> > Doesn't "logic level" usually mean "well characterized at Vgs
> > significantly LOWER than 5V"?

The term lacks some precision as I believe it was more a marketing term
which has caught on.

To satisfy most definitions, Zetex have some very nice small FETs with a 1.1
volt or so threshold (minimum turn on voltage). Most logic families will
drive these :-). Alas these may be available in SMT packages only. Typically
20v x 5A partsin pkg that can be lost if you sneeze. (very technical :-)).
I used one of these in a prototype self oscillating 1 cell to white LED
conveter recently with superb results. (2 bipolars plus FET/ more details in
due couurse).

Selection guide at

        http://www.zetex.com/3.0/b2-2.asp        <= ***** SUPERB devices
*****
        (even Roman will like the specs !   :-) )

MSOP-8, SO8, SOT23, SOT23-6 ...

They don't give Vth in table but all are specd at 2.5v and 4.5v

As an example the utterly superb ZXMN2A02X8 (where do they get these part
numbers from) claims

    Vth = 0.7v <- *********** Turns on with 0.7v drive  ***********
    20V
    7.6A
    1.8w
    Rdson 0.04r at Vgs = 2.5v / 0.02r at 4.5v
        (note while Vth is 0.7v it is still being enhanced more at 4.5v than
2.5v)
    MSOP8

Note that the Vds max mustn't be exceeded (sniff)
After hand soldering one of these in a non-PCB prototype layout it's a shame
to lose it :-(

Apart from price and size this would have to be one of the most useful
transistors available for amateur load driver use. Up to 7 amps with any
drive source in a truly tiny package.

Superb for dc to dc converters- but do watch Vds max !!!

There are lower rated parts available in even small packages.


        Russell McMahon

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