Telephone call-charge operating circuit - has compensating reservoir which is used to improve tariff relay operation

摘要

The telephone call-charge operating circuit consists of a full-wave bridge rectifier connected directly into one leg of the signalling circuit on the receiver side of a tariff-pulse blocking filter. The rectifier is connected to a diode chain (D1-4) and a storage capacitor. A three-transistor amplifier (2) is supplied from the telephone circuit pair via a bandpass filter (3) with tariff-pulses. The amplifier is powered from the diode-capacitor reservoir circuit. The amplifier output is connected to a relay winding which is part of the call-charge indicating equipment. The circuit provides positive operation of the indicator and allows higher pulse-rates to be achieved.