>>>>>>>>>>>>>>>>>> Notizia originaria <<<<<<<<<<<<<<<<<<
Il 9/30/99, 7:43:23 PM, Steve Chandler <[EMAIL PROTECTED]> ha scritto
sull‘argomento Heat Dissipation:
> There is probably a more appropriate list to ask this question,
> but I think it is probably important to linux-embedded anyway,
> so here goes.
> I'm putting together an embedded 486 system. I want to use
> just a heatsink on the CPU and no fan. It will be in sealed
> 1 rack unit 19" chassis.
Be weary about overall dissipation. If the whole caboodle is
dissipating e.g 50W, that is a lot for an enclosed and entrenched 1"
unit. The rise of the CPU temperature is relative to the ambient,
which in this case is the temperature inside the box. In a normal
fanned PC box the PSU fan sucks air into the case BEFORE dragging it
through the box so the ambient stays low.
> The board I have will support most, if not all, of the 486 CPU's
> and I am concerned about heat dissipation. As for speed,
> I'll probably need a DX2-66 or a little more.
I have used all types of 486's without fans, but with a large passive
heatsink in well ventilated enclosures. And I mount the heatsink
properly with a thin film of thermal grease, which makes several C/W's
of difference. BUT, in an heavily enclosed environment passive
heatsinking will be far less effective. Dissipating components in
enclosed boxes are often arranged so they can be fixed to the exterior
casing, but this would be difficult with a CPU.
> However, is there a huge difference in heat dissipation between,
> say, a DX2-66 and a DX4-100 since the DX4-100 actually has a
> slower external clock?
As far as CPU dissipation is concerned, it is the internal clock which
counts.
> Should I go with AMD, Cyrix or Intel? Maybe you all have heard
> the joke that Intel's logo is the electronic symbol for current.
Chip densities and processes are similar for similar processors, so
expect random variations in the first order, i.e. Probably not worth
the effort. Must it be x86? The ARM chip as used in the sidewinder
etc. Is much lower in dissipation. Have you looked inside portable
computers to see how they solve the problem?
> Finally, what are the advantages to 5V verses 3V? It seems
> obvious that a 3V chip is cooler so why in the world would anyone
> want a 5V one?
3V is better on chip, 5V is better for busses, and it is difficult to
be completely 5V, so you will end adapting somewhere along the line.
Apart from that, the only other considerations would be commercial,
price/performance/availability.
Note that if you can get very little low power, mega quiet fans which
if mounted on the rear of the enclosure in line with the CPU would do
a great job in keeping a good circulation over the heatink, could
easily be as effective as a CPU heatsink.
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