Patent ID: 6069950
Filing Date: 2000-05-30
Classification: H04M,Y02D

Abstract:
A current-limiting circuit for a battery-feed circuit of a digital communications line, comprising:a feed transistor for coupling a source of power to a lead of the digital communications line and limiting an amount of current flowing between the source of power and the lead to below a first value when a voltage across the feed transistor is below a second value;a high-impedance circuit for coupling the source of power to the lead in parallel with the feed transistor; anda control transistor connected to the feed transistor and causing the feed transistor to supply an amount of current to the lead that is less than the first value and greater than a third value and inversely proportional to the voltage across the feed transistor when the voltage is above the second value and below a fourth value, and further causing the feed transistor to cease supplying current to the lead when the voltage is above the fourth value so that the high-impedance circuit supplies an amount of current to the lead that is less than the third value when the voltage is above the fourth value.