Re: [SI-LIST] : inductor

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Thu Sep 28 2000 - 11:37:45 PDT


Muhammad

Well, because, that is the property of an inductor; you cannot change the
current in an inductor instantly, as well as you cannot change a voltage on a
capacitor instantly. Remember freewheeling diodes (in parallel with inductive
loads?) When say open drain drives a inductance (close "open drain"), and then
stops driving it, the current tries to escape the inductance and creates
enormous voltage spike on the load resistance (open "open drain"), sometimes
damaging it.

"Muhammad S. Sagarwala" wrote:

> I did not understand the last paragraph ..
>
> >The initial current flows into transmission line through the inductor (tr.
> line
> >is a resistor for the duration of the front). Then when the transition
> stops and
> >everything calms down, the current still flows in the inductor, creating a
> >overshoot. Potentially it can be bad enough overshoot to damage something.
>
> Why do you think the current would still keep flowing in the inductor even
> though it is in series
> with the transmission line which gets hooked up to a receiver ???????
>
> -----Original Message-----
> From: Michael Nudelman <mnudelman@tellium.com>
> To: Charles Grasso <chasgra@msn.com>
> Cc: KokTongTHAM <kt_tham@uti2000.co.jp>; si-list@silab.eng.sun.com
> <si-list@silab.eng.sun.com>
> Date: Thursday, September 28, 2000 8:44 AM
> Subject: Re: [SI-LIST] : inductor
>
> >An inductor as a terminator...khm...why not just terminate the line?
> >
> >Plus, do not forget - the transmission line effects are Only for transition
> >process (front). Once it stops, and the line is not terminated - the
> current
> >doesn't flow (infinite resistance of receiver).
> >If the inductor is in series with the transm. line (I would imagine so,
> since
> >you want to slow down the front) here what happens:
> >
> >The initial current flows into transmission line through the inductor (tr.
> line
> >is a resistor for the duration of the front). Then when the transition
> stops and
> >everything calms down, the current still flows in the inductor, creating a
> >overshoot. Potentially it can be bad enough overshoot to damage something.
> >
> >Charles Grasso wrote:
> >
> >> I most certainly would not recommend that. Add the correct termination
> >> and watch the ringing disappear! The inductor will add delay and more
> than
> >> likely exacerbate the ringing.
> >>
> >> I know that some folks add ferrites in place of series resistors and I
> would
> >> like
> >> to have a discussion on that. Comments?
> >> ----- Original Message -----
> >> From: "KokTongTHAM" <kt_tham@uti2000.co.jp>
> >> To: <si-list@silab.eng.sun.com>
> >> Sent: Thursday, September 28, 2000 3:07 AM
> >> Subject: [SI-LIST] : inductor
> >>
> >> > SI Gurus,
> >> >
> >> > I have told by an EMI engineer about using inductors can reduce ringing
> of
> >> > a transmission line effectively instead of series resistor. Can
> anyone
> >> > tell if this is true?
> >> > As far as I know, inductor can act as a filter to cut unwanted
> harmonnics.
> >> > How do we chose the suitable value for the inductor?
> >> >
> >> > Thanks.
> >> >
> >> > Regards,
> >> > KTTHAM
> >> >
> >> >
> >> >
> >> >
> >> >
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