Key telephone lamp control circuit

摘要

There is disclosed a circuit for providing various lamp signals to a line lamp of a key telephone station. The circuit is arranged with a single ac switch or triac for each line circuit. The triac is driven at the desired rate by a circuit which generates a series of phase-shifted digital zero crossing signals having the desired duty cycle rate. Advantage is taken of the fact that the triac only requires energization at the zero crossing of the ac signal.