power supply

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bob

I was looking at my power supply, and I noticed it has about 20 wires
connected to my motherboard. Why so many?

I was expecting maybe two - ground and +5V.

Thanks.
 
(e-mail address removed) wrote
I was looking at my power supply, and I noticed it has about
20 wires connected to my motherboard. Why so many?
Click to expand...

Basically because the pins on the motherboard
connector limit the current that is viable thru each pin.

It also makes the pcb design easier too.
I was expecting maybe two - ground and +5V.
Click to expand...

It makes more sense to have 3.3V and 12V rails as well now.
 
I was looking at my power supply, and I noticed it has about 20 wires
connected to my motherboard. Why so many?

I was expecting maybe two - ground and +5V.
Click to expand...

Well, the PSU has +5v, -5v, +12v, -12v, +3.3v and +5vsb outputs. Those
outputs with large current capacities (the +5v, +12v and +3.3v) require
more than one wire to handle the current. All of that current needs an
adequate return path. So, there are multiple return (black) wires as
well. And the PS_ON, and PWR_OK signals need wires as well.

Was this a serious question?
 
I was looking at my power supply, and I noticed it has about 20 wires
connected to my motherboard. Why so many?

I was expecting maybe two - ground and +5V.

Thanks.
Click to expand...

Two reasons -

1. A modern PC needs more than one voltage level such as
+12V, -12V, -5V, 3.3V and a separate low-power +5V in
addition to the main +5V rail.

2. Some of these rails need to supply so much current
(amperage) that a single wire and connector pin cannot do
the job reliably. Several wires and pins are used in
parallel so that a) the wires and contact points will not
overheat, and b) loss due to copper and contact resistances
will be minimised. This also applies to the ground return
line.

For quite some time now, modern PSUs have had four separate
wires supplying the processor in addition to the standard
20-pin ATX connector. More recently, the 20-pin connector
has been extended to have yet another four extra lines to
supply enough juice to power-hungry systems.
 
I was looking at my power supply, and I noticed it has about 20 wires
connected to my motherboard. Why so many?

I was expecting maybe two - ground and +5V.

Thanks.
Click to expand...


Google for the ATX spec to see the functions and voltages on
each rail.

There are multiples of some voltages for different functions
(5V vs. 5VSB) but mostly for carrying more current. By
using several smaller wires they are more flexible using low
cost wire than using larger wires. Further, using multiple
smaller wires helps to keep the connector modular, so lower
current wires don't have a smaller pin-connector and higher
current rails a larger connect.
 
What exactly is +5VSB?

Thank you.
Google for the ATX spec to see the functions and voltages on
each rail.

There are multiples of some voltages for different functions
(5V vs. 5VSB) but mostly for carrying more current. By
using several smaller wires they are more flexible using low
cost wire than using larger wires. Further, using multiple
smaller wires helps to keep the connector modular, so lower
current wires don't have a smaller pin-connector and higher
current rails a larger connect.
Click to expand...
 
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