Automatic voltage control device is based on two sections, fax modem operating section for checking signal received on telephone line, recognising ringing signal to start operation

摘要

The fax modem sections (1) and the voltage control section (2) regulate the voltage going to the voltage source section (204). The section (2) contains a counter (200) for monitoring the ringing signal, giving a ''1'' signal to an auxiliary voltage section (201) to pass a voltage to it and a signal to a voltage switching section (202), so that the function switching section (203) can decide on one of two conditions. The counter has a differential amplifier (207) for the ringing signal and its output goes to a latch (209) that stores an input signal corresponding to the ''1'' signal, so that the MOS transistor (205) can operate the relay (209) of the voltage switching section.