PWM is the abbreviation for Pulse Width Modulation. What is done in this circuit is to apply current pulses in the motor of which the total power depends on the duration of these pulses. Thus, if the pulses are short and well spaced the power is small and the motor turns slowly. If the pulse duration increases, the power increases and the motor rotates faster. The advantage of this system is that as the pulses have constant intensity (only the duration changes) the motor torque is maintained and it is possible to adjust the speed in very low values which is not possible in circuits that use rheostats. The circuit shown in the figure is then an oscillator that produces pulses whose duration can be set in a
