A magnetohydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery.
AC generators can be used as sources of steady current with a rectifier and a good ripple filter.
Pulsed DC generators can be used as sources of steady current with a good ripple filter.
An important usage of constant current power supplies is with LEDs.
Another use is in fluorescent lamps which have very dynamic electrical resistance and are optimally operated within a short range of currents.