JNTU
JNTU B.Tech II ELECTRONIC DEVICES AND CIRCUITS Previous Question Paper (March - 2022 - R13)
Answer any five questions. All questions carry equal marks.
Main
Derive the expression for transition capacitance CT and Junction capacitance CJ of a diode.
Answer
When a p-n junction is reverse-biased, the mobile charge carriers are depleted, creating a region of uncovered immobile ions known as the depletion region. This region acts like a dielectric between two conducting regions (p-type and n-type), forming a capacitor known as the transition or junction capacitance (CT or CJ).
For an abrupt junction, the depletion width W is given by:
Where ε is the permittivity, Vbi is the built-in potential, VR is the reverse bias voltage, and NA, ND are doping concentrations. Since CT = εA/W, substituting W yields:
This shows that CT is inversely proportional to the square root of the applied reverse voltage.
Justify the working of zener diode as a voltage regulator.
Answer
A Zener diode operates in the breakdown region when reverse-biased. Once the reverse voltage reaches the Zener breakdown voltage (VZ), the diode maintains a nearly constant voltage across its terminals despite significant changes in the current flowing through it.
In a voltage regulator circuit, the Zener diode is connected in parallel with the load resistance. A series resistor is used to limit the current and drop the excess input voltage. As the input voltage or load current varies, the Zener diode adjusts its internal current to keep the output voltage fixed at VZ. As long as the input voltage remains above VZ and the current stays within the diode's power dissipation limits, the output voltage remains regulated at a constant level.
Demonstrate the working of a fullwave rectifier with waveforms. How it is better than half wave rectifier?
Answer
Sign in to view the complete answer paper.
A full wave rectifier circuit with C-type capacitor filter is to supply a D.C. Current of 25 mA at 16V. If frequency is 50 Hz and ripple allowed is 4%. Calculate:
i) Required secondary voltage of the transformer.
ii) Ratio of Ipeak / Imax through diodes and the value of C required.
Answer
Sign in to view the complete answer paper.
Explain the input and output characteristics of a transistor in CB configuration. Mention one application of CB configuration.
Answer
Sign in to view the complete answer paper.
Draw the circuit diagram of an NPN junction transistor in CE configuration and describe its characteristics.
Answer
Sign in to view the complete answer paper.
Discuss different stabilization methods against variations in VBE and β.
Answer
Sign in to view the complete answer paper.
For the transistor amplifier circuit, when signal changes by 0.012 V, the base current changes by 9 µA and collector current by 1.3 mA. If the collector load RC = 5 KΩ, RL = 10 KΩ. Determine input resistance, current gain and voltage gain.
Answer
Sign in to view the complete answer paper.
Describe the operation of common drain FET amplifier and derive the equation for voltage gain.
Answer
Sign in to view the complete answer paper.
Draw the VI characteristics curves of enhancement MOSFET and explain. Indicate different regions of operation on it.
Answer
Sign in to view the complete answer paper.
Justify how Varactor diode can be used as a variable capacitance?
Answer
Sign in to view the complete answer paper.
Explain the working of Inductance filter connected at the output of a fullwave rectifier. Write all the corresponding waveforms.
Answer
Sign in to view the complete answer paper.
Illustrate and explain active region, saturation region and cut-off region in transistor characteristics.
Answer
Sign in to view the complete answer paper.
Determine the quiescent currents and the collector to emitter voltage for a Silicon transistor with β = 100 in the self biasing arrangements. The circuit component values are VCC = 12 V, RC = 2kΩ, Re = 0.1 kΩ, R1 = 100 kΩ and R2 = 5 kΩ. Find the stability factor S.
Answer
Sign in to view the complete answer paper.
Draw the JFET Small signal Model and explain it.
Answer
Sign in to view the complete answer paper.
Compare BJT, JFET and MOSFET.
Answer
Sign in to view the complete answer paper.