Uses differential amplifier and generator - giving spaced voltage pulses to power line to reduce consumption and avoid noise generation

摘要

The telephone line power supply circuit reduces the amount of power required by applying a train of power pulses to the line. An amplifier chain is coupled to each wire of the line and is driven by a pulse chain of typically 80 ms duration and 400 ms spacing. The amplifier chain comprises a differential amplifier which recieves the pulse chain, a switch having a control input coupled to the amplifier output and an output connected both to a voltage source and to the amplifier output. A further switch output is connected to a wire of the phone line and to an input of the amplifier. The supply circuit generates trapezoidal pulses in order to avoid introducing switching noise into the line and to avoid induction between lines.