Annular Form Factor Film Capacitors

An annular form factor dry film capacitor having the minimum possible equivalent series inductance (ESL) has been developed for short pulse applications requiring high currents at voltages below 10 kV DC. The annular design offers the lowest possible inductance at the system level and can be wound to a tolerance of plusmn1%. The narrow film width provides a low equivalent series resistance (ESR) and very large contact length; which when combined with customized metallized film will support high current levels without the need for foil electrodes. Single section units can provide working capacitance values of up to 650 muF at 4 kV DC and up to 9500 muF at 1 kV DC with symmetrical discharge currents. Multiple section capacitors can also be fabricated to provide for higher voltage operation at reduced energy density. Using film widths up to 65 mm, the possible inner diameter range is from 25.4 mm (1 in) to 254 mm (10 in), with the outer diameter ranging up to 406 mm (16 in). A prototype design is presented along with preliminary data for ESR, ESL, discharge currents, and life assessment.