Capacitors are used for energy storage and filtering. As there are many types of capacitors, each type has its advantages and performs best for different applications. The composition of a capacitor determines how it is used. Some commonly used capacitor types are tantalum, aluminum electrolytic, and ceramic.
An aluminum electrolytic capacitor is a polarized capacitor which uses an electrolyte to achieve a large capacitance. Two pieces of aluminum foil serve as the anode and cathode, separated by a paper space soaked in electrolyte. While they may allow for a large capacitance, there are a few significant disadvantages. The actual capacitance may drift over time and they typically have a 20% tolerance. Further, they have limited lifetime. In fact, the life of a power supply is often determined by the life of the aluminum electrolytic capacitors used on the power supply. Aluminum electrolytic capacitors are commonly used as filtering devices to reduce voltage ripple.
Tantalum capacitors are a subset of electrolytic capacitors. They use tantalum metal as the anode along with a cathode and an electrolyte. They generally have a high capacitance to volume ratio. Tantalum caps have great long term stability. They maintain their capacitance over time and since they do not dry out, they have an unlimited shelf life. They also have a low leakage current and contain a very thin dielectric layer, which allows for exceptional frequency characteristics. The drawback of using tantalum capacitors is their potentially dangerous failure mode. A voltage spike, for example, could trigger a chemical reaction within the capacitor, leading to smoke and flames. This can be prevented by using external protection devices, such as current limiters or thermal fuses.
Ceramic capacitors are capacitors in which the dielectric is a ceramic material. Multi-layer ceramic capacitors (MLCCs) are the most common type. MLCCs consist of up to 500 ceramic layers which allow for a higher capacitance ratings in small package. The capacitance values typically range from 1 nF to 100 uF. Larger capacitance values are limited to lower voltages. Their small size and lack of polarity make them beneficial to various applications.