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Standard Shield Using Bipolar NPN Transistors (MEC154E)

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. The shield shown in Figure 1 is a driver for stepper motor handling up to 1 A. It is appropriate if the transistors are BD135/BD17 or BD139.



Figure 1    Standard shield circuit using bipolar transistors.
Figure 1 Standard shield circuit using bipolar transistors.


The sequence of pulses to position the motor is applied to the inputs P1 to P4 for an appropriate translator (see the following blocks). The circuit needs about 12 mA per input to drive a 500 mA motor, making it compatible with TTL or CMOS logic.

The transistors can be replaced with powerful units. If low-gain transistors are used, you’ll probably need more current in the input. The next block, using Darlington transistors, can be important if high-power stepper motors are used. The transistors must be mounted on heat sinks.