# GTU previous years question papers – BE- Sem-III -Basic Electronics -December 2010

GUJARAT TECHNOLOGICAL UNIVERSITY

B.E. Sem-III Regular / Remedial Examination December 2010

Subject code: 131101

Subject Name: Basic Electronics

Total Marks: 70

Instructions:

1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.

(i)                        What is semiconductor? Define a hole in semiconductor

(ii)                       State the Pauli exclusion principle

(iii)                        Sketch the piecewise linear characteristics of p-n diode

(iv)                         (iv ) Define an electron volt (eV)

(v)                       State the mass-action law as an equation and in word.

(vi)                     What is cutin voltage? Write approx. value of cutin voltage for silicon and germanium diode

(vii)                   Write the equation for the volt-ampere characteristic a photo diode

(b) Draw and explain bridge rectifier circuit with capacitorfilter. Draw necessary   waveforms.

Q.2 (a) Draw the circuit of CE configuration of transistor. ExplainInput and output characteristics. Derive a = P / P+1 (b) (i) Draw symbol and explain briefly the working principle Breakdown diode and Tunnel diode

(ii)Write principle and applications of light emitting diode

OR

(b) (i) Describe the Hall effect. Which properties of a Semiconductor are determined from Hall effect experiment?

(ii) Explain electrical properties of germanium and silicon ( conductivity ,the mobility and the energy gape)

Q.3 (a) Draw following diode circuits with input and output Waveforms:

(i)    Voltage doublers circuit

(ii)   Positive clipping circuit

(iii) Negative clamper circuit

(b) (i) A 5kQ load is fed from a bridge rectifier connected with a transformer

secondary whose primary is connected to 460V, 50 Hz supply. The ratio of number of primary to secondary turns is 2 : 1. Calculate dc load current ,dc load voltage , ripple voltage and PIV rating of diode,

(ii) A 100^F capacitor when used as a filter has 12 V dc Across it with a terminal load resistor of 2.5kQ. If the rectifier is full wave and supply frequency is 50 Hz calculate the percentage of ripple in the output

OR

(a)        Explain the h-parameter model of CE amplifier with derive the expression for Ai , Av , Ri , Ro

(b)        Find hre in terms of the CB h-parameters

Q.4 (a) What is biasing? Why biasing is required for transistor? List biasing methods for transistor. Draw and explain the circuit of voltage divider biasing (b) Where CC configuration is used? Draw circuit of CC and CB configuration of transistor. Compare current gain ,voltage gain ,input impedance and output impedance of both

OR

Q.4 (a) A CE amplifier using npn transistor has load resistance RL connected between   collector and Vcc supply of + 16 V For biasing resistor , Ri is connected between Vcc and base Resistor R2 = 30 kQ is connected between base and ground. RE =

1kQ. Draw the circuit diagram and calculate the value of R1 , Rc ,stability factor S if Vbe = 0.2V, Ieq = 2 mA , Vceq = 6 V , a = 0.985 (b) Design a fixed bias circuit using silicon npn transistor Which has pdc = 150. The   dc biasing point is VCE = 5V And Ic = 5 mA Supply voltage is 10V.Write advantages and disadvantages of fixed bias circuit.

Q.5 (a) (i) Define the pinch-off voltage Vp .Sketch the depletion region before and after   pinch-off.

(ii)   Sketch the cross section of a P-channel enhancement MOSFET .Show two     circuit symbol for MOSFET

(b) Draw circuit of an idealized class-B push-pull power amplifier and explain its   operation with the help of necessary waveforms.

OR

Q.5 (a) (i) Compare different types of power amplifier based on conduction angle ,     position of Q-point , efficiency and distortion

(ii)   Draw circuit of transistor as a switch

(b)        A MOSFET has a drain- circuit resistance Rd of 100K and operates at 20 kHz.   The MOSFET parameters are gm = 1.6 mA/V, rd = 44K , Cgs = 3 Pf Cds = 1 pF ,Cgd = 2.8 pF.Calculate the voltage gain of this device .