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MAHATMA GANDHI INSTITUTE OF TECHNOLOGY
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Electronic Devices and Circuits Assignment
–
I (UNIT I & II)
1.
a) Explain about the operation of a p-n junction diode under forward bias and reverse bias. Draw the V-I characteristics. b) Draw the energy band structure of an open circuit PN junction and derive the expression for contact potential. 2.
a) Derive the expression for transition capacitance C
T
of a diode. b) When a diode is reverse biased with 6V, it has a junction capacitance of 10 pF. When the reverse bias is increases to 10V, the capacitance drops to 8.43 pF. Find whether it is abrupt or linear graded junction. 3.
Two p-n germanium diodes are connected in series opposing. A 5V battery is impressed upon this arrangement. Find the voltage across each junction at room temperature. 4.
a) Give the Fourier series representation of the output current wave in a half wave and full wave rectifier. Hence explain the necessity of filter circuit in rectifiers. b) For a full wave rectifier with a shunt capacitor filter derive expression for ripple factor using approximate analysis. 5.
a) A 230V, 60Hz voltage is applied to the primary of a 5:1 step down center tapped transformer used in a full wave rect
ifier having a load of 900Ω. If the diode resistance and secondary coil resistance together has a resistance of 100Ω. Determine a) dc voltage across the load, b) dc current flowing
through the load c) dc power delivered to the load d) PIV across each diode e) ripple voltage and its frequency. b) Compare rectifiers with all parameters. 6.
The zener diode regulates at 50V from 5 to 40 mA current. The supply voltage is 200V. a)
Calculate the R to allow voltage regulation from I
L
= 0 to I
L
= I
Lmax
. Find I
Lmax
. b)
If R is set as above and I
L
is fixed at 25mA, then what is the permissible range of V?
SET 1
MAHATMA GANDHI INSTITUTE OF TECHNOLOGY
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Electronic Devices and Circuits Assignment
–
I (UNIT I & II)
1.
a) Compare Zener breakdown and Avalanche breakdown. b)
Calculate the dynamic forward and reverse resistances of a PN junction diode at room temperature when the applied voltage is 0.25 V and the reverse saturation current is 2 µA. 2.
a) Derive the expression for transition capacitance C
T
of a diode. b) When a diode is reverse biased with 4V, it has a junction capacitance of 10 pF. When the reverse bias is increases to 8V, the capacitance drops to 8.43 pF. Find whether it is abrupt or linear graded junction. 3.
a) Explain the necessity of a bleeder resistor in an L
–
section filter used with a Full Wave filter. b)
A half wave rectifier has a load of 3.5kΩ
. If the diode resistance and secondary coil
resistance together have a resistance of 800Ω and the input voltage has peak value of 240V.
Calculate i)
peak, rms and average values of current flowing ii)
dc output power and iii)
efficiency of the circuit. 4.
In the circuit shown below assume that the voltage drop across a forward biased diode is 0.7V at 300K The small signal input Vi = Vm cos(
ω
t) where Vm = 100 mV. Find I
DC
and V
AC
. 5.
a) Give the Fourier series representation of the output current wave in a half wave and full wave rectifier. Hence explain the necessity of filter circuit in rectifiers. b) For a full wave rectifier with a shunt capacitor filter derive expression for ripple factor using approximate analysis. 6.
Explain breakdown mechanisms in a diode. b) Calculate the current I, I
Z
and I
L
when V = 40V. How will these values be affected if source voltage increases to 70V? Assume the breakdown voltage of zener diode is 10V,
R = 3KΩ, and R
L
=
2KΩ. Also determine the maximum power dissipation across the diode.
SET 2
MAHATMA GANDHI INSTITUTE OF TECHNOLOGY
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Electronic Devices and Circuits Assignment
–
I (UNIT I & II)
1.
Draw the V-I characteristics of a following circuit consisting of two Si diodes and also calculate the voltage drop across each diode if the reverse saturation current flowing through it is 1 µA. 2.
a) Draw the circuit of a full wave rectifier and explain its operation with relevant waveforms b) Derive the expressions for the following parameters of a full wave rectifier. i) Average or DC current I
dc
ii) RMS current I
rms
iii) Rectifier efficiency iv) Ripple factor v) Transformer Utilization factor (TUF) 3.
a) Compare different types of filters used in a power supply. b)
Derive the expression of a π –
section (CLC) filter. 4.
In the voltage regulator circuit shown below, the Zener diode current is to be limited to the range
5≤
iz
≤ 100
mA. Find the range of load current and load resistance. 5.
a) Explain the concept of diode capacitance. Derive expression for transition capacitance of a linear graded junction. b) Find the value of D.C. resistance and A.C resistance of a Germanium junction diode at 25
0
C with reverse saturation current, Io = 20
μA and at an applied voltage of 0.2
5V across the diode. 6.
a) Explain the necessity of a bleeder resistor in an L
–
section filter used with a Full Wave filter. b)
A FWR supplies a load requiring 300V at 200mA. Calculate the transformer secondary voltage for i) capacitor input filter using 10mF and ii) a choke input filter with a choke of 10 H and a capacitance of 10 µF.
SET 3
MAHATMA GANDHI INSTITUTE OF TECHNOLOGY
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING Electronic Devices and Circuits Assignment
–
I (UNIT I & II)
1.
a) List out the merits and demerits of Bridge type Full Wave rectifiers over centre tapped type Full Wave rectifiers. b)
The secondary voltages of a centre tapped transformer are given as 60V-0V-60V the total resistance of secondary coil and forward diode resistance of each section of transformer secondary is 62
Ω. Compute the following for a load resistance of 1 KΩ.
i) Average load current ii) Percentage load regulation iii) Rectification efficiency
iv)
Ripple factor for 240 V/50Hz supply to primary of transformer. 2.
a)
Show that the regulation of both the half wave rectifier and full wave rectifier is given by b)
The zener diode regulates at 50V from 5 to 40 mA current. The supply voltage is 200V. i)
Calculate the R to allow voltage regulation from I
L
= 0 to I
L
= I
Lmax
. Find I
Lmax
. ii)
If R is set as above and I
L
is fixed at 25mA, then what is the permissible range of V? 3.
In the circuit shown below assume that the voltage drop across a forward biased diode is 0.7V at 300K The small signal input Vi = Vm cos(
ω
t) where Vm = 100 mV. Find I
DC
and V
AC
. 4.
a) Draw the basic structure of Varactor diode and explain its operation. b) Explain the V-I characteristics of a Tunnel Diode with the help of energy band diagrams. 5.
a) Draw the circuit of zener voltage regulator. Explain its operation and also derive the expressions for minimum and maximum values of source resistor for the zener diode to work as a regulator. b) In a FWR with the capacitor filter, show that the ripple voltage is inversely proportional to the capacitance and is proportional to the load current. Calculate the ripple voltage when C = 1000µF and I
DC
= 10mA. The ac input voltage to the rectifier is V
m
Sin 314t. 6.
a) Explain the concept of diode capacitance. Derive expression for transition capacitance. b) Find the value of D.C. resistance and A.C resistance of a Germanium junction diode at 25
0
C with
reverse saturation current, Io = 25μA and at an applied voltage of 0.2V across the diode.
SET 4

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