"Jim Yanik" wrote in message
4...
"Arfa Daily" wrote in
news:O24eo.36157$r24.2988@hurricane:

Thanks for the insights Jeff. All interesting stuff. These are
dedicated games machines, not based on a PC in any way. The power
supply is specced to deliver 12v at 23 amps, yes, that's twenty
three amps ...

Almost all of this is potentially going into these two processors,
so not far off 300 watts between them. No mean task shifting the
heat off them !

Arfa



what processors(microprocessors?) run at 12V?
ISTR that today's uPs run mostly on 3.3V

Most other digital logic runs at 5V,I believe.

I think you wil find that most of your power is going into the video
drive (or LCD backlight) circuitry.

--
Jim Yanik


Er no. There are no backlights. Or display processor. These are X-Box
/ Playstation type boxes. Apart from some support circuitry in IC form
- which admittedly does gobble enough power to make it run hot enough
that a degree of heatsinking to the pcb shielding via thermal pads is
required - everything goes on in a pair of very large BGA processors,
one of which is the data processing engine, and the other of which is
the graphics processing engine. It is they which make use of the 12v,
and they which gobble the amps from it ...

The power supply does have other outputs, but these are all at very
low current availabilities, so will be for support logic and maybe
some core supplies for the two processors. Trust me when I say that
the two big chips is where all the power is going, and generating heat
that needs shifting
:-)

Arfa



Odd that BGA processors are using 12V instead of logic level voltages.

I'm surprised they don't use some sort of liquid or heat-pipe plumbing to
remove all that heat. Wasn't it the CRAYs that used liquid Freon to flood
the processor cabinet to dissipate al the heat built up?

--
Jim Yanik


Yes, I was amazed when I read the PSU specs. One of the versions is actually
specced 12v at 32 amps !! The PSU plugs directly onto the board via a pair
of brass pins as thick as those on a power cord for a kettle. The heat is
removed via a pair of flat plates that are connected to a network of sealed
copper pipes, a bit like you see on some Technics amps. I've no idea what is
inside those pipes. This whole assembly is cooled by a centrifugal fan that
idles at a very low speed. The heatsinks have to get up to blisteringly hot
before the processor thinks that it might be a good idea to ramp up the
speed of the fan a bit. I guess they have done this to try and keep the
thing quiet, but personally, I think it is a really poor bit of design. I am
looking at ways to make the fan idle faster, without compromising the auto
ramp up beyond that, when the processor deems it necessary, but
unfortunately, it's not quite as easy as a simple 'analogue OR' function,
because the fan is controlled digitally. It is supplied with a constant 12v,
but a third wire has a PWM signal placed on it by the CPU, and the fan's
internal electronics respond to that to control the speed.

Yes, it was the Cray. It had a central octagonal bus backplane as I recall.
The met office here in the UK used to use one for weather data number
crunching, but I think it has been replaced now.

Arfa