Single wire digital width modulation for fan control with tachometer feedback

• US 20020060544A1
• Filed: 11/21/2001
• Published: 05/23/2002
• Est. Priority Date: 11/21/2000
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Teggatz, Ross E., Teutsch, Alexander Noam, Baldwin, David John, Lata, Zbigniew Jan
• Granted Patent: US 6,563,284 B2
• Time in Patent Office: Days
• US Class Current: 318/599
• CPC Class Codes: G05B 11/28 using pulse-height modulation; using pulse-width modulation
• CPC Class Codes: H02P 6/085 in a bridge configuration

Abstract

The present invention relates to a motor drive system which comprises a fan controller circuit operable to generate a PWM control signal for control of a motor speed. The fan controller circuit comprises a current detection circuit and a motor speed determination circuit. The system further comprises a fan driver circuit operable to drive a motor at a duty cycle based on the PWM control signal from the fan controller circuit. The fan driver circuit comprises a current sink circuit operable to draw current from the PWM control signal when the PWM control signal is high and when the motor reaches a predetermined position. In the addition, the current detection circuit is operable to detect the current draw on the PWM control signal and provide an indication signal to the fan speed determination circuit associated with such detection. Further, the motor speed determination circuit is operable to determine the speed of the motor based upon a timing associated with successive current draw detections. The present invention also relates to a method of determining a motor speed which comprises driving a motor at a duty cycle dictated by a PWM control signal and detecting a predetermined rotor position of the motor. The method further comprises generating a current pulse based on the rotor position, wherein the current pulse is convolved with the PWM control signal, detecting the current pulse, and determining the motor speed using successive detected current pulses.

Claims

1. A motor driver system having tachometer feedback, the system having a motor controller circuit operable to generate a pulse width modulation (PWM) control signal, and a motor driver circuit operable to driver a motor at a duty cycle associated with the PWM control signal, comprising:

a motor position detection circuit operable to generate a signal associated with a predetermined position of a rotor of the motor;

a current pulse generation circuit operable to generate a current pulse associated with the PWM control signal in response to the signal from the motor position detection circuit; and

a motor speed determination circuit operable to determine a speed of the motor using the current pulse.

2. The system of claim 1, wherein the motor controller circuit comprises one integrated circuit chip and the motor driver circuit comprises another integrated circuit chip, and wherein the current pulse comprises a current draw on the PWM control signal when the PWM control signal is at a high digital voltage level, wherein the current pulse is convolved with the PWM control signal.

3. The system of claim 2, wherein the current pulse generation circuit comprises a transistor having a terminal coupled to the PWM control signal and a control terminal coupled to the motor position detection circuit, wherein when the signal of the motor position detection circuit transitions, the transistor conducts when the PWM control signal is at the high digital voltage level and draws current for a predetermined amount of time.

4. The system of claim 3, wherein the motor speed determination circuit comprises:

a timer circuit operable to generate data indicating a period of time between successive current pulses associated with the PWM control signal; and

a decoder circuit operable to determine a speed of the motor based on the data provided by the timer circuit.

5. The system of claim 4, wherein the timer circuit is operable to collect timing data associated with a plurality of successive current pulses and generate data indicating an average period of time between successive current pulses.

6. The system of claim 3, wherein the decoder circuit is operable to determine the speed of the motor based on the data provided by the timer circuit and also on data associated with a type of motor employed in the system.

7. The system of claim 2, wherein the motor position detection circuit comprises a Hall sensor operable to determine the motor position based on a magnetic flux of the rotor which is a function of a motor position.

8. The system of claim 7, wherein the motor position detection circuit further comprises a comparator circuit operable to receive a differential input signal from the Hall sensor and output a digital signal having a transition frequency which is a function of a zero crossing of the differential input signal.

9. A motor drive system, comprising:

a motor controller circuit operable to generate a PWM control signal for control of a motor speed, the motor controller circuit comprising;

a current detection circuit; and

a motor speed determination circuit;

a motor driver circuit operable to drive a motor at a duty cycle based on the PWM control signal from the motor controller circuit, the motor driver circuit comprising;

a current sink circuit operable to draw current from the PWM control signal when the PWM control signal is high and when the motor reaches a predetermined position,

wherein the current detection circuit is operable to detect the current draw on the PWM control signal and provide an indication signal to the motor speed determination circuit associated with such detection, and

wherein the motor speed determination circuit is operable to determine the speed of the motor based upon a timing associated with successive current draw detections.

