BEX100 - Basic Electricity
Semiconductors
Diodes
Unit Objectives:
• Understanding the materials that make up
a basic diode
• Describe the basic function of a diode
• Define the different types of diodes and
understand their operating principles
• Identify schematic symbols representing
the different types of diodes
• Describe the various applications for
diodes
Introduction
• Semiconductors are a class of material
between conductors and insulators
• Materials such as selenium, copper oxide, and
gallium arsenide, are all semiconductors
• Of the various semiconductor materials
available the two most common are silicon and
germanium
• Many diodes are manufactured from these
two materials
Semiconductors
• Both silicon and germanium have a tight
crystal molecular structure
• In order for these materials to be useful
for the manufacturing of diodes they must
be “doped”
• Doping involves adding another material (an
impurity) to the silicon and germanium in
its molten state
Semiconductors
• The doping of silicon may include the addition
of phosphorus which would result in a “N-Type”
material
• N-Type materials contain an excess of
electrons
• Doping silicon with boron will create a “P-Type”
material
• P-Type materials have an absence of electrons
Semiconductors
• Applying voltage to a doped crystal of
silicon would cause an orderly flow of
electrons from one terminal source of the
voltage to the other
• The higher the content of phosphorus in
the silicon, the more free electrons that
will be available for conduction
Diodes
• Current is only allowed to pass in one direction only
• The schematic symbol for a diode indicates
direction of current flow
• Current always flows from “anode to cathode”
Diode Applications
Rectification
• the conversion of AC current to DC current
Circuit control
• the directing of current flow
Clamping protection
• preventing damage to solid state components
by voltage spikes
• maintaining circuit voltage within a specified
range
Integrated Diode Types
Forward Bias Connection
• Connecting positive
voltage to “P” material
• Negative voltage to “N”
material
• Allows the current to
flow
• When placed in a circuit
the diode is considered
to be “forward biased”
Reverse Bias Connection
• Reversing the polarity of
the power source to the
diode creates a “reverse
bias” connection
• The attraction of the
electrons and holes to the
opposite polarity moves
the holes and electrons
away from the junction
• No current will flow
Diode Operating Principles
•Current will flow if the voltage supplied causes
holes and electrons to congregate at the junction
•Current will not flow if the voltage supplied causes
the junction area to be void of electrons and holes
Diode Rectifiers
• AC current flows first in one
direction and then in another
direction
• Diodes can rectify the AC
current to a DC current
• AC current directed through
the diodes, is forced to flow
through the resistor in the
same direction
• “Full-Wave” rectifiers have
two diodes (forward/reverse
bias) for each alternation
Diode Leakage Current
• A diode connected in a reverse bias
condition will “leak” a very small amount of
current
• Increasing the voltage across the diode will
cause it to reach its “maximum reverse
voltage” or “peak inverse voltage”
• Maximum voltage ratings protect the diode
from damage
Zener Diodes
• Zener diodes are specifically designed to conduct
current in a “reverse bias” condition
• The “P” and “N” materials are heavily “doped” during
manufacturing
• However these diodes will only conduct current at a
predetermined voltage
• Used in “control circuits”
Clamping Diodes
• Clamping diodes “protect”
circuits from surge currents
• Magnetic induction occurs
when current to an
electromagnet is turned off
• Clamping diodes give the
voltage surge a safe path to
follow
• Directs surges away from
sensitive solid state
components
Clamping Diode Operation
LED’s Light Emitting Diodes
• Basically a standard type of
diode
• Contains a small “window”
which allows light to be
emitted when forward
biased
• Usually operates on low
voltages
• Uses less energy than a
conventional bulb
• Creates less heat energy
Testing Diodes
• The “diode test” feature on a DVOM increases
the voltage to the test leads to assure accurate
testing of the diode
Elizabethtown Technical College
Basic Electricity BEXS100/101
Text: STG – Specialized Electronics Training
Diodes