Output characteristics of an n-p-n transistor in CE configuration is shown in the Fig. Determine

(i) dynamic output resistance (ii) dc current gain and (iii) ac current gain at an opererating point `V_(CE)=10V`, when `I_(B)=30muA`.

Explanation

(i)From graph, at `I_(B)=30muA`,
`DeltaI_(C)=3.6-3.4=0.2mA`,
`DeltaV_(CE)=12-8=4V`.
Dynamic output resistance,
`R_(0)=(DeltaV_(CE))/(DeltaI_C)=(4V)/(0.2mA)=20kOmega`
(ii) From graph, at `V_(CE)=10V,I_(B)=30muA`,
`I_(C)=3.5mA`,
`beta_(ac) I_C/I_B=(3.5mA)/(30muA)=(3.5xx10^(-3)A)/(30xx10^(-6)A)=116.7`
From graph, at `V_(CE)=10V, DeltaI_(B)=40-30=10muA`,
`DeltaI_(C)=(4.7-3.5)=1.2mA`
`beta_(ac)=(DeltaI_(C))/(DeltaI_(B))=(1.2mA)/(10muA)=(1.2xx10^(-3))/(10xx10^(-6))=120`