Electronic Devices and Circuits (131303) QUESTION BANK THIRD SEMESTER


1. How a PN junction can be formed?
2. List out the common diode applications?
3. Define avalanche and zener breakdown?
4. What are the current components of diode?
5. Draw and explain the VI characteristics of pn junction diode.
6. Define Peak Inverse voltage of a diode.
7. Differentiate between static and dynamic resistance of a diode.
8. Although zener diode is operated in the reverse breakdown region, but it does not burn. Why?
9. Differentiate between avalanche and zener breakdown.
10. Discuss the operation of pn diode under forward and reverse biasing.
11. Define forward recovery time and reverse recovery time ? 
12. What are the basic elements of regulated power supply?
13. What is ripple factor?
14. What is a rectifier?
15. Define regulation of a rectifier?
16. Define efficiency of a rectifier?
17. What is a filter and state its types?
18. What is SMPS?
19. Define intrinsic stand –off ratio?
20. What is a regulator and state its types?
21. “Transistor is called current controlled device” Why?
22.  Define drift current and diffusion current.
23. What is meant by Threshold or cut-in voltage? Vr? Give its value for silicon and germanium.
24. Define dynamic resistance. If bulk resistance is 4 W and forward current IF = 2.5 milliamps 25. What is the ac resistance?
26. The leakage current in a certain diode is 25mA at 25 degree Celsius . Find the change in temperature required for a leakage Current of 40mA.
27. State law of junction.
28. Define Reverse saturation current.
29. What is the principle of operation of LCD?
30. Discuss the relative advantages and disadvantages of  LEDs and LCDs.
31. What are optoelectronic device Optoelectronic device are light operated (photoelectronic) devices, light emitting device or devices that modify light
32.   Write down the classification of optoelectronic device
         a) Photo emissive b) Photoconductive or photovoltaic
33. Define luminescence Light can be emitted by a solid when it is stimulated by the
      source of incident energy. This phenomenon is called luminescence
34. What are the types of luminescence?
        a) Photoluminescence b) Electroluminescence
35 . Define photoluminescence
           It is incident energy is in the form of photons, then it is called
36. Define electroluminensence
          If the radiation is produced by the application of an electric
         field, it is termed as electroluminescence
37. Which colour of light is emitted by GaAs, Gp, GaAsp
        GaAs - Infra red radiation (invisible) GaP - Red or Green
          GaAsP - Red or Yellow
38. Define injection laser diode
        When the emitted light is coherent, (ie) essentially   
        monochromatic, then such a diode is refered to as an injection  
        laser diode
39. What are the liminations of LCD?
       * It requises an external or internal light source * Temperature
   range is limited to about 60oC * Lime time is limited due to chemical
40. What are the two types of LCDs?
       a) Dynamic scattering type LCD b) Field effect LCD
41. Name the crystal materls used to LCD?
      a) Nematic b) Cholesteric
42. What are the types of liquid crystal cells?
         a) Transmittive type b) Reflective type
43. What re the advantages of LCD?
      * They require less voltage * They are economical
       * They have a low power consumption
44. What are the disadvantages of LCD?
        * They are slow devices (ie) turn On & turn OFF time
           are quite   large
        * They occupy large area * Their life span is quite small
45. What is the main difference between laser & LED?
        Laser emits monochromatic or coherent light whereas LED
           emits incoherent light
46. What are the disadvantages of using laser diode?
         Because of high-energy density, a laser beam is quite
         dangerous eye protection must be worn when working with
         these devices
47. Define injection laser diode
       Laser diode which operates in a pulsed manner are termed
        injection laser diodes
48. Define continuous wave laser diode
      Laser diode which produce a continuous output are refered as
       continuous wave laser diode
49. Define dark current
      In photodiode when no light is applied, there is a minimum
      reverse leakage current called as dark current
50. Give some applications of photo diodes
        They are used as demodulators, encoders, optical
        communication system, high speed counting and switching
        circuits, computer card punching etc.
51. What is photovoltaic effect?
       If a PN junction is open circuited the energy is used to create a
        potential difference which is proportionl to the incident light. This
        phenomenon is clled pen[hotovoltaic effect


