Electronics Fundamentals - I.doc

7/27/2019 Electronics Fundamentals - I.doc

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Electronics Fundamentals 1The Solid State

Conductors, Insulators and SemiconductorsMobile electrons and holes:For a material to conduct electricity, it must contain charges that are free to move whena potential difference is applied across it. These are known as mobile or free electrons.It is important to recognize that when an electron moves from a valence band into aconduction band it leaves a vacant site, or hole, in valence band. This hole can bethought of as a positive charge and also act as a current carrier.

Electrons move in holes because these holes are like vacant positions where somethingshould be fill up. The hole therefore appears to move through the material in responseto an external electric field or voltage. In a pure semiconductor crystal, there are equalnumber of holes and free electrons.

Metals: The ConductorsThere are very few electrons in metal conductors in their upper energy level or valenceband. Therefore, if we give an electron some additional energy by applying a potentialacross the conductor, the electron will still be apply to occupy a higher allowed energywithin the valence band. In metals the valence electrons easily move under theinfluence of an electric field and in a sense behave like a gas.Materials such as copper, silver and aluminum are therefore good conductors. In metals,only the outermost valence electrons, which are most weakly bound to the atom, carrythe current.Good conducting materials are Silver, Copper, Gold, Aluminum, and Mercury.
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Insulators:Materials such as glass, rubber and ceramic are good insulators. Insulators have no freeelectron but little bit. Their uppermost energy band completely filled. The electrons arefirmly bound in the valence band and no conduction occurs. Some electrons are free tomove, but number is small comparing conductors.Semiconductors:A third class of materials, known as semiconductors, having properties betweeninsulators and conductors. Silicon and germanium are two common semiconductors.These materials are poor to conduct at low temperature, but as the temperature risesmore electrons become free and carry the current and they begin to conduct.

As some semiconductors readily absorb light energy many are black (Silicon, GaAs,Galena) though with some shine.The conductivity of semiconductors therefore rises with temperature and light intensity.This is the opposite effect to that found in good conductors where the resistance to the

follow of current increases with increasing temperature and definitely in such situationconductivity decreases.
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CONDUCTORS, RESI STORS ,INSULATORS AND COLOR CODES

Electromagnetic Spectrum

DIODESDiodes are usually made from semiconductor materials, Silicon and Germanium being

the most common. Early types of semiconductor diodes were made from Selenium andGermanium, but Silicon is used today for the vast majority of devices. Seleniumrectifier diodes may be found in antique radios but are obsolete and are normallyreplaced by modern silicon types. Some germanium types are still used however,because of a number of useful properties that germanium possesses and silicon doesnot, although specialized types of silicon diodes are taking over uses previously given togermanium diodes.Figure 1. Diodes


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1. Germanium point contact diode 2. Silicon rectifier diode 3. Silicon high voltage (800V) switching diode 4. EHT (20kV) rectifier diode

5. Silicon bridge rectifier diode

A diode is a one-way conductor. It has two terminals, the anode or positive terminal andthe cathode or negative terminal. Basically a diode will only pass current when its anodeis made more positive than its cathode.In Figure 1 above, the cathode on the single diodes (numbered 1,2,3 and 4) is indicatedby a band around one end of the diode. In the circuit symbols shown in Figure 2, thecathode is shown as a bar and the anode as a triangle. The positive and negative (plusand minus) symbols shown on the Bridge rectifier (No.5) indicate the polarity of the DC

output and not the anode or cathode of the device.Fig 2. Diode Circuit Symbols.

Which way does current flow?Conventional current flows from the positive (anode) terminal to the negative (cathode)terminal although the movement of electrons is in the opposite direction, from cathodeto anode.Fig 3. Conventional current flow through a diode.

Diodes are the simplest of all the semiconductor devices, but have a very widerange of uses, including:

Rectification changing A.C. power to D.C. power. Demodulation recovering audio or video information from radio signals. Illumination light emitting diodes, made from materials such as Gallium


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Phosphide rather than silicon, replace filament lamps in many applications. Stabilisation. Zener diodes can be used to set very precise voltage values insuch circuits as d.c. power supplies. Protection diodes can be used to protect circuits from being damaged by suchthings as wrong polarity supply connection, and abnormally high voltages orcurrents.Diodes are made from two differently doped layers of semiconductor material that

form a "PN junction".*The P type material has a surplus of positive charge carriers (holes) and the N type,a surplus of electrons.*Between these layers, where the P type and N type materials meet, holes andelectrons combine, with excess electrons combining with excess holes to cancel eachother out, so a thin layer is created that has neither positive nor negative chargecarriers present.

