_________________________________________________________________ Semiconductor Diodes
biased. Notice at point C, the reverse bias voltage is 80 volts and the current is only
100 microamperes. This results in 800k ohms of resistance, which is considerably larger
than the resistance of the junction with forward bias. Because of these unusual features, the
PN junction diode is often used to convert AC into DC (rectification).
Figure 1-20. PN Junction Diode Characteristic Curve
PN JUNCTION APPLICATION
1-78. So far we have mentioned only rectification as one application for the diode.
Variations in doping agents, semiconductor materials, and manufacturing techniques have
made it possible to produce diodes that can be used in many different applications.
Examples of these types of diodes are signal diodes, rectifying diodes, zener diodes
(voltage protection diodes for power supplies), varactors (amplifying and switching
diodes), and many more. Two of the most commonly used diodes are the signal diode and
rectifier diode.
Half-Wave Rectifier
1-79. One of the most important uses of a diode is rectification. The normal PN junction
diode is well suited for this purpose as it conducts very heavily when forward biased (low
resistance direction) and only slightly when reverse biased (high-resistance direction). If
we place this diode in series with a source of AC power, then the diode will be forward and
reverse biased every cycle. Since, in this situation, current flows more easily in one
direction than the other, rectification is accomplished. The simplest rectifier circuit is a
half-wave rectifier (see Figure 1-21) that consists of a diode, an AC power source, and a
load resistor.
23 June 2005
TC 9-62
1-23
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