Telecommunications line current supply circuit - uses two differential transistor amplifiers, first as master and second as follower

摘要

A telecommunication line supply circuit is designed for a telephone exchange terminal. The circuit has two continuous current generators one of which is the "Master" the other the "Follower". The 'Master' generator supplied a first conductor of the line, whilst the 'Follower' generator supplies a second conductor of the line. The 'Follower' has a control circuit which ensures line impedance matching. The 'Master' generator has also a control circuit which regulates the value of continuous current supplied to the line to is resistance value whatever the value of the resistance. The 'Master' generator control circuit is designed so that the current provided by the 'Master' generator is constant as long as the lines resistance is less than a step resistance value. The current is reduced in value as a function of the resistance value of the line when its value is greater than the step value.