Power Supply Voltages? What is What?

[dugans]

This question came to mind out of a couple of other threads:

POWER Supplies: What lines power what?

The question came up from why low 5v rails can cause instability-
Does anyone know EXACTLY why this is?

And exactly what does each line supply power to?

I just hate not knowing these things!

 

[Placid]

This question came to mind out of a couple of other threads:

POWER Supplies: What lines power what?

The question came up from why low 5v rails can cause instability-
Does anyone know EXACTLY why this is?

Because when the power supply reaches its max current output the voltage reading starts to drop off, when the cpu cant get the current its trying to get its like a car enigine that runs out of gas, sputters and stops working.

And exactly what does each line supply power to?

Generally the motherboard and the cards can use all the different voltages but the cpu is the biggest power user and most all boards use the +5v line for the cpu, fans the +12v, hard drives,cd roms, ect use the +12v and the +5v

I just hate not knowing these things!

 

[MrX]

I actually thought that the 3.3v was used for powering onboard peripherals (pci cards, cpu, ram etc), 5v used on hard drives and 12v used for fans and certain other CDroms, drives etc? Please correct me if I am wrong as I have had ongoing discussions about this one, here and elsewhere.

 

[Placid]

Every motherboard can be different, depending on how its designed it can step up or down and invert any voltage sent from the power supply and use it anywhere.
So you would need to get the schematics for the particular board you are questioning and look at them.
Most motherboard manufactures will tend to use similar designs and and voltages from the power supply.
It would not make alot sence to use -12v then step it down to -5v then invert it to supply +5 to a componet when there is already a +5v line coming from the power supply.

Here is a schematic for a intel 440bx motherboard.


ftp://download.intel.com/design/intarch/schems/bxflexMBschems.pdf

 

[YMAN]

Re: Re: Power Supply Voltages? What is What?

This question came to mind out of a couple of other threads:

POWER Supplies: What lines power what?

The question came up from why low 5v rails can cause instability-
Does anyone know EXACTLY why this is?

Because when the power supply reaches its max current output the voltage reading starts to drop off, when the cpu cant get the current its trying to get its like a car enigine that runs out of gas, sputters and stops working.

And exactly what does each line supply power to?

Generally the motherboard and the cards can use all the different voltages but the cpu is the biggest power user and most all boards use the +5v line for the cpu, fans the +12v, hard drives,cd roms, ect use the +12v and the +5v

I just hate not knowing these things!

The reason 5v lines can cause instability is YES, the power
starts to drop off, also the 5v line usually has the POOREST
regulation, It can also be caused by power supplys that have
poor filtering!

The 3.3V line, powers devices such as MEMORY, and PCI/AGP
agp cards, chipsets etc.