Since there are no charge carriers in this Depletion Layer no current can flowacross it.*In effect a small natural potential is set up within the semiconductor material thathas an opposite polarity to the P and N type layers, and because of this narrow band ofreversed potential, no current can flow through the diode.

*When a voltage is applied across the junction however, so that the P type anode ismade positive and the N type cathode negative, provided that the applied voltage isgreater than the natural junction potential of the depletion layer, the positive holes areattracted across the depletion layer towards the negative cathode, also the negativeelectrons are attracted towards the positive anode and current flows.

When the diode is reverse biased (the anode connected to negative and the cathodeto the positive voltage), the positive holes are attracted towards the negative voltageand away from the junction. Likewise the negative electrons are attracted away fromthe junction towards the positive voltage applied to the cathode. This action leaves agreater area at the junction without any charge carriers (either positive or negative)

left. This causes the depletion layer to widen. It is depleted of charge carriers and so isan insulator. As higher voltages are applied in reverse polarity to the diode, thedepletion layer becomes wider still, since the applied voltage is attracting more chargecarriers away from it. The diode will not conduct with a reverse voltage (a reverse bias)applied. Once the voltage is applied in the forward direction (positive to anode andnegative to cathode) again, current will flow; in this case as the voltage is increasedmore current flows. The increase in current does not follow a straight-line relationship,as it would do if the voltage was being increased across a resistor. To begin with nocurrent flows until the applied voltage reaches the "junction potential". Once this isovercome (at about 0.15V for germanium diodes and about 0.6V for silicon), current

rises sharply as the diode conducts.Diode I / V CharacteristicsThe operation of diodes (as with other semiconductor devices) is often described by aspecial graph called a "characteristic curve". These graphs show the relationshipbetween the currents and voltages associated with the different terminals of the device.An understanding of these graphs helps in understanding how the device operates.For diodes the characteristic curve is called an I / V curve because it shows therelationship between the voltage applied between the anode and cathode, and theresulting current flowing through the diode. A typical I / V characteristic is shown inFigure 4.

Fig 4. Typical Diode I / V Characteristic


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The axes of the graph show both positive and negative values and so intersect at thecentre. The intersection has a value of zero for both current (the Y axis) and voltage(the X axis). The axes +I and +V (top right) show the current rising steeply after an

initial zero current area. This is the forward conduction of the diode when the anode ispositive and cathode negative. Initially no current flows until the applied voltage is atabout the forward junction potential, after which current rises steeply showing that theforward resistance (I / V) of the diode is very low; a small increase in voltage giving alarge increase in current.The -V and -I axes show the reverse biased condition (bottom left). Here, although thevoltage increases, hardly any current flows. This small current is called the leakagecurrent of the diode and is typically only a few micro-amps with germanium diodes andeven less in silicon. If a high enough reverse voltage is applied however, there is a point(called the reverse breakdown voltage) where the insulation of the depletion layerbreaks down, and a very high current suddenly flows. In most diodes this breakdown ispermanent and a diode subjected to this high reverse voltage will be destroyed. InZener diodes however, this point is used to give the diode its special ability to stabilisethe applied voltage: If the voltage increases at this point heavy current flows andreduces the voltage. The breakdown in a Zener diode is not destructive due to its specialconstruction.

OHMS LAWOhms, Volts & Amperes.The resistance of a conductor is measured in Ohms and the Ohm is a unit named after

the German physicist George Simon Ohm (1787-1854) who was the first to show therelationship between resistance, current and voltage. In doing so he devised his lawwhich shows the inter-relationship between the three basic electrical properties ofresistance, voltage and current. It demonstrates one of the most important relationshipsin electrical and electronic engineering.Ohms Law states that: "In metallic conductors at a constant temperature andin a zero magnetic field, the current flowing is proportional to the voltageacross the ends of the conductor, and is inversely proportional to theresistance of the conductor."In simple terms, provided that the temperature is constant and the electrical circuit is

not influenced by magnetic fields, then: With a circuit of constant resistance, the greater the voltage applied to a circuit, themore current will flow. With a constant voltage applied, the greater the resistance of the circuit, the lesscurrent will flow.Notice that Ohms law states "In metallic conductors" This means that the law holds


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good for materials which are basically metal, but there are some materials (mainly non-metals) to which Ohms Law does not strictly apply. Here however, in talking aboutOhms Law, these nonmetals will not be discussed.Rather than trying to remeber the whole of Ohms law, the three electrical properties ofvoltage, current and resistance by single letters:Resistance is indicated by the letter R and is measured in units of Ohms, which have thesymbol (Greek capital O).Voltage is indicated by the letter V (or sometimes E, especially in the USA) and ismeasured in units of Volts, which have the symbol V.Current is given the letter I (we don't use C as this is used for Capacitance)and ismeasured in units of Amperes (often shortened to Amps), which have the symbol A.By using the letters V, I and R to express the relationships defined in Ohms Law givesthree simple formulae:

Each of which shows how to find the value of any one of these quantities in a circuit,provided the other two are known. For example, to find the voltage V (in Volts) across aresistor, simply multiply the current I (in Amperes) through the resistor by the value of

the resistor R(in Ohms).

