Shared Memory

Peter Hiscocks phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org
Mon Jan 31 22:11:10 UTC 2005


Just so no one goes away with the wrong idea: lower voltage doesn't
*necessarily* mean lower power - the current might increase at a lower
voltage. Power is the product of voltage and current. If the motor is more
efficient, then that will result in lower power and I'll bet it's a matter
of now being able to operate from the motor at 5 volts at a reasonable
current. A lower voltage motor is not necessarily more efficient.

On the other hand, lower supply voltages on integrated circuits result in
lower power dissipation, as a matter of the chip design, and charging and
discharging the chip capacitances. In that case, a lower voltage means you
charge the capacitances with a smaller total charge, which means less
current, which means smaller power dissipation.

Peter


On Mon, Jan 31, 2005 at 04:10:15PM -0500, Taavi Burns wrote:
> On Mon, 31 Jan 2005 15:53:24 -0500, Lennart Sorensen wrote:
> > SATA has a new power connector, and future SATA specs will require the
> > drives to start using 5V and 3.3V only while current IDE drives use 5V
> > and 12V.  This will make a difference in power consumption (voltage
> > converters are not 100% efficient after all and electronics today don't
> > use 12 or even 5V).
> 
> Well, I'm pretty sure that the electronics haven't used 12V for a good 15 years
> either; that would have been for the motors in ye olde 5.25" full-height HDs.
> Note that your CD and DVD drives are half-height.  You do the math.  :)
> 
> Since the newer drives are all small anyway, nobody has to use a 12V motor
> anymore, and the electronics are all 3.3V, too.
> 
> Neat detail, though.  :)
> 
> -- 
> taa
> /*eof*/
> --
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-- 
Peter D. Hiscocks                         	   
Department of Electrical and Computer Engineering    
Ryerson University,                    
350 Victoria Street,
Toronto, Ontario, M5B 2K3, Canada

Phone:   (416) 979-5000 Ext 6109
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Email:   phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org
URL:     http://www.ee.ryerson.ca/~phiscock
--
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