PWM

Pulse width modulation (PWM) is a method for controlling the average voltage or power delivered to an electrical load by rapidly switching a signal on and off. The central parameter is the duty cycle, the fraction of each switching period that the signal is high. By adjusting the duty cycle while keeping the switching frequency constant, the load experiences a controllable average voltage without dissipating excess heat in the control element.

PWM can be generated with digital timers in microcontrollers, dedicated PWM controllers, or analog circuitry that compares a periodic ramp waveform with a reference signal. The switched output can drive the load directly, as in switch-mode power supplies and motor drivers, or be filtered to produce a smoother voltage for some applications. In many cases, higher switching frequencies reduce audible noise and improve dynamic response, though they may raise switching losses.

Applications include DC motor control, stepper motor drivers, buck and boost converters, class D audio amplifiers, and LED dimming. The technique offers high efficiency since the active device switches between fully on and fully off states, minimizing linear losses, and allows fast response to control signals. Disadvantages include switching losses at high frequencies, electromagnetic interference, and the need for proper filtering or dead-time in bridge configurations to prevent shoot-through. Design considerations cover selecting an appropriate switching frequency, duty-cycle resolution, dead time, and measures to mitigate EMI, along with feedback and protection schemes for stable operation.