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 NXP Semiconductors


  • Bipolar Stepper Motor Control

  • Created: Feb 03, 2014

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Summary

This circuit can be applied in positioning and velocity control applications without the need for external position feedback. In the field of lasers and optics, this circuit is applicable in precision positioning equipment such as linear actuators, linear stages, rotation stages, goniometers, mirror mounts, and other uses in manufacturing. It can also be used in consumer electronics such as disk drives, flatbed scanners, computer printers, slot machines, image scanners, compact disc drives, and camera lenses.


A stepper motor is a brushless, synchronous electric motor that converts digital pulses into mechanical shaft rotation. It divides a full rotation into a number of equal steps, and as a result, the motor’s position can be controlled to move and hold at any one of these steps without a feedback sensor; provided that the motor is carefully sized for the application. Bipolar motors have a single winding per phase and the current in the winding needs to be reversed to allow the reversal of the magnetic pole. By precisely controlling the current in each motor phase, you can divide a motor’s fundamental step angle into smaller microsteps. These steps can be sequenced together to move the rotor at various speeds corresponding to the sequence rate, microstepping results in better positional resolution, less resonance and lower audible noise.


The bipolar motor has two windings, one for the positive phase and another winding for the negative phase. Each winding can carry a positive current, a negative current, or no current. A binary counter receives clock pulses to which it counts up or down which corresponds to the motor turning to the left or right respectively. The rotary counter used in this circuit is the HEF4516B which is an edge-triggered synchronous 4-bit binary counter. The state of the counter is decoded to produce the states of the motor rotation. The HEF4001B NOR gate and the HEF4030B XOR gates are used for the decoding circuit. These ICs have output levels that are fully buffered for the highest noise immunity and pattern insensitivity to output impedance to provide stability for the decoding circuit. To allow direction reversal of the current in the motor windings, each winding must be wired into a bridge circuit as shown in the schematic. For the positive phase, a combination of the BC517 NPN transistors in bridge are used while a combination of the BC517 NPN and BC807 PNP transistors are used for the negative phase.

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