The electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics". They are used in relatively high-current and low-frequency electrical circuits, particularly in power supply filters, where they store charge needed to moderate output voltage and current fluctuations in rectifier output. There are two types of electrolytics; aluminum and tantalum. The tantalum capacitor is a highly reliable type of electrolytic capacitor, which is available in both solid-bodied and separately encased forms. The encased "wet" variant is not used often in modern designs. Surface mount tantalum capacitors are widely used in circuit designs because of their volumetric efficiency, basic reliability and process compatibility.
The low leakage and high capacity of tantalum capacitor favors their use in sample and hold circuits to achieve long hold duration, and some long duration timing circuits where precise timing is not critical. They are also often used for power supply rail decoupling in parallel with film or ceramic capacitors which provide low ESR and low reactance at high frequency. Compared to aluminum electrolytics, tantalum capacitors have very stable capacitance, little DC leakage, and very low impedance at high frequencies. However, unlike aluminum electrolytics, they are intolerant of positive or negative voltage spikes and are destroyed (often exploding violently) if connected in the circuit backwards or exposed to spikes above their voltage rating.
Moreover, tantalum capacitors are more expensive than aluminum-based capacitors and generally only available in low-voltage versions, but because of their smaller size for a given capacitance and lower impedance at high frequencies they are popular in miniature applications such as cellular telephones.
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