EMI on diagnostics and control circuits due to switching power supplies

This paper deals with the electro magnetic interferences (EMI) induced on diagnostics and control circuits of fusion experiments, due to fast common mode voltages (Vcm) transients. The Vcm can excite the circulation of noise currents through parasitic capacitances, which couple different parts of the circuit designed to be isolated one to another. Equivalent electric circuits of the phenomena observed in RFX have been derived, which explain the induced noises and have been utilized to identify suitable correction measures; the paper describes these analyses and the experience gained in coping with the reduction of these types of EMI interferences.