ESR

          The main (if not only) limiting factor in high-frequency performance (in switching power supplies, for example) for large filter capacitors is the equivalent series resistance or ESR.  In fact, switcher designers tend to think of capacitors in terms of their ESR instead of their capacitance.  A lot of work has gone into developing new low-ESR capacitor technologies and improving existing ones.  Kemet, for example, has introduced a series of SMD tantalums that are made of three capacitors in one package, for reduced ESR and better frequency response.  Table 4 shows representative ESRs for various capacitor types, taken from literature from several manufacturers.  The actual ESR will depend on the manufacturer, capacitor working voltage, and other factors. "Low ESR" means different things to different manufacturers.  For aluminum electrolytics, ESR drops as working voltage increases, and I suspect that some designers of video equipment use aluminum capacitors with high working voltages to get lower impedance in the video frequency range.  ESR is also dependent on capacitor shape; tall and thin electrolytics tend to have lower ESRs than short, squat ones.

          Film and ceramic capacitors, if actually available in the sizes shown, would be expected to have lower ESRs than any of the electrolytics.  Several manufacturers make non-TCNQ polymer-aluminum capacitors and claim performance as good as or slightly better than OS-CON capacitors. 

Table 4  "Typical" ESR Values of Some Capacitors, in Ohms