Re: Single PSU to supply multiple (mini-ITX) motherboards
- From: nospam@xxxxxxxxxx (Paul)
- Date: Mon, 13 Feb 2006 06:05:11 GMT
In article <1139778155.295378.150860@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"skotl" <scott.leckie@xxxxxxxxxxx> wrote:
Hi all,
thought I'd run a theory past the electronically minded amongst you.
I'm going to power 4 mini-ITX boards from a single ATX PSU and I intend
parallel cabling all of the power leads, apart from PWROK and PSON#.
It seems to me that I need to feed both of these to each of the mobos,
but that I should protect each of them from back-feed with a diode. I'm
not sure which way round they should go, tho, because PSON# is active
low, from mobo to PSU and PWROK is active high, from PSU to mobo.
So, I reckon I'm going to do this;
(PSU) PSON---------->|------pin 14 (Mobo1)
|
|--->|------pin 14 (Mobo2)
(PSU) PWROK--------->|------pin 8 (Mobo1)
|
|--->|------pin 8 (Mobo2)
Any thoughts, advice?
Cheers,
Scott
AFAIK, PS_ON is open collector. There should not be a problem
connecting PS_ON signals from multiple motherboards together,
up to the limits of leakage current. The pullup to +5VSB inside
the PSU would determine how many PS_ON signals can be run in
parallel.
The thing is, when one of the four motherboards activates PS_ON,
the power will go to all four motherboards in parallel and they
will all power up at the same time. Is that what you wanted ?
To get the four motherboards to go to sleep, all motherboards that
are currently asserting PS_ON, will have to be told to stop. That
means that four users, running four copies of Windows, will have
to select S3 Standby, in order for the machine to go to sleep.
That looks messy, and I don't know how the four motherboards
will respond to still being powered, while they are supposed to
be sleeping. (The machines will not go to standby at the same
instant.)
Note that recently, a power conversion device was created, which
is compact and plugs into the ATX 20 pin connector. If you run
four of those power converters from an ATX power supply 12V output,
you would get independent control of the four Mini-ITX motherboards.
In effect, your old ATX power supply becomes a "brick" feeding
four power converters. To make the ATX supply into a "brick",
all that is needed is to connect PS_ON to COM on that PSU.
ATX PSU as source ------ 12V out ---------- Compact ATX
of +12V ------ COM ------------- Converter
PS_ON COM |
| | Mini-ITX
+------+
So, buy four of these, one ATX power supply, and at least you
will have a working solution. If you place a toggle switch
in place of the wire between PS_ON and COM, that will allow
you to turn off the ATX PSU at the end of the say. It will
have to be switched on, before using one of the four
Mini-ITX machines. You must calculate the number of amps
total, as determined by the actual operating power of the
Mini-ITX boards, in order to determine if the +12V output
of the ATX PSU is sufficient for the job.
http://www.mini-itx.com/store/?c=10#picoPSU
HTH,
Paul
.
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