Film Capacitors with Low Internal Inductance

It is shown experimentally that the turns between tabs and the tab straps themselves are the major sources of internal inductance in a buried-foil capacitor with conventional flagged tabs. For example, two tab straps each 4 mm wide and 32 mm long contribute about 46 nH of inductance. A unique tab structure in which two conventional tabs were assembled and inserted as a low-inductance fiat cable and which largely eliminates the sources of internal inductance is described. An internal inductance of 3 to 7 nH was measured for a 0.4-µF capacitor with this tab structure whereas inductances of 34 to 56 nH were measured for similar capacitors with conventional tabs.