In the circuit of the figure we used a potentiometer of 1 k ohm. We can use a larger potentiometer, with smaller control current, using the control of the figure that uses two transistors in the Darlington configuration. In this circuit the current of transistor Q1 is controlled by transistor Q2 which, in turn, is controlled by the potentiometer of 10 k ohm. In this way the current in the motor and therefore its speed can be adjusted precisely by the potentiometer. An advantage of using a low current component is that we can use long, thin wires to power it. This means that the control potentiometer can stay well away from the controlled appliance, installed in a small box or panel, for example.
