Driving method of unipolar two-phase stepper motor

The excitation drive equivalent circuit of a unipolar two-phase stepper motor is shown in Figure 1. "Excitation" is also called "excitation", which refers to the process of generating a magnetic field by exciting a current through a coil. The stator magnetic pole has four poles that are opposite to each other, as shown in Figure 1.

Figure 1

When driving, the relative magnetic poles must be opposite in polarity. For example, if magnetic pole 1 is N, magnetic pole 3 must be S, so that the torque that drives the rotor to rotate can be generated.

In the two-phase winding shown in Figure 1, each phase winding has a center tap that divides the winding into two. As can be seen from the figure, the positive pole of the power supply is connected to the center tap, and the four pins of the winding are connected to a switch (S1~S4) respectively. When S1~S4 are turned on in sequence, a rotating magnetic field will be formed and the rotor will rotate. In this mode, the direction of the current in the winding is fixed, so it is called a unipolar drive mode.

Figure 2 shows the driving circuit of a unipolar two-phase stepper motor. The four gate control tubes (VT1 to VT4) are equivalent to four switches. The pulses generated by the pulse signal generating circuit are sequentially added to the control grid of the gate control tube, which will make the gate control tube conduct according to the pulse law and drive the stepper motor to rotate step by step.

Figure 3 shows the practical circuit of a unipolar two-phase stepper motor.

Figure 2

Figure 3

The pulse distribution circuit of this line adopts PMM8723, which distributes the input pulses to control the four windings in time sequence.

Transistor, 4 transistors control the current of the stator winding. Pin 1 is the signal input terminal for clockwise rotation direction.

The foot is the signal input terminal for counterclockwise rotation direction, and the rotation direction of the stepper motor can be controlled by selection.

A current limiting resistor is connected in series at the power supply control end of each winding to provide overcurrent protection. An anti-peak pulse absorption diode is provided between the collector of each transistor and the power supply end to prevent the reverse voltage generated when the winding is cut off from breaking through the drive transistor.