BEX100 - Basic Electricity SemiconductorsDiodes

Unit Objectives: Understanding the materials that make up a basic diodeUnderstanding the materials that make up a basic diode Describe the basic function of a diodeDescribe the basic function of a diode Define the different types of diodes and understand their operating principlesDefine the different types of diodes and understand their operating principles Identify schematic symbols representing the different types of diodesIdentify schematic symbols representing the different types of diodes Describe the various applications for diodesDescribe the various applications for diodes

Introduction Semiconductors are a class of material between conductors and insulatorsSemiconductors are a class of material between conductors and insulators Materials such as selenium, copper oxide, and gallium arsenide, are all semiconductorsMaterials such as selenium, copper oxide, and gallium arsenide, are all semiconductors Of the various semiconductor materials available the two most common are silicon and germaniumOf the various semiconductor materials available the two most common are silicon and germanium Many diodes are manufactured from these two materialsMany diodes are manufactured from these two materials

Semiconductors Both silicon and germanium have a tight crystal molecular structureBoth 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”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 stateDoping 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” materialThe doping of silicon may include the addition of phosphorus which would result in a “N-Type” material N-Type materials contain an excess of electronsN-Type materials contain an excess of electrons Doping silicon with boron will create a “P-Type” materialDoping silicon with boron will create a “P-Type” material P-Type materials have an absence of electronsP-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 otherApplying 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 conductionThe 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 currentthe conversion of AC current to DC current Circuit control the directing of current flowthe directing of current flow Clamping protection preventing damage to solid state components by voltage spikespreventing damage to solid state components by voltage spikes maintaining circuit voltage within a specified rangemaintaining 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 junctionCurrent 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 holesCurrent 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 currentA 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”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 damageMaximum 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