Choosing an inductor to filter a power supply for audio

[OradFarez]

inductor filter power supply

Hello,

Can anyone give me advice on finding the right inductor for the output of a power supply intended to drive an audio amplifier? It's a 5V supply at about 300mA maximum. The value I am looking at is likely somewhere from 4.7 to 10uH. I think I want to make a PI filter to act as a low pass circuit. The idea is to keep out the switching noise from the power supply (switching at 600KHz).

I'm trying to understand the important specifications like DCR and SRF. Obviously a low DCR is best and so choosing an inductor that might handle a bit more current than needed helps there, but what about SRF? I see these power inductors rated way up in the tens or hundreds of MHz. Then there is the Quality factor (Q). What should I be looking for when trying to keep all noise (switching and fast current changes) out of my audio stage?

Thank you so much!

 

[FvM]

audio inductors best

I think, in your application, there are no critical parameters except DCR. For up to 10 uH, rod core inductors are probably the best solution for wide band interference suppression up to many 100 MHz. If the high frequency range doesnt matter, any ferrite inductor with suitable DCR is applicable.

In addition, you should think about possible high Q issues with LC filters, that may cause inacceptable oscillations during load transients. ESR of electrolytic capacitors is a natural method for Q reduction, otherwise RC series elements can be added to the filter.