10. The system of claim 9, further comprising a position detection circuit operable to detect the predetermined position of the motor and generate a signal associated therewith.

11. The system of claim 10, wherein the position detection circuit comprises a Hall sensor operable to detect a magnetic flux of a rotor of the motor which varies as a function of rotor position, and further operable to output a differential signal associated therewith.

12. The system of claim 11, wherein the position detection circuit further comprises a comparator circuit coupled to the Hall sensor, wherein the comparator circuit is operable to generate a digital signal which is a function of the differential signal of the Hall sensor.

13. The system of claim 12, wherein the digital signal of the comparator circuit transitions from one digital value to another digital value when the differential signal experiences a zero crossing.

14. The system of claim 9, wherein the current sink circuit comprises:

a transistor having a terminal coupled to the PWM control signal from the fan controller circuit and a control terminal; and

a strobe control circuit coupled to the control terminal of the transistor, wherein the strobe control circuit is operable to generate a control signal based on the predetermined position of the motor, and wherein the control signal controls a conduction of the transistor, wherein the conduction of the transistor results in the current draw on the PWM control signal.

15. The system of claim 9;

wherein the current detection circuit comprises;

a resistor on an output portion of the motor controller circuit, wherein a PWM control signal output port is coupled to the resistor; and

a comparator circuit having two input terminals coupled across the resistor, wherein when the PWM control signal experiences a current draw from the current sink circuit, a voltage develops across the resistor, causing an output of the comparator circuit to transition, thereby generating a current draw indication.

16. The system of claim 9, wherein the motor speed determination circuit comprises:

a timer circuit operable to generate data indicating a period of time between successive current draws on the PWM control signal; and

a decoder circuit operable to determine the motor speed using the data from the timer circuit.

17. The system of claim 16, wherein the decoder circuit is further operable to determine the motor speed using data relating to a type of motor being employed in the system.

18. The system of claim 16, wherein the decoder circuit is further operable to determine an average motor speed using data from the timer circuit indicative of a plurality of successive current draws on the PWM control signal.

19. The system of claim 9, wherein the motor controller circuit and the motor driver circuit comprise separate integrated circuit chips, and wherein the PWM control signal and current draw associated therewith are resident on a single communication wire between the two chips.

20. A method of determining a motor speed, comprising:

(a) driving a motor at a duty cycle dictated by a PWM control signal;

(b) detecting a predetermined rotor position of the motor;

(c) generating a current pulse based on the rotor position, wherein the current pulse is convolved with the PWM control signal;

(d) detecting the current pulse;

(e) repeating steps (b)-(d); and

(f) determining the motor speed using successive detected current pulses.

21. The method of claim 20, wherein detecting a predetermined rotor position of the motor comprises:

monitoring a magnetic flux associated with the rotor, wherein the flux is a function of a position of the rotor;

detecting a motor pole based on the monitored magnetic flux; and

generating a signal indicative of the detected motor pole.

22. The method of claim 20, wherein generating the current pulse comprises:

coupling a transistor to the PWM control signal;

coupling a control terminal of the transistor to a signal which reflects the detected rotor position, wherein when the predetermined rotor position is detected the transistor is turned on for a predetermined period of time; and

sinking current associated with the PWM control signal for the predetermined period of time in which the transistor is conducting, thereby generating the current pulse which is convolved with the PWM control signal.

23. The method of claim 20, wherein detecting the current pulse comprises:

directing the generated current pulse through a resistive component; and

detecting a voltage across the resistive component, wherein when the detected voltage exceeds a predetermined threshold, a generated current pulse is detected.

24. The method of claim 20, wherein determining the motor speed comprises:

determining a time period between successive detected current pulses; and

determining the motor speed based on the time period.

25. The method of claim 24, wherein determining a time period between successive detected current pulses comprises determining a time period between a plurality of successive detected current pulses, and determining the motor speed based on an average time period between the plurality of successive current pulses.

26. The method of claim 24, wherein determining the motor speed further comprises determining the motor speed based on the time period and a type of motor being employed in the system.