>I'm buffering the pin
>with p- and n- channel enhancement mosfets---Zetex zvp4105a and Zetex
vn10lp,
>respectively.  The leds work but are dim.  The problem is that the fets
don't
>sat.  (I simulated the pic by tying the gates to Vdd and Vss manually).
When
>I lifted the gate of the N-ch to 9V the led lit as it shoud.  I'm wondering
>if I'm using the wrong units, or is there a way to saturate the channel at
a
>lower Vgs?

Well when you look at the spec sheet on the Zetec web site, the VN10LP needs
about 10V VGS to saturate, it shows a Rds of about 7.5 ohm with 5V gate
drive.The ZVP4105A does not give a gate voltage for saturation but does
indicate a 10 ohm Rds for gate voltage of -5V. From the sound of it I am not
surprised they do not turn on very brightly.

You need to look for transistors classed as Logic Level FETS. Ones I have
been looking at, but not used yet from Zetex are ZXMD63N03X and ZXMD63P03X.
These are both dual FETS in MSOP8 packages and look to saturate with about
4.5V on the gate for 10A current, and about 3V for 1A current.

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