At 07:10 PM 8/7/2008, you wrote:
>Hello all, I just found a flaw in a design due to me not paying
>attention to an important spec.
>
>I'm trying to high-side switch an input from 3 AA batteries wired in
>series, and I'd like it to work down to 2.5V or lower if possible.....
...

>Thoughts?

You should look a little harder! There are many P-channel MOSFETs rated
at Vgs = -2.5V and even -1.8V with Rds(on) of << 1 ohm.

Here's one: http://www.vishay.com/docs/73253/si1403bd.pdf
and another http://www.vishay.com/docs/71412/71412.pdf

Both fairly inexpensive. If you want to spend a bunch more, you can get into
ridiculously low Rds(on) territory:

http://www.vishay.com/docs/72085/si4423dy.pdf

Searching hint: MOSFETs rated at low Vgs usually have a low maximum Vds.


>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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