OBJECTIVES
1.Understand diodes.
2.List diode materials.
3.Explain forward bias.
4.Explain reverse bias.
5.Understand diode testing.
6.List diode applications.
7.Explain zener diode operation.
8.Understand zener diode testing.
9.List zener diode applications.
10. Explain how to maintain semiconductor devices.
RESOURCES
Textbook
•Chapter 5: Diode Applications and Troubleshooting (pp. 107 – 130)
Interactive CD-ROM
•Quick Quizzes®
•Illustrated Glossary
•Flash Cards
•Interactive Troubleshooting Simulations
•Chapter Reviews
•Media Clips
Study Guide
•Chapter 5: Diode Applications and Troubleshooting (pp. 53 – 64)
Resource Guide CD-ROM
•Interactive Illustrations: Chapter 5
•PowerPoint® Presentation: Chapter 5
•Assessments: Chapter 5
INSTRUCTIONAL POINTS
Use the Chapter 5 Interactive Illustrations and the Chapter 5 PowerPoint® Presentation to reinforce key concepts.
1.Understand diodes.
•A diode is an electronic component that allows electrons to pass through it in only one
direction.
•Semiconductor diodes are the most widely used diodes because of their small size and
weight.
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17
18 Solid State Devices and Systems Instructor’s Resource Guide
•The schematic symbol representing a diode consists of a triangle that represents the anode
and a straight line that represents the cathode. Electrons flow from the cathode to the anode,
or against the triangle. Figure 5-1.
2.List diode materials.
•Diodes are typically made from semiconductors. A semiconductor is material that has electrical conductivity between that of a conductor (high conductivity) and that of an insulator
(low conductivity).
•Free electrons (carriers) are electrons in a material that allow the conduction of electricity.
By adding certain impurities through a process called doping, the materials become very
conductive when a voltage of the proper polarity is applied.
•Pure silicon and germanium crystals are prepared for use in diodes by doping. Doping is
the addition of impurities to the crystal structure of a semiconductor to allow electron flow.
•N-type material is semiconductor material created by doping a region of a crystal with
atoms of an element that has more electrons in its outer shell. Figure 5-2.
•P-type material is semiconductor material created by doping a region of a crystal with atoms of an element that has fewer electrons in its outer shell, which creates empty spaces,
or holes. Figure 5-3.
•Holes are the missing electrons in the crystal structure. These holes are represented as
positive charges.
3.Explain forward bias.
•Forward-bias voltage is voltage applied with polarity that allows a diode to act as a conductor.
•Forward-bias voltage occurs when the anode of a diode is positive and the cathode is negative. When a diode is forward-biased, the polarity of the voltage source causes the free
electrons and holes to move toward the depletion region. Figure 5-8.
•The carriers bridge the depletion region and cause it to close. In this condition, carriers
are available from one end of the diode to the other, allowing electrons to flow with little
resistance.
4.Explain reverse bias.
•Reverse-bias voltage is voltage applied with opposite polarity that allows a diode to act
as an insulator. Reverse-bias voltage occurs when the anode of a diode is negative and the
cathode is positive.
•When a diode is reverse-biased, the polarity of the voltage source causes the free electrons
and holes to move away from the depletion region. Figure 5-9. This action increases the
size of the depletion region and prevents electron flow.
5.Understand diode testing.
•The polarity of the diode can be determined with a DMM, and the diode can also be checked
for opens and shorts.
•A DMM set to measure resistance can be used to determine which end of a diode is the
cathode and which end is the anode. This is possible because the DMM is a voltage source
with a definite polarity.
•The diode indicates a low resistance in forward bias and a high resistance in reverse bias.
Figure 5-11.
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Instructional Plan Chapter 5 — Diode Applications and Troubleshooting 19
•The best way to test a diode is to measure the voltage drop across the diode when it is
forward-biased.
•A DMM in the diode test mode is used to test the voltage drop across a diode. Figure 5-12.
6.List diode applications.
•Diode applications include rectifiers, clipping circuits, and clamping circuits.
