A METHOD FOR CURRENT SUPPLY TO A SUBSCRIBER TELEPHONE FROM A TELEPHONE EXCHANGE

摘要

A method in current feed to a subscriber telephone from a telephone exchange in which there is arranged a voltage source (11). A differential amplifier (1) senses the potential difference between the poles of the voltage source (11), and after lowpass filtering (2) a reference voltage (UREF) is added (3). The thus-obtained sum voltage is allowed to constitute the reference value in the system. The arithmetical mean value of the pole potentials of the voltage source is utilized as a corresponding actual value. The difference between these reference and actual values is allowed to control a current tap in equal phase from both poles of the voltage source.