APPARATUS FOR GENERATING OUTPUT SIGNAL WHICH GIVES SYNCHRONIZING INFORMATION EXPRESSING AC TRUNK LINE VOLTAGE FREQUENCY FROM THE AC TRUNK LINE VOLTAGE

摘要

A periodic signal, at the frequency of the AC mains supply voltage, contains signal pulses, each having a duration that is substantially shorter than half the period of the AC mains supply voltage. The periodic signal is coupled to a high frequency transformer to form a periodic output signal that is applied to a time-of-day measurement circuit that provides time-of-day display information for a television receiver. The transformer provides conductive isolation between the time-of-day measurement circuit and the AC mains supply voltage source.