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.