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Glossary of Capacitor Terms

-C-

• Capacitance
  
• Cathode
  
• Cathode Foil
  

Capacitance, Electrostatic

Ability of conductors, separated by dielectrics, to store electrostatic charges. The charge Q is directly related to the product of capacitance C and voltage V as

Q = CV.

Capacitance is directly proportional to the area of either conductor A (called plates in the parallel-plate capacitor) and indirectly proportional to the distance between the plates d :

C = epsilonA / 4pid

where epsilon is the dielectric constant of the medium between the plates.

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Cathode

An electrode through which current leaves any nonmetallic conductor. An electrolytic cathode is an electrode at which positive ions are discharged, or negative ions are formed, or at which other reducing reactions occur. The negative electrode of a galvanic cell; of an electrolytic capacitor.

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Cathode Foil

An aluminum electrolytic capacitor is typically composed of an anode foil, a cathode foil and separator material which are wound together and impregnated with an electrolyte. The cathode foil typically does not have an aluminum oxide layer acting as the dielectric. The aluminum foil (12.7 to 40 microns) is electrochemically etched to increase it's surface area, and therefore its capacitance. A thin layer of aluminum oxide naturally grows on the surface of the foil, but is only equivalent to approximately 0.5 to 1.5 volts.

Non-polar and bi-polar capacitors utilize two anode foils instead of anode and cathode foils. Each foil would thus be capable of supporting the full rated DC+AC voltage.

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Updated: 24 March 2000

Copyright © 1996-2000 Tyra T. Buczkowski. All rights reserved.