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Microsim and filter design



Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Folks!

I've recently unearthed a potentially (pardon the pun) very
useful circuit for filter application.  I've passed the
details to Terry off list and his response I have put below.
The file referred to, transients.zip, which is around 65k,
should appear shortly at

http://hot-streamer-dot-com/temp/transients.zip

This circuit promises to perform very well with much less
power consumed than the conventional filters we have been
using up to now.  For those who relate to this, the file
includes a theoretical derivation (Heaviside's operational
calculus) of its operation.  I'd be grateful if those of you
with microsim experience would give this filter circuit the
once-over (or more, depending if it rings ;-)  I'd suggest
values of 20mH for "little L", 160mH for L, 1nF for C and
6,9k for R.

Thanks.
Dunckx
______________________________________

Hi Dunckx,

This is indeed a very interesting idea.  I am not sure a
resistor across
the coil will provide the needed damping but I am not sure
it won't
either...  More study is needed!!  Maybe you should mention
this to the
whole list.  I have a lot to do in the next few days and I
won't have a
chance to study it at the moment.

The equations are nice but MicroSim is definitely the tool
to work on this
one.  It can determine the parameters exactly and do the
analysis that is
needed easily.  This may be a pretty big deal so wee need to
be sure it
gets looked into.  I forget things easily so don't let me
forget O;-)

Cheers,

Terry


At 11:59 PM 1/20/2001 +0000, you wrote:
>Hi Terry!
>
>I've just been re-reading a real gem of a little book in
>Dad's collection of old radio and electronic stuff which he
>left me when he passed on, and I think I've come across an
>interesting way to keep spikes of all sorts out of
>transformers, but it will need a bit of microsim modelling
>to confirm.  I've attached a zip file called transients.zip
>which contains three .gif files, a few pages from this
book.
>The book is: "The Simple Calculation of Electrical
>Transients" subtitle "An Elementary Treatment of Transient
>Problems in Linear Electrical Circuits by Heaviside's
>Operational Method" by G.W. Carter, MA, AMIEE, 1945,
>Cambridge University Press and Macmillan, New York.  It's a
>real beauty.  Short but sweet!
>
>I've wanted to keep some inductance in filters to keep out
>rf more efficiently.  I've also wanted to use a choke which
>allows resonance with the break rate (as I like high break
>rates this involves only millihenry values) and this
circuit
>will at any rate allow the use of some choke (resonant or
>not) plus it will consume very little power from the supply
>:-)
>
>In the diagram fig 45 in transients1.gif "little L" (comes
>out "l" in this font!) is the rf choke, and L at least
eight
>times that value.  R is then 1.54 x sqrt( "little L" / C)
>where C is the filter cap.  This gives critical damping of
a
>unit shock at the floating end of the filter.  Anyhow, the
>text explains it better than that as you will see.
>
>I'd be grateful for your impression of this.  If it looks
>good, it'll save hods of watts being used to fry ceramic
>instead of air :-)  But I am left wondering as to the
>appropriate wattage rating of the damping resistor.
>
>Dunckx