•A rectifier is a device consisting of diodes that convert AC power to DC power by allowing electrons to flow in only one direction. The simplest form of rectifier is the half-wave
rectifier. Figure 5-16.
•A clipping circuit is also referred to as a voltage limiter. A voltage limiter is an electronic
circuit that consists of diodes used to control voltage where large voltage changes are
expected. Figure 5-18.
•A clamping circuit is a circuit that holds the voltage or current to a specific level. The main
function of a clamper is to provide a DC reference level for a signal voltage. The clamper
effectively raises or lowers the positive or negative peaks of a signal to zero or some other
desired reference level. Figure 5-19 and Figure 5-20.
7.Explain zener diode operation.
•A zener diode is a semiconductor device used as a voltage regulator. Figure 5-22.
•When a source voltage is applied to a zener diode in the forward direction, there is a
breakover voltage and forward current. Figure 5-23.
•When a source voltage is applied to a zener diode in the reverse direction, the current
remains very low until the reverse voltage reaches reverse (zener) breakdown.
•When a voltage that is not normally obtainable from standard zener diodes must be regulated,
several zener diodes can be connected in series to achieve proper voltage. Figure 5-26.
8.Understand zener diode testing.
•A zener diode provides voltage regulation. If it fails, the zener diode must be replaced in
order to return the circuit to proper operation.
•An oscilloscope is used for testing the characteristics of a zener diode in an operating situation. Figure 5-27.
•An oscilloscope displays the dynamic operating characteristics of the zener diode. The
horizontal axis of the oscilloscope represents the voltage across the zener diode while the
vertical axis represents the current.
9.List zener diode applications.
•Zener diode applications include voltage regulator, clipping and limiting, and oscilloscope
calibration.
•A series regulator is a zener diode that is used as a voltage regulator. Figure 5-28.
•A shunt regulator is a zener diode installed in parallel with a current-limiting resistor.
• A zener diode that is supplied with alternating current and connected as a shunt regulator
is capable of limiting either the positive or negative parts of an AC cycle. Figure 5-29.
•A stable voltage source that is not affected by line voltage variations is typically necessary
to calibrate an oscilloscope. A zener diode can be incorporated into existing oscilloscope
circuitry to provide a calibration voltage. Figure 5-31.
 2012 by American Technical Publishers, Inc.
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20 Solid State Devices and Systems Instructor’s Resource Guide
10.Explain how to maintain semiconductor devices.
•Test equipment and soldering irons should be checked to make certain there is no leakage
current from the power source. If leakage current is detected, isolation transformers should
be used.
•Always connect a ground between test equipment and a circuit before attempting to inject
or monitor a signal.
•Ensure test voltages do not exceed maximum allowable voltage for circuit components and
semiconductors. Never connect test equipment outputs directly to a semiconductor circuit.
•Battery eliminators should not be used to furnish power for semiconductor equipment
because they have poor voltage regulation and high-ripple voltage.
•All circuits should be checked for defects before replacing a semiconductor.
• The power must be removed or disconnected from the equipment before replacing a semiconductor.
•Using conventional test probes on equipment with closely spaced parts often causes
accidental shorts between adjacent terminals. These shorts can cause damage or ruin a
semiconductor. To prevent these shorts, the probes can be covered with insulation, except
for a very short length of the tips.
REVIEW

Have learners review content using the following:
•Textbook
 Chapter 5 Review Questions (p. 129)
•Interactive CD-ROM
 Quick Quiz®: Chapter 5
 Flash Cards:
 Terms and Definitions: Chapter 5
 Interactive Troubleshooting Simulations:
 Testing Diodes
 Chapter Reviews: Chapter 5
 Media Clips:
 Diodes
 Testing Diodes
•Study Guide
 Chapter 5 Review Questions (pp. 53 – 58)
 Chapter 5 Activities (pp. 59 – 64)
 Review answers with learners.
EVALUATION
 Evaluate comprehension of chapter content.
•Assessments
Chapter 5 Test (generated from Test Banks on the Resource Guide CD-ROM)
 2012 by American Technical Publishers, Inc.
All rights reserved