1990
1. Which of the following effects can be caused by a rise in the temperature ?
a. Increase in MOSFET current
b. Increase in BJT current
c. Decrease in MOSFET current
d. Decrease in BJT current
Answer: B & C
Solution : https://www.youtube.com/watch?v=BoRoLQ2eN6o
1. Which of the following effects can be caused by a rise in the temperature ?
a. Increase in MOSFET current
b. Increase in BJT current
c. Decrease in MOSFET current
d. Decrease in BJT current
Answer: B & C
Solution : https://www.youtube.com/watch?v=BoRoLQ2eN6o
1991
1.
Discrete transistors
T1 and T2 having maximum collector current rating of 0.75 Amp are connected in
parallel as shown in figure. This combination is treated s a single transistor
to carry a total current of 1 Amp, when biased with self bias circuit. When the
circuit is switched ON, T1 draws 0.55 Amp and T2 draws 0.45 Amp. If the supply is kept on continuously,
ultimately it is very likely that………….
a. T1 gets damaged and T2 will be safe
b. Both T1 and T2 get damaged
c. Both T1 and T2 will be safe
d. T2 gets damaged and T1 will be safe
b. Both T1 and T2 get damaged
c. Both T1 and T2 will be safe
d. T2 gets damaged and T1 will be safe
Answer: A
2.
In the figure shown,
all transistors are identical and have a high value of beta (β). The voltage VDC
is equal to ……………
1992
1. In a transistor
having finite β, the forward bias across the base
emitter junction is kept constant and the reverse bias across the collector
base junction is increased. Neglecting the leakage across the collector base
junction and the depletion region generating current, the base current
will………….. (Increase / Decrease / Remains constant).
2. If the transistors in
figure, have high values of β and a VBE of 0.65 volts,
the current I flowing through the 2 KΩ resistance will
be…………
Answer: A
3. A PNP transistor
shown in figure has uniform doping in the emitter, base and collector regions,
where in the doping concentrations are 1019 cm-3, 1017
cm-3 and 1015 cm-3 respectively. The minority
carrier diffusion lengths in the emitter and the base regions are 5 µm
and 100µm respectively.
Assuming low level
injection conditions and using law of the junction, calculate the collector
current density and the base current density due to base recombination.
[Suitable
approximations may be made if required.]
In all the regions of
transistors, Dp = 8 cm2/sec, Dn = 16 cm2/sec,
ni = 1.5 X 1010 cm-3, KT/q = 26 mV and q =
1.6 X 10-19 C.
Answer:
Solution :
1993
1. The reverse
saturation current of the collector base junction (ICBO) of a BJT is
found to be 10 nA at low collector voltages. The low current amplification
factor (α) is 0.98. Find out the change in
collector current with its base open (ICEO) when the collector
voltage is increased such that α increases by the 1 %.
1994
1. Match the following :
Answer: a-2, b-3, c-1
Solution : https://www.youtube.com/watch?v=GWjW0DVZkSI
2.
In the common emitter amplifier shown, the transistor has a forward current
gain of 100, and a base to emitter voltage of 0.6 volts. Assume ICO
to be negligible. Choose value for R1 and R3 such that
the transistor has a collector current of 1 mA and a collector to emitter
voltage of 2.5 volts.
1995
1. The breakdown voltage
of a transistor with its base open is BVCEO, that with emitter open
is BVCBO then
a.
BVCEO = BVCBO
b.
BVCEO >
BVCBO
c.
BVCEO <
BVCBO
d.
BVCEO not
related to BVCBO
Answer: C
Solution : https://www.youtube.com/watch?v=sX-wk56YviU
2. A BJT is said to be
operating in the saturation region, if
a.
Both the junctions
are reverse biased
b.
Base emitter junction
is in reverse biased, and base collector junction is forward biased
c.
Base emitter junction
is in forward biased, and base collector junction is reverse biased
d.
Both the junctions
are forward biased
Answer: D
Solution : https://www.youtube.com/watch?v=vafpJ7FB9xE
3. The Ebers – Moll
model is applicable to
a.
Bipolar junction
transistors
b.
nMOS transistors
c.
Unipolar Junction
transistors
d.
Junction field effect
transistors
Answer: A
Solution : https://www.youtube.com/watch?v=Xi6e2_7L2Sk
4. A transistor having α = 0.99 and VBE = 0.7
volts, in the circuit shown, then the value of the collector current will
be…………
Answer: 3.725 mA
Solution : https://www.youtube.com/watch?v=2SJ3DMImgPk
5. The circuit shown in figure, supplies
power to an 8 Ω loud speaker. The values of IC
and VCE for this circuit will be
Answer:
3.725 mA and 16.4 Volts
3.725 mA and 16.4 Volts
Solution : https://www.youtube.com/watch?v=ENXTOwOfeoE
6. In a Bipolar junction transistor, if
Answer: a-3, b-5, c-3
Solution : https://www.youtube.com/watch?v=9FDC-pX_y4s
1996
1. In bipolar junction
transistor(BJT), at room temperature, if the emitter current is doubled, then
the voltage across its base emitter junction
a.
