This DC motor control circuit with an operational amplifier 741 operating as a voltage follower which is connected to the inverting input not the speed and direction of rotation of a potentiometer VR1. When VR1 is in position, the op amp output is close to zero and both Q1 and Q2 is OFF.
When VR1 is turned toward the positive supply, the output is a positive signal and supply the current Q1 and Q2 will be the engine OFF. When VR1 is turned to the negative supply, the circuit operational amplifier output to the negative voltage and turns off Q1 and Q2 which reverses the direction of rotation of the motor.
741 Op-Amp PinoutAs the potentiometer VR1 is moving toward the ends, the speed increases in the direction you are becoming. The Q1 TIP3055 NPN power transistor has a collector current ratings of 15A and 60V DC VCE0. The MJE34 PNP power transistor Q2 has a sheet collector current of 10 A and 40 V DC VCE0.
