Motor drive circuit

1. A motor drive circuit comprising:

a control circuit configured to control a drive current to a drive coil of a motor;

a locking protection circuit configured to control an operation of the control circuit so that the drive current is in response to a rotation signal not being generated for a predetermined time period although the drive current is being supplied to the drive coil; and

a prohibition circuit configured to prohibit the locking protection circuit from controlling the control circuit in response to the rotation signal not being generated for the predetermined time period, wherein the prohibition circuit prohibits the locking protection circuit from controlling the control circuit during a time period during which a power supply voltage is lower than a predetermined voltage, and wherein the prohibition circuit includes:

a comparison circuit configured to compare a voltage according to the power supply with a reference voltage; and

a gate circuit configured to prohibit the locking protection circuit from controlling the control circuit in accordance with an output of the comparison circuit, in a case where the voltage according to the power supply voltage is lower than the reference voltage.

2. The motor drive circuit according to claim 1 , wherein the prohibition circuit prohibits the locking protection circuit from controlling the control circuit during a time period during which a power supply voltage is lower than a predetermined voltage.

3. The motor drive circuit according to claim 1 , wherein the voltage according to the power supply voltage is a voltage obtained by dividing the power supply voltage by a voltage-dividing resistor.

4. The motor drive circuit of according to claim 1 , further including a drive circuit configured to supply the drive current to a drive coil of a motor.

5. A method for controlling a motor comprising generating a drive circuit control signal to control a drive circuit for the motor in response to a locking protection signal from a locking protection circuit, wherein the locking protection signal is in response to a rotation signal not being generated for a predetermined time period although a drive current is being supplied to the drive coil, and wherein the locking protection signal is prohibited from controlling the drive circuit control signal during a time period during which a power supply voltage applied to the drive circuit is less than a reference voltage in response to a prohibition signal from a prohibition circuit, wherein the prohibition circuit includes:

a comparison circuit configured to compare a voltage according to the power supply with a reference voltage; and

a gate circuit configured to prohibit the locking protection circuit from controlling the control circuit in accordance with an output of the comparison circuit, in a case where the voltage according to the power supply voltage is lower than the reference voltage.

6. The method of claim 5 , wherein generating the motor control signal comprises:

generating a shifted power supply voltage; and

generating a comparison signal in response to comparing the shifted power supply voltage with the reference voltage.

7. The method of claim 6 , wherein generating the shifted power supply voltage comprises reducing the power supply voltage signal.

8. The method of claim 6 , further including generating the locking protection signal in response to a level of a drive current for the motor.

9. The method of claim 8 , further including generating the locking protection signal in response to the level of the drive current being zero.

10. The method of claim 8 , further including generating the locking protection signal in response to a back electromotive voltage.

11. The method of claim 10 , further including generating the rotation signal in response to a rotation of the motor being stopped for a predetermined time; and using the rotation signal and the comparison signal to generate the drive control signal.

12. The method of claim 11 , wherein generating the rotation signal includes using the back electromotive voltage generated by the motor.

13. The method of claim 6 , further including generating a locking protection signal in response to a period of a rotation signal being longer than a predetermined time.

14. The method of claim 13 , further including using the comparison signal and the locking protection signal to generate the drive circuit control signal.

15. A method for controlling a motor, comprising:

generating a rotation signal;

generating a power supply level indicator signal in response to a voltage level of a power supply; and

using the rotation signal and the power supply indicator signal to generate a control signal to control the motor and further including using the control signal to prohibit a locking protection circuit from controlling a control circuit, wherein the control signal to prohibit the locking protection circuit is generated from a prohibition circuit that includes:

a comparison circuit configured to compare a voltage according to the power supply with a reference voltage; and

a gate circuit configured to prohibit the locking protection circuit from controlling the control circuit in accordance with an output of the comparison circuit, in a case where the voltage according to the power supply voltage is lower than the reference voltage.

16. The method of claim 15 , further including binarizing a back electromotive voltage and generating the rotation signal in response to the binarized back electromotive voltage.

17. The method of claim 15 , wherein generating the power supply indicator signal comprises:

generating a shifted power supply voltage by voltage shifting the voltage level of the power supply; and

comparing the shifted power supply voltage with a reference voltage.

18. The method of claim 17 , wherein using the control signal to prohibit the locking protection circuit from controlling the control circuit includes prohibiting the locking protection circuit from outputting the control signal to stop a drive current to the control circuit.