Peak current regulation for stepper motors

1. A method for controlling a stepper motor, the method comprising:

calculating a duty cycle of a current provided to the stepper motor;

comparing a difference between the calculated duty cycle and a base duty cycle of current provided to the stepper motor under a base load condition, to a reference duty cycle value; and

adjusting a peak current level of the current provided to the stepper motor responsive to the comparison.

2. The method of claim 1 , wherein adjusting the peak current level comprises:

increasing the peak current level responsive to the calculated duty cycle being greater than the reference duty cycle; and

decreasing the peak current level responsive to the calculated duty cycle being less than the reference duty cycle.

3. The method of claim 1 , wherein calculating the duty cycle comprises calculating an average duty cycle of the current provided to the stepper motor over a half-cycle of a current waveform.

4. The method of claim 1 , wherein the base duty cycle and the reference duty cycle are user-configurable values.

5. The method of claim 1 , wherein a mechanical load is not coupled to the stepper motor in the base load condition.

6. The method of claim 1 , wherein the reference duty cycle is of a current provided to the stepper motor under a maximal load condition, and with a maximal peak current level.

7. The method of claim 1 , comprising comparing the difference to an upper threshold value and to a lower threshold value, wherein the upper threshold value equals the reference duty cycle value plus a first amount, and wherein the lower threshold value equals the reference duty cycle value minus a second amount.

8. A device adapted to be coupled to a stepper motor and operable to control the stepper motor, the device comprising:

a processing device having a first output adapted to be coupled to the stepper motor and a second output, the processing device configured to:

calculate a duty cycle of a current provided to a stepper motor; and

output, at the second output, a calculated duty cycle signal indicative of the calculation;

at least one register coupled to the processing device and configured to store a base duty cycle value of current provided to the stepper motor under a base load condition, and to store a reference duty cycle value;

a subtractor coupled to the processing device and to the at least one register, the subtractor configured to:

receive the calculated duty cycle signal; and

provide a subtractor signal responsive to a difference between the calculated duty cycle and the base duty cycle value; and

an error amplifier coupled to the subtractor and to the at least one register, the error amplifier configured to:

receive the subtractor signal;

compare the subtractor signal to the reference duty cycle value; and

provide an error signal responsive to the comparison;

wherein the processing device is further configured to adjust a peak current level of the current provided to the stepper motor responsive to the error signal.

9. The device of claim 8 , wherein the processing device is configured to:

increase the peak current level responsive to the error signal being a positive value; and

decrease the peak current level responsive to the error signal being a negative value.

10. The device of claim 8 , wherein the duty cycle calculated by the processing device comprises an average duty cycle of the current provided to the stepper motor over a half-cycle of a current waveform.

11. The device of claim 8 , wherein the at least one register is a user-configurable register.

12. The device of claim 8 , wherein the reference duty cycle is of a current provided to the stepper motor under a maximal load condition, and with a maximal peak current level.

13. The device of claim 8 , wherein the error amplifier is a hysteretic comparator configured to:

compare the subtractor signal to an upper threshold value; and

compare the subtractor signal to a lower threshold value;

wherein the upper threshold value equals the reference duty cycle value plus a first amount, and the lower threshold value equals the reference duty cycle value minus a second amount.

14. A system adapted to be coupled to a stepper motor and operable to control the stepper motor, the system comprising:

a driver coupled to the stepper motor, the driver configured to control a voltage applied to the stepper motor; and

a controller coupled to the driver, the controller configured to:

calculate a duty cycle of a current provided to the stepper motor;

compare a difference between the calculated duty cycle and a base duty cycle of current provided to the stepper motor under a base load condition, to a reference duty cycle value; and

adjust a peak current level of the current provided to the stepper motor responsive to the comparison.

15. The system of claim 14 , wherein the controller is configured to:

increase the peak current level responsive to the calculated duty cycle being greater than the reference duty cycle; and

decrease the peak current level responsive to the calculated duty cycle being less than the reference duty cycle.

16. The system of claim 14 , wherein the duty cycle calculated by the controller comprises an average duty cycle of the current provided to the stepper motor over a half-cycle of a current waveform.

17. The system of claim 14 , wherein the base duty cycle and the reference duty cycle are user-configurable values.

18. The system of claim 14 , wherein a mechanical load is not coupled to the stepper motor in the base load condition.

19. The system of claim 14 , wherein the reference duty cycle is of a current provided to the stepper motor under a maximal load condition, and with a maximal peak current level.

20. The system of claim 14 , wherein the controller is configured to compare the difference to an upper threshold value and to a lower threshold value, wherein the upper threshold value equals the reference duty cycle value plus a first amount, and wherein the lower threshold value equals the reference duty cycle value minus a second amount.