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INVERTEC V300-I
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E-5
THEORY OF OPERATION
Drawing B above shows the FET in an
active mode. When the gate signal, a posi-
tive DC voltage relative to the source, is
applied to the gate terminal of the FET, it is
capable of conducting current. A voltage
supply connected to the drain terminal will
allow the FET to conduct 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.
An FET is a type of transistor. FETs are
semiconductors well suited for high-fre-
quency switching.
Drawing A above shows an FET in a pas-
sive 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 com-
ponents connected to the source. The cir-
cuit is turned off like a light switch in the
OFF position.
FIGURE E.5 — FIELD EFFECT TRANSISTOR OPERATION.
SOURCE
TERMINAL
GATE
TERMINAL
DRAIN
TERMINAL
DRAIN (N)
N CHANNEL
SUBSTRATE (P)
SOURCE (N)
(0 VOLTS)
GATE
TERMINAL
(+ 6 VOLTS)
DRAIN (N)
ELECTRONS
SOURCE (N)
B. ACTIVE
A. PASSIVE
FIELD EFFECT TRANSISTOR (FET) OPERATION
