Patent ID: 8461795

Claim:
A motor drive device comprising: a signal generator for generating control signals of a second input method that include a polarity signal for indicating the polarity of an excitation current that flows to a motor, and a current amount signal for indicating the amount of said excitation current, from control signals of a first input method that include a clock signal for indicating a stepping drive period of the motor, and an excitation method switching signal for indicating an excitation method of said motor; and a drive unit for step-driving said motor on the basis of the control signals of the second input method that are generated by said signal generator; wherein said signal generator generates control signals of the second input method from the control signals of the first input method and controls the torque vector of said motor so that the correlation between the number of pulses of said clock signal and the phase of the torque vector of said motor is held in common for all the excitation methods, with the excitation method having the greatest number of steps being used as a reference, that the torque vector of said motor as a rule is maintained in the same phase as before switching when the excitation method is switched, and that the torque vector is in the closest phase in the rotation direction of said motor in a case in which there is no phase that is the same as the phase prior to switching.