Cooling advice URGENTLY sought!!

General Schvantzkoph wrote:
On Mon, 21 Jun 2004 20:54:31 +0100, wrote:


"Ben Pope" wrote in message
...
General Schvantzkoph wrote:
Power is V^2/R so reducing the core
voltage reduces the power dramatically.

I think that heat production in a chip is more about capacitance
than resistance. The voltage and capacitance (and switching time)
will affect the amount of current that flows, and that will
determine the heat production.

Ben

Capacitive Reactance (Xc)
If you had a pure Capacitive circut then the P = V^2/(Xc) might be
correct Of course, it's a ton more complicated than this in a
processor..
and I would have to wonder just how much total capacitance there is
in a processor (I wouldnt guess it's a lot given it's size)
;P

The leakage current is the resistive part, the capactance is
reactive. The capactive part dominated in earlier generations but as
line widths have become smaller the leakage has become much more
significant. In both cases the power is related to the square of the
core voltage. The reactive part is linearly related to the frequency,
so reducing the clock frequency reduces the reactive power. If you
lower the clock frequency and lower the core voltage you get a very
large reduction in power.

I wish I'd paid more attention in Physics!