This circuit (see Fig. 1.) produces the power to drive a bipolar stepper motor. The rotation speed and the rotation direction of the stepper motor can be changed.
This circuit consists of two integrator circuits (A1, A3) and the amplifier (A2) connected in series. This connection provides necessary feedback to get the oscillation. The circuit is using the quad operational amplifier LM324. The capacitor C1 is used in the feedback network of the amplifier A2, this capacitor corrects the phase. It helps the stepper motor to start and to achieve synchronous rotation.
Fig. 1. Circuit diagram of the driver for a bipolar stepper motor.
A1..A3 - LM324; VT1, VT3 - D40K1; VT2, VT4 - D41K1.
The frequency of the generator can be adjusted with the potentiometers R3 and R6 within a range from 8 Hertz to 80 Hertz. The rotation direction of the bipolar stepper motor can be reversed by the switch S1. Push-pull emitter followers based on the complementary transistors V1..V4 (power Darlington transistors) amplify the signal to a level suitable for the bipolar stepper motor.