Stepper motor: Voltage- or current control

 

In the data sheet of the stepper motor you get the information about the maximal operating voltage and current per coil. You should never exceed the maximal allowed current but you can exceed the maximal voltage by observing the maximal current.

 

The higher is the rotor speed the more back emf is induced in the coils. The induced voltage has opposite direction to the supply voltage and therefore decrease the current over the coil. The lower the current the lower the torque!

          How can we work against this proceeding?

We increase the supply voltage. But be careful at low speed, Here the motor could be damaged. There are two different methods with the following names:

  1. L/R-Drive
  2. L/nR-Drive

By the L/R-Drive method the coil voltage has a value so that in the still stand of the motor maximally the allowed current is in the coil.

By the L/nR-Drive method we connect a resistance in series to the coil to control the voltage over the coil.

IN both methods you control the voltage but not the current!

A better method is the current control also called Chopping-Drive.  => 

(*) Spule = coil  (*) EMK = emf