Patent ID: 8063601

Claim:
A motor driving circuit for adjusting speed of a motor by changing an output voltage, one end of the motor being coupled to a variable voltage source, the motor driving circuit comprising: a motor-driving unit for driving the motor, comprising a first end coupled to another end of the motor, a second end coupled to a ground and a third end; a control unit coupled between the first end and the third end of the motor-driving unit for controlling the voltage between the first end and the third end of the motor-driving unit; and a determining unit coupled between the variable voltage source and the control unit for controlling the control unit to adjust the voltage between the first end and the third end of the motor-driving unit according to a magnitude of the voltage of the variable voltage source; wherein the control unit comprises: a first switching device coupled between the first end of the motor-driving unit and a first end of a voltage-dropping device; and a second switching device coupled to the first end of the voltage-dropping device.