Microstepper motor control circuit PWM output coupled to H-bridge gates

Patent metadata

Field	Value
Publication number	US-10084402-B2
Application number	US-201615296031-A
Country	US
Kind code	B2
Filing date	Oct 17, 2016
Priority date	Oct 17, 2016
Publication date	Sep 25, 2018
Grant date	Sep 25, 2018

Abstract

A stepper motor control system includes stepper motor error reduction. For example, first and second power switches respectively energize and de-energize a stepper motor coil during each cycle for pulse-width modulating (PWM) the coil current. During a cycle including a zero crossing microstep, a calibrator detects a type of a body diode effect that occurs in the second power switch when the second switch stops de-energization of the coil. A selected offset is adjusted in response to the type of detection of the body diode effect of the second power switch. Adjusting the selected offset controls the trigger time for a comparator for comparing an offset reference voltage to a motor voltage developed in response to the coil current. Progressively adjusting the selected offset over successive cycles compensates for delays of components in the PWM control loop and reduces errors resulting from, for example, process, voltage, and temperature variations.

First claim

What is claimed is:

1. A microstepper control circuit comprising:
(a) a sensing voltage input;
(b) a current generator having a current output;
(c) an emulation field effect transistor having a source and a drain coupled between the current output and a ground and providing an emulation voltage between the emulation field effect transistor and the current generator;
(d) a digital calibrator having an input coupled to the sensing voltage input and a determined offset code output;
(e) an offset digital to analog converter having an input coupled to the emulation voltage, an input coupled to the determined offset code output, and an offset emulation voltage output;
(f) comparator circuitry having a first input coupled to the sensing voltage input, a second input coupled to the offset emulation voltage output, and an output; and
(g) pulse width modulation circuitry having an input coupled to the output of the comparator and an output coupled to a gate of the emulation field effect transistor.

2. The microstepper control circuit of claim 1 in which the current generator is a sine digital-to-analog converter current generator.

3. The microstepper control circuit of claim 1 in which the current generator is programmable.

4. The microstepper control circuit of claim 1 in which the offset digital to analog converter selectively offsets the emulation voltage in response to the determined offset code.

5. The microstepper control circuit of claim 1 in which the digital calibrator includes an input coupled to the pulse width modulation circuitry.

6. The microstepper control circuit of claim 1 in which the drain of the emulation field effect transistor is coupled to the current generator and the source is coupled to the ground through a resistor.

7. The microstepper control circuit of claim 1 in which the first input of the comparator circuitry is a non-inverting input and the second input is an inverting input.

8. A process comprising:
(a) generating a first control signal to turn on and off a first transistor for energizing a stepper motor coil;
(b) generating a second control signal after the first control signal turns off the first transistor to turn on and off a second transistor for de-energizing the stepper motor coil;
(c) detecting a polarity of a first body diode voltage of the second transistor when the second control signal is turned off;
(d) offsetting a first emulation voltage from a first emulation transistor in response to the detected polarity of the first body diode voltage of the second transistor to generate a first offset emulation voltage;
(e) comparing the first offset emulation voltage to the first body diode voltage; and
(f) adjusting the turn off time of the second control signal in response to the comparing.

9. The process of claim 8 including:
(a) generating a third control signal to turn on and off a third transistor for energizing the stepper motor coil;
(b) generating a fourth control signal after the third control signal turns off the third transistor to turn on and off a fourth transistor for de-energizing the stepper motor coil;
(c) detecting a polarity of a second body diode voltage at the fourth transistor when the fourth control signal is turned off;
(d) offsetting a second emulation voltage from a second emulation transistor in response to the detected polarity of the second body diode voltage of the fourth transistor to generate a second offset emulation voltage;
(e) comparing the second offset emulation voltage to the second body diode voltage; and
(f) adjusting the turn off time of the fourth control signal in response to the comparing.

10. The process of claim 8 including setting a first current generator to provide the first emulation voltage.

Assignees

• Texas Instruments Inc

Inventors

• Saw Sooping
• Jain Anuj
• Okyere Jeffrey
• Qu Wen Chao

Classifications

• H02P8/22

  Control of step size; Intermediate stepping, e.g. microstepping · CPC title

• H02P8/12

  Control or stabilisation of current · CPC title

• H02P8/34

  Monitoring operation (H02P8/36 takes precedence) · CPC title

• H02P6/085

  in a bridge configuration · CPC title

• H02P8/32 Primary

  Reducing overshoot or oscillation, e.g. damping · CPC title