Tab Electronics Guide to Understanding Electricity ... - Sciences Club

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Transistors
Figure 6-5 illustrates a practical example of a common-base amplifier.
Common-base amplifiers have the unique characteristic of a variable
input impedance dependent on the emitter current flow. The equation
for calculating the input impedance is
Z in
167
26
Ie
where I e
is the emitter current in milliamps.
As can be seen from the previous equation, the input impedance is
low. Furthermore, common-base amplifiers have a high output impedance,
and a power gain slightly higher than common-emitter amplifiers.
Transistor Amplifier Comparisons
The common-emitter configuration is used in applications requiring
reasonably high voltage and power gains. The output is inverted. Common-emitter
amplifiers have low input impedances, and high output
impedances.
The common-collector configuration is used for impedance-matching
applications. Common-collector amplifiers have high input impedances
with low output impedances. Voltage gain is considered at unity, and the
output is noninverted.
Figure 6-5
Practical example
of a commonbase
transistor
amplifier.
Input
+
5 F
470 k
Q1
2N2222
100 k
4.7 k
5 F
Output
25
F
+
10 k
9 V
9 V