12 May
2005
12 May
'05
2:02 p.m.
>>>> "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 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