JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year ELECTRONIC DEVICES AND CIRCUITS Previous Question Paper (May/June - 2019 - R13)
Part A is compulsory which carries 25 marks. Answer all questions in Part A. Part B consists of 5 Units. Answer any one full question from each unit. Each question carries 10 marks.
Part A
Find the value of dc resistance of a Ge junction diode, if the temperature is 250 C and I0 = 20µA with an applied voltage of 0.1V.
Answer
The diode current is given by I = I0(e^(V/ηV_T) - 1). For Ge, η = 1. At T = 25°C, V_T = 26mV. With V = 0.1V and I0 = 20µA, I = 20µA * (e^(0.1/0.026) - 1) ≈ 20µA * (46.96 - 1) ≈ 0.919mA. The DC resistance R_dc = V/I = 0.1V / 0.919mA ≈ 108.8 Ω.
Briefly discuss the semiconductor photo diode.
Answer
A photodiode is a PN junction device operated in reverse bias that converts light energy into electrical current. When photons with energy greater than the bandgap strike the depletion region, they generate electron-hole pairs. The resulting reverse saturation current is proportional to the intensity of the incident light, making it useful for light detection and optical communication.
What are the limitations of zener voltage regulator circuit?
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Compare half wave rectifier and full wave rectifier.
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What is Early Effect?
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Given an NPN transistor for which αN = 0.98, ICO = 2mA. A common emitter connection is used and VCC = 12V, RL = 4.0 KΩ. What is the minimum base current required in order that the transistor enter its saturation region.
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Define thermal stability.
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Define Thermal Runaway and Thermal Resistance.
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What are applications of JFET and MOSFET devices?
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Explain how FET acts as a voltage regulator.
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Part B
Derive the expression for contact difference of potential V0 in an open circuited p-n junction.
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Explain Transition capacitance and Diffusion capacitances.
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Explain the principle operation of varactor diode.
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Write the differences between Tunnel Diode and PN Diode.
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Obtain the expression for ripple factor in the case of Half Wave Rectifier with π filter.
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A diode whose internal resistance is 20 Ω is to supply power to a 1000 Ω load from a 110V (rms) source of supply. Calculate:
- The peak load current
- The DC load current
- AC load current
- The DC diode voltage
- The total input power to the circuit
- % regulation from no load to the given load. Assume Half wave rectifier.
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Explain the working of a bridge rectifier with a neat circuit diagram and with relevant wave forms.
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Compare C, L, L-section and π-section Filters in all respects.
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Explain the construction and working of BJT.
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In a CB configuration current amplification factor is 0.90 and emitter current is 1mA. Determine base current.
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Describe the V-I characteristics of a transistor in common collector configuration and explain.
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What is the significance of negative resistance region? Explain how UJT exhibits this characteristics?
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Draw the fixed bias circuit and derive the expression for the stability factor S. What are the limitations of this circuit?
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In a voltage divider bias circuit, VCC = 20 V and RC = 1.5 kΩ, the Q point is VCE = 8V and IC = 4mA. Stability factor S = 12 and β = 50. Find R1, R2 and RE.
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Derive the expressions for all gains and Impedances of a CE Amplifier using h-parameters.
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Obtain the expression for the pinch off voltage VP in the case of n-channel JFET.
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Draw the structure of p-channel MOSFET and qualitatively explain the static drain and gate characteristics of the device.
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Derive an expression for voltage gain, Input Impedance and output impedance of CG amplifier at low frequencies.
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For the emitter follower with RS = 0.5KΩ and RL = 5KΩ, calculate AI, Ri, AVS and R0. Assume hfe=50, hie=1KΩ, hoe=25μA/V.
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