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Kinds of Capacitors

Tantalum Capacitors

There are a number of different capacitor families available, each of which has defining characteristic features. Some families are good for storing large amounts of charge yet may have high leakage currents and bad tolerances. Other families may have great tolerances and low leakage currents but may not have the ability to store large amounts of charge. Some families are designed to handle high voltages yet may be bulky and expensive. Other families may not be able to handle high voltages but may have good tolerances and good temperature performance.

Some families may contain members that are polarized or non polarized in nature. Polarized capacitors, unlike non polarized capacitors, are specifically designed for use with dc fluctuating voltages (a non polarized capacitor can handle both dc and ac voltages). A polarized capacitor has a positive lead that must be placed at a higher potential in a circuit and has a negative lead that must be placed at a lower potential. Placing a polarized capacitor in the wrong direction may destroy it. (Polarized capacitors’ limitation to use in dc fluctuating circuits is counterbalanced by extremely large capacitance.) Capacitors also come in fixed or variable forms. Variable capacitors have a knob that can be rotated to adjust the capacitance level.

These capacitors include both aluminum and Tantalum Capacitors. They are manufactured by an petrochemical formation of an oxide film onto a metal (aluminum or tantalum) surface. The metal on which the oxide film is formed serves as the anode or positive terminal, the oxide film acts as the dielectric, and a conducting liquid or gel acts as the cathode or negative terminal. Tantalum electrolytic capacitors have larger capacitance per volume ratios when compared with aluminum electrolytic.

A majority of electrolytic capacitors are polarized. Electrolytic capacitors, when compared with non electrolytic capacitors, typically have greater capacitance but have poor tolerances (as large as _100 percent for aluminum and about _5 to _20 percent for tantalum), bad temperature stability, high leakage, and short lives. Capacitance range from about 1 μF to 1 F for aluminum and 0.001 to 1000 μF for Tantalum Capacitors, with maximum voltage ratings from 6 to 450 V. Polarized marking (negative lead) ++ Radial lead Axial lead Ceramic This is very popular no polarized capacitor that is small and inexpensive but has poor temperature stability and poor accuracy. It contains a ceramic dielectric and a phenol coating. It is often used for bypass and coupling applications. Tolerances range from _5 to _100 percent, while capacitance range from 1 pF to 2.2 μF, with maximum voltages rating from 3 V to 6 kV.

This is a very popular non polarized capacitor that is reliable, inexpensive, and has low leakage current but poor temperature stability. Capacitance range from 0.001 to 10 μF, with voltages ratings from 50 to 600 V. This is an extremely accurate device with very low leakage currents. It is constructed with alternate layers of metal foil and mica insulation, stacked and encapsulated. These capacitors have small capacitance and are often used in high-frequency circuits (e.g., RF circuits). They are very stable under variable voltage and temperature conditions. Tolerances range from _0.25 to _5 percent. Capacitance range from 1 pF to 0.01 μF, with maximum voltage ratings from 100 V to 2.5 KV.