Re: NFB101 part 3

On Wed, 28 May 2008 13:06:44 +0100, Ian Thompson-Bell
<ruffrecords@xxxxxxxxxxx> wrote:

Part 3 of NFB101 is now available for download as a pdf here:

http://www.ianbell.ukfsn.org/nfb101/nfb101.pdf

Comments welcome.

Cheers

Ian


There is a typo equation #2, 2nd equation from top of page. It should
be An=Vo/Vs=Ao/(1+BAo) and not An=Vo/Vs + Ao/(1+BAo).
I looked at it, and my brain did a ctrl-alt-del, had to work it out
on a *** of paper.

On page 8, your circuit shows Ra1=60K, and no mention in the text
except "anode resistance ra". I assume "ra" should be "Ra1".

The funny little symbol you use to represent the tube is not one I'm
familiar with, although it might be common in some places. Maybe it
would be worth putting in a brief description of how to use it. It's
pretty obvious if you already know the overall concepts.... but it
would throw off the beginners.

I'm more used to seeing the feedback circuit as a single ended
circuit, where there is one line coming back from the the output, goes
through a block whose transfer gain is "Beta", one line comes out, and
runs into a difference circuit such that the input to amplifier Ao is
(Vs-B*Vo). There's really no difference between yours and the one I'm
used to, except for students it is simpler with the "single ended"
pproach, and it is very workable with op-amps. This stuff can get
pretty weird for laymen, I find that to make it sink in, every
possible step to make things simpler must be taken.
The other thing to make it a bit easier to digest, would be to drop
references to "s", except where the concept is introduced. You will be
using the "jw" part of the "s", seeing as the exponential transient
part isn't used for steady-state analysis. The "s" is more academic,
but students find the "jw" term a BIT more understandable. Of course,
they need to be familiar with handling vectors and complex numbers,
and dealing with "phasors" and rectangular values.
This is pretty tough stuff for a newby, from my experience, some
20-100 hrs are required to go from DC experience through AC, feedback
circuits, bode analysis, etc. For college students who are just
beginning circuit analysis, your 33 pages would be quite intimidating!
Apart from that, your document is a pretty good refresher.

-Paul

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