Transistor vs diode.

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raul260291

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Hello Everyone,
I am getting confused with transistor and diode stuff. in the active region the characteristics of a transistor i.e acting as voltage controlled current source it resembles a diode.
Even the equations are same including the small signal model equations.
Ic=Is*exp(Vd/Vt) and gm(transconductance)=Ic/Vt.
What is the benefit of using transistor over diode.
 

raul260291 said:
Ic=Is*exp(Vd/Vt) and gm(transconductance)=Ic/Vt.
What is the benefit of using transistor over diode.
Click to expand...

Hi Raul,
at first - the transistor is a three-terminal device in contrast to the diode with only two terminals.
This alone does not answer your question - however, the main difference is that in the above formula the voltage Vd
* is the voltage across the diode (that means: the voltage across the two terminals that see the current)
* is the voltage across the B-E junction of the transistor, which means: NOT across the two terminals through which the current Ic goes.
Thus you can control the current Ic with the voltage Vd - and Ic can be much larger than the current which is driven by Vd directly through the B-E path.
 
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