Patent ID: 8604744

Claim:
A drive circuit for a motor having a first coil, a second coil and a rotor, the motor drive circuit comprising: a driver unit configured to supply currents, whose phase differ from each other, to the first coil and the second coil, respectively; an induced voltage detector configured to detect a voltage across the first coil or that across the second coil when said driver unit is in a high impedance state as viewed from the first coil or the second coil, and configured to detect an induced voltage occurring in the first coil or the second coil; and a control unit configured to generate a drive signal based on an input signal set externally and adjust the drive signal in accordance with the induced voltage detected by said induced voltage detector so as to set the adjusted drive signal in said driver unit, said induced voltage detector including: a differential amplifier circuit configured to differentially amplify an electric potential across the first coil or that across the second coil; an analog-to-digital converter circuit configured to convert an analog value outputted from the differential amplifier circuit into a digital value and output the converted digital value to said control unit; a first switch configured to connect or disconnect a first terminal of the first coil and a first input terminal of the differential amplifier circuit; a second switch configured to connect or disconnect the first terminal of the first coil and a second input terminal of the differential amplifier circuit; a third switch configured to connect or disconnect a second terminal of the first coil and the first input terminal of the differential amplifier circuit; a fourth switch configured to connect or disconnect the second terminal of the first coil and the second input terminal of the differential amplifier circuit; a fifth switch configured to connect or disconnect a first terminal of the second coil and the first input terminal of the differential amplifier circuit; a sixth switch configured to connect or disconnect the first terminal of the second coil and the second input terminal of the differential amplifier circuit; a seventh switch configured to connect or disconnect a second terminal of the second coil and the first input terminal of the differential amplifier circuit; and an eighth switch configured to connect or disconnect the second terminal of the second coil and the second input terminal of the differential amplifier circuit.