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# Multiple choice question for engineering

## Set 1

1. When latch-up occurs in an IGBT
a) Ig is no longer controllable
b) Ic is no longer controllable
c) the device turns off
d) Ic increases to a very high value

Answer: b [Reason:] After latch-up the collector emitter current is no longer in control of the gate terminal.

2. A latched up IGBT can be turned off by
a) forced commutation of current
b) forced commutation of voltage
c) use of a snubber circuit
d) none of the mentioned

Answer: a [Reason:] Forced commutation of current is the only way to turn off a latched up IGBT.

3. The static V-I curve of an IGBT is plotted with
a) Vce as the parameter
b) Ic as the parameter
c) Vge as the parameter
d) Ig as the parameter

Answer: c [Reason:] V-I curves are plotted for Ic vs Vce with the controlling parameter (Vge) as a parameter.

4. Latch-up occurs in an IGBT when
a) Vce reaches a certain value
b) Ic reaches a certain value
c) Ig reaches a certain value
d) the device temperature reaches a certain value

Answer: b [Reason:] Latch up occurs when the current through the device (Ic) collector current increases beyond a certain value.

5. In an IGBT, during the turn-on time
a) Vge decreases
b) Ic decreases
c) Vce decreases
d) none of the mentioned

Answer: c [Reason:] Vce decreases from 0.9 to 0.1 of the initial value whereas others increase.

6. Choose the correct statement
a) IGBTs have higher switching losses as compared to BJTs
b) IGBTs have secondary breakdown problems
c) IGBTs have lower gate drive requirements
d) IGBTs are current controlled devices

Answer: c [Reason:] Due to its high gate impedance, IGBTs require less gate drive current.

7. The approximate equivalent circuit of an IGBT consists of
a) a BJT & a MOSFET
b) a MOSFET & a MCT
c) two BJTs
d) two MOSFETs

Answer: a [Reason:] Gate of the MOSFET forms the gate terminal of the IGBT, the source of MOSFET is connected to the base of the BJT and drain to the collector.

8. An IGBT is also know as
a) MOIGT (Metal oxide insulated gate transistor)
b) COMFET (Conductively modulated FET)
c) GEMFET (Grain modulated FET)
d) all of the mentioned

Answer: d [Reason:] All of the above mentioned are alternate names of IGBTs.

9. The body of an IGBT consists of a
a) p-layer
b) n-layer
c) p-n layer
d) metal

Answer: a [Reason:] IGBT has a p-n-p structure with fingers of n+ layers into the p layer. The p layer has the largest cross section and forms the body of the IGBT.

10. At present, the state-of-the-art semiconductor devices are begin manufactured using
a) Semiconducting Diamond
b) Gallium-Arsenide
c) Germanium
d) Silicon-Carbide

Answer: d [Reason:] All of the above mentioned can be used but Si-Ca has certain advantages over the other materials.

## Set 2

1. The MOSFET combines the areas of _______ & _________
a) field effect & MOS technology
b) semiconductor & TTL
c) mos technology & CMOS technology
d) none of the mentioned

Answer: a [Reason:] It is an enhancement of the FET devices (field effect) using MOS technology.

2. Which of the following terminals does not belong to the MOSFET?
a) Drain
b) Gate
c) Base
d) Source

Answer: c [Reason:] MOSFET is a three terminal device D, G & S.

3. Choose the correct statement
a) MOSFET is a uncontrolled device
b) MOSFET is a voltage controlled device
c) MOSFET is a current controlled device
d) MOSFET is a temperature controlled device

Answer: b [Reason:] It is a voltage controlled device.

4. Choose the correct statement(s)
i) The gate circuit impedance of MOSFET is higher than that of a BJT
ii) The gate circuit impedance of MOSFET is lower than that of a BJT
iii) The MOSFET has higher switching losses than that of a BJT
iv) The MOSFET has lower switching losses than that of a BJT
a) Both i & ii
b) Both ii & iv
c) Both i & iv
d) Only ii

Answer: c [Reason:] MOSFET requires gate signals with lower amplitude as compared to BJTs & has lower switching losses.

5. Choose the correct statement
a) MOSFET is a unipolar, voltage controlled, two terminal device
b) MOSFET is a bipolar, current controlled, three terminal device
c) MOSFET is a unipolar, voltage controlled, three terminal device
d) MOSFET is a bipolar, current controlled, two terminal device

Answer: c [Reason:] MOSFET is a three terminal device, Gate, source & drain. It is voltage controlled unlike the BJT & only electron current flows.

6. The arrow on the symbol of MOSFET indicates
a) that it is a N-channel MOSFET
b) the direction of electrons
c) the direction of conventional current flow
d) that it is a P-channel MOSFET

Answer: b [Reason:] The arrow is to indicate the direction of electrons (opposite to the direction of conventional current flow).

