Pulse Width Modulation Fans Delta Electronics Pulse Width Modulation (PWM) Fans regulate the voltage signal between fully on and fully off, controlling the speed of a fan with low power loss in the switching device. When a switch is off, there is practically no current, and when it is on, there is almost no voltage drop across the switch. As a result, power loss is close to zero. Delta Electronics PWM Fans offer a wide range of airflow options as well as heights and widths.