Phase cutting is a form of pulse width modulation (PWM) for power limiting, applied to AC voltages. As in all forms of PWM, phase cutting works by using a solid state switch, such as a triac, to only allow current to flow for part of the time. Phase cutting makes use of the AC voltage variations to control the duty cycle, the switch turns on when the voltage reachs a certain level and turns off when the voltage reachs the ground level. This allows altering the duty cycle easily and economically.
