Improvement of Surge Immunity by Using Transformer-isolation in an Active EMI Filter

Improvement of surge immunity due to transformer-isolation in an active EMI filter (AEF) is investigated. The surge influence on active circuit parts is analyzed by experiments. Maximum peak voltage and pulse duration of the surge transient voltages transferred to active circuit parts of a current-sense current-compensation (CSCC) AEF are measured in the cases with direct capacitive coupling and transformer-isolated coupling, respectively. The surge immunity of the designed transformer-isolated CSCC AEF is validated under numerous 4kV surge tests and VNA measurement.