Let’s consider the functional diagram below:
The D/A converter outputs a voltage directly related to the potentiometer position. However, the D/A converter’s output current is limited and not enough to drive a motor. A power operational amplifier (op-amp) circuit, configured as a noninverting amplifier can drive the motor at the higher currents required. In effect, the power amp will serve as a buffer between the D/A converter and the motor.
The circuit below shows the components used along with their interconnections.
The OPA 547 can be powered by a bipolar (±) 9 V supply instead of a standard bipolar 15 V supply. With an input resistor of 10 kꭥ and a feedback resistor of 1 kꭥ, the power amp circuit has a gain of 1.1, therefore, the voltage from the D/A converter is not amplified a lot, but the circuit is able to source ample current to the dc motor.
You can also read: Pulse Width Modulation (PWM) Speed Control of a DC motor
