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what does the -5v do???

post #1 of 5
Thread Starter 
i have 3 or 4 psu's laying around where when i tested them with a powersupply tester the tester will say that the -5v doesn't work anyways i want to know what the -5v is for and do i need it as it seems that the psu's do work with out the -5v for a few of my rigs i just basiclly want to know what the -5v is used for and if i really need it

its just bugging me not knowing if i should junk the psu's or not
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post #2 of 5
On a modern day system, the -5v rail powers nothing. In fact, it had been removed from ATX spec in 2002~2003 and will not be on most PSUs sold today. If you happen to own a PSU that has it, it would mean it is based on a design where the majority of the power draw is on the 3.3v/5v, and it is recommended not to use it to power any modern day system.

If your PSU Tester say it's doesn't work, it probably mean you don't have it. However, even if that is the case, these testers are very inaccurate, and I would suggest in investing in a digital multimeter to test your PSU.
Edited by qwan456 - 7/9/13 at 6:56pm
post #3 of 5
It's for legacy support, in case your Haswell motherboard has an ISA slot and you need to run an audio card or hard disk controller made back in the 1980s.

The following isn't 100% correct: Each MOSFET in a chip needs to be electrically isolated from the others, and one way to do that is by surrounding each with electrically insulating material. But that makes chips costlier to build, so most chips instead build the individual MOSFETs right into the big chunk of silicon and isolate them by applying a negative voltage between the chunk of silicon and each MOSFETs. It's the same as diodes connected backwards to the power supply -- they just don't conduct. Originally that negative voltage came from outside, but for the past few decades it's been generated internally by the chip, from the chip's regular positive supply voltage.
post #4 of 5
Thread Starter 
thats actually what i was thinking it was for older systemes cuz i relised that the antec earthwatts 650 i have doesn't evan have the -5v wire and is only 23 pins instead of 24 well now i know thanks for the info and hopeful my next build wont have an isa slot rolleyes.gif
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post #5 of 5
Quote:
Originally Posted by ozlay View Post

thats actually what i was thinking it was for older systemes cuz i relised that the antec earthwatts 650 i have doesn't evan have the -5v wire and is only 23 pins instead of 24 well now i know thanks for the info and hopeful my next build wont have an isa slot rolleyes.gif

if i go in my closet ill find plenty of ISA slots. but you surely wont ISA was discontinued circa pentium 3 i believe
Edited by PCSarge - 7/15/13 at 12:43pm
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Orange Angel
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BOINC me! (TM)
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CPUMotherboardGraphicsRAM
i5 2500k @ 4.4Ghz ASUS P8Z77-I Deluxe  Sapphire Nitro R9 380X 16GB Mushkin Blackline 2133mhz @11-11-11-31-1T 
Hard DriveHard DriveHard DriveCooling
Samsung 840 EVO 120GB intel 320 series 80GB Western Digital Black 1TB EK Supreme LTX CSQ [Canadian Special Edition] 
CoolingCoolingCoolingCooling
MCP 35X 10W W/ EK CSQ X-TOP EK Coolstream PE 240 Bitspower Multi Tank 80 Bitspower Matte Black Rotary Fittings/ Feser Ma... 
OSMonitorMonitorKeyboard
Windows 10 Professional 64-Bit Samsung 32 Inch 4K TV Acer S231H Ducky Shine 3 Tuhaojin 
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Antminer S3 Antminer S3 4x Cougar Vortex V12-HP PWM Fans EVGA 500B 500W PSU, Corsair GS700 700W PSU 
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2x Factory S3 Steel Cowl Case 
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i5 750 EVGA P55 Classified 200 XFX Radeon 6850 Refrerence XFX Radeon 5770 XXX 
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