1. Define “punch through” in early effect.
2. Write short notes on heat sink.
3. Explain transistor as an amplifier.
4. Calculate the values of Icand Ie for a transistor with  =0.97 and
   Icbo =10A.IB is measured as 50A. 
5. Sketch the h-parameter equivalent circuit for  a  CE transistor.
6. Explain how transistor is used as rectifier?
7.  Why is transistor called a current controlled device ?
8. Why is collector region is greater than emitter region? 
9. Explain about the depletion layers of the transistors.
10. Give the classification of power transistor based on
(i)  Frequency of operation.
(j)  Current capacity.
11. Give the relationship between Alpha and Beta.
12. Draw and explain input and output characteristics of CB
13. How does early effect affect the BJT characteristics in CB
14. What are the limitations of h parameters?
15. Define Transistor
     Transistor consists of two junctions formed by sandwitching either
      P-type or N-type semiconductor between a pair of opposite types.
16. Write the current amplification factor for a CB transistor.
           a = Change in Collector Current at constant VCB / Change in  
        emitter current
17.  Write the formula for input resistance in a CB transistor
       Input resistance = Change in base - emitter voltage / Change in
        emitter current at constant VCB
18.  Write the current amplification factor for a CE transistor.
         b = Change in Collector Current / Change in base current at
         constant VCE
19 . Define transistor action.
          A transistor consists of 2 coupled PN junctions. The base is a
         common region to both junctions and makes a coupling
    between them. Since the base regions are smaller, a significant    
 interaction between junctions will be available. This is called
  transistor actions.
20.  Define delay time
       It is defined as the time required for the current to rise from 0 to
       10% of its maximum value.
21. Define rise time
      It is the time required for the current to rise from 0 to 90
       percentage of the maximum value.
22. Define turn-on time
          It is the time required for the current to rise from 0 to 90
           percentage of the maximum value ton = td + tr
23.. Define fall time
       It is the time required for the Collector current to fall from 90 to 10
       percentage of Ics.
24. Define Storage time
      It is the time required to fall from 100 to 90 percent of Ics.
25. Define turn-off time
     It is the time required to fall from 100 to 90 percent of Ics.
26 . Define hybrid parameters.
        Any linear circuit having input and output terminals can be  
      analysed by four parameters(one measured on ohm, one in mho
       and two dimensionless) called hybrid or h-parameters.
27. What are the use of h - Parameters?
        It perfectly isolates the input and output circuits. Its source and
         load currents are taken into account.
 28 . Define power transistors 
         Power transistors are those which handle a large amount of
          current and also dissipates large amount of power across  
         collector base junction.
29 . Define current amplification factor in CC transistor.
         g =Change in emitter current /Change in base current at
         constant VCE
30.   Which is the most commonly used transistor configuration?
      The CE Configuration is most commonly used. The reasons are

         * High Current gain * High voltage gain * High power gain

          * Moderate input to output ratio.

31 What are the values of input resistance in CB, CE & CC
       CB - Low about 75 CE - Medium About 750 CC - Very high about    
32.   Write the voltage and current equation for hybrid parameters.
             V1 = h11i1 + h12V2 i2 = h21i1 + h22V2
33.   What are the values of h-parameters?
           h11 = V1/ i1 ; h12 = V1 / v2 ; h21 = i2 / i1 ; h22 = i2 / v2
 34.  h – parameter is applied to linear circuit : True or False.

      UNIT   - III

1.                 Sketch and explain the basic structure of an N channel junction      
      field effect  transistor.
2.                  What are the advantages and disadvantages of JFET over BJT?
3. Why is FET known as a unipolar device?
4. Draw and explain the small signal low frequency model of   
5.  Draw and explain the transfer curve of MOSFET in
              enhancement mode.
 6. Distinguish between JFET and MOSFET.
 7. How do you protect the MOSFET gate?
 8. Describe the various FET parameters.
 9. What is a channel?

           It is a base like structure which determines the type of FET

10. What are the advantages of FET

         * Input impedance is very high. This allow high degree of               
             isolation between the input & output Circuit.

          *Current carriers are not crossing the junctions hence noise is   
                highly reduced.

          * It has a negative temperature Co-efficient of resistance . This
             avoids the thermal runaury .

            * It has a smaller size, longer life high efficiency.

