electrolytics

Electrolytics refer to electrolytic capacitors, a family of polarized capacitors that achieve large capacitances by using a metal oxide dielectric formed by anodization and an electrolyte to convey charge. They are widely used where high capacitance in a small package is required. The two common families are aluminum electrolytic capacitors and tantalum electrolytic capacitors, with polymer variants also available. Aluminum types come in radial, axial, and surface-mount form factors; tantalum types are typically smaller and often offered with solid or gelled electrolytes.

Construction and operation: In aluminum electrolytics, etched aluminum foil serves as the anode. An oxide layer is grown by anodizing, acting as the dielectric. The electrolyte provides conductive paths between the anode and cathode, completing the capacitor. Tantalum devices use a porous tantalum anode with a tantalum pentoxide dielectric and a conductive electrolyte. The electrolyte type influences leakage, equivalent series resistance (ESR), and temperature performance; solid polymer electrolytes generally yield lower ESR and longer life.

Characteristics: Electrolytics offer capacitances from microfarads to tens of thousands of microfarads with voltage ratings from a few volts to several hundred volts. They are polarized and exhibit relatively higher leakage currents and tolerances compared with film capacitors. Temperature and aging affect capacitance and ESR; tantalum parts can fail catastrophically under surge or reverse polarity, hence derating is common.

Applications and reliability: Widely used for power-supply filtering, decoupling, and energy storage. Common failure modes include electrolyte drying, leakage, and venting; proper polarity, avoidance of reverse bias, and appropriate derating improve reliability. Advances include solid polymer electrolytics and low-ESR surface-mount types.