24 Jun
2013
24 Jun
'13
2:38 p.m.
On Mon, Jun 24, 2013 at 01:19:13PM -0500, Jim Brain wrote:
Obviously, the first thought was a complete custom
supply. My
interest was never in power design, so I am ill-equipped (and
uncertain of my abilities) to design such an item myself. Thus, I
started looking for a manufacturer that could design one.
Absolute requirements:
5VDC at 4.3A.
9VAC at 9VA unregulated
Sounds like a tough one, price-wise at least (I've done a couple of
go-rounds of 8" floppy power supply designs and the far cheaper of the two
is still surprisingly expensive to build, not to mention super-tedious
because of all the different values of tiny SMT parts). But in both cases
(off-mains and DC-DC) I had terrific luck with free manufacterer-supplied
software. Power Integrations has downloadable software for their nicely
integrated off-mains parts which worked nicely (although it took some
searching to find triple-insulated magnet wire and the right forms to wind
my own transformers). Prototype worked but cost me around $200 and the 400
VDC hot side just scares the hell out of me (especially if it was going to
be in kit form).
And of course NatSemi/TI has the WEBENCH DC-DC stuff that runs in a web
browser and gives you many alternative designs to choose between based on
various criteria. Everything I do with their parts Just Works.
Getting 9VAC out of an SMPS design sounds tricky though. I looked into the
same kind of thing a bit (wondering whether having an output for AC spindle
motors that takes care of 120/240 V and 50/60 Hz differences would be worth
the trouble, to make any drive work in any country) and decided it was over
my head and probably very expensive. Maybe you can cheat (and cover 90% of
users) if you know what the 9VAC is really used for though? I mean, do
peripherals ever really use it to drive another transformer, or rectify
negative voltages out of it? Maybe just having a switch that makes it put
out pulsed +9VDC (yech) for xfmrs, or straight pos or neg DC, could cover
the cases? Just yammering here...
John Wilson
D Bit