The Super Capacitor: Operation And Application

EE 63 October 1988 THE SUPER CAPACITOR: OPERATION AND APPLICATION Power supply back-up capacitors with a capacitance between several tens of milli-farads and tens of farads are currently available from a number of manufacturers. In spite of their huge capacitance, these devices are physically very small with sizes varying between that of a button cell and a matchbox. The use of CMOS memory elements in combination with a back-up battery to give a non-volatile memory is fairly stan- dard these days. But non-rechargeable batteries often go flat quite unexpected- ly, and the lifetime of NiCd types is also limited. Fortunately, the current con- sumption of CMOS circuits has been significantly reduced over the past few years, and memories need only be pow- ered from a back-up supply for as long as the main power supply is off, which may last from a few seconds to a few weeks. With this in mind, the choice of the capacitor as a back-up supply is not surprising. However, the size and elec...