High voltage is required for a number of applications. One is the electrical system
used to propel either hybrid- or all-electric vehicles. Auto manufacturers typically
wish to operate such systems at over 200V. For high voltage applications of this
kind it is desirable that individual cells produce the highest possible voltage, as
fewer cells are necessary. Also, 36–42V systems are being developed for starter,
lighting and ignition systems in internal combustion engine automobiles.
Despite the implications of energy quality, it is important that the voltage characteristics
of electrochemical energy storage systems match the requirements of the
intended application. It is not always necessary to have the highest possible cell
voltage, as this could lead to wastage in some applications. An example is the use
of batteries to power semiconductor circuits. The semiconductor industry is continually
working to reduce the size of circuit components in order to get more of them
per unit area of silicon wafer, i.e. to increase the packing density. The smaller the
length of the gate in MOS devices, the lower the voltage required to operate the device,
and the lower the Joule heat output. This latter factor is becoming particularly
critical for applications in portable devices, like laptop computers.
Data on the time dependence of the typical operating voltage of low power semiconductor
devices are shown in Fig. 1.5.