Film Capacitors

Film capacitors are insulated with polyester, polycarbonate, polypropylene, polystyrene, or other dielectric materials. Polyester film capacitors offer a high dielectric constant and high dielectric strength with volumetric. Metallized polyester film provides excellent self-healing properties, allowing capacitors to withstand high-pulsed voltages without breaking the dielectric. Polycarbonate film capacitors offer very low temperature dependency, wide operating temperature range, good long-term stability and low losses. Polypropylene film capacitors provide very low losses, low dielectric absorption, and high dielectric strength. They also offer very high insulation resistance and negative temperature coefficient. Polystyrene film capacitors provide extremely low losses, low dielectric absorption, good long-term stability, very high insulation resistance and a small negative temperature coefficient. 

Selecting film capacitors requires an analysis of general specifications such as form factor and capacitance type, and a full complement of performance specifications. There are two basic form factors or configurations for film capacitors: leaded and surface mount. Leaded film capacitors have leads for connections to circuits. Surface mount film capacitors or chip film capacitors do not. There are two choices for capacitance type: fixed and variable. Fixed capacitors have a nonadjustable capacitance value. With variable film capacitors, specific capacitance values can be set via an adjustment mechanism, typically a potentiometer. Performance specifications for film capacitors include capacitance range, capacitance tolerance, equivalent series resistance (ESR), DC rated voltage range, AC rated voltage range, rated current, leakage current, pulse rise time, dissipation factor, insulation resistance, and operating temperature.   

Film capacitors differ in terms of product features, approvals and applications. Polarized capacitors may be operated safely with only one DC polarity. By contrast, nonpolar capacitors can be operated without regard to polarity. Film capacitors that are destined for sale in European Union (EU) countries must with Restriction of Hazardous Substances (RoHS). In the United States, film capacitors that are designed for military applications must meet military specifications (MIL-SPEC). Polyester capacitors are used in bypassing and coupling applications. Uses for polycarbonate capacitors include timers and filters, as well as high ambient temperature applications. Polypropylene capacitors are used in stable oscillators, sample-and-hold circuits, and pulse-handle circuits. Like other types of film capacitors, polystyrene capacitors can be used in timers and filters.

• Energy Density of Film Capacitors for ETC Gun Applications
  In the late 1980s and early 1990s a significant effort was made to improve the energy density of capacitor for the ETC gun application where the pulse width is typically in the millisecond range. At...
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• Capacitor Engineering Bulletin: Polarization and Leakage Current Characterizations of High Voltage, Film Capacitors
  It is an unfortunate fact that "real" capacitors differ from ideal capacitors in many respects. Real capacitors include parasitic inductance and resistance, and vary in capacitance with temperature,...
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• Pulse Power Capacitors - US Army Research Program Has Yielded Millisecond Discharge High-Voltage Film Capacitors with Sub-Microsecond Discharge on the Horizon
  The US Army Research Laboratory has sponsored a capacitor development program for film dielectric capacitors. The program has evaluated dielectric materials for high energy density capacitors from...
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Part Numbers for Film Capacitors