BED important questions: By B.Suresh and N.Suresh







Unit I

1.   (a)  Draw the Energy Band Diagrams of
              i.  conductor
              ii.  semiconductor and
             iii.  Insulator and discuss the nature of their conductivities
2.   (a)  Define law of junction.
        (b)  Explain the Fermi’s level in intrinsic semiconductor.    
3.  (a)  Explain about semiconductor, Insulator & Conductor with neat sketch.
       (b)  State the Einstein relationship for semiconductor.
4.   (a)  Explain about Drift and Diffusion currents in semiconductors.                                         
5.   (a)  Define mobility, conductivity and diffusion and obtain the Einstein’s relation.
        (b)  In a typical n-type semiconductor, the Fermi level lies 0.5 ev below the conduction band at 300 K. Find its new position when temperature in increased to 6000 K.  
6. (a) Derive the expression for Hall voltage VH.
   (b) What are the applications for Hall voltage?
7. (a) Discuss the significance of Forbidden Band Gap energy in Energy-Band Diagrams with reference to the difference in cut-in voltages for Silicon and Germanium diode working under forward Bias conditions.

Unit II

1. (a) Explain how temperature effects on p-n junction diode.
    (b)The reverse saturation current IS at T=3000K of a PN junction germanium diode is 50 micro amps. Calculate the forward bias voltage Vf to be applied across the junction to obtain a forward current If of 50 mA ?
2. a) Write a note on diffusion and transition capacitances across a pn junction diode.
    (b) Discuss the impact of forward and reverse bias voltages applied to semiconductor diodes on the Transition region widths and junction capacitances.
3. Short notes on
      i)LED ii)Photo Diode  iii)Varactor Diode  iv) PIN Diode
4.   (a)  What are the various applications of p-n junction diode?  Explain them.
        (b)  What are the specifications of p-n junction diode?  Explain how reverse
Saturation current varies with temperature both in Si and Ge diodes.
 5.   (a)  How does the reverse saturation current of diode varies with temperature.  Explain.
        (b)  Draw  the  energy  band  diagram  of  p-n  diode  for  no  bias,  forward  bias  and
             Reverse bias and explain.                                                         
6.   (a)  Draw the basic structure of a Varactor diode and explain its characteristics.
        (b)  Write the diode equation and discuss the effect of temperature on diode current.                                                                                
        (c)  Explain about the characteristics of zener diode.
7.   (a)  Explain the terms avalanche breakdown and ‘zener breakdown’.  What do you
            Mean by voltage and zener current?  How does zener diode regulate the d.c. voltage.
        (b)  A  certain  pn-junction  diode  has  a  leakage  current  of  10−14 A  at  room  temperature of      270   C and 10−9A at 1250C. The diode is forward biased with a   constant current source of 1mA at room temperature.  If current is assumed to remain constant.  Calculate the junction barrier voltage at room temperature and at 1250C.    

UnitIII

1. (a) Explain the application of a semiconductor diode as a rectifier.
(b) Draw the input signal and output signal of a Half Wave rectifier circuit.
(c) Derive the expression for VDC and VR.M.S of H W R output signal.
(d) Derive the expression for ripple factor ‘γ ’ of a Half Wave rectifier circuit

2. (a) Explain the working of Bridge Rectifier circuit with necessary waveforms in the circuit .
(b) A HWR has a load of 3.5 KΩ .If the diode resistance and secondary    coil resistance together have a resistance of 800 Ω and the input voltage has a signal voltage of peak value 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
 3.   (a)  Define the following terms of a half wave rectifier with resistive load:
               i.  Ripple factor
              ii.  Peak inverse voltage
             iii.  Rectification efficiency.
        (b)  A 230 V, 60Hz voltage is applied to the primary of a 5 :  1 step down, center tapped transformer used in a full wave rectifier having a load of 900Ω. If the diode resistance and the secondary coil resistance together has a resistance of 100Ω, determine:
               i. dc voltage across the load
              ii. dc current flowing through the load
             iii. dc power delivered to the load
             iv. PIV across each diode.
              v. Ripple voltage and its frequency.                                            
4.   (a)  Draw the circuit diagram of HWR. Explain its working.  What is the frequency of ripple in its output
        (b) A voltage of 200 cos wt is applied to HWR with load resistance of 5 KΩ.  find the maximum d.c current component, r.m.s. current, ripple factor, TUF and rectifier efficiency.                                                                                                                  
5.   (a)  A 15-0-15 Volts (rms) ideal transformer is used with a full wave rectifier circuit
             with diodes having forward drop of 1 volt.  The load is a resistance of 100ohm
             and a capacitor of 10,000µf is used as a filter across the load resistance.  Cal-
             Calculate the dc load current and voltage.
        (b)  Explain  the  working  of  the  Half  wave  rectifier  circuit  with  neat  sketch  of
             waveforms at various points in the circuit.                                        
        (c)  From the definition of gm and rd obtain expression for µ.
   6.   (a)  Draw the block diagram of a regulated power supply and explain its operation.
        (b)  Define line regulation and load regulation.  Give their typical numerical values.

