MAL213664182E3

Aluminum Electrolytic Capacitors

Aluminum electrolytic capacitors (AECs) are widely used in applications requiring large capacitance values in small packages. These capacitors are used extensively in AC and DC filters, power factor correction, and switching power supply circuits because of their excellent cost-performance ratio. Their structure is made up of several stacked layers of aluminum oxide dielectric, cathode foil, electrolyte, spacer, and anode foil. The high capacitance value of this type of capacitor stems from the high dielectric constant of the aluminum oxide. Since the capacitance value is inversely proportional to its working voltage, AECs usually feature an operating voltage range spanning up to 630 Vac.In a typical AEC capacitor, the anode and cathode foil are etched into a honeycomb-like pattern, known as a rolled foil. This helps to increase the surface area between the two foils, and achieved a high capacitance within a small volume. The anode foil then undergoes electrochemical treatment to form a layer of alkaline aluminum oxide with a thickness of almost three microns to act as the dielectric. This oxide layer along with the two metal foils act as the two plates of the capacitor. A semi-solid electrolyte is used to separate the two foils, and is also conductive enough to keep the cathode foil at a constant potential.When a voltage is applied across the two foils, the electrolyte generates electrical polarization between them. The side with positive potential experiences an enrichment of positive charges, while the negative potential side has an enrichment of negative charges. This electric polarization forms an additional capacitive layer, which increases the capacitance value of the capacitor. This extra capacitance layer is known as the ‘Korotkoff effect’.In AECs, the characteristics of the capacitor’s dielectric and the amount of capacitance depend on their working temperature. As the temperature increases, the thickness of the dielectric layer decreases, and this causes a decrease in capacitance value. This is why it is important to select AECs with a working temperature range that is suitable for the application. This is because capacitors that experience high working temperatures are more prone to failure.AECs come in different sizes and shapes, ranging from small rectangular and cylindrical packages to large can-shaped packages. Depending on the application, they can rated with a capacitance range of 1uF to 10,000uF.In summary, aluminum electrolytic capacitors (AECs) are high-value capacitors with excellent cost-performance ratio. They are widely used in AC and DC filters, power factor correction, and switching power supply circuits. Their structure is made up of several alternating layers of aluminum oxide dielectric, cathode foil, electrolyte, and anode foil. The high capacitance value of the capacitor stems from the high dielectric constant of the aluminum oxide. The Korotkoff effect also helps to increase the total capacitance value. Depending on the application, AECs may be rated with a capacitance range of 1uF to 10,000uF.