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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

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Bex100 basic electricity

BEX100- Basic Electricity



Unit objectives
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


  • 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


  • 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


  • 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


  • 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


  • 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
Diode Applications


  • 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

Forward bias connection
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
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

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
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
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

  • 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

  • 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

Led s light emitting diodes
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
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 CollegeBasic Electricity BEXS100/101Text: STG – Specialized Electronics TrainingDiodes