11. What are the advantage of MOSFET compared to JFET?

          The input impedance of MOSFET is higher than that of JFET

12. What are the two modes of MOSFET?

               (a) Depletion mode (b) Enhancement mode

13. Why UJT is called so?

      UJT has only one PN junction so it is called as uni junction transistor

14. What are the advantages of SCR and TRIAC?
     SCR performs rectification, inversion and regulation of power flow    
    TRIAC is a bidirectional switch and hence it can conduct in both   
     the direction.

15.  Define breakdown voltage
      The applied voltage at which the thyristors conducts heavily    
       without  gate voltage.

16. Define latching current

It is the minimum current required to latch the device from off to ON state

17. Define holding current
       It is defined as the minimum current required to hold the device
       into conduction.

18. Define turn - on time
        It is the time taken by the SCR to reach to its full conduction
         from the time the trigger is applied.

19. Define turn - off time
     It is the finite time taken by the SCR after application of the   
      reverse voltage to switch the device off.
20. What are the advantage of SCR?
        Switching speed is high No moving parts. So it gives noiseless
         operation at high frequency It controls large current in the load
         by means of small gate current Occupies less space

21. Give some applications of thysistor?
          Used for power control Used for speed control of a d.c shunt

22. Define finger voltage
        It is defined as the minimum voltage which is required between
         anode and the cathode of thyristor to trigger into conduction

23. What is the name for solid state equivalent of thyristor

24. Define inter-base resistance
        It is the resistnce offered by the silicon bar

25. Define pinch-off voltage
      It is the drain source voltge above which the drain current become

26. What are the differences between JFET & BJT
         jFET                                                                   BJT
1. Unipolar device                                           1. Bipolar device
2. High input impedance              2. Low input impedance due
                                                                to forward bias
3. Voltage driven device               3. Current driven device
4. Gain is characterised
by transconductance              4. Gain is chracterised by voltge gain
5. Low noise level                  5. High noise level

27. . What is amplification factor
            It is the product of drain resistnce and transconductance    
           m=Rd x gm Rd=Drain resistnce gm=Transconductance

28. Define drain resistance
          It is the ratio of change in drain source voltage to change in drain current at constant gate source voltage.

 UNIT   - IV

1. What is a single tuned amplifier?
2. What are the disadvantages of tuned amplifiers?
3. What are double tuned amplifiers?
4. What are the advantages of stagger tuned amplifier?
5  What is feed back?
6. What are feed back amplifiers?
7. What are the types of feed back?
8. What is negative feed back?
9. What is positive feedback?
10 Which feedback increases the gain of the amplifier?
11.State Barkhausen criterion.
12. Give the classification of oscillators.
13. Define feedback factor .
14. Draw the schematic representation of Hartley oscillator.
15. In Hartley oscillator calculate L2 if L1 = 15mh ,C=50pF
   mutual inductance of  5µH and frequency of oscillations is 168 KHz.
16. Compare the frequency response characteristics of an amplifier with and    
       Without Feedback.
17.What is the condition for the sustained oscillation?
18. Draw the colpitt oscillator
19. Why is RC –phase shift oscillator is preferred for the generation of low
    Frequency ? Derive the frequency of oscillation for the same.
20.  Explain in detail
                            ( i ) Voltage-shunt feedback amplifier              
                                  (ii ) current – series feedback amplifier
21. What are the conditions for sustained oscillator or what is Barkhausen criterion?
22. State the frequency for RC phase shift oscillator.

 UNIT   - V

1. What do you understand by wave shaping circuits?
2. Which elements are used in linear and non-linear wave shaping circuits?
3. Why there is need of wave shaping circuits?
4. What do you mean by differentiator circuits?
5. What do you mean by integrator circuits?
6. What do you mean by clipping circuits?
7. What do you mean by clamping circuits?
8 . What do you mean by positive clipper circuits?
9. What do you mean by negative clipper circuits?
10. hat do you mean by positive clamping circuits?
11. What do you mean by negative clamping circuits?
12. Sketch the output waveforms from a differentiating circuit     
13. when the input is a saw-tooth wave.
14. Sketch the output waveforms from a differentiating circuit
      when the input is a square wave.
15. Mention the advantages of oscillator.
16 . With a neat diagram explain the action of phase shift oscillator.
17. Explain the concept of multivibrator.

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