G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
G05F1/10—Regulating voltage or current
G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is DC
G05F1/52—Regulating voltage or current wherein the variable actually regulated by the final control device is DC using discharge tubes in series with the load as final control devices