Aluminum electrolytic capacitors use an electrolytic process to form the dielectric. Wet electrolytic capacitors have a moist electrolyte. Dry or solid electrolytic capacitors do not. There are two basic configurations or form factors for aluminum electrolytic capacitors: leaded and surface mount. There are also several different mounting styles. Leaded capacitors have leads for connections to circuits. They use through hole technology (THT) to mounts component on a printed circuit board (PCB) by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board. Surface mount capacitors or chip capacitors do not have leads or use THT. Instead, SMT capacitors have a flat surface that is soldered to a flat pad on the face of the PCB. Mounting styles for aluminum electrolytic capacitors may also use bolts, brackets, and poles.
Features and Specifications
Aluminum electrolytic capacitors differ in terms of capacitance type, product features, and package specifications. Fixed capacitors have a nonadjustable capacitance value. With variable capacitors, specific capacitance values can be set via an adjustment mechanism, typically a potentiometer. In terms of features, some aluminum electrolytic capacitors are polarized or self-healing. Polarized capacitors can be safely operated with only one direct current (DC) polarity. Self-healing capacitors can withstand high-pulsed voltages without breaking the dielectric. Aluminum electrolytic capacitors that meet military standards or comply with Restriction of Hazardous Substances (RoHS) are also available. With regard to packaging, leaded aluminum electrolytic capacitors may use axial leads, radial leads, flying leads, tab leads, screw leads, gull-wing leads, or J-leads. SMT capacitors are also commonly available.
Selecting Aluminum Electrolytic Capacitors
Selecting aluminum electrolytic capacitors requires an analysis of performance specifications and packing methods. Performance specifications include capacitance range, capacitance tolerance, DC rated voltage range (WVDC), leakage current, equivalent series resistance (ESR) and operating temperature. There are three basic packing methods for aluminum electrolytic capacitors: tape reel, tray or ail, and shipping tube or stick magazine. Aluminum electrolytic capacitors that are packed in tape reel assemblies include a carrier tape with embossed cavities for storing individual components. Electronic components that are packed in trays (rails) fit matrices of uniformly-spaced pockets. Capacitors that are packed in shipping tubes use stick magazines that are made of rigid polyvinylchloride (PVC) and extruded in industry-standard sizes.
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