. or Tan delta)

A measure of the losses in a capacitor expressed as the ratio of the E.S.R. of a capacitor to its reactance at a specific frequency and temperature.

#### dv/dt Rating

The maximum voltage rise (or discharge) time a capacitor can withstand being damaged.

#### EDLC

See supercapacitors

#### Electrolyte

A current-conducting solution between the electrodes of a capacitor used to replenish the dielectric in an aluminum electrolytic capacitor.

#### Equivalent Series Resistance (E.S.R.)

The sum of all the internal resistances of a capacitor measured in ohms. Expressed mathematically as ESR = D.F.*Xc.

**Farad**

The basic unit of a measure of a capacitor. A capacitor charged to 1 volt with a charge of 1 coulomb would have a capacitance of 1 farad. 1 microF = .000001 Farads.

**Film Capacitors**

A capacitor made up of two metal plates seperated by a plastic(polymer) dielectric material.

#### Frequency

The rate at which an alternating or pulsating wave repeats itself expressed in cycles per second (C.P.S.) or hertz (Hz).

#### Impedance (Zc)

The total opposition offered to alternating or pulsating current measured in ohms. Impedence is the vector sum of the resistive and reactive components of a capacitor expressed mathematically as

#### Insulation resistance

The ratio of the DC voltage applied to the terminals of a capacitor and the resultant leakage current flowing through the dielectric and over its surface after the initial charging current has ceased expressed in megohms or as time constant megohm x microfarads.

#### Leakage Current

Measure of the stray direct current flowing through capacitor after DC voltage is impressed on it.

#### Metallized Capacitor

A capacitor where a thin layer of metal is vacuum-deposited directly onto the dielectric.

#### Ripple Current

The total amount of alternating and direct current that can be applied to a capacitor under specific conditions without causing a failure.

#### Snubber Capacitor

Capacitors used independently or with other circuit elements to suppress voltage transients in electrical circuits.

#### Supercapacitors

Supercapacitors also called ultracapacitors or Electric double layer capacitors (EDLC) are capacitors made up of 2 metal plates with a carbon dielectric material and a conductive electrolyte.

#### Surge Voltage (SV)

The maximum DC voltage a capacitor can tolerate under any circumstances for a short period of time without suffering any damage.

#### Tolerance

The maximum deviation from a nominal capacitance value at specific conditions expressed as a percentage of nominal capacitance.

#### Voltage

The force or electrical pressure which causes current to flow through a conductor.

#### Ultra Capacitor

See supercapacitors

#### Working Voltage (WVDC)

The maximum DC voltage applied to a capacitor for continuous operation at maximum rated temperature.