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Bipolar Stepper Motor Controller

Here's a little circuit that simplifies interfacing to bipolar stepper motors. It's similar to a common unipolar design available on the internet. However, I modified it to use a pair of MOSFET-based H-bridges. In addition, I added an enable signal so that the motor windings can be disabled to save power. Since there are diodes embedded in the transistors, there's no need to add flyback current protection across the motor windings.

A couple of notes: ORCAD does not explicitly show the power connections for the logic devices so be sure and connect the flip-flop and XOR gate packages to +5 and ground. The MOSFETs specified in this design are surface mount and can handle about 500mA. If you don't want to lay out a printed wiring board, then I would recommend the use of Surf boards from Captial Advance (http://www.capitaladvanced.com) these handy devices let you prototype with SMT devices.

If your motor requires more current then you will have to select bigger transistors. The threshold voltage of the transistors should be in the range of two to three volts to guarantee saturation.

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