Doubles
b.
Halves
c.
Increases by about 20
mV
d.
Decreases by about 20
mV
Answer: C
Solution : https://www.youtube.com/watch?v=j7ws9Ebk4x4
2. If a transistor is
operating with both of its junctions forward biased, but with the collector
base forward bias greater than the emitter base forward bias, then it is
operating in the
a.
Forward active mode
b.
Reverse active mode
c.
Reverse saturation
mode
d.
Forward saturation
mode
Answer: C
Solution : https://www.youtube.com/watch?v=4MkPYKEIJ2Y
3. The common emitter
short circuit current gain β of a transistor
a.
Is a monotonically
increasing function of the collector current IC
b.
Is a monotonically
decreasing function of IC
c.
Increases with IC,
for low IC, reaches maximum and then decreases with further increase
in IC.
d.
Is not a function of
IC.
Answer: C
Solution : https://www.youtube.com/watch?v=XfSBJGUsxFM
1997
1. In a common emitter
BJT amplifier, the maximum usable supply voltage is limited by
a.
Avalanche breakdown
of base emitter junction
b.
Collector base
breakdown voltage with emitter open (BVCBO)
c.
Collector emitter
breakdown voltage with base open (BVCEO)
d.
Zener breakdown
voltage of the emitter base junction
Answer: B
Solution : https://www.youtube.com/watch?v=MvgbR_ljMtk
2. In the cascade amplifier circuit shown,
determine the values of R1, R2 and RL such
that the quiescent current through the transistors is 1 mA and the collector
voltages are VC1 = 3 volts, and VC2 = 6 volts. Take VBE
= 0.7 volts and assume β of the transistors is very high and
base currents to be negligible.
Answer: 59 kΩ, 31 kΩ, 3 kΩ
Solution : https://www.youtube.com/watch?v=rAgjdD4Zhrg
3. Find static noise margins
for a BJT inverter shown in figure. Transistor used is an NPN type with the
specifications as follows.
Answer: (NM)L = 1.3 volts, (NM)H = 3.5 volts
Solution : https://www.youtube.com/watch?v=sKKZZGk1MKc
4. For a typical NPN
transistor, the following data are available :
WC = 20 µm and collector
doping = 5 X 1018 cm-3
WE = 1 µm and emitter doping
= 10 X 1019 cm-3
Base doping = 5 X 1015
cm-3
Minority carrier life
time in the base region is τn = 5 µsec.
Answer: τt = WB2/2DB, β = τn/τt and α = β/β+1
Solution : https://www.youtube.com/watch?v=e32CFF9BjUk
1999
1. The early effect in a
bipolar junction transistor is caused by
a.
Fast turn ON
b.
Fast turn OFF
c.
Large Collector –
Base reverse bias
d.
Large Emitter – Base
forward bias
Answer: C
2. In the cascode
amplifier shown in figure, if the common emitter stage (Q1) has a
Transconductance of gm1 and the common base stage (Q2)
has Transconductance of gm2, then the overall Transconductance g = Io
/ Vi of the cascode amplifier is
a.
gm1
b.
gm2
c.
gm1/2
d.
gm2/2
Answer: A
2000
1. In circuit shown,
assume that the transistor is in active region. It has a large β and its base emitter
voltage is 0.7 volts. The value of IC is
a.
Indeterminate since RC
is not given
b.
1 mA
c.
5 mA
d.
10 mA
Answer: B
Solution : https://www.youtube.com/watch?v=h1mXFKwlnbQ
2001
1. The transistor shunt
regulator shown in figure has a regulated output voltage of 10 volts, when
input varies from 20 volts to 30 volts. The relevant parameters for the zener
diode and the transistor are: VZ = 9.5 volts, VBE = 0.3
votls, β = 99. Neglect the current throught RB.
Then the maximum power dissipated in the zener diode (PZ) and the
transistor (PT) are
Answer: C
2002
1. If the transistor in
figure is in saturation, then
Answer: D
Solution : https://www.youtube.com/watch?v=eGQmSi1Xdxk
2. Each transistor in
figure, has a dc current gain βdc = 50, cut in voltage Vγ
= 0.65 volts and VBEsat = 0.75 volts. The output voltage Vo
for T2 in saturation can be as high as 0.2 volts. Assume 0.7 volts
drop across a conducting PN junction.
