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Consider a Darlington amplifier. In the self bias network, the biasing resistances are 220kΩ and 400 kΩ. What can be the correct value of input resistance if hfe = 50 and emitter resistance = 10kΩ.(a) 141 kΩ(b) 15 MΩ(c) 20 MΩ(d) 200 kΩI had been asked this question during an online exam.The query is from Cascade and Darlington Amplifier topic in chapter General and Feedback Amplifiers of Analog Circuits |
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Answer» CORRECT option is (a) 141 kΩ To elaborate: R’ = 220k||400k = 142 kΩ RI = (1+hfe)^2RE = 26MΩ RI’ = 26M||142k = 141.22 K. |
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