7. The controlling parameter in MOSFET is
a) Vds
b) Ig
c) Vgs
d) Is

Answer: b [Reason:] The gate to source voltage is the controlling parameter in a MOSFET.

8. In the internal structure of a MOSFET, a parasitic BJT exists between the
a) source & gate terminals
b) source & drain terminals
c) drain & gate terminals
d) there is no parasitic BJT in MOSFET

Answer: b [Reason:] Examine the internal structure of a MOSFET, notice the n-p-n structure between the drain & source. A p-channel MOSFET will have a p-n-p structure.

9. In the transfer characteristics of a MOSFET, the threshold voltage is the measure of the
a) minimum voltage to induce a n-channel/p-channel for conduction
b) minimum voltage till which temperature is constant
c) minimum voltage to turn off the device
d) none of the above mentioned is true

Answer: a [Reason:] It is the minimum voltage to induce a n-channel/p-channel which will allow the device to conduct electrically through its length.

10.The output characteristics of a MOSFET, is a plot of
a) Id as a function of Vgs with Vds as a parameter
b) Id as a function of Vds with Vgs as a parameter
c) Ig as a function of Vgs with Vds as a parameter
d) Ig as a function of Vds with Vgs as a parameter

Answer: b [Reason:] It is Id vs Vds which are plotted for different values of Vgs (gate to source voltage).

## Set 3

1. In the output characteristics of a MOSFET with low values of Vds, the value of the on-state resistance is
a) Vds/Ig
b) Vds/Id
c) 0
d) ∞

Answer: b [Reason:] The o/p characteristics Is a plot of Id verses Vds, which for low values of Vds is almost constant. Hence, the on-state resistance is constant & the slop is its constant value.

2. At turn-on the initial delay or turn on delay is the time required for the
a) input inductance to charge to the threshold value
b) input capacitance to charge to the threshold value
c) input inductance to discharge to the threshold value
d) input capacitance to discharge to the threshold value

Answer: b [Reason:] It is the time required for the input capacitance to charge to the threshold value, which depends on the device configuration. The device can start conducting only after this time.

3. Choose the correct statement
a) MOSFET suffers from secondary breakdown problems
b) MOSFET has lower switching losses as compared to other devices
c) MOSFET has high value of on-state resistance as compared to other devices
d) All of the mentioned

Answer: b [Reason:] MOSFET has lower switching losses due to its unipolar nature & less turn off time. All of the other statements are false.

4. Which among the following devices is the most suited for high frequency applications?
a) BJT
b) IGBT
c) MOSFET
d) SCR

Answer: c [Reason:] MOSFET has the least switching losses among the rest of the devices.

5. Choose the correct statement
a) MOSFET has a positive temperature co-efficient
b) MOSFET has a high gate circuit impedance
c) MOSFET is a voltage controlled device
d) All of the mentioned

Answer: d [Reason:] MOSFETs are voltage controlled devices. They have high gate circuit impedance and are PTC devices.

6. Consider an ideal MOSFET. If Vgs = 0V, then Id = ?
a) Zero
b) Maximum
c) Id(on)
d) Idd

Answer: a [Reason:] Gate current = 0 so device is off (ideally).

7. For a MOSFET Vgs=3V, Idss=5A, and Id=2A. Find the pinch of voltage Vp
a) 4.08
b) 8.16
c) 16.32
d) 0V

Answer: b [Reason:] Use Id = Idd x [1-Vgs/Vp]2.

8. How does the MOSFET differ from the JFET?
a) JFET has a p-n junction
b) They are both the same
c) JFET is small in size
d) MOSFET has a base terminal

9. The basic advantage of the CMOS technology is that
a) It is easily available
b) It has small size
c) It has lower power consumption
d) It has better switching capabilities

Answer: c [Reason:] Complementary MOS consumes very less power as compared to all the earlier devices.

10. The N-channel MOSFET is considered better than the P-channel MOSFET due to its
a) low noise levels
b) TTL compatibility
c) lower input impedance
d) faster operation

Answer: d [Reason:] The N-channel are faster than the P-channel type.

## Set 4

1. The p-region has a greater concentration of __________ as compared to the n-region in a P-N junction.
a) holes
b) electrons
c) both holes & electrons
d) phonons

Answer: a [Reason:] Holes are the majority charge carriers in p-type material.

2. A p-type semiconductor material is doped with ____________ impurities whereas a n-type semiconductor material is doped with __________ impurities
a) acceptor, donor
b) acceptor, acceptor
c) donor, donor
d) donor, acceptor

Answer: a [Reason:] Donor impurities denote an electron to the n-type material making it a electron majority carrier & vice-versa.

3. In the p & n regions of the p-n junction the _________ & the ___________ are the majority charge carriers respectively.
a) holes, holes
b) electrons, electrons
c) holes, electrons
d) electrons, holes

Answer: c [Reason:] Holes are the majority charge carriers in p-type material & vice-versa.

