UHD1C222MHD1TO

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UHD1C222MHD1TO application field and working principle

Aluminum electrolytic capacitors, or simply electrolytic capacitors, are capacitors in which the anode electrode is an oxide layer of aluminum in which a large number of aluminum oxide molecule layers have been formed. This oxide layer acts as the dielectric layer and the cathode electrode is an electrolyte. They are polarized capacitors with a positive and a negative terminal as traditional capacitors, but require a voltage at the positive terminal higher to the one at the negative terminal. Aluminum electrolytic capacitors are typically characterized by a large capacitance value per unit volume than other surface-mount capacitors of same dimensions and typically have a working voltage range from 6.3 to 450 volts. Upside of aluminum electrolytic capacitors is that they achieve a high capacitance at a relatively low cost, while their downside is that they are not suitable for low-frequency applications or high-temperature environments due to their inherent ESR (equivalent series resistance) and ESL (equivalent series inductance) values.

Application fields

Aluminum electrolytic capacitors are widely used in different type of applications like power supplies, dc-dc converters, output smoothing, signal filtering, buck and boost converters, etc. They are the preferred solution for most power supplies as they can provide high capacitance values in a relatively small package.

Working principle

Aluminum electrolytic capacitors are polar devices. The dielectric in this type of capacitor is an oxide layer formed on the aluminum foil that forms the anode, which is sprayed or dipped in an electrolyte bath. This oxide layer acts as an insulator but it can conduct electricity under certain conditions. The negative electrode of the capacitor is the electrolyte itself, usually with a gel or paste form. The oxide layer on the anode is the capacitor dielectric and the anode and electrolyte form the capacitor plates. When a voltage difference is applied between the two electrodes an electric current passes through the oxide layer between them and the capacitors electrical characteristics are determined by its geometric size and the properties of the oxide layer and electrolyte.

As the voltage is increased, the current increases until a point is reached where a rectifying effect starts to take place (called Reverse Breakdown Voltage or Dielectric Strength) and the current decreases, until there is a balance which is called the Leakage Current. This leakage current is the main cause of losses in the capacitor so, generally, capacitors with a lower leakage current have better performance.

The capacitance of aluminum electrolytic capacitors is affected by the applied voltage, temperature, frequency, and other environmental factors. The capacitance is also affected by electrolyte composition, and types of oxide layers. For instance, the capacitance can decrease with increasing frequency or temperature, meaning aluminum electrolytic capacitors are not suitable for low-frequency or high-temperature applications.

These capacitors are not suitable for high-frequency applications due to their higher ESR (equivalent series resistance) values. The ESR is caused by the leakage current and, as said before, the lower the leakage current is, the lower will be the ESR. The ESR also depends on the capacitors construction and reduces with increasing capacitance, so the smaller capacitors have relatively higher ESR values. The same happens with the ESL (equivalent series inductance) which is also affected by its construction and size.

Conclusion

Aluminum electrolytic capacitors are widely used in different applications due to their relatively low cost and small size. They are polarized capacitors and their capacitance and electrical characteristics depend on the construction of the capacitor, the oxide layer and the electrolyte. The capacitance varies depending on the applied voltage, temperature, frequency, and other environmental factors. Aluminum electrolytic capacitors are not suitable for low-frequency, high-temperature, or high-frequency applications due to their inherent ESR (equivalent series resistance) and ESL (equivalent series inductance) values.

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