Patent ID: 7099461

Claim:
A protection circuit for telecommunications equipment powered remotely through a twisted pair subscriber loop, comprising: a charge storage circuit, coupled to the subscriber loop through an arm switch in parallel with an inrush resistor, for storing charge received from the subscriber loop, the charge storage circuit coupled to the telecommunications equipment for providing the charge thereto; a fault detection circuit for setting a first signal during a period of normal operation of the protection circuit and for resetting the first signal for a predetermined period during a fault said fault detection circuit including a threshold selection circuit for outputting one of two voltages to a positive input of a voltage comparator; a delay circuit for implementing the change in threshold output a short time after a change of state of said arm switch; a processor adapted for setting an arm signal during the period of normal operation of the protection circuit; and, an AND logic circuit coupled to the arm switch, fault detection circuit, and processor for comparing the first and arm signals to set a third signal for closing the arm switch during the period of normal operation and to reset the third signal for opening the arm switch during the predetermined period during the fault; whereby the charge storage circuit continues storing charge through the inrush resistor during the fault.