Problem Facing while designing an EMI Filter for CE102 test (MIL-STD-461)

Thread Starter


Joined Oct 11, 2018
Hello everyone,

I am designing an EMI Filter for CE102 test, Presently simulating the circuit in LTSPICE tool.
So to Filter, I want to create Power supply (say, 230VAC, 50Hz) with noise (1V, 1MHz) added to it, So that I can be sure that my circuit filters out noise and delivers applied power properly.

My question is How to add two signals in LTSPICE, Where power and frequencies are totally different and provide it to the circuit as input ?

Awaiting for your reply...!



Joined Feb 8, 2018
A voltage source has zero impedance unless specified otherwise, so you just connect them in series.

Beware of simulations of filters. It will work well if the filter is accurately modeled, but simple models are inadequate. For example, a practical inductor used for filtering will have distributed capacitance that will impair its ability to attenuate high frequencies. Different physical constructions will have different capacitances (e.g. in toroidal common mode chokes, the windings are sometimes made with a sort of two step forward one step back arrangement rather than continuous layers laid over top of each other; the capacitance between input an output ends of the windings, where the voltage differential is largest, is reduced this way). Common mode inductors will have imperfect coupling so there will me normal mode inductance (which is usually not a bad thing). Component datasheets are sometimes rather unhelpful with these details.

[EDIT] Accurately modeling actual noise sources is much more of a challenge.