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Driving a Stepper Motor with PNP Transistors (MEC156E)

This circuit was adapted from my book Robotics, Mechatronics and Artificial Intelligence (sold out) published in the United States. It can be used as a control shield for stepper motors in a mechatronics or robotics project or as a building block for simple projects. Depending on the application, the stepper motor can be driven from negative logic (inverted pulses). Instead of adding logic inverters, you can use this block, which operates with negative logic (see Figure 1).


Figure 1    Stepper motor shield using PNP transistors.
Figure 1 Stepper motor shield using PNP transistors.



Each winding is on when the input of the corresponding transistor is set to the low logic level. The circuit must be connected to a sequencer or other circuit to give the desired sequence of pulses to make the motor run or to put it in a predetermined position. Using the recommended transistors, the block can drive motors with up to 1 A from TTL or CMOS logic. See Chapter 3 if you want to use more powerful transistors.