Re: New Monitor: Center tapped transformer

Fine. What do they cost?

----- Original Message -----
From: jeff hendrix <jhendrix@Quark.Com>
To: <vectorlist@lists.cc.utexas.edu>
Sent: Monday, November 08, 1999 11:24 AM
Subject: RE: New Monitor: #2 CIRCUIT FOR REVIEW

> All the atari color xy games have a 50VAC center tapped transformer
already
> built in.
>
> -jeff
>
> -----Original Message-----
> From: James Nelson [mailto:nelsonjjjj@didactics.com]
> Sent: Monday, November 08, 1999 8:34 AM
> To: vectorlist@lists.cc.utexas.edu
> Subject: 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 11:56:12 1999