Determine
(a) The minimum value IB2 necessary to keep T2 saturation.
(b) The maximum permissible value for the resistance RB1.
(c) The worst case high input (logic 1)
and the worst case low input
(logic 0)
for which T2 will be either in saturation or in cut off.
Answer: (a) 96 µA (b) 14.5 kΩ (c) 2.1 volts and 1.35 volts
Solution : https://www.youtube.com/watch?v=J4uyyFXmVM4
2003
2004
1. The impurity commonly
used for realizing the base region of a silicon NPN transistor is
a.
Gallium
b.
Indium
c.
Boron
d.
Phosphorous
Answer: C
Solution : https://www.youtube.com/watch?v=NkcGfnAzVvE
2. If for a silicon NPN
transistor, the base to emitter voltage (VBE) is 0.7 volts and
collector to base voltage (VCB) is 0.2 volts, then the transistor is
operating in the
a.
Normal active mode
b.
Saturation mode
c.
Inverse active mode
d.
Cutoff mode
Answer: A
Solution : https://www.youtube.com/watch?v=EWiTi5LriHE
3. Consider the
following statements S1 and S2.
S1: the β of a BJT reduces if
the base width is increased
S2: the β of a BJT increases
if the doping concentration in the base is increased
Which of the
following is correct?
a.
S1 is
FALSE and S2 is TRUE
b.
Both S1
and S2 are TRUE
c.
Both S1
and S2 are FALSE
d.
S1 is TRUE
and S2 is FALSE
Answer: D
Solution : https://www.youtube.com/watch?v=91xuzfdvnqk
4. Assuming VCEsat
= 0.2 volts and β = 50, the minimum base current (IBmin)
required to drive the transistor in figure to saturation is
Answer: A
Solution : https://www.youtube.com/watch?v=OhDfZeDskwo
5. The given figure is
the voltage transfer characteristic of
Answer: C
Solution : https://www.youtube.com/watch?v=lPY4XzAWeSg
6. The neutral base width of a bipolar
transistor biased in the active region is 0.5 µm. The maximum
electron concentration and the diffusion constant in the base are 1014
cm-3 and Dn = 25 cm2/sec respectively.
Assuming negligible recombination in the base, the collector current density is
a. 800 A/cm2
b. 8 A/cm2
c. 200 A/cm2
d. 2 A/cm2
Answer: B
Solution : https://www.youtube.com/watch?v=y5ivXtuocFU
7. Assuming that the β of the transistor is
extremely large and VBE = 0.7 volts, IC and VCE
in the circuit shown are
Answer: C
Solution : https://www.youtube.com/watch?v=ETrg3InTVmY
2005
1. For NPN transistor
connected as shown in figure, VBE = 0.7 volts. Given that the
reverse saturation current of the junction at room temperature is 10-13
Amp, then the emitter current is
Answer: C
Solution : https://www.youtube.com/watch?v=3HVbE9qCcH8
2006
1. The phenomenon known
as “early effect” in a BJT refers to a reduction of the effective base width
caused by
a.
Electron – hole
recombination at the base
b.
The reverse biasing
of the base collector junction
c.
The forward biasing
of emitter base junction
d.
The early removal of
stored base charge during saturation to cutoff switching
Answer: B
Solution : https://www.youtube.com/watch?v=V-2EhtZEJBw
2007
1. The DC current gain (β) of a BJT is 50.
Assuming that the emitter injection efficiency is 0.995, the base transport
factor is:
a.
0.980
b.
0.985
c.
0.990
d.
0.995
Answer: B
Solution : https://www.youtube.com/watch?v=VlsDefl-uG0
2. Group I lists four
different semiconductor devices. Match each device in Group I with its
characteristic property in Group II.
Answer: C
Solution : https://www.youtube.com/watch?v=iwERJKn2hUU
3. For the BJT circuit
shown, assume that the β of the transistor is very large and VBE
is 0.7 volts. The mode of operation of the BJT is
a.
Cut off
b.
Saturation
c.
Normal active
d.
Inverse active
Answer: B
Solution : https://www.youtube.com/watch?v=iXf86EM2YOM
2008
2009
2010
1. In a uniformly doped
BJT, assume that NE, NB and NC are the
emitter, base and collector doping in atoms/cm3 respectively. If the emitter
injection efficiency of the BJT is close to unity, which of the following
conditions is TRUE?
Answer: B
2011
1. For the BJT Q1
in the circuit shown, β = ∞, VBEon
= 0.7 volts, VCEsat = 0.7 volts. The switch is initially closed. At
time t=0, the switch is opened. The time at which Q1 leaves the
active region is
a.
10 ms
b.
25 ms
c.
50 ms
d.
