Power MOSFET Basics
DESCRIPTION:
employ semiconductor
processing techniques that are
similar to those of today's VLSI
circuits, although the device
geometry, voltage and current
levels are significantly different
from the design used in VLSI
devices. The metal oxide
semiconductor field effect
transistor (MOSFET) is based
on the original field-effect
transistor introduced in the
70s. Figure 1 shows the
device schematic, transfer
characteristics and device
symbol for a MOSFET. The
invention of the power
MOSFET was partly driven by
the limitations of bipolar power
junction transistors (BJTs)
which, until recently, was the
device of choice in power
electronics applications.
Although it is not possible to
define absolutely the operating
boundaries of a power device,
we will loosely refer to the
power device as any device
that can switch at least 1A.
The bipolar power transistor is
a current controlled device. A
large base drive current as
high as one-fifth of the
collector current is required to
keep the device in the ON
state.
Also, higher reverse base drive
currents are required to obtain
fast turn-off. Despite the very advanced state of manufacturability and lower costs of BJTs, these
limitations have made the base drive circuit design more complicated and hence more expensive than the
power MOSFET.
processing techniques that are
similar to those of today's VLSI
circuits, although the device
geometry, voltage and current
levels are significantly different
from the design used in VLSI
devices. The metal oxide
semiconductor field effect
transistor (MOSFET) is based
on the original field-effect
transistor introduced in the
70s. Figure 1 shows the
device schematic, transfer
characteristics and device
symbol for a MOSFET. The
invention of the power
MOSFET was partly driven by
the limitations of bipolar power
junction transistors (BJTs)
which, until recently, was the
device of choice in power
electronics applications.
Although it is not possible to
define absolutely the operating
boundaries of a power device,
we will loosely refer to the
power device as any device
that can switch at least 1A.
The bipolar power transistor is
a current controlled device. A
large base drive current as
high as one-fifth of the
collector current is required to
keep the device in the ON
state.
Also, higher reverse base drive
currents are required to obtain
fast turn-off. Despite the very advanced state of manufacturability and lower costs of BJTs, these
limitations have made the base drive circuit design more complicated and hence more expensive than the
power MOSFET.
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