Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech II ELECTRONIC DEVICES AND CIRCUITS Previous Question Paper (November/December - 2018 - R15)
Note: This question paper contains two parts A and B. 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.
Part A
Draw the V-I characteristics of varactor diode.
Answer
The V-I characteristic of a varactor diode is similar to a standard p-n junction diode in reverse bias. The curve plots reverse voltage (VR) on the x-axis and reverse current (IR) on the y-axis, showing a very small leakage current until the breakdown voltage is reached. The defining characteristic is the non-linear relationship between the depletion layer capacitance (CT) and the applied reverse bias voltage.
Explain how does the reverse saturation current of a p-n diode vary with temperature.
Answer
The reverse saturation current (Io) of a p-n diode increases significantly with temperature. For silicon diodes, Io approximately doubles for every 10°C rise in temperature. This occurs because thermal energy generates more minority charge carriers, which are the primary contributors to the reverse saturation current.
Define the percentage of regulation.
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What is the need of rectifier? List different types of rectifiers.
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Illustrate CE cutoff region.
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Explain the base spreading resistance.
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What is thermal runaway?
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List and briefly explain three sources of instability of collector current.
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What are the different types of FETs?
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What is pinch-off voltage? Give its expression.
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Part B
Derive the expression for transition capacitance CT of a diode.
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Draw the small signal model of Tunnel Diode operating in the negative resistance region.
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Draw and explain the graph indicating the variation of minority carrier density with distance in a p-n junction diode under forward biased condition.
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Write the equation for Volt-Ampere characteristics of a photo diode.
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Draw and explain the circuit of a half-wave rectifier with capacitor filter.
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Explain the design of Full wave bridge rectifier.
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A half wave rectifier has a load of 3.5 KΩ. If the diode resistance and the secondary coil resistance together have a resistance of 800Ω and the input voltage has a signal voltage of 240 V, calculate i) Peak, average and rms value of current flowing. ii) dc power output. iii) ac power input iv) Efficiency of the rectifier.
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Compare inductor and capacitor filters.
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Explain the input and output characteristics of a transistor in CB configuration.
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Draw the circuit diagram of an NPN junction transistor in CE configuration and describe its characteristics.
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Illustrate and explain active region, saturation region and cut-off region in transistor characteristics.
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Explain the hybrid small signal model for common collector configuration.
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Draw a transistor amplifier using self bias (CE configuration) and explain the operation.
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Discuss the stabilization against variations in VBE and β.
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Draw and explain the Collector feedback biasing.
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Describe the analysis of Transistor Amplifier circuit using h-parameters.
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Explain how FET works as voltage variable resistor.
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Compare BJT and FET.
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Explain the constructional features of a depletion mode P-channel and Enhancement mode MOSFET and explain its basic operation.
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