What are the advantages and disadvantages of a Darlington pair?
The main advantage is you get a ton of current gain (round about the square of an individual transistor of the same type).
Yes, you could use two dissimilar transistors.
Main disadvantage is Vbe is effectively doubled to about 1.4V, and, just two transistors (though typically you get them in one package).
No, they cannot generate power &quot;by themselves&quot;. It's a semiconductor, not an energy source.