Question

Consider the following circuit, where source current = 10mA, hfe = 50, hie = 1100Ω, then for the transistor circuit, find output resistance RO and input resistance RI.

(a) RO = 0, RI = 21Ω

(b) RO = ∞, RI = 0Ω

(c) RO = ∞, RI = 21Ω

(d) RO = 10, RI = 21Ω

This question was addressed to me in homework.

I'm obligated to ask this question of Hybrid Equivalent Model in division Transistor Biasing and Low Frequencies of Analog Circuits

Answer 1

Correct choice is (c) RO = ∞, RI = 21Ω

The explanation is: Since hoe is not given, we can consider it to be small; i.e 1/hoe is neglected, open circuited. Hence output resistance RO = ∞.

Input resistance = hie/(1 + hfe) = 1100/51 ≅ 21Ω.