Hi dear doctor Mostafa,
For the unipolar stepper motor the driver circuit is simpler and thus cheaper. That is because based on the motor windings configuration (where there is a center-tap point), the driver need not to reverse the current. No need for current direction reversal to change the magnetic poles. As can be seen in Fig.1, the magnetic poles are changed by switching ON the left section of the winding, and then the right section, interchangeably. For instance, if the center-tapped point is connected to the +ve terminal of the supply, when the left winding's section is switched to the -ve terminal of the supply, and then the right winding's section is swithed to the -ve terminal of the supply as well (interchangeably), then, although the driver current direction is fixed, current directions in a winding's sections are different and thus different magnetic poles will be obtained. An example is a 5 leads motor. However, it may also come with 6 leads, but when it is wired, two will be connected to the same supply terminal as common. While for the bipolar stepper motor, the driver circuit is more complicated, and contains double switching devices. There is no common terminal. An example is a 4 leads motor. The current that the driver supply should be a reversible current to reverse the magnetic poles as can be seen in Fig. 2.
According to the above, at any instant during operation, half number of windings of the unipolar motors are active, while all windings of the bipolar motor are active. And generally unipolar motors' tourque is less than equaly sized bipolar ones.
Figs 3 and 4 depicts wiring and dirver contents of a unipolar and a bipolar motors respectively.
Best Regards
Hi dear doctor Mostafa,
For the unipolar stepper motor the driver circuit is simpler and thus cheaper. That is because based on the motor windings configuration (where there is a center-tap point), the driver need not to reverse the current. No need for current direction reversal to change the magnetic poles. As can be seen in Fig.1, the magnetic poles are changed by switching ON the left section of the winding, and then the right section, interchangeably. For instance, if the center-tapped point is connected to the +ve terminal of the supply, when the left winding's section is switched to the -ve terminal of the supply, and then the right winding's section is swithed to the -ve terminal of the supply as well (interchangeably), then, although the driver current direction is fixed, current directions in a winding's sections are different and thus different magnetic poles will be obtained. An example is a 5 leads motor. However, it may also come with 6 leads, but when it is wired, two will be connected to the same supply terminal as common. While for the bipolar stepper motor, the driver circuit is more complicated, and contains double switching devices. There is no common terminal. An example is a 4 leads motor. The current that the driver supply should be a reversible current to reverse the magnetic poles as can be seen in Fig. 2.
According to the above, at any instant during operation, half number of windings of the unipolar motors are active, while all windings of the bipolar motor are active. And generally unipolar motors' tourque is less than equaly sized bipolar ones.
Figs 3 and 4 depicts wiring and dirver contents of a unipolar and a bipolar motors respectively.
Best Regards
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