c. Junction Diode Voltage Regulator. There are silicon diodes designed for a
specific breakdown voltage with reverse bias.
This diode is known as a zener
diode. When the breakdown voltage is exceeded, current through the diode increases
very rapidly, while the voltage across the diode remains relatively constant. This
characteristic makes the diode useful as a voltage regulator.
d. Varactor. The barrier voltage created at the junction of a semiconductor
diode allows it to serve as a capacitance because of the separated charges.
The
amount of junction capacitance can be controlled by the reverse voltage.
designed for this effect of a voltage-sensitive capacitance are known as varactors.
e. Amplifiers.
(1) In electron tubes such as the triode, tetrode, and pentode, the plate
current is varied when the input signal is varied.
When a load
resistance is placed in the plate current path, the varying current
will cause a varying voltage across the load resistor as shown in
figure 1-10.
The amplitude of the varying input signal is small
compared with the amplitude of the varying voltage
Figure 1-10.
Comparison of input and output waveforms.
across the load resistor. The increase in amplitude between input and
output signals is known as the gain of the amplifier. An electron-tube
amplifier stage is shown in A of figure 1-11.
Figure 1-11.
Electron-tube and transistor amplifier.
309 L1
11
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