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Question:

Output characteristics of an n-p-n transistor in CE configuration is shown in the figure. Determine: (i) dynamic output resistance (ii) dc current gain and (iii) ac current gain at an operating point VCE=10V, when IB=30µA

Solution:

(i) Dynamic output resistance is given as: R0 = (ΔVCE/ΔIC)Iβ constant = 12V/(3.6mA - 7.4×10⁻³A) = 40.2 × 10³Ω = 20kΩ
(ii) dc current gain βac = IC/IB = 3.5mA/30µA = 3.5 × 10⁻³A / 30 × 10⁻⁶A = 116.67
(iii) ac current gain βac = ΔIC/ΔIB = (4.7 - 7.5)mA/(40 - 26)µA = 1.2 × 10³ × 10⁻⁶A = 120