Consider the circuit arrangement shown in figure (1) for studying input and output characteristics of n-p-n transistor in CE configuration.
Select the values of `R_(B)` and `R_(C )` for a transistor whose `V_(BE)=0.7V`, so that the transistor is operating at point Q as shown in the characteristics shown in figure (2). Given that the input impedance of the transistor is very small and `V_(C C)=V_(BB)=16V`, also find the voltage gain and power gain of circuit making appropriate assumptions.

Explanation

Graph in figure-2 is for `I_(B)=30muA`. For point Q on it, `I_(C )=4mA=4xx10^(-3)A and V_(CE)=8V`
For output part of above figure,
`V_(C C)=I_(C )R_(C )+V_(CE)`
`therefore 16=(4xx10^(-3))R_(C )+8`
`therefore R_(C )=(8)/(4xx10^(-3))=2xx10^(3)Omega=2kOmega`
For input part of above figure-1,
`V_(B B)=I_(B)R_(B)+V_(BE)`
`therefore 16=(30xx10^(-6))R_(B)+0.7`
`therefore R_(B)=(15.3)/(30xx10^(-6))=5.1xx10^(5)Omega=510xx10^(3)Omega`
`=510kOmega`
Voltage gained,
`A_(V)=beta(R_(C ))/(R_(B))=((I_(C ))/(I_(B)))((R_(C ))/(R_(B)))`
`therefore A_(v)=((4xx10^(-3))/(30xx10^(-6)))((2xx10^(3))/(510xx10^(3)))`
`therefore A_(V)=0.52`
Power gained,
`A_(P)=A_(V)A_(i)=A_(V)beta=A_(V)((I_(C ))/(I_(B)))`
`therefore A_(P)=0.52xx(4xx10^(-3))/(30xx10^(-6))`
`therefore A_(P)=69.33`