Phil Weldon wrote:
'Paul' wrote:
First of One wrote:
As you know, some power supplies made by Seasonic and PCP&C are
really single-rail, but were advertised as multi-rail at one time
because it was fashionable. Now single-rail supplies are trendy, you
see all kinds of monster PSUs re-labeled with 50A or even 70A ratings
on the 12V.


I just wish the industry had some standards for this. It shouldn't boil
down to some review site opening the thing with a screwdriver, to figure
out how it works, and how it can be used
_____

There IS a standard; see
http://www.formfactors.org/developer...X12V_1_3dg.pdf
and
http://www.formfactors.org/developer..._Rev_1_2 .pdf
) .

The idea behind the separate current limited + 12 VDC rails is to avoid
a fault condition that can draw 500 or more Watts before safety circuits
kick in.

Phil Weldon

"Paul" wrote in message ...
First of One wrote:
As you know, some power supplies made by Seasonic and PCP&C are
really single-rail, but were advertised as multi-rail at one time
because it was fashionable. Now single-rail supplies are trendy, you
see all kinds of monster PSUs re-labeled with 50A or even 70A ratings
on the 12V.


I just wish the industry had some standards for this. It shouldn't boil
down to some review site opening the thing with a screwdriver, to figure
out how it works, and how it can be used.

Paul


I've heard of the 240VA limit from IEC60950, but it appears to be
optional to support it.

http://www.pcpower.com/technology/myths/

"PC Power and Cooling is once again leading the industry. All of
our power supplies now feature a large, single 12-volt rail. The
design is favored by major processor and graphics companies,
complies with EPS12V specs (the 240VA limit is not a requirement)
and is approved by all major safety agencies such as UL and TUV.3"

I'm not going to argue the merits of that statement, because I don't have
a copy of the appropriate spec that calls up the 240VA limit. I understand
it is traceable to something like 60950, but don't have a copy.

I was referring more to the architecture of the supplies. While formfactors
has a design document for dual rail supplies, I'm not aware of any standard
for tri or quad rail supplies. (Maybe design guidance comes from some
server spec ?) And the assignment of connectors, seems to be largely left
to chance. On the plus side, I am finding more documentation than I used
to. A few years ago, it used to be really frustrating to find out
what the wiring plan was. (Took a review article, to get the story. The
manufacturer couldn't be bothered to list it.)

Paul