GIGI questions

[Tony Duell]

> 
> >>>>> "Tony" == Tony Duell <ard at p850ug1.demon.co.uk> writes:
> 
>  Tony> The VR241 is, of couree, a Hitachi chassis. A rather unpleasant
>  Tony> design, actually. The PSU is driven by the horizotal
>  Tony> oscillator, via a winding on the flyback IIRC. Of course the
>  Tony> PSU powers the horizontal section. ...
> 
> If you think that's bad, how about the VR201?  It may have seemed like

I have no problem at all with the VR201. It's a pretty standard and 
simple design.

> a cute idea to use 12 volts to power a CRT, but it turns out to be a
> major mistake.

Actually, it's very common. Many mono monitors do the same thing. OK, the 
mains PSU may be intenral, but it's common for said PSU to give out one 
voltage at around 12V, to use that directly to run the CRT heater and 
some of the low-level circuitry, and to get the other voltages from the 
flyback, which in turn is powered by the 12V supply.

The IBM 5151 does this, so does a little Zenith MDA monitor I have (but 
that has the craziest PSU I've ever seen [1]). The IBM PortablePC has a 
12V-powered monitor.

KME (Kent Modular Electronics) made a mono monitor that ran off 48V. It 
was used, with slight differences on the PERQ 2T1, where it ran off the 
55V output from the main PSU via a linear regulator, and on the 
Whitechapel MG1, where it ran from the 24V PSU output via a step-up 
switching regulator (no, I am serious, and that 24V output was used for 
nothing else....)

[1] A free-running chopper driving a transformer producing about 18V. 
This is half-wave rectified and brought down to 12V with a linear 
regulator. This combines the reliability of a switcher with the 
efficiency of a linear ;-) When mine blew up spectacularly (shorted turns 
on the chopper transformer, took out most of the primary side 
components), I replaced the whole mess with a normal mains transformer. 
It was actually smaller..... Oh yes, that linear regulator takes its 
referencee not from a zener or an IC regulator, but from the green 
power-on LED...

-tony