100 ms
Answer: C
Solution : https://www.youtube.com/watch?v=yVQ61kRpIsQ
2. For a BJT, the common
base current gain α = 0.98 and the collector base junction reverse bias
saturation current, ICO = 0.6 µA. This BJT is connected in the
common emitter mode and operated in the active region with a base current (IB)
of 20 µA. The collector current IC for this mode of operation is
a.
0.98 mA
b.
0.99 mA
c.
1.0 mA
d.
1.01 mA
Answer: D
Solution : https://www.youtube.com/watch?v=V103i22HX0Y
2012
2013
1. In the circuit shown
below, the silicon NPN transistor Q has a very high value of β. The required value
of R2 in KΩ to produce IC = 1 mA
is
a.
20
b.
30
c.
40
d.
50
Answer: C
Solution : https://www.youtube.com/watch?v=seLmVm94TqY
2014
Set – 1
(15th February 2014 (Forenoon))
1. A BJT is biased in
forward active mode. Assume VBE = 0.7 volts, KT/q = 25 mV and
reverse saturation current IS = 10-13 Amp. The
Transconductance of the BJT (in mA/volt) is…..
Answer: 5785
Solution : https://www.youtube.com/watch?v=nAh0aTdVp84
SET – 2
(15th February 2014 (Afternoon))
1. An increase in the
base recombination of a BJT will increase
a.
the common emitter DC
current gain, β
b.
the breakdown voltage
BVCEO
c.
the unity gain cutoff
frequency, fτ
d.
the Transconductance
gm
Answer: B
Solution : https://www.youtube.com/watch?v=mY6YLyFzlyc
SET –
3 (16th February 2014 (Forenoon))
1. In the circuit shown,
the PNP transistor has |VBE| = 0.7 volts and β = 50. Assume that RB
= 100 KΩ. For Vo to be 5 volts, the
value of RC (in KΩ) is ……..
Answer: 1.07
2. In the circuit shown,
the silicon BJT has β = 50. Assume VBE = 0.7
volts and VCEsat = 0.2 volts. Which one of the following statements
is correct?
a.
For RC = 1
kΩ,
the BJT operates in the saturation region
b.
For RC = 3
kΩ,
the BJT operates in the saturation region
c.
For RC =
20 kΩ, the BJT operates in the cutoff region
d.
For RC =
20 kΩ, the BJT operates in the linear region
Answer: B
Solution : https://www.youtube.com/watch?v=zd_NFD2CN8E
SET - 4 (16th February 2014 (Afternoon))
1. If the emitter
resistance in a common emitter voltage amplifier is not bypassed, it will
a.
Reduce both the
voltage gain and the input impedance
b.
Reduce the voltage
gain and increase the input impedance
c.
Increase the voltage
gain and reduce the input impedance
d.
Increase both the
voltage gain and the input impedance
Answer: B
2. Consider two BJTs
biased at the same collector current with area A1 = 0.2 µm x 0.2 µm and A2 =
300 µm x 300 µm. assuming that all
other device parameters are identical, KT/q = 26 mV, the intrinsic carrier
concentration is 1 x 1010 cm-3, and q = 1.6 x 10-19C,
the difference between the base emitter voltages (in mV) of the two BJTs (i.e.
VBE1 – VBE2) is …………….
Answer: 380
3. A BJT in a common
base configuration is used to amplify a signal received by a 50Ω antenna. Assume KT/q
= 25 mV, the value of collector bias current (in mA) required to match the
input impedance of the amplifier to the impedance of the antenna is ………..
Answer: 0.5
2015
1.
In
the circuit shown, the BJT has a current gain (β) of 50. For an emitter
base voltage VEB = 600 mV, the emitter collector voltage VEC
(in volts) is_______________
2.
If
the base width in a bipolar junction transistor is doubled, which one of the
following statements will be TRUE?
a.
Current
gain will increase
b.
Unity
gain frequency will increase
c.
Emitter
base junction capacitance will increase
d.
Early
voltage will increase
Answer: C
Answer: C
Solution
: https://www.youtube.com/watch?v=bdDtbyWDUeM
3. An NPN BJT having
reverse saturation current Is = 10-15 A is biased in the
forward active region with VBE =700 mV. The thermal voltage (VT)
is 25 mV and the current gain (β) may vary from 50 to 150 due to
manufacturing variations. The maximum emitter current (in µA) is
____________________________
Answer: 1446
Solution : https://www.youtube.com/watch?v=-Ff_pmSDNlQ
Answer: 1446
Solution : https://www.youtube.com/watch?v=-Ff_pmSDNlQ
A base current of 1mA is to be given in order to drive the BJT into saturation. The approximate ratio of the resistances R1:R2 such that the current through R2 is also 1mA, is
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