Step sequence

AN235

6/23

Doc ID 1679 Rev 2

2

Step sequence

With either motor configuration, the motor makes one step each time the polarity of the

current in the stator winding changes. For a motor with one pole pair on the rotor, this

corresponds to 4 steps per electrical cycle. Figure 3 shows the step sequence and idealized

current waveform for a two-phase bipolar stepper motor. In Figure 3, each time the current

in one of the windings is reversed, the motor makes one step of 90°. Of course no stepper

motors would want to use such a course step. Typical stepper motors are 1.8° or 7.5° per

step corresponding to 200 or 48 steps per rotation. A 200 step per rotation motor would

have 50 pole pairs on the rotor and need 50 electrical cycles per mechanical rotation.

Figure 3.

Full-step sequence for a two-phase bipolar motor

In Figure 3 the current is reversed to make each step. However it is possible to have an

intermediate, half-step, position by simply switching the current in one coil off before

switching it on in the reverse direction. Figure 4 shows the sequence for half-step drive and

the idealized current waveform for a two-phase bipolar stepper motor. In half-step we now

have 8 half-steps per electrical cycle and have doubled the effective resolution of the

stepper motor.

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AM16501v1