lecture 1 sharil
Post on 06-Apr-2018
221 Views
Preview:
TRANSCRIPT
-
8/3/2019 Lecture 1 Sharil.
1/24
Chapter 1INTRODUCTION
-
8/3/2019 Lecture 1 Sharil.
2/24
Learning Outcomes
explained the basic structure of atoms
Differentiated the properties of insulators,conductors, and semiconductors
Understand covalent bonding
Identify the properties of both p and ntype materials
Understand both forward and reverse
biasing of a p-n junction
Explained the basic operation of a diode
At the end of this topic, students should be able to:
-
8/3/2019 Lecture 1 Sharil.
3/24
Bohr model of an atom
As seen in thismodel, electronscircle the nucleus.Atomic structureof a materialdetermines itsability to conduct
or insulate.
-
8/3/2019 Lecture 1 Sharil.
4/24
The ability of a material to conduct current isbased on its atomic structure.
The orbit paths of the electrons surrounding
the nucleus are called shells.
The less complete a shell is filled to capacity themore conductive the material is.
Each shell has a defined number of electrons itwill hold. This is a fact of nature and can bedetermined by the formula, 2n2.
The outer shell is called the valence shell.
Consist of 3 partical: electron (-ve charged),proton (+ve charged), neutron (uncharged)
-
8/3/2019 Lecture 1 Sharil.
5/24
Ionization
The process of losing a valenceelectron
Atom loses its valence electronand becomes a positive ion
Escaped valence electron , the
atom becomes a negative ion
-
8/3/2019 Lecture 1 Sharil.
6/24
Conductor easily conducts electrical current . Singleelement material, such as copper, silver gold andaluminum
Insulator - does not conduct electrical current
Semiconductor pure (intrinsic) state is neither a goodconductor nor a good insulator, such as silicon,germanium and carbon. Characterized by atoms withfour valence electrons
Conductor, Insulator, and Semiconductor
-
8/3/2019 Lecture 1 Sharil.
7/24
The valence shell determines the ability of material toconduct current.
A Copper atom has only 1 electron inits valence ring. This makes it agood conductor. It takes 2n2
electrons or in this case 32 electronsto fill the valence shell.
A Silicon atom has 4 electrons in itsvalence ring. This makes it asemiconductor. It takes 2n2 electrons
or in this case or 18 electrons to fillthe valence shell.
Conductors, Insulators, and Semiconductors
-
8/3/2019 Lecture 1 Sharil.
8/24
Covalent Bonding
Covalent bonding is a bonding of two or more atoms by the
interaction of their valence electrons to strengthen and stablingthe atom bonding structure.
-
8/3/2019 Lecture 1 Sharil.
9/24
Certain atoms will combine in this way to form a crystal
structure. Silicon and Germanium atoms combine in thisway in their intrinsic or pure state.
Covalent Bonding
-
8/3/2019 Lecture 1 Sharil.
10/24
N-type and P-type Semiconductors
Other atoms with 5 electrons suchas Antimony are added to Silicon toincrease the free electrons.
Other atoms with 3 electrons such asBoron are added to Silicon to create adeficiency of electrons or hole charges.
The process of creating N and P type materials is called
doping. Will improve the electrical characteristics of Si & Ge
N-type P-type
-
8/3/2019 Lecture 1 Sharil.
11/24
Introduction
Forward bias
Current flows
Reverse Bias
No current flow
The basic function of a diode is to restrict current flow to one
direction. Constructed by joining an n and p type material together.
-
8/3/2019 Lecture 1 Sharil.
12/24
The Depletion Region
With the formation of the p
and n materials combinationof electrons and holes at thejunction takes place.
This creates the depletion
region and has a barrierpotential. This potentialcannot be measured with avoltmeter but it will cause asmall voltage drop.
p region n region p region n region
-
8/3/2019 Lecture 1 Sharil.
