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THEORY OF OPERATIONS
FIGURE E-8 – FIELD EFFECT TRANSISTOR OPERATION
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| GATE | |
SOURCE | TERMINAL | |
(0 VOLTS) | ||
TERMINAL |
SOURCE (N)
DRAIN
TERMINAL
DRAIN (N)
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SUBSTRATE (P) | N CHANNEL |
A. PASSIVE
GATE TERMINAL (+ 6 VOLTS)
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SOURCE (N)
DRAIN (N)
ELECTRONS
B. ACTIVE
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FIELD EFFECT TRANSISTOR (FET) OPERATION
An FET is a type of transistor. FETs are semiconduc- tors well suited for
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.
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.