4. The n-region has a greater concentration of _________ as compared to the p-region in a P-N junction diode.
a) holes
b) electrons
c) both holes & electrons
d) phonons

Answer: b [Reason:] Electrons are the majority charge carriers in n-type material.

5. Which of the below mentioned statements is false regarding a p-n junction diode?
a) Diode are uncontrolled devices
b) Diodes are rectifying devices
c) Diodes are unidirectional devices
d) Diodes have three terminals

Answer: d [Reason:] Diode is a two terminal device, anode & cathode are the two terminals.

6. In the p & n regions of the p-n junction the _________ & the ___________ are the minority charge carriers respectively.
a) holes, holes
b) electrons, electrons
c) holes, electrons
d) electrons, holes

Answer: d [Reason:] Holes are the minority charge carriers in n-type material & vice-versa.

7. Lets assume that the doping density in the p-region is 10-9 cm-3 & in the n-region is 10-17cm-3, as such the p-n junction so formed would be termed as a
a) p n
b) p+ n
c) p n+
d) p+ n+

Answer: b [Reason:] Doping density is greater in the p-region compared to the n-region.

8. When a physical contact between a p-region & n-region is established which of the following is most likely to take place?
a) Electrons from N-region diffuse to P-region
b) Holes from P-region diffuse to N-region
c) Both of the above mentioned statements are true
d) Nothing will happen

Answer: c [Reason:] When p & n region come together diffusion takes places & a depletion region is established with opposite charges on both the sides of the junction.

9. Which of the following is true in case of an unbiased p-n junction diode?
a) Diffusion does not take place
b) Diffusion of electrons & holes goes on infinitely
c) There is zero electrical potential across the junctions
d) Charges establish an electric field across the junctions

Answer: d [Reason:] A potential difference is established across the junctions due to recombination of holes & electrons. This growing filed (barrier potential) stops the further diffusion.

10. Which of the following is true in case of a forward biased p-n junction diode?
a) The positive terminal of the battery sucks electrons from the p-region
b) The positive terminal of the battery injects electrons into the p-region
c) The negative terminal of the battery sucks electrons from the p-region
d) None of the above mentioned statements are true

Answer: a [Reason:] The diode is forward biased, positive is connected to p & vice-versa, as such batter provides EMF to drive electrons from n-region to p-region.

## Set 5

1. If V & I are the forward voltage & current respectively, then the power loss across the diode would be
a) V/I
b) V2 I2
c) I2 V
d) VI

Answer: d [Reason:] Simply power (P) is voltage into current i.e. VI

2. The power loss in which of the following cases would be the maximum?
a) When both V & I are minimum
b) When both V & I are maximum
c) When only V is maximum
d) When only I is maximum

Answer: b [Reason:] P=VI Hence, it would be maximum when both V and I are maximum.

3. Even after the forward current reduces to zero value, a practical diode continues to conduct in the reverse direction for a while due to the
a) resistance of the diode
b) high junction temperature
c) stored charges in the depletion region
d) none of the mentioned

Answer: c [Reason:] Due to the stored charges during the earlier current flow, even when the current reduces to zero due to some structural properties of the device, the device takes time to sweep out the stored charges.

4. For a p-n junction diode, the peak inverse current & the reverse recovery time are dependent on
a) inverse voltage
b) forward Voltage
c) di/dt
d) all of the above mentioned

Answer: c [Reason:] It only depends upon the number stored charges which depends upon the rate of change of current.

5. In an AC-DC converter, a diode might be used as a
a) voltage source
b) phase angle controller
c) freewheeling Diode
d) filter

Answer: c [Reason:] In converters diodes are used to feed the energy back to the load in case of an inductive load.

6. When the p-n junction diode is forward biased, the width of the depletion region __________
a) increases
b) decreases
c) remains Constant
d) increases than Decreases

Answer: b [Reason:] When forward biased depletion layer decreases & finally it collapses to allow the current flow.

7. When the p-n junction diode is reversed biased, the width of the depletion region __________
a) increases
b) decreases
c) remains Constant
d) none of the above mentioned

Answer: a [Reason:] When reverse biased depletion layer increases until the breakdown value is reached.

8. In case of a practical p-n junction diode, the rise in the junction temperature ___________
a) decreases the width of the depletion region
b) increases the barrier potential
c) increases the width of the depletion region
d) width of the depletion region increases but the barrier potential remains constant

Answer: a [Reason:] The rise in temperature excites the charges, which go & recombine with the charges in the depletion region decreasing its width. Higher the temperature, lesser is the E.M.F required to turn on the device.

9. In the equilibrium state, the barrier potential across a unbiased silicon diode is _________
a) 0.3 V
b) 0.7 V
c) 1.3 V
d) 0 V