Lincoln Electric INVERTEC V300-PRO SVM105-B Service Manual page 28

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SOURCE (N)
SOURCE (N)
An FET is a type of transistor. FETs are semiconduc-
tors well suited for high-frequency switching because
they are capable of going from full off to full on much
more quicklfy than other types of semi-conductors.
Drawing A above shows an FET in a passive mode.
There is no gate signal, zero volts relative to the source
and, therefore, no current flow. The drain terminal of
the FET may be connected to a voltage supply; but
since there is no conduction, the circuit will not supply
current to downstream components connected to the
source. The circuit is turned off like a light switch in the
OFF position.
THEORY OF OPERATION
FIELD EFFECT TRANSISTOR OPERATION
GATE
TERMINAL
SOURCE
(0 VOLTS)
TERMINAL
SUBSTRATE (P)
A. PASSIVE
GATE
TERMINAL
(+ 6 VOLTS)
B. ACTIVE
V300-PRO
DRAIN
TERMINAL
DRAIN (N)
N CHANNEL
DRAIN (N)
ELECTRONS
Drawing B above shows the FET in an active mode.
When the gate signal, a positive DC voltage relative to
the source, is applied to the gate terminal of the FET, it
is capable of conducting current. A voltage supply con-
nected to the drain terminal will allow the FET to con-
duct and henceforth supply current to downstream
components. Current will flow through the conducting
FET to downstream components as long as the gate
signal is present. This is similar to turning on a light
switch
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