A two-wire telephone line interface circuit comprises a driver circuit for supplying direct current on the line, a controlled voltage generator, a sensing circuit for monitoring the line current, a control circuit for controlling an output voltage of the voltage generator, and a switching circuit. The...http://www.google.fr/patents/US5323461?utm_source=gb-gplus-shareBrevet US5323461 - Telephone line interface circuit with voltage switching
Telephone line interface circuit with voltage switching
