JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III INDUSTRIAL ELECTRONICS Previous Question Paper (August - 2022 - R16)
Answer any five questions. All questions carry equal marks.
Main
With a neat diagram, explain cascode amplifier.
Answer
A cascode amplifier is a two-stage amplifier configuration consisting of a common-emitter (CE) stage followed by a common-base (CB) stage. The CE stage provides voltage gain, while the CB stage acts as a current buffer, significantly reducing the Miller effect by keeping the collector voltage of the first transistor nearly constant.
The circuit diagram consists of transistor Q1 in CE configuration with its collector connected to the emitter of transistor Q2, which is in CB configuration. The output is taken from the collector of Q2. This arrangement results in high input impedance, high output impedance, and a very high voltage gain, while simultaneously offering excellent high-frequency performance due to the elimination of the Miller capacitance feedback.
Draw the circuit of Darlington emitter follower with voltage divider bias. Calculate input impedance, voltage gain and output impedance. Take β1= β2=100. R1=R2=100kΩ; RE = 5kΩ, Take re = 100Ω.
Answer
A Darlington emitter follower consists of two transistors connected such that the emitter of the first drives the base of the second. Given: β1=β2=100, R1=R2=100kΩ, RE=5kΩ, re=100Ω.
1. Input Impedance (Zi): The input resistance of the Darlington pair is approximately β1β2RE. With biasing resistors R1 and R2 in parallel (R_B = R1||R2 = 50kΩ), the total input impedance is Zi = R_B || (β1β2RE) = 50kΩ || (100*100*5kΩ) ≈ 50kΩ.
2. Voltage Gain (Av): The voltage gain of an emitter follower is approximately 1. For a Darlington pair, Av = (β1β2RE) / (β1β2RE + hie1 + β1*hie2). Given the values, Av is very close to unity, typically Av ≈ 0.99.
3. Output Impedance (Zo): The output impedance is seen looking into the emitter of the second transistor. Zo = re2 + (R_source / β2), where R_source is the output impedance of the previous stage. Assuming a low source impedance, Zo ≈ re2 = 100Ω.
Draw the block diagram of instrumentation amplifier and analyze its various parameters.
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With a neat circuit, explain in detail about double ended difference amplifier.
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With a neat circuit, explain the basic op-amp shunt regulator with load resistor.
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In an application, a power supply has voltage regulation of 1%. No load voltage is 30V. Find full load voltage Vfull load?
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Explain adjustable three terminal voltage regulator in detail.
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Give the comparison between linear and switched mode voltage regulators.
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Explain the Two transistor model of Thyristor with necessary mathematical equations.
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Describe the SCR characteristics in brief along with modes of operation.
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Draw and explain the circuit diagram of Class C commutation.
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Explain SCR triggering circuit in brief.
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Describe the operation of single phase inverters, three phase inverters.
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Classify the firing circuits for line commutated converter.
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Explain the principle of induction heating.
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Describe the modes of metal transfer in arc welding.
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