1
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State the full form of MOSFET.
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|
Metal oxide
field effect transistor
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2
|
How many terminals the MOSFET consists of?
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Three
terminals : Source, Drain and Gate
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3
|
Describe the main advantage of the Power MOSFET over other
semi conductor devices.
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|
Advantages
of the MOSFET
- Low input
power
- High switching
speed
|
4
|
Whether the MOSFET is voltage controlled or current controlled
device? Why?
|
|
Voltage
controlled device
- The MOSFET is
a voltage controlled majority charge carrier device in the output current is
controlled by the input voltage.
- The conduction of current in the n channel
MOSFET is done only by electrons whereas the current conduction in the p
channel is done by holes.
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5
|
What is reason behind the name MOSFET?
|
|
The majority
charge carriers in the MOSFET are controlled by gate voltage. The gate is
insulated by metal oxide layer therefore it is called as MOSFET.
|
6
|
Describe the different types of MOSFET.
|
|
Types
of MOSFET
- Depletion
enhancement MOSFET : ( 1 ) N channel and ( 2 ) P channel
- Enhancement
MOSFET : ( 1 ) N channel and ( 2 ) P channel
|
7
|
Which are the operating mode of the Depletion enhancement ( DE
) MOSFET?
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|
The operating
mode of DE MOSFET
- Depletion mode
- Enhancement
mode
|
8
|
Whether the MOSFET is operated at low voltage?
|
|
No,
the MOSFET is not operated below 500 Voltage.
|
9
|
What do you mean by the Depletion mode and Enhancement mode in
the MOSFET?
|
|
Depletion
mode
- When the
negative gate to source voltage is applied to N channel MOSFET, it is called
as depletion mode of the MOSFET.
Enhancement
mode
- When the
positive gate to source voltage is applied to N channel MOSFET, it is called
as enhancement mode of the MOSFET.
|
10
|
Why the vertical structure of the MOSFET is used?
|
|
The vertical
structure of the MOSFET is used in order to achieve
- High current
rating and
- High break
down voltage
|
11
|
Whether the doping level in the P type material and N type
material is same in the N channel MOSFET?
|
|
Doping
level
- The two ends n+
type material is heavily doped whereas the middle P type material is
moderately doped in the N channel MOSFET.
- The n- drift layer has
lowest doping level.
|
12
|
Which parameter greatly affects the breakdown voltage of the n
channel MOSFET?
|
|
n-
drift drain layer
|
13
|
Which parameter affects the ON state resistance of the MOSFET?
|
|
Geometric
shape of source regions
|
14
|
In which type of MOSFET, there is no physical channel?
|
|
Enhancement
MOSFET
|
15
|
Explain the term : Cut off region and ohmic region
|
|
Cut
off region
- When the gate
to source voltage is less than the threshold voltage, the MOSFET is operated
in the cut off region.
- The applied voltage must be less than the break down
voltage of the MOSFET.
- No drain current flows.
Ohmic
region
- The MOSFET is
operated in the ohmic region when the gate to source voltage is greater than
the gate to source threshold voltage ( VGS > VGS (TH) ).
- The drain
current is almost directly proportional to drain to source voltage for small
value drain to source voltage.
|
16
|
In which region, the power dissipation is very high in the
MOSFET?
|
|
Active region
|
17
|
Give reason : There is no current flow between drain to source
in the MOSFET without gate bias.
|
|
The current
does not flows between drain to source in the
MOSFET without gate bias due to two back to back PN junction diode
|
18
|
Describe the disadvantage of the planner type MOSFET
construction.
|
|
The planner
type construction has long source to drain channel therefore large on state
resistance.
|
19
|
Which are the resistances present in the internal circuit of
the MOSFET?
|
|
Internal
resistance in the MOSFET
- Source region
resistance
- Drift region
resistance
- Drain
resistance and
- Channel
resistance
|
20
|
Describe the effect of gate to source voltage on the on state
drain to source resistance.
|
|
As the gate to
source voltage increases, the on state drain to source resistance decreases
and vice versa.
|
21
|
What is main reason for switching delay in the MOSFET?
|
|
The main
reason for switching delay is due to charging and discharging of input and
output capacitors in the MOSFET.
|
22
|
Give reason : The parallel connection of the MOSFET is easily
done.
|
|
The on state
resistance of the MOSFET has positive temperature co – efficient therefore
the parallel connection is easily done.
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23
|
Why the switching speed of the Power MOSFET is higher than the
bipolar transistors?
|
|
Switching
speed
- The Power
MOSFET is a unipolar device.
- The current
conduction is done through only majority charge carriers.
- The turn off delay
does not occur due to recombination of minority charge carriers.
- Therefore
the speed of the Power MOSFET is higher than the bipolar transistors.
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24
|
State the applications of the Power MOSFET.
|
|
Applications
of Power MOSFET
- Speed control
of AC and DC motors
- Switching
device in stepper motor controllers
- Lighting
control
- Medical equipment
- Relays
- Induction
heating
- Robotics
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