Telephone set ringing current injection device

A telephone set line circuit ringing current injection device comprising a hybrid circuit having feeding terminals connected to a ringing current generator, and outputs connected to a subscriber's lines;

• said hybrid circuit comprises a pair of power transistors connected between said feeding terminals and said outputs;
• each power transistor including a diode connected across its collector-to-emitter path with the emitter being connected to the anode of the diode;
• and a resistor connected in series with the output of the power transistor and one of said outputs;
• a control flip-flop having an output coupled to the bases of said power transistors, said flip-flop having a clock input which is connected to a central unit for receiving a synchronization signal for validating a ringing order when the voltage on a subscriber's line is on hook or zero;
• said control flip-flop's clock input being connected to said central unit for receiving a ringing order, and said control flip-flop having a reset input connected to an output of a line loop detector for resetting said flip-flop when the receiver of the called telephone set is off hook.