# common collector power amplification

#### mentaaal

Joined Oct 17, 2005
451
Hey guys, we are currently studying the transistor in college and i was looking at the common collector mode of transistor amplification and i dont understand how there can be a current gain when the voltage gain remains roughly the same???
I mean say for example beta for the transistor is 100.
So the current gain for the load will be beta plus 1 (according to this website?)
How is this possible? I mean say the signal source places 4 volts across the load. the current say is X. Then the current going through the load should be 100x + 1 right? then if thats the case surely the voltage across the load will be V=RI : V = R[100Ibase +1]I would be something like over 400 volts?
Surely if the current going through a resistor increases the voltage across that resistor has to increase in accordance with ohms law??

#### beenthere

Joined Apr 20, 2004
15,819
The common collector arrangement makes voltage gain impossible. The output voltage across the load is always .7 volts less than the base voltage. The load limits the current according to ohm's law - I = E/R.

So, the way to look at it is that the base current is the emitter current divided by (beta + 1).