Re: [SI-LIST] : power supply filtering and bypassing

Richard Wheeler (richard@wheeler.com)
Fri, 06 Mar 1998 20:19:21 -0800

Ray,

I thought I remembered a ferrite bead model from Intusoft. Look at
www.intusoft.com/tech.htm

Then download Intusoft Technical Articles : RFOsc.Pdf - New Models (RF Beads)
Simulate RF Oscillators.

This note shows a SPICE model for a non-linear RF bead. I haven't tried it but the
frequency response looks right.

Richard

Ray Anderson wrote:

> In reply to Jeff's posting (attached below since it never
> made it to the list due to a wrong address), I've got a couple
> comments and questions related ferrite inductor models.
>
> Here is a typical ferrite bead model that I've extracted
> utilizing an HP4194 Impedance analyzer.
>
> ----+------L-----+-----
> | | L=18.47uH
> +------C-----+ C=1.4pF
> | | R=1.6K
> +------R-----+
>
> The problem I've found is that this model has a limited
> frequency range over which the model to hardware correlation
> is good. The frequency dependent nature of the ferrite material
> makes this simple topology model diverge quite a bit from
> reality at higher frequencies. Some of the special ferrite
> blends that vendors use in EMI suppressors are quite non-linear
> wrt frequency.(I've seen quite a delta as low as 10MHz on a
> number of ferrite bead inductors). Also, it doesn't account
> for saturation of the ferrite due to DC current.
>
> I've never been able to get a model out of a ferrite vendor
> that I felt was any better.
>
> Does anyone have any comments and/or suggestions on ways and
> means of extending the model to account for frequency and
> current dependency? (or perhaps have run across any good
> articles or papers addressing the issue)
>
>
> -Ray Anderson
> Sun Microsystems Inc.
>
> > Date: Fri, 6 Mar 1998 16:14:46 -0500 (EST)
> > From: "Jeff M. Gloudemans" <c22jmg@koptsv01.delcoelect.com>
> > To: owner-si-list@silab.eng.sun.com
> > Subject: Re: Re[2]: [SI-LIST] : power supply filtering and bypassing
> >
> > John,
> >
> > I've had good luck modelling ferrite beads as a parallel RLC. Usually I
> > charcterize and extract the model myself. This way I can optimaze it over the
> > frequency range of interest. At one time I did get some RLC models from TDK
> for
> > some of their surface mount ferrites.
> >
> > I'd probably have little fear of resonance effects if paralelling ferrites
> since
> > they are quite lossy.
> >
> > Jeff Gloudemans
> > Delphi Delco Electronics Systems
> >