However, it is entirely possible to use a BJT so that one voltage controls another without violating the known laws of physics!
Now from that link I suspect you are not suggesting using an op amp.
The whole point of a BJT is that it is driven by current, not voltage. That current might be small but it is current never the less because it is current that makes the transistor work. FETs on the other hand are voltage devices and draw negligible current apart from the initial charging of the gate source capacitance. All three configurations of the transistor are called a voltage buffer on that page.
Lets look at each in turn:-
-
Common emitter - the normal way I would recommend, base current determines collector current
-
Common base - note the page says this is not suitable for a TTL voltage buffer, it has a low gain and typically I use this for video coupling.
-
Common collector better known as an emitter follower. - This has no voltage gain but a current gain, you do not need a base resistor because of the feedback on the emitter keeping the emitter / base voltage stable. However this is 0.7V so this means when you use it as a voltage buffer you loose 0.7V. Used with the Due that will reduce the voltage output from 3V3 to 2.6V. When lighting an LED this will not be high enough for blue and white LEDs although it is enough for red and green. Again I would not recommend this due to the voltage drop that it produces.