Abstract: This relates to a phase control circuit for regulating the amount of power applied to an a.c. device by triggering on a thyristor at some time during each half cycle of an a.c. signal applied thereto. The thyristor turns off at the next zero crossover of the a.c. signal. When a first counter reaches a predetermined state, a trigger pulse is generated. The length of time it takes the first counter to reach the predetermined state can be varied by periodically loading the first counter with the contents of an up/down counter. The contents of the up/down counter may be varied by an operator or by associated circuitry.