Pulse Width Modulation (PWM) | Circuit Design Fig. 1: Block Diagram of Pulse Width Modulation (PWM) he (ON time + OFF time) time of the pulse as constant. The (ON time + OFF time) of a pulse is called ‘Period’ of the pulse, and the ratio of the ON time or OFF time with the Period is called the ‘Duty Cycle’. PWM - Pulse Width Modulation for DC Motor Speed and LED Pulse-Width Modulation (PWM) allows for electronic control over DC motor speed or LED brightness. This articles features schematics and photos of circuits for making PWM without a microcontroller, but instead uses a 74AC14 logic inverter chip, diodes, a capacitor, and potentiometer.