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I am creating a pcb that splits a single USB input into 3 outputs (one with data/power carried, two with just power), and I was wondering what is the best way to reduce noise on the power line as this is being made for a low noise environment (for radio work).

I currently have a simple capacitor on the vcc/ground which would reduce the noise a bit, but is there a better way? I have read about LC filters and it seems this would work better than just a plain capacitor. Does anyone have some values that of common inductors that I can source out to add to my project to reduce DC noise on the USB power?

I also have switches which open/close the power outputs and I am worried about voltage spikes when you go to turn on the hardware. Is it possible to filter these by placing a capacitor in parallel to the switch output and ground?

Finally how may I add protection to the circuit to protect the hardware in case of a failure of the pcb? I was thinking about adding a diode for some form of over voltage protection but I am worried about the voltage drop.

Thank you for your time and any answers you can give me.

edit:: Been watching more and more videos mostly relating to quad copter noise filtering for their wireless camera systems. It seems that generally the larger the inductor the better, although a 400-600uH inductor seems to work well with a decoupling capacitor. Does anyone have any other input of the size of inductor that would work to filter most of the noise on a USB power connection?

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  • \$\begingroup\$ Keep in mind that copters need to filter noise due to large noisy inductive motors. USB in general, only has about as much noise as expected from a typical computer powersupply, or laptop charging circuit, but that's about it. \$\endgroup\$ – Passerby Oct 6 '14 at 5:19
  • \$\begingroup\$ Have you read the following question (Second Answer)? electronics.stackexchange.com/questions/37318/… \$\endgroup\$ – Botnic Dec 5 '14 at 7:42
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Could you specify more information, such as load conditions per port, source port info, etc?

One way you might solve this is to use LTSpice or similar simulator to play around with various loads and filtering capabilities.

LC filters can be effective, but the current can require a very large inductor. The larger the inductor, the smoother the current ripple. You may consider adding a TVS shunt for any spikes.

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  • \$\begingroup\$ The current would be a max of 500ma as that is the maximum draw for a USB2.0 port. The actual current draw would be less than that most likely around 300ma. Would a LC filter still be worth while or is there better ways to filter such minimal current? \$\endgroup\$ – randy newfield Sep 6 '14 at 7:10
  • \$\begingroup\$ It should be fine, but I highly recommend you simulate it. Shoot for small current ripple to minimize current spikes. Size the shunt cap based on the max switching you want to allow. Be careful of the LC resonant frequency or else you may amplify a harmonic you didn't want and then either damage something or introduce spurious noise. You can dampen this with a resistor in series with the shunt cap. \$\endgroup\$ – Whistle1560 Sep 13 '14 at 17:45
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Use 1mH Inductor usually there is 350mA in seris from 5Vbus and then 1-10uF cap from incductor to GND to make LC filter.

Here is Image with result when there is noise added to the 5V DC:

enter image description here

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