a servosystem for controlling the voltage in x - ray generators includes a system for controlling the voltage of the primary of a high voltage transformer for feeding the x - ray tubes . a servosystem controls the position and adjustment of acceleration , uniform movement and braking , and supplies a direct current motor , of the permanent magnet type and of standard manufacture , which moves the brushes of a three - phase or mono - phase toroidal autotransformer , the operation of which fixes the primary voltage of the high voltage transformer which , in turn , supplies a voltage to an x - ray tube .