> So, putting a ferrite bead in series with the power supply feeding some
> 'stuff', do they prevent noise on the supply lines from coming back to
> the source?  For instance, a DC/DC module feeds 3 circuits, each having
> a bead. If noise is injected back onto the supply from the devices, it
> would stand to reason the bead would help prevent it from being
> transferred to the other devices?  Correct? Comments?

Yes, to the limit of what the ferrite beads can filter out.  These are
really small inductors.  They only filter out the highest noise
frequencies.  Look up the inductance spec and do the math.

Note that you've essentially got two ferrite beads in series between any
two devices, but only one between the power supply and each device.  If
power supply noise is a big issue, a DC-DC converter may not be
appropriate.  It will probably make more noise than the devices being
powered.

If you need to use a DC-DC converter for efficiency but can't stand much
noise and crosstalk, consider separate linear post regulators for each
device.  Better yet, design the circuits to be more tolerant.


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