SLOA312 December   2021 DRV8412 , DRV8424 , DRV8426 , DRV8428 , DRV8434 , DRV8436 , DRV8803 , DRV8804 , DRV8805 , DRV8806 , DRV8844 , DRV8847 , DRV8932 , DRV8935 , DRV8955

PRODUCTION DATA  

  1.   Trademarks
  2. 1Introduction
  3. 2Principle of Operation
    1. 2.1 Unipolar Stepper Motors
    2. 2.2 Bipolar Stepper Motors
  4. 3How to Drive Unipolar Stepper Motors with DRV8xxx Drivers
    1. 3.1 Driving Unipolar Motor with Four-channel Low-side Driver
    2. 3.2 Driving a Unipolar Motor with a Bipolar Driver
    3. 3.3 Driving Unipolar Motor with Four-channel Half-Bridge Driver
      1. 3.3.1 Driving in Full-step Mode
        1. 3.3.1.1 Full-step Mode with One Phase ON
        2. 3.3.1.2 Two Phases ON
      2. 3.3.2 Driving in Half-step Mode
      3. 3.3.3 Example Pseudocode
        1. 3.3.3.1 Code for Full-step with One Phase ON
        2. 3.3.3.2 Code for Full-step with Two Phase ON
        3. 3.3.3.3 Code for Half-step
  5. 4References

2.1 Unipolar Stepper Motors

Unipolar stepper motors have two windings per phase. The common wiring configuration for unipolar motors is four wires connected to the motor windings (A+, A-, B+ and B-) and a center tap on each phase. The center taps can be electrically isolated; or they can be shorted electrically. The center taps are generally connected to the motor voltage supply, VM.

GUID-DE126731-8062-40A6-A326-C7F95ABF3AE3-low.jpgFigure 2-1 Unipolar Stepper Motor

Current flows from VM supply to only one half of a winding at any given time. The center tap allows the magnetic field to be reversed without having to reverse the direction of current in a winding. The tradeoff is that because only half of each winding is used at a given time, unipolar steppers result in lower torque and efficiency.

However, as current flows only in a single direction, the driver electronics for unipolar stepper motors can be simpler compared to bipolar stepper motors. Only four low-side MOSFETs and circulating diodes are sufficient to drive a unipolar stepper motor.