-5V, What does it do?

[nihili]

What does the -5V line do in an ATX power supply?

I'm trying to convert a WTX power supply for use with an ATX board, and the WTX doesn't have a -5V line. Is the -5V really necessary? Can I substitute something else? Is there a way of creating a -5V line?

nihili

[flounder43]

I don't know, you wouldn't think that it would be there, if it were not used...

However, look at the AMD builder's guide RE: power supplies:

http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26003.pdf

Note that on page 5 and forward from there, when they detail how to figure power consumption, they don't even list the -5. They do not seem concerned about it.

[flounder43]

Also, nihili, this might be helpful, the ATX specs and standards...

http://www.formfactors.org/

Note, on page 21 of the ATX Spec.( http://www.formfactors.org/developer/specs/atx/atx2_1.pdf ), where voltage tolerances are listed, the -5V has the comment "(if used)"...

There is also a Spec specifically discussing ATX power supplies...http://www.formfactors.org/developer/specs/atx/atx12vPSDGV1.pdf

In that spec, according to the revision history on page 2, you will note that the -5 has been removed from the Spec tables.

[nihili]

Thanks flounder. I'm hoping the revision history indicates that I can get by without one. I'd still like to know what it was there for in the first place. If I can manage to convert this PSU, it should be pretty decent. I just wnat to be careful as I do it.

Anyone else?

nihili

[RoadWarrior]

It's there for the original RAM chips for the original IBM PC, I guess it's STILL there because they figured you might wanna use a 384K base memory expansion card, filled with HIGH SPEED! 200ns memory, that needed 2 wait states even on a 4.77Mhz 8088.

Road Warrior

[nihili]

I've successfully converted this to ATX. Details here (http://forum.oc-forums.com/vb/showthread.php?s=&postid=1007894#post1007894).

nihili