Matt Krass said:
I'm diving back in to discrete component circuit design again after
a few years, and I'm blanking out, is there any functional
difference between an n-channel transistor and an NPN, same for
p-channel PNP transistors?
*If* the device is a MOSFET (and not a JFET), you can *almost* treat
them the same as BJTs, at least for switching.
Similarities:
drain = collector
source = emitter
gate = base
driving base relative to source enables current from drain to
source.
Differences:
BJTs are current controlled current devices.
MOSFETS are voltage controlled resistor devices.
The response curve is different.
So, where driving a BJT with a base current (Ibe) enables a much
larger collector current (Ice), driving a MOSFET with a gate voltage
(Vgs) reduces the drain-source resistance (Rds). Also, the gate has a
small capacitance, so you not only have to drive it ON, but you have
to drive it OFF too. The capacitance also affects the frequency
response, so model it if you're doing high frequency work.