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1)
What is meant by leakage flux?
Part of the primary
flux as well as the secondary flux completes the path through air and links
with the respecting winding only. Such a flux is called leakage flux. Leakage
fluxes link with the respective windings only and not to both the windings.
2)
Define voltage regulation of a
transformer?
The regulation
is defined as change in the magnitude of the secondary terminal voltage, when
full load ie, rating load of specified power factor supplied at rated voltage
is reduced to no load, with primary voltage maintained constant expressed as
the percentage of the rated terminal voltage.
3)
What is an ideal transformer?
A transformer is
said to be ideal if it satisfies following properties:
·
It has no losses.
·
Its windings have zero resistance.
·
Leakage flux is zero ie, 100% flux produced by primary links with the
secondary.
·
Permeability of core is so high that negligible current is required to
establish the flux in it.
4)
What is difference between latch and
flip-flop?
A flip-flop
continuously checks its inputs and correspondingly changes its output only at
times determined by clocking signal.
A latch is a
device which continuously checks all its input and correspondingly changes its
output, independent of the determined by clocking signal.
5)
What are the types of flip-flop?
There are basically four main
types of flip-flops: SR, D, JK, and T.
6)
Explain how transistor acts as a switch?
The
areas of operation for a transistor switch are known as the Saturation
Region and the Cut-off Region.
This
means then that we can ignore the operating Q-point biasing and voltage
divider circuitry required for amplification, and use the transistor as a
switch by driving it back and forth between its "fully-OFF" (cut-off)
and "fully-ON" (saturation) regions as shown below.
7)
Draw and Explain the SCR V-I characteristic?
Vak = +ve & Vg = 0
·
When a positive voltage is applied to
anode with respect to cathode, the junctions J1 and J3 are
forward biased, but the junction J2 is reverse biased.
·
The SCR is in its forward blocking
state. At this time the Gate signal is not applied.
·
As shown in figure a small amount of
forward leakage current is flows through the device.
Vak = + & Vg = +ve
·
When the small amount of
positive voltage is applied, while positive voltage is applied to anode with
respect to cathode, the junction J3 becomes forward biased.
·
Thus the SCR conducts a large value of
forward current with small voltage drop. With the application of gate signal
the SCR changed from forward blocking state to forward conducting state. It is
called as latching. Without gate signal it happens at forward breakdown
voltage (Vfbd).
·
When the gate signal value is increased,
the latching happens for low Vak voltages as mentioned in the figure. In the
presence of forward current (i.e. after the thyristor is turned on by a
suitable gate voltage) it will not turn off even after the gate voltage has
been removed.
·
The thyristor will only turn off when
the forward current drops below holding current. The holding current is defined
as the minimum current required to hold the SCR in the forward conduction
state.
Vak = -ve
·
When a negative voltage is applied to
anode with respect to cathode, the junctions J1 and J3 are reversed biased, but
the junction J2 is forward biased. The SCR is in its reverse blocking
state.
·
As shown in figure a small amount of
reverse leakage current flows through the device.
·
If the applied voltage is more than
reverse breakdown voltage, the device will collapse and the large amount of
current flows through it.
8)
Compare MOSFET and BJT.
MOSFET
|
BJT
|
Less Power handling
capability
|
More Power handling
Capability
|
Fast switching speed
|
Low switching speed
|
Low on state resistance
|
High On state
resistance
|
No second breakdown
voltage
|
Has second breakdown
voltage problem
|
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