Re: [Gumstix-users] Neat project

[Alexandre P. N. <al...@om...>]

ken staton escreveu:

>On 6/1/06, Alexandre Pereira Nunes <al...@om...> wrote:
>
>  
>
>>That's not a very fair comparison: linear regulators tend to be very
>>inneficient, while switching step-down are generally better than
>>    
>>
>
>the real comparison is the mAh spec on an AA vs a 9V.
>
>---
>ken
>  
>

The fact that there are today recharghable AA cells with higher ma/h 
than most 9v cells out there is common sense.

However, the example clearly puts a lot of pressure on the 9v cell so 
that it's durability is further stressed by the fact that the 7805 is 
turning power into heat. The step-up regulator showns a very impressive 
efficiency of 82% on that setup. What I was pointing out is that 
comparing that to a 7805 is not fair. If the guy have a >90% efficiency 
on the 9v step-down case, then the case would be more realistic, and so 
would the effective ma/h demand by the load.

Of course, if the battery still have sufficient greater capacity to 
spent it still wins in an more absolute sense, but that was not my point 
at all. I just don't like the impression of the looser being shown as 
worsen than it could be, it's not a fair comparison  :-)

- Alexandre