Electrical – How to use to filter noise from 5V power supply with multiple consumers


I want to create a PCB board that would have:

  • input – 5V wall outlet USB charger or for example MeanWell Din power supply
  • output – 3 usb ports that would be used by RPI-like devices. (5V 2A max each).

Question – since all devices would share same power line and I can expect noise from the consumers – could you please point at extra circuit items that I should use ?

I would imagine that it should contain capacitors from 5V to ground near each output and probably optional input capacitor (not sure if needed with quality power supply's).

And I would also assume that RPI-like devices have already some input filtering in place, so probably it would be overkill.

Also, there would be no data lines included, just the power lines.

Best Answer

If you are really worried about power supply noise from the "consumers" to affect others, a common-mode choke circuit of this type can be very effective:

coomon-mode choke circuit Source: https://www.murata.com/~/media/webrenewal/products/emc/emifil/knowhow/26to30.ashx

If high-frequency switching noise from digital ICs is your concern, you may want to look into ferrite beads as, when properly chosen, they can block most of the high-frequency conducted noise: https://www.analog.com/en/analog-dialogue/articles/ferrite-beads-demystified.html

Using ferrite beads to reduce switching power noise it's not so effective as they are essentially a tiny resistance at the frequency of power supplies (~hundreds of kHz). In my opinion, the better method is the common-mode choke. You could also design an LC filter (for differential noise only), however, the inductor may end-up being too big to fit on your PCB.

Keep in mind that it is possible but rather unlikely that one device affects the other, it will have to be a very specific frequency component that disturbs the behavior of one of the "consumer" devices. Most devices have their own input filtering too so it's okay to keep your power side "dirty" (as long as it does not prevent its own operation). In your case, I would tend to just go for a combination of decoupling capacitors to filter out from kHz (~10-100uF) to GHz range (~100pF-10nF) and place as close as possible to each USB connector power feed line.