FreeLists / si-list / [SI-LIST] Ferrite Bricks on power Supplies

["Chris Chalmers" <cchalmers@xxxxxxxxxxx>]

Gents,
I have seen on certain power supply circuits the use of ferrite bricks.
These have been
 put on the end of power supply before it goes on to the plane of a PCB.
I.E
Unregulated power supply-> regulated supply-> output caps-> ferrite brick.

The impedance of these bricks at 100MHz is around 30ohms.  These are to
control
 and absorb HF current draws from the supply changing them in to heat and
reducing
 the emissions.  I was always under the impression that the power supply
impedance
 should be as low as possible across a broad range of frequencies.  All that
you
 are doing by adding the ferrite brick is adding inductance.  What is the
real answer?

Best Regards

Chris


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