JNTU
JNTU B.Tech II ELECTRONIC DEVICES AND CIRCUITS Previous Question Paper (September - 2021 - R18)
Answer any five questions. All questions carry equal marks.
Main
Compare Full Wave Rectifier (FWR) and Bridge rectifier.
Answer
| Parameter | Full Wave (Center-Tapped) | Bridge Rectifier |
|---|---|---|
| Number of Diodes | 2 | 4 |
| Transformer Requirement | Center-tapped transformer required | No center-tap required |
| Peak Inverse Voltage (PIV) | 2Vm | Vm |
| Transformer Utilization Factor (TUF) | Low (approx 0.693) | High (approx 0.812) |
| Complexity | Simple wiring | Complex wiring |
The Center-Tapped Full Wave Rectifier utilizes a transformer with a center tap to provide two out-of-phase voltages, allowing conduction during both half-cycles. However, it requires a larger, more expensive transformer. The Bridge Rectifier uses four diodes in a bridge configuration, eliminating the need for a center-tapped transformer and resulting in a higher TUF, making it more efficient for high-power applications.
How a diode is used as switch and define all switching times.
Answer
A PN junction diode acts as an electronic switch by controlling the flow of current. When the diode is Forward Biased (Anode potential > Cathode potential), it acts as a closed switch (low resistance path). When Reverse Biased (Anode potential < Cathode potential), it acts as an open switch (high resistance path). Due to charge storage effects, the transition between these states is not instantaneous.
The switching times are defined as:
- Storage Time (ts): The time interval between the instant the input voltage switches from forward to reverse bias and the instant the diode current drops to 10% of its initial reverse current. During this time, the minority carriers stored in the depletion region are removed.
- Transition Time (tt): The time taken for the diode current to drop from 10% of its reverse value to the final steady-state reverse leakage current. This corresponds to the decay of the depletion region charge.
- Reverse Recovery Time (trr): The sum of storage time and transition time (trr = ts + tt). It represents the total time required for the diode to recover its blocking capability after being switched from forward to reverse bias.
What is meant by ripple factor and derive the expression for Half Wave Rectifier (HWR).
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A diode whose internal resistance is 20Ω is to supply power to a 100Ω load from 110V (R.M.S) source of supply. Calculate: i) Peak Load Current ii) DC Load Current iii) AC Load Current iv) % Regulation from No load to given load.
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Explain about input and output characteristics of a transistor when it is connected in common base configuration.
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Determine IC, IE and α for a transistor circuit having IB=15μA and β=150.
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Explain the collector to base bias method along with circuit diagram and derive the stability factor for it.
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Draw the fixed bias circuit and explain it. Write the draw backs of it.
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Explain the construction of JFET and write down principle of operation of JFET.
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Explain the operation of varactor diode with neat diagram.
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Explain the working principle of Tunnel diode and explain how it works as an Oscillator.
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Explain how the zener diode is used for regulation purpose.
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Draw the circuit diagram of CB amplifier and explain its operation in detail.
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In the CE amplifier calculate the mid frequency voltage gain and lower 3-dB point. The transistor has h-parameters hfe=400 and hie=10kΩ, the circuit details are Rs=600Ω, RL=5KΩ, Re=1KΩ, Vcc=12V, R1=15KΩ, R2=2.2.KΩ and Ce=50μF.
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What are the values of ID and gm for VGS = -0.8V if IDSS and VP are given as 12.4mA and -6V respectively?
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Sketch the circuit of CS amplifier and derive the expression for voltage gain at low frequencies.
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