On 2003.05.26 23:47 Tony Duell wrote:
There are several good references on SMPSU design
I should feed google... ;-)
(the section in 'The Art of
Electronics' 2nd edition is a good staring point),
Unfortunately I don't
own this book. When I tried to order it from .de,
the cost was prohibitive.
and these DEC PSU
bricks are a pretty standard step-down regualtor circuit.
Well, it looks like the
H7441 has some funky design tricks.
The only unconvention feature is that the controller
is
a 723 chip, not a special SMPSU chip.
The H745 has a 723, the H7441 has two OPAs
and two NE555. The H745 looks
quite simple and I think I understand what the different parts do, but
the H7441??? One OPA seams to do some over current protection, one the
voltage regulation. So the NE555 are doing the ON / OFF timing??? Have
to dig deeper into that...
Unfortunately it doesn't seam as simple as the SGI Indigo2 PSU repair I
did today. I had a close look at the PCBs of the PSU and saw
electrolyte... The machine seams to run stable again, now that I
replaced the electrolyte capacitor in question. :-)
--
tsch??,
Jochen
Homepage:
http://www.unixag-kl.fh-kl.de/~jkunz/