Pulse-width modulation (PWM)

Instead of throttling power with a component that wastes the difference as heat, PWM switches a transistor fully on or fully off many times per second. The fraction of time it is on, the duty cycle, sets the average power delivered. It is how motor drivers set speed and torque, LED drivers dim, switching power supplies regulate voltage, and heaters are proportionally controlled.

Frequency is a design choice with consequences: too low and motors whine audibly, LEDs flicker on camera and heaters cycle visibly; too high and switching losses and electromagnetic emissions rise. Fast switching edges are a major source of interference, so PWM design and layout show up directly in EMC testing.