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View Full Version : How important is a -5V line on a PSU?


K404
08-18-2005, 11:12 AM
Can I get away without one? I`m rewiring a PCP+C which doesnt have a -5V line but the PSU is set up for server motherboards. I`m hoping to wire it for normal mobos, which have a -5V line. Any infomation welcome :)

Thanks guys

Kenny
Squid_Spit
08-18-2005, 07:59 PM
The -5v line is not used in today's computers, thats why some psu's dont even have them.
IvanAndreevich
08-18-2005, 08:12 PM
Squid_Spit
Apparently, he's going to be using it on a server board of unknown age. So how can you generalize it as "today's computers"? Do you know what the -5V is used for?
Dave in Daytona
08-18-2005, 09:23 PM
Can I get away without one? I`m rewiring a PCP+C which doesnt have a -5V line but the PSU is set up for server motherboards. I`m hoping to wire it for normal mobos, which have a -5V line. Any infomation welcome :)

Thanks guys

KennyWhat mobo's? :confused:
craig588
08-19-2005, 05:12 AM
The ATX spec says that no -5V line is required anymore, if your mobo doesn't comply with it it's time for a new mobo because the spec hasn't required the -5V line for a long time.
KILLorBE
08-19-2005, 05:33 AM
Can I get away without one?
Most likely you can get away without the -5V and -12V line.

AFAIK the -12V is only/rarely used on the serial port and the -5V line is used on ISA slots (Pin B5 on the ISA slot, Pin 18 on the ATX connector).

I could be wrong tho.
K404
08-19-2005, 05:34 AM
Sorry...My fault for not being clear. By "normal" I meant our desktop overclocking systems...

I posted elsewhere and they agreed that the -5V line could be skipped...I`ve rewired the PSU and it works like a charm. :)

I`m surprised that "new" PSUs with the 24-pin mobo plugs and the latest ATX spec have -5V lines though... My Tagan 480- has one as well.

Thanks for the replies

Kenny :)
IvanAndreevich
08-19-2005, 03:12 PM
AFAIK ATX 2.0 spec doesn't have the -5V line.
ridczak
10-25-2005, 01:11 AM
-5V rail is used in OCZ DDR Booster. So bad I know it now, after I bought it. :( Probably I will chnage to Tagan TG480-U22 soon :)
Dave in Daytona
10-25-2005, 09:05 AM
-5V rail is used in OCZ DDR Booster. So bad I know it now, after I bought it. :( Probably I will chnage to Tagan TG480-U22 soon :)It is only used for the digital display, it will still work without a -5V rail,
but you must use a DMM to measure the Vdimm. :toast:
josi
10-27-2005, 06:12 AM
Absence of –5V line is not a big problem, it can be always taken from –12V line via LM7905 or similar negative voltage regulator.