_______________________________________________________________________ Special Devices
SUMMARY
3-97. Now that we have completed this chapter, the following is a short review of the
more important points. Answer the check-on-learning questions, found after the summary,
to determine how much you have learned from this chapter.
ZENER DIODE - a PN junction that is designed to operate in the reverse-bias
breakdown mode. When the applied voltage reaches the breakdown point, the
Zener diode, for all practical purposes, becomes a short circuit. The reverse
bias and breakdown mode of operation causes the Zener diode to conduct with
(in the direction of) the arrow in the symbol. Two theories are used to explain
the breakdown action of Zener diodes. The ZENER EFFECT explains the
allows the valence band of one material to overlap the energy level of the
conduction band of the other material. This situation allows electrons to tunnel
across the PN junction at the point where the two energy bands overlap. Zener
diodes that operate above 5 volts are explained by the AVALANCHE
EFFECT, in which free electrons colliding with bound electrons cause an ever-
increasing number of free current carriers in a multiplying action. The Zener
diode is used primarily as a voltage regulator in electronic circuits.
23 June 2005
TC 9-62
3-37
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