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For the given circuit, input resistance RI = 20Ω, hfe = 50. Output resistance = ∞. Find the new values of input and output resistance, if a base resistance of 2kΩ is added to the circuit.

For the given circuit, input resistance RI = 20Ω, hfe = 50. Output resistance = ∞. Find the new values of input and output resistance, if a base resistance of 2kΩ is added to the circuit. Correct Answer RI = 59Ω, RO = ∞

RI = 20k = hie/(1+hfe) = hie/51 hie =1020 Ω Hence, after adding base resistance, RI’= (hie+RB)/(1+hfe) = (1020+2000)/51 ≅ 59Ω There is no change in output resistance or current gain due to an extra base resistance. RO’ = ∞.

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