# hybrid model of transistor

Discussion in 'General Electronics Chat' started by raks_universe, Nov 17, 2009.

1. ### raks_universe Thread Starter Active Member

Mar 15, 2009
67
0
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)//

continuing....

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)//

continuing...
(∂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*

2. ### sudharshan.panduranga Active Member

Apr 10, 2008
61
1
Because Vb is depending on Ib and Ic is depending on beta and Ib.
Ib and Vc 'll not change by any parameters,

3. ### raks_universe Thread Starter Active Member

Mar 15, 2009
67
0
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)......

Last edited: Nov 20, 2009

Mar 15, 2009
67
0