PWM (Pulse-width modulation) regulates the voltage signal between fully on and fully off, controlling the speed of a fan. The PWM function is commonly used in OEM cases. Delta also provides standard PWM through distribution channels. Delta's internal PWM signal control fans deliver a variety of advantages over external PWM controlled devices:

Learn more about Delta's PWM here: https://www.onlinecomponents.com/featured/delta-products-27/delta-fans-pwm-series-and-ip55ip65-rated-series?id=239