Immunity response of fourth order input EMI filter for DC/DC converters of spacecraft subsystems

Spacecraft subsystem level EMC tests have revealed that the conducted emissions at the input of DC/DC converters tend to go above the relevant MIL-STD-461C/D/E limits. A low pass fourth order input filter is required at the input of the DC/DC converter for reducing this conducted emission to a level that is below the MIL-STD limits. The filter is a bilateral network. It not only cuts off the noise emanating from the DC/DC converter but also enhances the immunity of the converter to input power line transients and other noise voltages on the bus. This paper presents the immunity response characteristics of the fourth order input EMI filter without and with parasitic elements. Simulation was done by the circuit simulator SPICE.