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1. Stepper motor status

Motors have various classification methods. For example, if we use the voltage types to classify, there are AC motors and DC motors. When we use the rotation speed and power frequency to classify, there are synchronous motors and asynchronous motors.

Figure 1 is the stepper motors' positional relationship in small motors series.

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We can know from figure 1.2 that stepper motor belongs to DC drive synchronous motors, but it can not drive directly by power of DC or AC, it needs to be equipped with drivers to use. So if we want to operate stepper motor we should equip it with drive circuit. This is the same as DC brushless motor, because DC brushless should use drive circuit to connect motor stater with DC power supply.

2. The function of stepper motor drive circuit.

The mission of stepper motor drive circuit is switching current of DC power by sequential instruction to each phase coil of stepper motor. Figure 1.3 is schematic diagram of three-phase VR type stepper motor windings plus power supply, in which the driving circuit is represented by switches.

In figure 1.3, when the switch is on ,the first phase winding is connected, while switching to the order of the second phase, S1 will turn on into a OFF state, S2 will turn into a ON state. In this way, motor rotor rotates a fixed angle, the fixed angle is only depends by the relationship of the number of stator and number of rotor teeth, this is the inherent step angle of the motor rotation. Similarly, S3 turns a ON state sequentially, S2 turns into OFF, motor rotor rotates a step angle again. In turn, once the circuit is switched, the motor rotates at an inherent angle.

If switching n times, the rotor rotates the n times angle of the step angle; is there is no instruction, then the rotor stops to rotate. The motor takes the step angle as a step, the rotating angle is decided by the structure of the motor, if we connect the load to motor axis, we can control the position of the rotation angle; change the switching speed (pulse frequency) of switch , then the rotation speed can be changed. Therefore, changing rotation speed is to change the switching frequency of switch S1, S2 and S3 in Figure 1.3, that is, the switching frequency of switch S1, S2 and S3 is directly proportional to the rotor speed.

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Figure 1.3 Schematic diagram of stepping motor driving circuit

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