The switch more power supply topic seems to pop up more frequently these
days. It has always been of interest to me although I have not pursued
any designs lately. Some 40+ years ago, I built switch mode supplies to
replace the dynamotors and vibrators in my AM mobile rigs. Of course
back then we just called them "transistor supplies". They were always
free running multivibrators and ran at frequencies between 100 Hz and 2
kHz due to speed limitations of the germanium transistors and slow
rectifier diodes. I wound a few toroids myself but usually scrounged
them from commercial radios, etc.
Since I have a current need for a few HV supplies (rebuilding the
VHF/UHF station with 3-4 separate amps + supplies), I keep thinking
about building some "modern" switchers.
Some questions come to mind after reviewing the Feb 91 QEX article.
The circuit in the article uses a huge line filter cap which makes step
start seem necessary. What is the actual maximum 120 ripple permissible
for a supply like this? How much smaller can you make the filter cap and
still be OK? I would like to be able to start/stop the supply with the
PTT switch for reasons which I won't go into here. I don't mind a large
inrush current if I can make the design handle it.
The core material is typo'd in the article schematic and I can't make it
out. Any body know what the actual material was?
The transformer design seems weird. I've built VHF amps like that but
see no reason to make the supply transformer that complicated. Is there
some valid reason to do so? Seems like a large diameter toroid with
conventional windings would do just fine and be easier to construct.
The "H-bridge" seems to be the choice these days. Is that for
efficiency? My "classic" supplies just used a push-pull arrangement with
a center tapped primary. Seems simpler, but surely there must be a
reason why the larger supplies don't seem to use push-pull although all
the smaller ones sure do.
Seems like it would be a good idea to make smaller "stackable" supplies.
Say something like 700 VDC at 2.0 amps max, then stack them in series to
get what you need, 1400V, 2100V, 2800V, 3500V. Like that.
I see no reason for feedback for voltage regulation. My old T-supplies
were very stiff and the supply in the article claims 50 volts drop from
ZSAC to full load. Arguments for or against? Simpler is always better as
far as I'm concerned.
Is there a good reference for design of this type of switcher someplace.
Preferably on-line. I have all sorts of design aids for tiny little
computer type supplies but nothing here for BIG stuff.
Discussion appreciated.
73, Larry
Larry - W7IUV
DN07dg
http://w7iuv.com
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|