Electronic Devices - May 2012

Electronics Engineering (Semester 3)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks. 1 (a) If input Vi is 1khz square wave with 30vpp voltage applied to a given circuit with practical diode of silicon. Determine Vo and draw waveform? :-IMAGE(5 marks) 1 (b) For the fixed biased configuration given,determine the following?
(i) I_BQ,I_{CQ (ii) VCEQ
(ii) VBE
(iv) VBC :-IMAGE}(5 marks) 1 (c) Explain basic construction of a n-channel JFET and explain working of n channel JFET for VGS=0 and VGS<0 and draw ID v/s VDS characteristic of the same?(5 marks) 1 (d) If IE=3.2mA, hfe=150, hoe=25?mho and hob=0.5?s for transistor then determine and draw:
(i) the common emitter hybrid equivalent ckt
(ii) the common base re model ckt?
(5 marks) 1 (e) Compare ?L? and ?C? filter ckt? (5 marks) 2 (a) For a standard voltage divider bias configuration of C-E amplifier with RE bypassed by a capacitor CE the following data is given
Vcc=22V, R1=56k?, R2=8.2k?, RC=6.8k?, RE=1.5k?, Ci=Co=10&mu:F,
CE=20&mu:F, ?=90
Determine
(a) re
(b) Zi
(c) Zo for ro =??
(d) Av for ro=??
(e) Re calculate parameters of part (b) through (d) if ro=1/hoe=50k? and compare the result? :- IMAGE (12 marks) 2 (b) A power transistor is used as a switch. Calculate the currents, output voltage and power dissipated in the transistor for the given ckt when V1=0V and 12V. Circuit and transistor parameters are: RB=240?, VCC=12V, VBE(on)=0.7V, VCE(sat)= 0.1V, ?=75. Assume the load is a motor with an efficient resistance of RC=5?? :-IMAGE(8 marks) 3 (a) design a full wave bridge rectifier to meet particular specifications. It should produce a peak output voltage of 12V and deliver 120mA to the load RL. Output must be with a ripple of not more than 5%. An input line voltage of 120V(rms). 60 Hz is available? (8 marks) 3 (b) Draw and explain working of a voltage doubler circuit? (6 marks) 3 (c) The zener diode regulator circuit shown has an input voltage (V_ps) that varies between 10 V and 14 V and load resistance varies between 20? and 100&Omega. Assume 5.6V zener diode is used and assume IZ_(min)=0.1 IZ_(max). Find the value of R_i required and the minimum power rating of the diode.(6 marks) 4 (a) Determine the following for the given network IDSS=9mA and Vp=-3V.
(1) I_DQ and V_GSQ
(2) V_DS
(3) V_D
(4) V_S
You can use graphical method.:- IMAGE (10 marks) 4 (b) Draw npn BJT common collector (emitter follower) amplifier circuit and derive equation for small signal voltage gain ?Av? using r? model? (10 marks) 5 Design a single stage CS JFET amplifier using potential divider biasing for the following specifications:-
V0=2V
Fl=20Hz
ID=3.3?0.6mA
|Av|=11
Use BFW11.
Calculate R_i, R_oo(max) for the design amplifier? :-IMAGE (20 marks) 6 Design a single stage CE BJT amplifier using BC 147A to satisfy the following specifications:-
|Av|?120
SICO?8
VCC=24V
RL=10kW
Fl is better than 10Hz
ICQ=3mA
Estimate Ri and Ro of designed amplifier. If Ri?3k&omega is a new specification added then without changing the selected transistor suggest suitable modification in the above design. What sacrifices you have made? (20 marks)

write a short note (any three)

7 (a) Construction, working and transfer characteristic of n channel enhancement type MOSFET?(7 marks) 7 (b) Comparison of performance of CE, CB, and CC BJT amplifier?(7 marks) 7 (c) Construction, process of electroluminescence of light emitting diode(LED)?(7 marks) 7 (d) Multistage amplifier?(7 marks) 7 (e) Photodiodes and schottky diode?(7 marks)