than pure silicon, or negatively doped, i.e. the added substance has an
excess of valence electrons. In either case, electric current can flow
under the right conditions.
A strong charge applied to the central positively doped layer in the
transistor allows a current to flow between the two negatively doped
A Output
Lightly
negatively
doped
Lightly
positively
doped
Input
current
1
mmm
ΓΓ
—
current
^Ββ 1
M mmm 1
+ +|
—
γ Earth
Strongly
negatively
doped
Figure 2.2 A transistor
layers, but if there is no charge or if it is weak then it will prevent its
flow. In this way the transistor acts like a switch, allowing current to
flow or no ...
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