I have used 2N7000 to drive things from a PIC on many projects. 5 V Supply.
I put a 100K-1M to ground and some small value to PIC in series, 1K ?
While initializing the port in software, there may be a high input=20
momentarily turn on the fet ( spike). The parallel resistors takes care=20
of that.
The series may kill some pulse coming through from the output through=20
the capacitance of the fet, and the series limits its effect?.

Makes debug easier to separate parts or gives places to get a probe on. =20
If I have a PIC in a socket and take it out, the fet does not turn on=20
from leakage.
But, I never worry about cost of a few resistors, I like the convenience=20
for testing and trouble shooting.
Just the way I do it!  Most anything works.
Mike


On 6/18/2011 3:45 PM, M.L. wrote:
> On Sat, Jun 18, 2011 at 6:37 PM, V G<x.solarwind.x@gmail.com>  wrote:
>
>> If you're using a MOSFET, you don't (and I think shouldn't) use any
>> resistors. MOSFETs have a very high input impedance and are voltage driv=
en.
>> Drive the gate directly.
>>
>>
> Sort of;
> They have "infinite" DC resistance but the gate is a capacitor. If you tr=
y
> to make a capacitor go from zero volts to some other value very quickly, =
you
> get very high currents.
> I =3D C*dV/dT
>
> The PIC can probably handle switching a small MOSFET gate with no resisto=
r,
> without causing harm, but it wouldn't be my choice. I would always limit =
the
> maximum current to the data sheet spec using a series resistor.

--=20
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