Unit IV

  1.a) With neat diagram explain the various  current components in an pnp transistor.
  b) Explain the input and output characteristics of a transistor in CB configuration.    
2. (a) Derive the relation between α  and  β of the BJT.
 (b) Explain how transistor can be used as an amplifier
3. (a) Draw the circuit and explain the characteristics of BJT (input and output characteristics) in C.E. configuration.
4.a) What is meant by operating point? Explain how to stabilize it?
(b) Differentiate bias stabilization and compensation techniques.
5. Draw the h-parameter equivalent circuit of a basic amplifier and derive the expressions for Current gain, Input impedance and Voltage gain.
 b) The hybrid parameters for a transistor used in CE configuration are hie=1KΩ, hfe=150, hre=1.2 ×10-4, hoe=25×10-6Ω-1. The transistor has a load resistance of 10k in the collector and is supplied from a signal source of resistance 5K . Compute the values of input impedance, output impedance, current gain and voltage gain.
6.   (a)  Explain bias compensation using sensistors.
        (b)  Discuss the phenomenon of ‘Thermal runaway’ in Transistor operation.  
        (c)  Derive the expression for stability factors S.
7. (a)  The reverse saturation current in a transistor is 8µA. If the transistor common
             base  current  gain  is  0.979,  calculate  the  collector  and  emitter  current  for  40 µA base current.                                                                    
 (b)  Calculate the quiescent current and voltage of collector to base bias arrangement using the following data:   V cc  =10V, R b=100KΩ, Rc =2KΩ, β =50 and also specify a value of Rb so that Vce =7V.   
Unit V

1. (a) For a small signal JFET iD = f(VGS , VDS). Obtain expressions for iD and hence define gm, rand µ.
(b) From the definition of gm and rd obtain expression for µ.
2. (a) Draw the circuit and explain the drain and gate characteristics of a JFET in C.S. configuration.
 (b) Find the values of VDS and VGS. Given ID=5mA,VDD=10V, RD=1KΩ, RS=500Ω.
 3. (a) Draw the two transistor version of an SCR and explain its firing characteristics with this circuit.
(b) What is meant by Pinch off voltage pinch of locus of JFET? Mark Pinch of locus form drain characteristic.  
4.   (a)  An N-channel JFET having VP  = - 4V and IDSS = 12 ma is used as common source  FET  amplifier  with  potential  divider  biasing  circuit. The  parameter values  are  VDD =24V.  RS  =  1KΩ  ;  RL  =  1.25KΩ  ;  R1 =  450KΩ  and  R2 = 90KΩ .  Draw the circuit with these parameters and explain the circuit working as amplifier
 (b)  Draw the D.C equivalent circuit of the above amplifier circuit and determine
the values of drain current ID and VDS . 
5.   (a) Draw  a  diagram  showing  the  structural  details  of  N-Channel  depletion  and Enhancement MOSFET device.                                                            
(b)  Draw a circuit diagram with biasing voltages to obtain the Drain characteristics  and  the  Transfer  characteristics  of N-Channel  Depletion  Enhancement MOSFET device.                                                                         
 (c)  Draw  the  Drain  characteristics  of  DE  MOSFET.  Discuss  the method  of  obtaining  the  output  characteristics  of  the  Depletion  Enhancement  MOSFET device.  Show the salient features on the device characteristics               
 (d)  Mention the reason for calling MOSFET device as Insulated Gate MOSFET
6.  (a)  Sketch the circuit symbols for
              i.  n-channel JFET  ii.  p-channel JFET  iii.  n-channel enhancement type MOSFET
             iv.  p-channel enhancement type MOSFET   v.  n-channel depletion type MOSFET and
             vi.  p-chanel depletion type MOSFET.  And compare JFET and MOSFETs

Unit VI

1.  Draw the circuit diagram of a RC phase-shift oscillator and discuss its operation. Obtain an expression for its frequency of oscillation.
2.a) What is an oscillator? Explain.
3. (a) Explain with circuit diagram a negative feedback amplifier and obtain expressions for its closed loop gain.
(b) The gain of an amplifier is decreased to 1000 with negative feedback from its gain of 5000. Calculate the feedback factor and the amount of negative feedback in dB
4.   (a)  An amplifier has a gain of -100 and a distortion of 8%.  What is the effect of introducing negative feedback with feedback factor of 0.05?
        (b)  Find Af  for a CE stage with an un bypassed emitter resistor.                     
5.   (a)  Draw the weinbridge oscillator circuit and explain its working.
        (b)  Calculate the value of ‘C’ used in the weinbridge circuit that determines the Oscillator frequency of 10 KHZ. Assume R=50 KΩ in the weinbridge circuit.
        (c)  Derive the expression for feedback factor in the wein bridge circuit.
6.a)  Classify the amplifiers based as feedback topology and give their block diagram. How
        the input and output impendence are effected in each case?
  b)    Draw the circuit diagram of a current feedback circuit and derive Expressions for
        Voltage gain and output resistance, and input resistance.                
BED important questions: By B.Suresh and N.Suresh BED important questions: By B.Suresh and N.Suresh Reviewed by Suresh Bojja on 8/21/2015 11:21:00 AM Rating: 5

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