Operational amplifier DC motor driver
Using a simple operational amplifier and some other common electronic components can be designed a very simple DC motor driver that can be used for a 200mA motor application .
Rb sets the bias point for transistors Q1 and Q2.
Because Vbe(ON) varies greatly with temperature, a guardband is required to prevent Q1 and Q2 from conducting simultaneously. RB should be selected such that the transistors do not conduct until lM equals the op amp quiescent supply current, Isy . The transistors will begin to conduct at about Vbe (on) = 0.5V. In this project : RB= [vbe(on)/(lSY+ Im)]= 0.5/(0.0025 + 0.0025)=100 ohms
To maximize voltage swing across the motor, V1 must be minimized. If at full load V1 = 0.2V with V+ = 15V and VBE1 = 0.8V, the voltage across the motor will be:
VM = (V+ - 2) - VBE1 - V1 = (15 - 2) - 0.8 - 0.2 = 12.0V
Vin may be scaled with a resistive divider as:
VIN= (R1 + R2)/R2
With R1 = 240k and R2 = 10k, VIN =5 volt lM = 200mA.