CONTROLLING DEVICE OF MOTOR

PURPOSE: To lessen the error owing to the distortion of a small generated voltage or the effect of noise by a method wherein a voltage corresponding to a current flowing through a motor is led out, the time constant of a firing generating circuit is changed in accordance with the voltage and control is made so that the power consumed by the motor becomes constant. CONSTITUTION: When the current of a motor 4 increases, the current flowing through a conductive resistor L1 becomes large, too, and a led-out voltage corresponding to the current becomes large. A firing signal generating circuit 8 is controlled by an input current control circuit 12 so that a firing signal is generated in delay, and thereby the firing of a bidirectional three-terminal thyristor 12 is delayed, the phase angle of the current flowing through the motor 4 becomes small and a power being controlled to be low. When the current of the motor 4 becomes small, the led-out voltage of the conductive resistor L1 becomes small, too, the firing signal generating circuit 8 generates the firing signal earlier by the input current control circuit 12, the firing of the bidirectional three-terminal thyristor 5 is quickened the phase angle of the current flowing through the motor 4 becomes large and the power is being controlled to be high.