Re: New Monitor: #2 CIRCUIT FOR REVIEW

OK, I found some cheap non inductive power resistors, and I can include the
fuses to save the yoke from fire.
I'll fix the mute resistor (thanks for catching that), and of course put big
caps at the device.

Now, If you don't want a switcher, I'm all for not building the dang thing,
but can you (or anyone) help me find out where we can get a supply of
inexpensive new, high power 200W? 110VAC in to 48VAC out center tapped
transformers so I can derive the +/- 30VDC. By inexpensive, I mean like $20
ish, not $50. Alternatively, we could use two 24V 100W transformers (not as
pretty.)

I'll get a new schematic out soon

Thanks,
James

----- Original Message -----
From: Rodger Boots <rlboots@cedar-rapids.net>
To: <vectorlist@lists.cc.utexas.edu>
Sent: Monday, November 08, 1999 2:35 AM
Subject: Re: New Monitor: #2 CIRCUIT FOR REVIEW

> It is I, the mighty Circuit Shredder, returned for a rematch. So, let's
see
> where the nasty surprises are this time.
>
> First of all, I know you all want it, but stay away from switching power
> supplies for a vector monitor. Switchers work great with stable loads but
have
> one hell of a time when the loads keep changing (exactly what a vector
monitor
> does). With very careful design a high-frequency switcher could be made
to
> work, but design of one is not for the faint of heart.
>
> Ignore sense resistor inductance at your own peril. Or better yet, look
at a
> game where somebody has put in normal wirewound resistors in something
like a
> Tempest. See all the little jaggies in the lines? There is nothing that
says
> you can't use 10 10 ohm 1 watt non-wirewound resistors in parallel you
know.
> You even spread the heat out better that way as a bonus.
>
> I know the spec sheet says you don't need a fuse, but put one there
anyway. You
> don't need a shorted IC (it's not a matter of IF, it's a matter of WHEN)
burning
> up a yoke. Or at least getting the yoke wires hot enough to shatter the
CRT. I
> know it's far-fetched, but PLEASE keep the fuse.
>
> Mute pin (pin 8) can't be tied directly to the negative supply, there must
be
> resistance there. Say 22 k ohms or so. This pin is a current (not
voltage)
> driven pin. 22 K ohms will give you a touch over 1 mA. Current has to be
over
> .5 mA, but the graphs all stop at 10 mA (all bets are off when you leave
the
> graph).
>
> The power supply .1 uF capacitors will need at least some heavy
electrolytics
> across them (100 uF or more). All of these will need to be VERY close to
the
> amplifier pins.
>
> R1 and R7 need to be VERY close, preferably the same pad group. If the
power
> supply caps and IC ground connect to the same group it's better yet.
>
> For the real purists out there, the resistance on each of the input pins
of the
> amp should be close to the same. Practice is just too picky for words,
but has
> to do with thermal stability (amongst other things). And get the value of
R2
> down. This beast driving an inductive load is going to be hard enough to
> stabilize without unexpected phase shifts from high value resistors.
>
> That's enough of that, I guess. The parts you have marked as "none" are
going
> to be real interesting to pick. You might want to use the original
monitor
> board design as a guide for at least a starting point since these are very
> dependent on yoke inductance. OR find an engineer that know his poles
from his
> zeroes to calculate them for you. I never was any good at the pole/zero
stuff,
> but without it it will be hard to get things stable. I suppose you could
dump
> it all into a Spice simulation and see what flies. At least some good
starting
> numbers could be arrived at that way.
>
>
> James Nelson wrote:
>
> > Hi everybody!
> >
> > This deflection circuit design is very simple, and that's the beauty of
it
> > :-)
> >
> > The LM3886 has all kinds of protection built in to it, so many of our
past
> > concerns are finally addressed, such as overvoltage, undervoltage,
> > overloads, shorts, thermal runaway & instantaneous temperature peaks!
> >
> > I will probably need to design an on-board switching power supply and a
> > decent spot killer (I'm not sure if it justifies a microprocessor at
this
> > point) as well as connectors for hookup. There may be a special
oscillator
> > for Sync inputs on the conversion monitor. This would stabilize the
High
> > Voltage section.
> >
> >
http://www.angelfire.com/nh/northamericantelecom/images/deflectionamp02.gif
> >
> > Don't mind the wrong symbol for the yoke.
> > Fuses are not required due to the protection inherent to the 3886.
> > I believe the sense resistor inductance, in this design, is unimportant
due
> > to yoke inductance being orders of magnitude more significant. 1-10
uH -vs-
> > 1 mH.
> >
> > Please keep in mind, I'm trying to keep the parts cost to an absolute
> > minimum so the max people can afford it. It also means, hopefully, that
I
> > won't have to invest $5000 in a parts stock just to have 20 boards on
the
> > shelf.
> >
> > Design comments, complaints and criticisms, as usual, are requested.
> >
> > Thanks everyone!
> >
> > James
> >
> > http://www.angelfire.com/nh/northamericantelecom
> > low cost regular phone service click links to 6.9c or 5.9c no monthly
fees!
>
>
Received on Mon Nov 8 09:43:28 1999