You and I seem to be at odds on this all the time
MOSFETS are more expensive, but for a one-off project thats only an extra 50 cents or so. They can also handle higher currents, and don't require resistors, making it easier for a beginner that wouldn't know how to calculate optimal values. The PWM optimized types are perfect for driving motors and stuff . . .
Plus, normal transistors are old technology for old people
(here is where you counter my argument lol)
OK, since I have to
It's not the prize of a MOSFET that I'm on about, although I remember as a kid, I would stretch my budget as long as possible by annoying the salesmen for next to peanuts
It's simply that they have different applications and you'll always get the best result by using the component most optimum for a given task.
IRF510 (TO-220) over a BC547 (TO-92) for a 12mA load... You be the judge.
The "higher current" depends on what device you pick and I seriously don't see many circuits being discussed here that need all that substantial powers, so in general, this is not a valid argument at all - more an apples vs. pears.
For instance, we can compare something like a 2N7000 (the MOSFET equivalent of a "TUN") to a BC546, then you have two valid candidates for a serious discussion.
They are very alike in the "usual parameters" (max. current, max voltage etc).
2N700 has a V_ds_on of 0.4V @ V_gs = 4.5V and I_d of 75mA - not particular impressive.
If pulsed, it can handle up to 0.5A, at which the V_ds_on goes up to 2.5V
and needs a V_gs of 10V - not impressive either.
What else... Switching speed 2N7000 = 10ns i.e. 100MHz (300MHz for the BC546).
Nope, I'm really not impressed.
So, the critical voices would ask, where would the 2N7000 be the best choice...
As an example, in eg. a 12..20V circuit which needed very narrow pulses of 1A, say for IR comms, it would certainly be better than the BC546 (which would die screaming).
You should always use a gate resistor (or a tiny inductance like a ferrite bead), or you risk oscillations, or driver latch-up if driven from eg. CMOS.
There's a common misconception that you don't need current to drive a MOSFET gate, but that doesn't hold true, as the gate capacity needs current, more so if you want clean switching.
When currents get above 10A or so, MOSFETs will usually be the best choice.
When eg. there's little drive voltage BjT's will usually be the best choice.
In 3.3V circuits, you need quite exotic MOSFETs to do what just about any BjT can do.
The knowledge to calculate a switching transistor can be acquired in 10 minutes flat and for most projects like switching a buzzer (or other stuff), anything between 470 Ohm and 10k will do as a base resistor, so it really aren't rocket science (and what's the fun if you don't have to learn little bits here and there
"PWM optimized" is a marketing term used (by Vishay AFAIK) and just covers a fast switching MOSFET. It's allways best to get the fastest switching device, when you operate with large currents at high frequencies (hundreds of kHz and up) - to minimize switching losses.
Fast switching is best for any high current, high frequency switching application, whether PWM or not.
MOSFETs will improve in switching speed over time. Every one and his uncle is working on getting the gate capacitances and propagation times down and they're still in their (2nd) infancy when it comes to potential I think.
But, I don't see the 'bots build here as totally cutting edge, so chasing tiny bits of efficiency is completely wasted, if you throw your circuits in a chassis welded from water pipes or similar.
For a 5kHz PWM control driving the motor of a 5kg robot, I seriously doubt that you will see any difference ("PWM optimized" contra regular fast types) worth mentioning.
Yes, BjT's are for oooold knowledgeable people... But we don't mind sharing our wisdom with kids like you, so that you can all reap the benefits of our ancients potions and spells
(If anything sounds messy or doesn't make sense, it's probably because my GF keeps bugging me that dinner is getting cold, so gotta post NOW