Subscriber line interface circuit providing regulated current

Apparatus for providing drop current to a telephone subscriber, comprising:

• a source of supply current;
• means for switching said supply current on and off;
• means for storing a portion of said supply current and providing the remaining portion as said drop current to said subscriber when said supply current is switched on and for providing said stored supply current as said drop current to said subscriber when said supply current is switched off;
• means for sensing said drop current;
• and
• said switching means comprising means responsive to said sensing means for switching said supply current off when said drop current is above a predetermined amount.

A circuit for coupling a central office to a telephone subscriber comprising:

• a first and second terminal in electrical contact with said telephone subscriber;
• means for receiving voice information from said central office;
• means, connected to said first terminal, for coupling said received voice information to said telephone subscriber;
• power supply having a first supply terminal said second supply terminal providing supply current, with said second terminal coupled to said second supply terminal;
• means for generating a stream of pulses;
• means connected to said first supply terminal for enabling current to flow from said first supply terminal when a pulse is generated;
• storage means coupled to said enabling means for storing a portion of said supply current flowing from said first supply terminal and providing the remainder of said supply current to said first terminal when said supply current is enabled;
• means for sensing current flowing from said storing and providing means to said first terminal and from said second terminal to said second supply terminal;
• means for disabling said supply current flowing from said first supply terminal when the sum of the currents sensed by said sensing means reaches a predetermined threshold and when said supply current flowing from said first supply terminal is enabled;
• and
• means for providing said stored portion of said supply current from said storage and providing means to said first terminal when said supply current flowing from said first supply terminal is disabled.