An apparatus for controlling an on-vehicle generator is provided. The
apparatus comprises a switching element, current detecting unit, setting
unit and driving unit. The switching unit turns on/off an exciting
current to an exciting winding of the generator, the switching element
being driven responsively to a driving signal having an adjustable duty
ratio. The setting unit sets the duty ratio based on (i) a difference
between an output voltage of the generator and a target voltage value and
(ii) a condition in which an electric load is disconnected from the
generator, wherein the duty ratio is allowed to lower than a minimum
value of the duty ratio depending on a generated state of the generator.
The minimum value allows the exciting current to flow at a lower limit
detectable by the current detecting unit, The driving unit drives the
switching element based on the driving signal.