Module 7—Introduction to Solid-State Devices and Power Supplies
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FORWARD BIAS is an external voltage that is applied to a PN junction to reduce its barrier
and, therefore, aid current flow through the junction. To accomplish this function, the external voltage is
connected so that it opposes the electrostatic field of the junction.
REVERSE BIAS is an external voltage that is connected across a PN junction so that its
voltage aids the junction and, thereby, offers a high resistance to the current flow through the junction.
The PN JUNCTION has a unique ability to offer very little resistance to current flow in the
forward-bias direction, but maximum resistance to current flow when reverse biased. For this reason, the PN
junction is commonly used as a diode to convert ac to dc.
The PN JUNCTION’S APPLICATION expands many different areas-from a simple voltage protection
device to an amplifying diode. Two of the most commonly used applications for the PN junction are the
SIGNAL DIODE (mixing, detecting, and switching signals) and the RECTIFYING DIODE
(converting ac to dc).
The METALLIC RECTIFIER or dry-disc rectifier is a metal-to-semiconductor device that acts
just like a diode in that it permits current to flow more readily in one direction than the other. Metallic
rectifiers are used in many applications where a relatively large amount of power is required.
DIODE CHARACTERISTICS is the information supplied by manufacturers on different types of
diodes, either in their manuals or on specification sheets.
DIODE RATINGS are the
limiting value of operating conditions of a diode. Operation of the diode outside of its operating limits could
damage the diode. Diodes are generally rated for: MAXIMUM AVERAGE FORWARD CURRENT, PEAK
RECURRENT FORWARD CURRENT, MAXIMUM SURGE CURRENT, and PEAK REVERSE VOLTAGE.
The SEMICONDUCTOR IDENTIFICATION SYSTEM is an
alphanumerical code used to distinguish one semiconductor from another. It is used for diodes, transistors, and
many other special semiconductor devices.
DIODE MARKINGS are letters and symbols placed on the diode by manufacturers to distinguish
one end of the diode from the other. In some cases, an unusual shape or the addition of color code bands is used
to distinguish the cathode from the anode.
The STANDARD DIODE COLOR CODE SYSTEM serves two purposes
when it is used: (1) it identifies the cathode end of the diode, and (2) it also serves to identify the diode by
DIODE MAINTENANCE is the procedures or methods used to keep a diode in good operating
condition. To prevent diode damage, you should observe standard diode safety precautions and ensure that diodes
are not subjected to heat, current overloads, and excessively high operating voltages.
DIODE can be accomplished by using an ohmmeter, the substitution method, or a dynamic diode tester. The
most convenient and quickest way of testing a diode is with an ohmmeter.
ANSWERS TO QUESTIONS Q1. THROUGH Q36.
A1. An electronic device
that operates by virtue of the movement of electrons within a solid piece of semiconductor material.
It is the decrease in a semiconductor’s resistance as temperature rises.
A3. Space systems, computers,
and data processing equipment.
A4. The electron tube requires filament or heater voltage, whereas the
semiconductor device does not; consequently, no power input is spent by the semiconductor for conduction.
A5. Anything that occupies space and has weight. Solid, liquid, and gas.
A6. The atom.
Electrons-negative, protons-positive, and neutrons-neutral.
A8. The valence shell.
A10. A negatively charged atom having more than its normal amount of electrons.
A11. The energy
levels of an atom in a solid group together to form energy bands, whereas the isolated atom does not.
A12. The width of the forbidden band.
A13. The number of electrons in the valence shell.
A14. Covalent bonding.
A15. Electron flow and hole flow.
A17. P-type crystal.
A19. To convert
alternating current into direct current.
A20. Toward the arrow.
A23. N-type material.
A24. Depletion region.
A27. Any device that draws current.
A28. A pulsating dc voltage.
A30. Forward bias.
A31. A characteristic curve.
A32. They are
the limiting values of operating conditions outside which operations could cause diode damage.
A36. The diode is open or has a high-forward
Introduction to Matter, Energy, and Direct Current, Introduction
to Alternating Current and Transformers, Introduction to Circuit Protection,
Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques,
and Schematic Reading, Introduction to Generators and Motors,
Introduction to Electronic Emission, Tubes, and Power Supplies,
Introduction to Solid-State Devices and Power Supplies,
Introduction to Amplifiers, Introduction to
Wave-Generation and Wave-Shaping Circuits, Introduction to Wave Propagation, Transmission
Lines, and Antennas, Microwave Principles,
Modulation Principles, Introduction to Number Systems and Logic Circuits, Introduction
to Microelectronics, Principles of Synchros, Servos, and Gyros,
Introduction to Test Equipment, Radio-Frequency
Communications Principles, Radar Principles, The Technician's Handbook,
Master Glossary, Test Methods and Practices, Introduction to Digital Computers,
Magnetic Recording, Introduction to Fiber Optics