CONTROLLER FOR DC MOTOR

摘要

A controller for DC motor is provided with an FET (206) which is connected between one end of a motor (201) and the positive electrode of a battery EB, a diode (203) through which the electric current having flown through the motor (201) is passed when the switch (220) of the battery EB is turned off, a means for measuring the current flowing through the motor (201) which comprises a shunt resistor (203a), a differential amplifier (203b), and a low-pass filter (203c), and a controller (250) which PWM-controls the turn-on/off of the FET (206) so that the measured value of the current flowing through the motor (201) is coincident with a target value. The controller (250) sets a very small value as the target value when the switch (220) of the battery EB is turned off and supplies the very small current to the motor (201). Therefore, the FET which drives the motor of a bicycle with auxiliary motor is protected at a low cost without adding any extra component.