> The question is, if I'm adding this on the low side, as long as the
> high side is greater or equal to the gate voltage, am I ok? For now
> the MOSFET high side will be at 5V, same as Vdd, but in the future I
> might want it a bit higher to switch something else (say 12V). I
> believe I'm fine at 12V, but I want to make sure that having the high
> side at 5V and the gate voltage (coming from the PIC) at 5V won't
> cause something I haven't thought of.

What you need to look out for is the VDS, VGS and VGSth.

If the source is at GND, the drain voltage should not go above maximum rati=
ng=20
for VDS, which is up to 60V in your case.=20

You also have to make sure that VGS never exceeds absolute maximum for the =
VGS,=20
which is +-18V for your transistor. If you are switching higher voltages wi=
th=20
the inductive loads and the source is connected with wires (and not directl=
y to=20
a good ground plane) you might want to put a transient voltage protection=20
(tranzorb) between the gate and source to make sure that the +-18V is never=
=20
exceeded, even for a very short time. If the source is connected to a good=
=20
groundplane that is common with the PIC, this should not be a problem.

Another thing that you might not have thought of is the internal gate sourc=
e=20
capacitance which is very important if you are going to switch from a=20
relatively weak driver (the pic output) with a high frequency (PWM). If thi=
s=20
capacitance is too high, the switching will be slow which will cause the=20
transistor to operate in the linear region for a relatively long time for e=
ach=20
switch on and off and this will cause power dissipation in the transistor. =
You=20
might need a driver between the PIC and the MOSFET. This capacitance tends =
to=20
get larger with larger transistors so picking a transistor that is not too =
big=20
for your needs might also be important.

/Ruben


=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124
200 39 Malm=F6 Sweden
Tel +46 40142078
ruben@rjjournal.net
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

--=20
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