Choosing ferrite size for an LC filter, are these assumptions I am making, ok ?

Thread Starter


Joined Oct 8, 2021
Hi there !


I am pulling inductors from a dead and cheap ATX PSUs. I want to use these inductors to build a basic/crude LC filter to handle 100W max power. I dont have an oscilloscope to analyze the output, but hoping that the filter will be safe with low inductance and wont oscillate. These cheap SMPS designs advertise themselves as 250W~450W capacity. I am sure they are not telling truth but I have run these and measured current at the wall socket. They can certainly provide around 80W~100W without going up in smoke.

So I am thinking of plucking that primary inductor(that E core in between the two heat sinks), rewinding it for around 20uH~30uH of inductance. Along with around 2500uF of capacitance and some resistance because of lengthy wires I think It should take care of spikes (and ripples). The problem is in inductor sizing. Am I right in assuming that primary inductor as seen in the pic can handle around 12Vdc and 5A of max current ? Will it saturate ?

The second torroidal ferrite core you see in the above pic has 4 independent winding. I traced the circuit and they are the 12V1/12V2/5V/3.3V output rails. So can I assume that this torroid too can handle 12Vdc and 5A of max current ?
Last edited: