> They have "infinite" DC resistance but the gate is a capacitor. If you
> try to make a capacitor go from zero volts to some other value very
> quickly, you get very high currents.
> I =3D C*dV/dT

I'm not sure that a PIC pin has the drive capability to switch a FET
fast and hard enough. My preference for IR diodes is a fast-switching
low Vsat Zetex, eg ZTX451. FET-like transistor that can handle 1A

In higher voltage circuits with other FETs I'll include a zener to clamp
the gate voltage and quite a hard pull-down to assist turn-off. In a 5V
circuit would you anticipate a voltage swing on turn-off (from the gate
C) to cause problems, particularly spikes below Vss ?

Joe
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.