Question

A transistor is used in CE mode in an amplifier circuit. When a signal of 40 mV is added to base-emitter voltage, the base current changes by `40 muA` and collector by 6mA. The load resistance is `10 kOmega` . Calculate
(i) The current gain `beta`
(ii) The input resistance `R_(BE)`
(iii) Transconductance
(iv) Voltage gain

Answer 1

(i) `beta_(ac)=(DeltaI_(C))/(DeltaI_(B))=(6mA)/(40 muA)=(6xx10^(-3))/(40xx10^(-6))=1.5xx10^(2)=150`
(ii) Input resistance `R=(DeltaV_(BE))/(DeltaI_(B))=(40 mV)/(10 muA)=1000 Omega`
(iii) Transconductance `g_(m)=(DeltaI_(C))/(DeltaV_(BE))=(6mA)/(40mV)=0.15 Omega^(-1)`
(iv) Out put voltage `V_(0)=R_(L)DeltaI_(C)`
`=10xx10^(3)xx6xx10^(-3)`
=60 V
`:.` Voltage gain `=(V_(0))/(V_(i))=(60V)/(40 mV)`
`=1.5xx10^(3)`
=1500