DC motor speed control - with current feedback

The LM 1014 IC from National Semiconductor can be used to provide a constant speed control for small DC motors. A well known trick is used here. This takes into consideration the fact that when the motor current rises (due to an increase in load) the voltage across the motor will follow suit. The reason for this is that if the motor speed drops slightly the back EMF decreases which means that the motor current (given the same supply voltage) is going to increase. It follows that raising the voltage across the motor will increase the speed. Theoretically then, it is possible to hold the motor speed virtually constant in this way. However, in practice this system has a Um = B re (1 + R3) +1mR1 R3 Table R1, R2 and R3 should be selected so that R1 • R3 .s equal to the dynamic 5R2 1 impedance of the motor. How do you find this? A good start for the calcu- lation is to simply measure the resistance of the motor with a multi- meter and start with this value. Choose R1 to be slightly on...