I always thought transistors like the 2n2222 were voltage driven, but I read recently they are current driven. Given that, can I put 12v into the base of a 2n2222 if I use a resistor to limit the current into it? Or does the voltage max of 5v still apply?
Thanks
Transistors are current devices and MOSFETs are voltage devices.
You can put any voltage you want on the base, as long as you use the appropriate resistor value.
The simplified equation is always going to be: IB = (VB - VBE)/RB
Bipolar transistors (2n2222) are current driven, MOSFET transistors (that is what the "T" stands for) are voltage driven.
gpsmikey:
Bipolar transistors (2n2222) are current driven, MOSFET transistors (that is what the "T" stands for) are voltage driven.
Not really understand what you mean. That means Bipolar transistors can control the current, meanwhile MOSFET transistors will can control the voltage. Right?
Can you explain more in easy way. Sorry if my question is silly.
Can you explain more in easy way. Sorry if my question is silly.
It is nice to have one on one teaching, but, this is covered all over the internet.
There are 500,000 hits on Goggle for 'Transistor Tutorial' 
YouTube stuff:
https://learn.sparkfun.com/tutorials/transistors
.
CantSayIHave:
I always thought transistors like the 2n2222 were voltage driven, but I read recently they are current driven. Given that, can I put 12v into the base of a 2n2222 if I use a resistor to limit the current into it? Or does the voltage max of 5v still apply?Thanks
gpsmikey:
Bipolar transistors (2n2222) are current driven, MOSFET transistors (that is what the "T" stands for) are voltage driven.
I'd rephrase that as "should normally be current driven". The current is an exponential function of Vbe, so
its very sensitive to temperature and process variations, so you either ensure the external circuit controls
the current more than the voltage (high impedance), or that there is negative feedback applied to ensure
the base voltage keeps at the right place (in which case the base is voltage driven). The emitter-follower
circuit is voltage driven, but there the emitter current is controlled by the external circuit, so there is implicit
negative feedback via the emitter voltage.
True - I was trying to tip-toe along the edge of the pond without falling in the deep end 
saximus:
You can put any voltage you want on the base, as long as you use the appropriate resistor value.
Then the 'ABSOLUTE MAXIMUM' ratings in the spec sheets are just a JOKE??? RIGHT........
123Splat:
Then the 'ABSOLUTE MAXIMUM' ratings in the spec sheets are just a JOKE??? RIGHT........
The voltage maximum is so that you don't incur avalanche current through the BJT due to super high electric fields. These intense fields literally rip electrons from their bonds, and ram them into more electrons, causing uncontrollable current and burning your BJT. Even though BJTs are technically current controlled, you should still adhere to the absolute maximums.
123Splat:
Then the 'ABSOLUTE MAXIMUM' ratings in the spec sheets are just a JOKE??? RIGHT........
lol you people are always looking for ways to have a go at someone, aren't you?
The absolute maximum rating is for emitter-base reverse breakdown voltage, not base-emitter voltage. Perhaps I should have said you can put any voltage you want as long as you use the correct resistor and it is more positive than the emitter voltage?
saximus:
lol you people are always looking for ways to have a go at someone, aren't you?The absolute maximum rating is for emitter-base reverse breakdown voltage, not base-emitter voltage. Perhaps I should have said you can put any voltage you want as long as you use the correct resistor and it is more positive than the emitter voltage?
What do you mean by "you people"? :o
ChrisTenone:
What do you mean by "you people"? :o
I've just noticed a lot of people seem to enjoy pointing out faults in others' posts rather than providing any actual helpful information (as is the case with most internet forums I suppose).
Anyway, that's off topic so here's a link to a fairly easy to understand tutorial to add to the list LarryD provided.
Heh. I was just having a bit of a go - in humor!
And thanks for the transistor link!