Hazardous voltage protection circuit

摘要

A circuit for protecting telephone lines from AC hazardous voltages. The circuit includes an amplitude discriminator triggered at a predetermined voltage level connected to the telephone lines, and providing an output pulse for each zero voltage crossover of the hazardous voltage. A digital pulse counter counts a predetermined number of output pulses from the amplitude discriminator, which in turn operates a switch after the predetermined number of pulses are counted, opening the telephone lines between the central office and the telephone instrument until the hazardous voltage has been removed from the lines.