Stepper motor drivers

A stepper motor cannot be connected directly to a logic signal or a steady supply; it needs a driver, the electronic circuit that energises its coils in the correct order and at the correct current. The driver translates simple control inputs, often a step pulse and a direction signal, into the switched currents the windings require. Each step pulse advances the sequence by one position, and the direction line determines whether the field rotates clockwise or anticlockwise, so the controlling logic, such as a microcontroller, needs only to issue pulses.

The heart of the driver is a set of switches, usually transistors arranged as half- or full-bridges, that connect each winding to the supply in alternating polarities. For bipolar motors the bridge must reverse the current direction in each coil, while unipolar motors can be driven more simply by switching one end of centre-tapped windings. Good drivers also regulate the winding current, frequently by chopping it with pulse-width modulation, so that torque stays controlled and the motor does not overheat as speed and load change.

More capable drivers add micro-stepping, where the currents in adjacent coils are blended in graded levels to position the rotor between full steps. This increases resolution and greatly reduces vibration and audible noise. The driver therefore turns a stepper motor into a precise, smoothly controlled actuator, which is why stepper drivers are central to 3D printers, CNC machines, robots and laboratory equipment.

Frequently asked questions

Why does a stepper motor need a driver?

The driver supplies and sequences the relatively large coil currents the motor needs, and converts simple step and direction signals into the switched currents that move the rotor.

What is micro-stepping?

Micro-stepping blends the currents in adjacent coils in graded levels so the rotor stops between full steps, increasing resolution and reducing vibration and noise.

How does a driver control motor current?

Many drivers chop the winding current using pulse-width modulation to hold it at a set level, keeping torque steady and preventing overheating across different speeds and loads.