The output characteristics of an npn transistor in CE configuration are shown in Fig. 3.18. Determine for this transistor

(i) The dynamic output resistance,

(ii) The dc current gain and

(iii) The ac current gain at an operating point $V_{CE} = 10 V$ when $I_B = 40 \mu A$ .

Question

The output characteristics of an npn transistor in CE configuration are shown in Fig. 3.18. Determine for this transistor

(i) The dynamic output resistance,

(ii) The dc current gain and

(iii) The ac current gain at an operating point [latex]V_{CE} = 10 V[/latex] when [latex]I_B = 40 \mu A[/latex].

Accepted Answer

for[latex]V_{CE}=10V[/latex],[latex]I_{B} =40\mu A[/latex]
The operating Q is marked in Fig. 3.18. At the operating point Q, the collector
current [latex]I_C = 4.55 mA[/latex].
To determine the dynamic output resistance, let the small change in [latex]V_{CE}[/latex]from A
to B around the operating point Q be from 7.5 V to 12.5 V. The change in [latex]V_{CE}[/latex] is
[latex]\Delta V_{CE} =12.5-7.5=5V[/latex]
The corresponding change in [latex]I_C[/latex] at constant[latex]I_{B}=40\mu A[/latex] will be
[latex]\Delta I_{C}=4.7-4.3=0.4mA[/latex]
[latex] herefore r_{0}=\frac{\Delta V_{CE}}{\Delta I_C }[/latex]at constant[latex]I_{B}=40\mu A[/latex]
[latex]=\frac{5V}{0.4mA}=\frac{5}{0.4 imes 10^{-3}}[/latex]
[latex]=12.5 K\Omega[/latex]

Question 3.1: The output characteristics of an npn transistor in CE config...

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