8/3/2019 Constructia Condensatorului Cu Al

1/1

RUBYCON CORPORATION 1

TECHNICAL NOTES FOR ELECTROLYTIC CAPACITOR1. BASIC CONSTRUCTION OF ALUMINUM

ELECTROLYTIC CAPACITOR

Basic construction of aluminum electrolytic capacitor isshown in Fig. 1.1.

Aluminum electrolytic capacitor consists of anodealuminum foil formed with aluminum oxide film on thesurface as dielectric, cathode aluminum foil as collector,and liquid electrolyte as the real cathode, the electrolyteimpregnated in spacer paper put between both foils.

Aluminum oxide film, which is formed throughanodization (generally referred to as forming) ofaluminum foil in an appropriate electrolyte, is very thinand its thickness is in proportion to the voltage applied.

Fig. 1.1

(1) Anode: Substrate of anode aluminum foil

(2) Cathode: Liquid electrolyte

(3) Dielectric: Aluminum oxide film formed on thesurface of anode foil

(4) Cathode Foil: Electrically connects electrolyte toexternal terminal. Cathode foil is not requiredforming process to form oxide film, but it is coveredwith natural oxide film on the surface due to reactionof aluminum with oxygen in the air after etching. Itis said that this natural oxide film has thewithstanding voltage of 1 to 2 volts.

(5) Spacer Paper: Preventing physical contactbetween anode and cathode foil and holding

necessary amount of electrolyte.

Oxide film on anode foil withstands DC voltage onlywhen the capacitor is charged as positive polarity toaluminum substrate and negative to electrolyte. If thecapacitor is charged with reversed polarity, it will losewithstanding voltage property in a few seconds.These phenomena are called Valve Effect, which isthe reason why aluminum electrolytic capacitor haspolarity.If both electrode aluminum foil have formed oxide film,the capacitor will be a non-polarized capacitor.

Various papers report mechanism for valve effect ofaluminum, in which the predominant Hydrogen Ion

Theory is explained hereunder. When the systemincluding aluminum foil with anodic oxide film and anelectrolyte is charged so that the electrolyte is at thepositive side and the metal at the negative side,hydrogen ions gathered on the surface of the oxide filmpass through the film to reach the boundary betweenthe metal and the film and convert into hydrogen gasthrough discharge. Bubbles of hydrogen gas peel theoxide film off the aluminum substrate with expandingforce, so that electric current flows after penetration ofelectrolyte. On the contrary when the system ischarged with reversed polarity, anions with much largerdiameter gather on the surface of the film. Howeverthe film maintains voltage because such anions areunable to pass through the film due to their largerdiameter.

Anode

Dielectric

Spacer Paper + Cathode

Cathode Foil