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What Is a Stepper Motor Circuit?

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  • Written By: David Hylton
  • Edited By: A. Joseph
  • Last Modified Date: 24 October 2014
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A stepper motor circuit is a circuit in which a stepper motor is driven by a series of voltage pulses, which allows for its mechanical shaft rotation in discrete movements. Unlike a typical motor that rotates continually, a stepper motor does not have this continuous motion but rather moves in a discrete number of steps. A full revolution — a 360-degree turn — of a stepper motor is divided into a number of divisions. Some stepper motors might have as many as 200 divisions. This means that for a complete revolution to occur, the stepper motor must be sent 200 electrical voltage pulses, because a separate pulse must be sent for each step.

Besides specifying the number of voltage pulses sent to the stepper motor to determine shaft rotation, another chief characteristic that is determined by the user is the frequency of the pulses of the stepper motor, which controls its speed. To increase the speed of a stepper motor, the frequency of the pulses sent out to the motor is increased. To decrease the speed, the frequency of the pulses is decreased. This is necessary to do when a certain speed is desired for an application.

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There are three basic types of stepper motors, which are the variable reluctance stepper motors, permanent magnet stepper motors and hybrid stepper motors. A variable reluctance motor is a motor that consists of an iron rotor that is teethed and moves by attraction to energized stator poles. This type of motor does not contain any permanent magnets. This differs from a permanent magnet stepper motor, which does have a permanent magnet as its rotor but does not consist of any teeth.

In a permanent magnet motor, there are four magnetic poles that serve as energized windings to attract the rotor to move. Hybrid stepper motors combine the characteristics of both variable reluctance motors and permanent magnet motors. They are built using a permanent magnet rotor with multi-teethed stator poles.

A stepper motor circuit can be connected together by connecting the stepper motor to a stepper motor driver, which typically is a microcontroller. Stepper motors have input pins that allow digital pulses to be sent into them to control movement and speed of the motors. With a device such as a microcontroller, a stepper motor circuit can be programmed via software to control all aspects of control of the stepper motor. Thus, a user wouldn't have to manually send out pulses to the motor, which is not as nearly efficient as using software to program a stepper motor circuit.

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