Transient protection at a line interface

摘要

A protection circuit provides transient protection to a solid state circuit of a line interface for wired telecommunications media at a voltage level below the power supply of the solid state circuit and prevents transient currents from entering the power supply distribution where they might cause damage to the protected interface and other circuits. The protection circuit uses a MOSFET, the gate of which is provided with a bias derived from a power supply of the solid state circuit being protected. The bias causes the MOSFET to be always on such that the MOSFET provides an immediate and high transconductance path to ground for transient currents from the line interface.

主权项

1. A protection circuit for protecting at least one solid state circuit at a line interface, the protection circuit comprising:
at least one first transistor; at least one first bias supply for supplying a first bias current to said at least one first transistor; wherein the supplied first bias current is at least a current required to operate said first transistor; said first transistor and said first bias supply comprise a first protection circuit providing protection of a first polarity; at least one second transistor; at least one second bias supply for supplying a second bias current to said at least one second transistor, wherein the supplied bias current is greater than or equal to a bias current required to operate said second transistor; said second transistor and said second bias supply comprise a second protection circuit providing protection of a second polarity opposite to said first polarity; and at least one further transistor, wherein a gate of said at least one further transistor is derived from between the first said transistor and ground.