Three-phase brushless motor state identification

1. A method for determining the state of a brushless motor having first, second and third phases, comprising:

decoupling said motor from a power source;

determining whether said motor is rotating or non-rotating;

if the motor is rotating;

determining a first phase voltage state relative to a common voltage when a third phase voltage is within a predetermined range of said common voltage; and

determining a second phase voltage state relative to the common voltage when the third phase voltage is within the predetermined range of said common voltage; and

if the first phase voltage state and the second phase voltage state are the same, repeating said determination as to whether the motor is rotating or non-rotating.

2. The method of claim 1 , further comprising:

if the first phase voltage state and the second phase voltage state are the same, repeating said determination of the first phase and second phase voltage states,

wherein said determination of the first phase and second phase voltage states is repeated no more than a predetermined number of times.

3. The method of claim 2 , wherein, if said determination of the first phase and second phase voltage states is repeated said predetermined number of times, determining that the state of said motor is non-rotating.

4. The method of claim 1 , further comprising:

if the first phase voltage state is low and the second phase voltage state is high, and if said first and second phase voltage states are determined at a time when the third phase voltage is rising, then determining that the state of said motor is positive rotation.

5. The method of claim 1 , further comprising:

if the first phase voltage state is high and the second phase voltage state is low, and if said first and second phase voltage states are determined at a time when the third phase voltage is rising, then determining that the state of said motor is reverse rotation.

6. The method of claim 1 , further comprising:

if the first phase voltage state is low and the second phase voltage state is high, and if said first and second phase voltage states are determined at a time when the third phase voltage is falling, then determining that the state of said motor is reverse rotation.

7. The method of claim 1 , further comprising:

if the first phase voltage state is high and the second phase voltage state is low, and if said first and second phase voltage states are determined at a time when the third phase voltage is falling, then determining that the state of said motor is positive rotation.

8. The method of claim 1 , wherein determining whether the motor is rotating or non-rotating comprises:

providing two comparators, each of said comparators receiving the same phase voltage and each of said comparators receiving a differently biased version of said common voltage, and

if both outputs of said two comparators are the same polarity, determining that the state of said motor is rotating.

9. A method for determining the state of a brushless motor having first, second and third phases, comprising:

determining whether said motor is rotating or non-rotating;

if the motor is rotating;

determining a first phase voltage state relative to a common voltage when a third phase voltage is approximately equal to said common voltage; and

determining a second phase voltage state relative to the common voltage when the third phase voltage is approximately equal to said common voltage; and

if the first phase voltage state and the second phase voltage state are the same, repeating said determination of the first phase voltage state and the second phase voltage state.

10. The method of claim 9 , further comprising disconnecting the motor from a power source prior to performing said determination steps.

11. The method of claim 9 , wherein, if said determination of the first phase and second phase voltage states has been repeated a predetermined number of times, determining that said state of the motor is non-rotating.

12. The method of claim 9 , wherein, if the first phase voltage state and the second phase voltage state are the same, omitting repetition of said determination as to whether the motor is rotating or non-rotating.

13. The method of claim 9 , further comprising:

if the first phase voltage state is low and the second phase voltage state is high, and if said first and second phase voltage states are determined when the third phase voltage is rising, then determining that the state of said motor is positive rotation.

14. The method of claim 9 , further comprising:

if the first phase voltage state is high and the second phase voltage state is low, and if said first and second phase voltage states are determined when the third phase voltage is rising, then determining that the state of said motor is reverse rotation.

15. The method of claim 9 , further comprising:

if the first phase voltage state is low and the second phase voltage state is high, and if said first and second phase voltage states are determined when the third phase voltage is falling, then determining that the state of said motor is reverse rotation.

16. The method of claim 9 , further comprising:

if the first phase voltage state is high and the second phase voltage state is low, and if said first and second phase voltage states are determined when the third phase voltage is falling, then determining that the state of said motor is positive rotation.

17. The method of claim 9 , wherein determining whether the motor is rotating or non-rotating comprises:

providing two comparators, each of said comparators receiving the same phase voltage and each of said comparators receiving a differently biased version of said common voltage;

if both outputs of said two comparators are the same polarity, determining that the state of said motor is rotating.

18. A system for determining the state of a motor, comprising:

a motor that is associated with first, second and third phases and that is driven by a motor driving circuit;

a control circuit that couples to and controls the motor driving circuit;

a first comparator that receives a first biased version of a common voltage at one input and a first phase voltage, a second phase voltage, or a third phase voltage at another input, an output of said first comparator provided to the control circuit; and

a second comparator that receives a second biased version of a common voltage at one input and the first phase voltage, the second phase voltage, or the third phase voltage at another input, an output of said second comparator provided to the control circuit;

wherein, if the outputs of the first and second comparators are both positive or are both negative, the control circuit determines that the motor is rotating,

wherein, if the motor is determined to be rotating, the control circuit:

determines a first phase voltage state relative to the common voltage when a third phase voltage is approximately equal to said common voltage; and

determines a second phase voltage state relative to the common voltage when the third phase voltage is approximately equal to said common voltage, and

wherein, if the first phase voltage state and the second phase voltage state are the same, the control circuit repeats said determination of the first phase voltage state and the second phase voltage state.

19. The system of claim 18 , wherein, if the first phase and second phase voltage states are the same, the control circuit repeats said determination of whether said motor is rotating.

20. The system of claim 18 , wherein first and second bias voltages associated with said first and second biased versions of the common voltage have opposing polarities and have absolute values that are less than:

an absolute value of a maximum first phase voltage;

an absolute value of a maximum second phase voltage; and

an absolute value of a maximum third phase voltage.