hybrid model of transistor

Thread Starter


Joined Mar 15, 2009
our classes going on with hybrid model of transistor.i am including my class notes,pls clear my doubts in my basics.....

consider CE circuit,

the 4 variables are ib,ic,vb,vc.Among this ib and vc are taken as independent variable.
//(DOUBT)why ib ,vc are taken as independent and why not vb and ic are taken as independent variable.pls tell me the reason ?(DOUBT)//


vb=f1(ib , vc)
ic =f2(ib ,vc)

Making taylor series expansion,we get

Δvb=(∂f1/∂ib) Δib + (∂f1/∂vc) Δvc
Δic=(∂f2/∂ib) Δib + (∂f2/∂vc) Δvc
//(DOUBT)why we are making taylor series expansion here...(DOUBT)//

(∂f1/∂ib )= (∂vb/∂ib) = hie
(∂f1/∂vc) = (∂vb/∂vc) = hre
(∂f2/∂ib) = (∂ic/∂ib) = hfe
(∂f2/∂vc) = ( ∂ic/∂vc) = hoe

thus *vb = hie ib + hre vc*
* ic = hfe ib +hoe vc*

please solve my 2 doubts...............:confused:

Thread Starter


Joined Mar 15, 2009
Because Vb is depending on Ib and Ic is depending on beta and Ib.
Ib and Vc 'll not change by any parameters,
ib ,vc are taken as independent according to derivation

When vb (input voltage)is increased ib will increase,so why can't we take vb as an independent variable.....

And hence
why cant we write as
ib=(vb, vc)......
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