Understanding Stepper Motor Driver Circuits

Sinotech    May 27, 2014

Stepper MotorsDiver circuits directly influence the performance of stepper motors. A driver is an electrical circuit or component that controls another circuit or component in a device. Stepper motor manufacturers generally use driver circuits to optimize a motor’s driver system, meet winding parameters and make the best use of the winding space available.

Driver Circuits in Stepper Motors

In a stepper motor, including a micro stepper motor, winding resistance and inductance is vital to its operation. To do this, stepper motor manufacturers program L/R or chopper driver circuits to change the flux direction and current in the phase windings, as well as give the end-user the ability to control the amount of current in a winding.

L/R Driver Circuits

Also known as a constant voltage drive, an L/R circuit applies a constant positive or negative voltage to each winding for each step position in a motor. In this type of driver circuit, the winding is connected to a secondary voltage supply during a current’s build-up period. When the current is at the nominal level, the secondary voltage supply disconnects. Therefore, the winding current applies torque to shaft of the stepper motor. The maximum speed of a motor with L/R driver circuits is limited by the inductance at a particular speed because the voltage will eventually change faster than the current.

Chopper Driver Circuits

Chopper driver circuits, or constant current circuits, are optimal in regards to current control, build-up and reversal. In each winding, the driver circuits generate a constant current instead of applying a constant voltage. It applies a supply voltage to the winding that’s several times higher than the motor’s nominal voltage at each new step. Consequently, the winding’s current quickly rises. The controller monitors the current in each winding. When the current exceeds the specified limit, the voltage is turned off. Chopper drivers allow stepper motors to have higher torque at higher speeds, regardless of power supply voltage variations, than L/R driver circuits. They also offer shorter build-up and reversal times while minimizing supply current and power dissipation.

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