[sdiy] Choice of ferrite bead inductor

[Seb Francis]

Hi,

I need to choose a suitable ferrite bead inductor for power supply 
isolation but am a bit baffled by the myriad of different inductors out 
there.

Essentially I want to isolated power spikes caused by digital switching, 
etc. from sensitive analog parts of the circuit.  I will use a ferrite 
bead followed by a 10uF capacitor.  The 3 places I'm using this 
arrangement is:
- Where the +15V and -15V power comes onto the board.
- To create a separate clean 3.3V from the dirty 3.3V that powers the 
uProc, SRAM, etc.

Don't need a huge current capacity - 200mA should do it.  Needs to be 
SMD package, something like 0805, or bigger if necessary.

Could someone give me a quick pointer to a suitable inductor, or perhaps 
give me a rule of thumb by which I could select one myself?

Thanks,
Seb