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When V
GS
> 0,
⇒
Electrons form the current path as shown in Fig. 37. Thus, current from
the drain to the source
flows. Now, if we will increase the gate-to-source voltage, drain current will also increase.
Figure: 1. 38. Output characteristics of an n-channel enhancement power MOSFET
For
lower value of V
DS
, MOSFET works in a linear region where it has a constant resistance equal to
V
DS
/ I
D
.
For a fixed value of V
GS
and greater than threshold voltage V
TH
,
MOSFET enters a saturation
region where the value of the drain current has a fixed value.
Besides the output characteristics curves, transfer characteristics of power MOSFET is also shown in
Fig. 39.
Figure: 1. 39. Transfer characteristics of an n-channel enhancement power MOSFET
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Insulated-Gate Bipolar Transistor (IGBT)
IGBT combines the physics of both BJT and power MOSFET to gain the advantages of both worlds. It
is controlled by the gate voltage. It has the high input impedance like a power MOSFET and has low
on-state power loss as in case of BJT. There is no even secondary breakdown and not have long
switching time as in case of BJT. It has better conduction characteristics as compared to MOSFET due
to bipolar nature. It has no body diode as in case of MOSFET but this can be seen as an advantage to
use external fast recovery diode for specific applications. They are replacing the MOSFET for most of
the high voltage applications with less conduction losses. Its physical
cross-sectional structural
diagram and equivalent circuit diagram is presented in Fig. 40 to Fig. 41. It has three terminals called
collector, emitter and gate.
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