Patent ID: 7808751

Claim:
A magnetic interface circuit which comprises: a transformer having a first winding connected to an input circuit and a second winding connected to an output circuit, the first winding being fortified to provide protection against differential mode electrical surges on the input circuit side of the transformer; the transformer having parasitic inductance, capacitance and resistance and, saturating during a differential mode electrical surge, the parasitic inductance, capacitance and resistance and the saturation of the transformer acting to suppress the coupling of the electrical surge to the second winding; and at least one voltage limiting device connected in the output circuit to limit any voltage surges on the output circuit side of the transformer to a safe level, wherein there are three circuit side terminals and further including a three winding common mode choke, the voltage limiting device being connected to respective first and second ones of the circuit side terminals via respective first and second ones of the three windings of the three winding common mode choke and the third winding of the three winding common mode choke being connected to the third one of the circuit side terminals and to the second winding of the transformer.