BEX100 - Basic BEX100 - Basic ElectricityElectricitySemiconductorsSemiconductors

DiodesDiodes

Unit Objectives:Unit Objectives:• Understanding the materials that make Understanding the materials that make

up a basic diodeup a basic diode• Describe the basic function of a diodeDescribe the basic function of a diode• Define the different types of diodes and Define the different types of diodes and

understand their operating principlesunderstand their operating principles• Identify schematic symbols representing Identify schematic symbols representing

the different types of diodesthe different types of diodes• Describe the various applications for Describe the various applications for

diodesdiodes

IntroductionIntroduction• Semiconductors are a class of material Semiconductors are a class of material

between conductors and insulatorsbetween conductors and insulators• Materials such as selenium, copper oxide, Materials such as selenium, copper oxide,

and gallium arsenide, are all and gallium arsenide, are all semiconductorssemiconductors

• Of the various semiconductor materials Of the various semiconductor materials available the two most common are silicon available the two most common are silicon and germaniumand germanium

• Many diodes are manufactured from these Many diodes are manufactured from these two materialstwo materials

SemiconductorsSemiconductors• Both silicon and germanium have a Both silicon and germanium have a

tight crystal molecular structuretight crystal molecular structure• In order for these materials to be useful In order for these materials to be useful

for the manufacturing of diodes they for the manufacturing of diodes they must be “doped”must be “doped”

• Doping involves adding another Doping involves adding another material (an impurity) to the silicon and material (an impurity) to the silicon and germanium in its molten stategermanium in its molten state

SemiconductorsSemiconductors• The doping of silicon may include the The doping of silicon may include the

addition of phosphorus which would result in addition of phosphorus which would result in a “N-Type” materiala “N-Type” material

• N-Type materials contain an excess of N-Type materials contain an excess of electronselectrons

• Doping silicon with boron will create a “P-Doping silicon with boron will create a “P-Type” materialType” material

• P-Type materials have an absence of P-Type materials have an absence of electronselectrons

SemiconductorsSemiconductors

• Applying voltage to a doped crystal of Applying voltage to a doped crystal of silicon would cause an orderly flow of silicon would cause an orderly flow of electrons from one terminal source of electrons from one terminal source of the voltage to the otherthe voltage to the other

• The higher the content of phosphorus in The higher the content of phosphorus in the silicon, the more free electrons that the silicon, the more free electrons that will be available for conductionwill be available for conduction

DiodesDiodes

• Current is only allowed to pass in one direction Current is only allowed to pass in one direction onlyonly

• The schematic symbol for a diode indicates The schematic symbol for a diode indicates direction of current flowdirection of current flow

• Current always flows from “anode to cathode”Current always flows from “anode to cathode”

DiodeDiode ApplicationsApplicationsRectification Rectification • the conversion of AC current to DC currentthe conversion of AC current to DC currentCircuit controlCircuit control • the directing of current flowthe directing of current flowClamping protectionClamping protection• preventing damage to solid state preventing damage to solid state

components by voltage spikes components by voltage spikes • maintaining circuit voltage within a maintaining circuit voltage within a

specified rangespecified range

IntegratedIntegrated Diode TypesDiode Types

Forward Bias Forward Bias ConnectionConnection

• Connecting positive Connecting positive voltage to “P” voltage to “P” materialmaterial

• Negative voltage to Negative voltage to “N” material “N” material

• Allows the current to Allows the current to flowflow

• When placed in a When placed in a circuit the diode is circuit the diode is considered to be considered to be “forward biased”“forward biased”

Reverse Bias Reverse Bias ConnectionConnection

• Reversing the polarity of Reversing the polarity of the power source to the the power source to the diode creates a “reverse diode creates a “reverse bias” connectionbias” connection

• The attraction of the The attraction of the electrons and holes to the electrons and holes to the opposite polarity moves opposite polarity moves the holes and electrons the holes and electrons away from the junctionaway from the junction

• No current will flowNo current will flow

Diode Operating Diode Operating PrinciplesPrinciples

•Current will flowCurrent will flow if the voltage supplied causes if the voltage supplied causes holes and electrons to congregate at the holes and electrons to congregate at the junctionjunction•Current will not flowCurrent will not flow if the voltage supplied if the voltage supplied causes the junction area to be void of electrons causes the junction area to be void of electrons and holesand holes

Diode RectifiersDiode Rectifiers• AC current flows first in one AC current flows first in one

direction and then in direction and then in another directionanother direction

• Diodes can rectify the AC Diodes can rectify the AC current to a DC currentcurrent to a DC current

• AC current directed through AC current directed through the diodes, is forced to flow the diodes, is forced to flow through the resistor in the through the resistor in the same directionsame direction

• ““Full-Wave” rectifiers have Full-Wave” rectifiers have two diodes (forward/reverse two diodes (forward/reverse bias) for each alternationbias) for each alternation

Diode Leakage CurrentDiode Leakage Current• A diode connected in a reverse bias A diode connected in a reverse bias

condition will “leak” a very small amount condition will “leak” a very small amount of currentof current

• Increasing the voltage across the diode Increasing the voltage across the diode will cause it to reach its “maximum will cause it to reach its “maximum reverse voltage” or “peak inverse voltage”reverse voltage” or “peak inverse voltage”

• Maximum voltage ratings protect the Maximum voltage ratings protect the diode from damagediode from damage

Zener DiodesZener Diodes

• Zener diodes are specifically designed to conduct Zener diodes are specifically designed to conduct current in a “reverse bias” conditioncurrent in a “reverse bias” condition

• The “P” and “N” materials are heavily “doped” The “P” and “N” materials are heavily “doped” during manufacturingduring manufacturing

• However these diodes will only conduct current at However these diodes will only conduct current at a predetermined voltagea predetermined voltage

• Used in “control circuits”Used in “control circuits”

Clamping DiodesClamping Diodes

• Clamping diodes “protect” Clamping diodes “protect” circuits from surge currentscircuits from surge currents

• Magnetic induction occurs Magnetic induction occurs when current to an when current to an electromagnet is turned offelectromagnet is turned off

• Clamping diodes give the Clamping diodes give the voltage surge a safe path voltage surge a safe path to followto follow

• Directs surges away from Directs surges away from sensitive solid state sensitive solid state componentscomponents

Clamping Diode Clamping Diode OperationOperation

LED’s Light Emitting LED’s Light Emitting DiodesDiodes

• Basically a standard type Basically a standard type of diodeof diode

• Contains a small Contains a small “window” which allows “window” which allows light to be emitted when light to be emitted when forward biasedforward biased

• Usually operates on low Usually operates on low voltagesvoltages

• Uses less energy than a Uses less energy than a conventional bulbconventional bulb

• Creates less heat energyCreates less heat energy

Testing DiodesTesting Diodes

• The “diode test” feature on a DVOM The “diode test” feature on a DVOM increases the voltage to the test leads to increases the voltage to the test leads to assure accurate testing of the diodeassure accurate testing of the diode

Elizabethtown Technical CollegeElizabethtown Technical CollegeBasic Electricity BEXS100/101Basic Electricity BEXS100/101

Text: Text: STG – Specialized Electronics TrainingSTG – Specialized Electronics TrainingDiodesDiodes