[Patrick Turner]

Ian Iveson wrote:

Patrick Turner wrote

I have been on the lookout for a SMPS for a tube amp capable of
+500Vdc at 1 amp dc for larger style tubed power amps.

I've never seen or heard of anyone doing a SMPS with that
specification,
and not seen any schematic for one that I could for build myself.

I think you are the perfect candidate for the job. You have pretty
much all the skills and instrumentation required. As with valve amps,
the transformer is the crux of the matter. All the usual
considerations apply, in order to ensure stability and avoid
saturation.

I got a book from Newnes called "Demystifying Switching Power
Supplies", which probably contains all you need although the author
isn't very good at writing books. Seems to me you could quite easily
adapt a design for a forward converter. Just a matter of working out
how to use more turns on a secondary for the HT, finding suitable
output-side diodes and cap, scaling the voltage feedback, and
reworking the feedback compensation circuit to suit.

I gave up because simulation in this case takes much longer than
making a real circuit, and isn't reliable anyway because the devils
are in the small details of switching behaviour and parasitics. I
don't have fast enough instrumentation to prototype for real and am
too scared to attempt progress by successive approximation, given that
every error is likely to lead to total carnage.

cheers, Ian

One would have thought someone somewhere would have tried to make a
business
making SMPS capable of HV or at least 500V, which is only 1/2 a thousand
volts.

But it doesn't look like it has happened so far, but nobody has
ever addressed the design issues AND gone public about it all it seems,
AND got public
and hi-fi cognescenti acceptance
for such a radical PS solution to make a PS for 600VA at about 6Kg
instead of 26Kg.

I might be able to do something like this but
I always have so much to do I don't have a great deal of time to R&D
from the ground up.

One would think making a tranny that copes with switching
a chopped +350V supply but gives a peak output voltage of 500Vdc instead
of the usual
5 or 12V found in a PC would be doable, except that its all got to
happen fast,
so capacitance becomes a bother with such a wide V swing;
However they used to use oscillating transistor PS in auto apps to get
from
+12V to about +350V for mobile radios.
The switch speed has to be quick enough to get efficiency....
The old oscillators used for radios were not that efficient, but at
least
they were less likely to wear out like a vibrator supply.

Patrick Turner.