Driving 2-Phase Bipolar Stepping Motors: Part 1

In succession to the basic stepping motor characteristics described in the previous article, stepping motor driving is here explained. Driving is explained separately for a 2-phase bipolar stepping motor and for a 2-phase unipolar stepping motor; in this article, driving of a 2-phase bipolar stepping motor is addressed.

Driving 2-Phase Bipolar Stepping Motors: Driving Circuits

We begin with a basic block diagram of a 2-phase bipolar driving circuit example.

The 2-phase bipolar stepping motor can be driven by using 2 channels of the H-bridge drive circuit. This block diagram is an example of a circuit that uses PWM operation for constant-current driving; operation is basically the same as in?“Driving Brushed DC Motors Using PWM Output”.

There are two current regeneration modes, Slow Decay and Fast Decay, during which the motor current attenuates. Depending on the mode, current tracking may be poor, resulting in vibrations and noise. To deal with this, there are drivers equipped with a mix decay function for externally adjusting the ratio of Slow Decay to Fast Decay. Current regeneration modes will be explained in more detail in Part 2.

Below are shown waveforms for driving a 2-phase bipolar stepping motor with two-phase excitation (Slow Decay), 1-2 phase excitation (2-phase full torque, Slow Decay), 1-2 phase excitation (2-phase torque = single-phase torque, Slow Decay), and 1/4-step excitation (Slow Decay). What should be noted here are the relations between the input signals INxx and output voltages OUTxx and the output currents, as well as the number of steps. Steps can be made finer when using 1/4-step excitation, and currents also change more gradually, so that the motor can be rotated smoothly.

Next, the Slow Decay and Fast Decay current regeneration modes, as well as Mix Decay, will be explained.