[SI-LIST] AW: Ferrite Bead Vs. Inductor
- From: "Pommerenke, David" <davidjp@xxxxxxx>
- To: <yamma1106@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 16 Jan 2007 01:33:02 -0600
Group:
There are three differences between ferrite beads and inductors:
- phase angle at higher frequencies
- saturation behavior
- DC resistance
I think it is quite educational obtain the SPICE equivalent circuits of =
both (e.g. Coilcraft has SPICE circuits for inductors), the ferrite bead =
and the inductor and to plot the real and the imaginary part.
Complex none linear ferrite models: http://www.steward.com/spice.asp=20
Simple linear ferrite models: =
http://www.tdk.co.jp/etvcl/equivalent/bead.pdf
(see also a former discussion on this topic: =
//www.freelists.org/archives/si-list/12-2003/msg00090.html)
If you take a ferrite bead, e.g., 470 Ohm (at 100MHz) you will see about =
1-3uH inductance at low frequency. If you compare it to a 2uH inductor =
you will see that both are pretty similar (in real and imaginary part) =
at frequencies maybe up to 10MHz. Above the ferrites starts to turn its =
phase angle to zero degrees (the real part is large) and the inductor =
stays at 90 deg. The inductor will go through some sharp resonance but =
the ferrite will stay pretty lossy maybe up to 1GHz or higher.
What is the consequence? If your power distribution system has =
resonances in the low frequency range (let me say < 10MHz) both will act =
the same. If you system has resonances at higher frequencies the ferrite =
bead is cleary the better choice. From a filtering point of view? Both =
will filter quite well. Using the parasitics of the decoupling =
capacitors in SPICE you will see that decoupling of 20-40 dB can be =
achieved using a LC or Ferrite-C combination over a broad frequency =
range.
If you intend to use your ferrite bead at current levels that drive it =
into saturation I suggest to model the effect in spice. The models from =
Steward should predict this quite well.
Regards,
David Pommerenke
University Missouri Rolla - EMC laboratory
-----Urspr=FCngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx im Auftrag von ???
Gesendet: Mo 1/15/2007 6:55
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Ferrite Bead Vs. Inductor
=20
Hello, All.
=20
I am looking for a technique for sharing power source.
=20
Dut to power source limitation, I have to share 2 power, VDDA and VDDIO.
=20
So I want to reject coupling noise between those powers,
=20
Which is better, Ferrite Bead Vs. Inductor?
=20
=20
Case1) LC Filter
Case2) Ferrite Bead
Thanks for any idea or opinion.
And please let me know if you have this kind of experience.
=20
Best Regards,
YS Shin
=20
??? ????? ??, ???!
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