13/24
Forward and Reverse Bias
Voltage source or bias connections are+ to the p material and to the nmaterial
Bias must be greater than .3 V forGermanium or .7 V for Silicon diodes.
The depletion region narrows.
Voltage source or bias connections areto the p material and + to the n material
Bias must be less than the break downvoltage.
Current flow is negligible in most cases.
The depletion region widens.
Forward Bias Reverse Bias
-
8/3/2019 Lecture 1 Sharil.
14/24
Forward Bias Measurements With SmallVoltage Applied
In this case withthe voltage
applied is lessthan the barrierpotential so thediode for allpractical purposes
is still in a non-conducting state.Current is verysmall.
-
8/3/2019 Lecture 1 Sharil.
15/24
Forward Bias Measurements With AppliedVoltage Greater Than the Barrier Voltage.
With the appliedvoltageexceeding thebarrier potentialthe now fullyforward biaseddiode conducts.
Note that theonly practical lossis the .7 Voltsdropped acrossthe diode.
-
8/3/2019 Lecture 1 Sharil.
16/24
Ideal Diode Characteristic Curve
In thischaracteristiccurve we do notconsider thevoltage drop orthe resistiveproperties. Currentflow proportionally
increases withvoltage.
-
8/3/2019 Lecture 1 Sharil.
17/24
Practical Diode Characteristic Curve
In most cases weconsider only theforward bias voltagedrop of a diode. Once
this voltage isovercome the currentincreasesproportionally withvoltage.This drop isparticularly importantto consider in lowvoltage applications.
-
8/3/2019 Lecture 1 Sharil.
18/24
Complex Characteristic Curve of a Diode
The voltage dropis not the onlyloss of a diode.In some caseswe must takeinto accountother factorssuch as the
resistive effectsas well asreversebreakdown.
-
8/3/2019 Lecture 1 Sharil.
19/24
Troubleshooting DiodesTesting a diode is quite simple, particularly if the multimeter
used has a diode check function. With the diode check functiona specific known voltage is applied from the meter across thediode.
K A A K
With the diode check
function a good diode willshow approximately .7 V or.3 V when forward biased.
When checking in reversebias the full applied testingvoltage will be seen on thedisplay.
-
8/3/2019 Lecture 1 Sharil.
20/24
Troubleshooting Diodes
An ohmmeter can be used to check theforward and reverse resistance of a diode if
the ohmmeter has enough voltage to force thediode into conduction. Of course, in forwardbiased connection low resistance will be seenand in reverse biased connection highresistance will be seen.
-
8/3/2019 Lecture 1 Sharil.
21/24
Troubleshooting Diodes
Open Diode
In the case of an open diodeno current flows in eitherdirection which is indicated by the full checking voltagewith the diode check function or high resistance using an
ohmmeter in both forward and reverse connections.
Shorted Diode
In the case of a shorted diodemaximum current flowsindicated by a 0 V with the diode check function or lowresistance with an ohmmeter in both forward and reverseconnections.
-
8/3/2019 Lecture 1 Sharil.
22/24
Diode Packages
Diodes come in a variety of sizes and shapes. Thedesign and structure is determined by what type ofcircuit they will be used in.
-
8/3/2019 Lecture 1 Sharil.
23/24
Summary
P-materials are doped with trivalent impurities
N-materials are doped with pentavalent impurities
P and N type materials are joined together to form aPN junction.
A diode is nothing more than a PN junction.
At the junction a depletion region is formed. Thiscreates barrier which requires approximately .3 V for a
Germanium and .7 V for Silicon for conduction to takeplace.
Diodes, transistors, and integrated circuits areall made of semiconductor material.
-
8/3/2019 Lecture 1 Sharil.
24/24
Summary
When reversed biased a diode can only withstandso much applied voltage. The voltage at which
avalanche current occurs is called reverse breakdownvoltage.
There are three ways of analyzing a diode. Theseare ideal, practical, and complex. Typically we use a
practical diode model.
A diode conducts when forward biased and does notconduct when reverse biased
top related