Base current or Base Emitter Voltage

Hello,

I read in some books its Base emitter voltage is controlling the IC and base current is by product.
Any one knows the truth?
Thanks
Grittin

This is true, if you refer to Shockleys equation, or other functional explainations of transistor operation. The problem has been discussed in detail at edaboard.

Then how most of books say base current control IC?
Do we have any good document which i can refer for this?

Hi.

I assume that book of you stating that was reffering to a concrete circuit. It won't always be true.

In some TTL circuits, you actually feed an emitter, often on a bjt with multiple emitters.

Base current carries a poor relationship with everything else in BJT. Even in a matched pair, it is said to vary by 30%. The simple exponential relationship between Vbe and Ic is found to be good enough to define the transistor for 7 decades of collector current quite accurately.

Hi saro, So you to agree VBE is the is the once changing IC, And Ib is just bi product of changing vbe.
What i understand by changing VBE the able to reduce the depletion layer. Since base emiter is forward biased we gets IB as bi product.
But in time depletion type mosfet we kept a insulator which avoids current flow from gate to source. But the applied voltage changes the channel
is it right?

It's a pedantic distinction since you can't have one without the other.
Use whichever mental model makes it easier to understand or invent.
Personally I find thinking in terms of current more relevant to bipolar
design. Mostly all you want from Vbe, is to match. Bandgaps aside.

Hi Grittin,
when a voltage VBE is applied by a lowohmic voltage source, then minority carrier concentrations on both sides of the BE junction are increased which gives rise to minority carrier gradients in base and emitter.
npn BJTs are built in such a way that electron gradient in base is larger than hole gradient in emitter.
Therefore IC is larger than IB. (By a factor B.)
Of course one works the larger signal and defines IC as output signal. (Otherwise a diode would have been sifficient, no need for a transistor.)
If one uses a highohmic source and forces IB rather applies VBE, then the carriers arrange accordingly and within the transistor the same thing as above happens, only that the transistor reacts less sensitive to the linear IC(IB) than to the exponential IC(VBE) and is easier to control.

Rgds

Quote dick-freebird:
Personally I find thinking in terms of current more relevant to bipolar design.

Can you explain the function of a bipolar current mirror assuming that the BJT is a current controlled device?