Osmania University (OU) 2006-1st Sem B.E Electronics
B.E 2/4 (E.C.E)(I-SEMESTER)SUPPLEMENTARY EXAMINATION,APRIL,2006
Electronic Devices
Code No.: 10013
FACULTY OF ENGINEERING B.E. H/IV Year (ECE) I Semester (Supplementary) Examination, April 2006
ELECTRONIC DEVICES
Time : 3 Hours] [Max. Marks : 75
Answer all questions in Part A and any five questions from Part B.
Assume reasonable values of data wherever necessary.
Part A - (Marks: 25)
1. Define the term current density J. What is the expression for J in terms of
electron density and velocity? 3
2. Define ripple factor* and % regulation in rectifiers. 2
3. Explain the term thermal runaway. 3
4. What are the differences between MOSFET and JFET? 2
5. What are the differences-between light emitting diode and liquid crystal display? 3
6. Compare CC and CE configuration of transistor. 3
7. How UJT can be used as a relaxation oscillator? 3
8. Explain gain bandwidth product of BJT and FET. 2
9. In the case of collector to base bias circuit, if P = 40, = 4.7 kft and Rg - 80 K&, determine the value of stability factor S. 2
10. IfdofaBOTifs*0.99, determine its value of (3. 2
Part B - (Marks: 5x10 = 50)
11. (a) Derive the expression for the trajectoy of an electron in uniform retarding
field, when the initial velocity is making an angle 8 with the field. 5
(b) A charged particle having thrice the charge and mass twice that of an electron is accelerated through a potential difference VA of 50 volts, before it enters a uniform magnetic field of flux density B of magnitude 0.02 webers/m2 normally with the field find .
(i) The velocity of charged particle between entering the field.
(ii) Radius of the path
(iii) Time of one revolution. 5
12. (a) Explain the V-I characteristics of P-n junction diode. Derive the equation for
diode current. 5
(b) In a P-N junction Ge diode, find the value of the voltage for which the reverse current I0 will reach 75% saturation value at the room temperature y i' 5
13. (a) Derive the relation between a and p parameters of CB and CE operated
transistors. 5
(b) Sketch the profiles of majority and minority carrier currents in the base of an NPN transistor. Explain the transistor action with the helps pf tJtiee profiles. 5
: ! i h ; i > n ?'>! M :>
14. (a) Derive the relationship between IDS, IDSS and VGS in a JFET and plot the transfer
characteristics. 5
(b) Explain how JFET acts as a voltage variable resistor at low VDS values. 5
15. (a) Draw the hybrid-7i equivalent circuit of CE transistor at high frequencies. Derive
expressions for the feedback conductance gbc and output conductance gee. 5
(b) A junction transistor is to operate at the following operating point ICq= 2mA, vceq= 20v and ibq= 20A- Hie'following values for this operating point are the specifications of the transistor. p0 - 100, fT = 50 MHz, cob= 3pf, 1= 1.4KC, hre = 2.5 x 10-4, hoe = 20 pt mhos. Determine the hybrid-ti model parameters of the transistor. Assume that the operating temperature ib '3dOQ K. > < j; 5
16. (a) Draw the circuit of a bridge rectifier and compare its performance with a full
wave rectifier circuit using a mains transformer with centre tapped secondary winding. 5
(b) No load output voltage for a rectifier with L-section filter is 2Vm/n. Mention whether it is used with HWR or an FWR circuit. . . .,.:, , 5
17. (a) Draw the biasing circuits of MOSFET and explain. 5
(b) Draw the characteristics of a MOSFET and explain its modes and regions of operation. 5
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| Earning: Approval pending. |
