Aluminum Electrolytic Capacitors are a type of polarized capacitor that uses aluminum as the electrode material. They are widely employed in electronic circuits due to their high capacitance values and relatively low cost. Aluminum electrolytic capacitors are a type of wound capacitor. They are constructed with two aluminum foils - an anode foil and a cathode foil – separated by a paper spacer soaked in a liquid or gel-like electrolyte. Etching is done on the anode and cathode foil to increase its surface area and thereby increase the capacitance. When a positive voltage is applied to the anode, an insulating oxide layer with a thickness corresponding to the applied voltage is formed. This oxide layer acts as the dielectric in an electrolytic capacitor. A separator is a non-conductive material that prevents direct electrical contact between the anode and cathode while allowing ions to move freely.

Construction and Working Principle

Construction of Aluminium Electrolytic Capacitor

Key Electrical Parameters of Aluminum Electrolytic Capacitor

• Capacitance (C): It is a measure of the ability of the capacitor to store charge per unit voltage. These capacitors have values ranging from a few microfarads to thousands of microfarads. Capacitance increases with higher temperature and decreases with higher frequency.
• Equivalent Series Resistance (R_ESR): The ESR of an Aluminum Electrolytic Capacitor is a measure of internal resistance that causes power loss and heating within the capacitor.  It is mainly determined by the resistance of the electrolyte and decreases as temperature increases. Typical ESR value ranges from a few milliohms (mΩ) to a few ohms. 
• Rated Voltage (V_rated): It is the maximum continuous operating voltage that the capacitor can handle without failure. The rated voltage of aluminum electrolytic capacitors ranges between 6.3V to 450V, depending on the application and design.
• Equivalent Series Inductance (L_ESL): The equivalent series inductance of an aluminum electrolytic capacitor characterizes the effective self-inductance of the capacitor.
• Leakage Current (I_leakage): It is the small amount of current that leaks through the capacitor even when it is charged and no external load is connected. A lower leakage value of current is preferred for energy efficiency and longer capacitor life. Typical values range from a few microamperes (µA) to several milliamperes (mA), depending on the capacitor's size and voltage rating.

Aluminum electrolytic capacitors are utilized in various applications due to their unique combination of high capacitance, moderate energy density, and relatively high voltage ratings. They are used for power supply smoothing, energy storage, automotive, consumer electronics, backup power and industrial equipment.

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