Rotational Speed Control
The PWM driving signal is a digital signal repeating process of voltage ON/OFF at a constant frequency, which changes ratio of ON time per one cycle of this signal. The ratio is called duty ratio. When there is a change in duty ratio, average voltage changes as smoothly as an analog type. The ratio of digital signal voltage (E) and average voltage (V) is called duty ratio. Its relationship is expressed by V = E x duty ratio. When duty ratio is low, rotational speed of motor is slow. As duty ratio increases, rotational speed increases to increase torque. See Fig 1.