Note that when using these formulae the values ofV I and Rwritten into theformula must be in its BASIC UNIT i.e. VOLTS (not millivolts) Ohms (not kilohms) andAMPERES (not micro Amperes )etc.

Briefly 15K (kilohms) is entered as 15 EXP 03 and 25mA (milliAmperes) is enteredas 25 EXP -03 etc. This is easiest to do using a scientific calculator.How to use your calculator with the engineering notation used extensively in electronicsis explained in our free booklet entitled "Maths Tips" Download it here. or from our

Download pageDEFINITIONS.1 OHM

"The amount of resistance that will produce a potential difference (p.d.) or voltageof1 Volt across it when a current of1 Ampere flowing through it."1 AMPERE

"The amount of current which, when flowing through a resistance of1 Ohm willproduce a potential difference of1 Volt across the resistance."

(Although more useful definitions of an ampere are available)1 VOLT

"The difference in potential (voltage) produced across a resistance of1 Ohmthrough which a current of1 Ampere is flowing."

(Again alternative definitions using other quantities can also be used)

CURRENT & VOLTAGECurrent & Voltage in Resistor NetworksFinding the UnknownIn addition to working out the resistance, Ohms law can be used to work out voltagesand currents in resistor networks. Before trying this it would be a good idea to look at

some basic facts about resistor networks.
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In a SERIES CIRCUIT the same current flows through all components. Each componenthowever, will have a different VOLTAGE (p.d.) across it. The sum of these individualvoltages (VR1+VR2+VR3 etc) in a series circuit is equal to the supply voltage (EMF).In a PARALLEL CIRCUIT the same voltage is present across all components but adifferent CURRENT can flow through each component. The sum of these individualcomponent currents in a parallel circuit is equal to the supply current. (IS = IR1+ IR2+IR3 etc.)

The Potential Divider RuleIf two or more resistors are connected in series across a potential (e.g. A supplyvoltage), the voltage across each resistor will be proportional to the resistance of thatresistor. VR1 R1 and VR2 R2 etc.To calculate the voltage across any resistor in the potential divider, multiply the supplyvoltage (E) by the proportion of that resistor to the total resistance of all the resistors.For example if R2 is double the value of R1 there will be twice the voltage across R2 thanacross R1. It follows therefore, that the voltage across R1 will be one third of the supplyvoltage (E) and the voltage across R2 will be two thirds of the supply voltage (E). So, ifthe supply voltage and the resistor values are known, then the voltage across eachresistor can be worked out by PROPORTION, and once the voltage across each resistoris known the voltage at any point in the circuit can be calculated.


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RESISTORSResistor ConstructionResistors are components having a stated value of RESISTANCE. Many types of resistorsare used having different uses and construction. The most common types have a fixedvalue of resistance so are often called fixed resistors. They are shown on circuitschematic diagrams (theoretical diagrams that show how the circuit components areconnected electrically, rather than what a circuit looks like physically) using one of thefollowing symbols.

Various types of fixed resistors are used in circuits, they are the most numerous of allelectronic components and their most common job is to reduce voltages and currentsaround a circuit so that "active components", transistors and integrated circuits forexample, that carry out tasks such as producing or amplifying signals within the circuitare supplied with the correct voltages and currents to work properly.Resistors are also used in conjunction with other components such as inductors and

capacitors to process signals in many ways.Because resistors are "passive components" they cannot amplify or increase voltagescurrents or signals, they can only reduce them. Nevertheless they are a most essentialpart of any electronic circuit.

SMT (Surface Mount Technology)Many modern circuits use SMT resistors. Their manufacture involves depositing a film of

resistive material such as tin oxide on a tiny ceramic chip. The edges of the resistor arethen accurately ground, or cut with a laser to give a precise resistance (which dependson the width of the resistor film), across the ends of the device. Tolerances may be aslow as 0.02%. Contacts at each end are soldered directly onto the conductive print onthe circuit board, usually by automatic assembly methods. SMT resistors normally havea very low power dissipation. Their main advantage is that very high component densitycan be achieved.


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Voltage Doubler CircuitTo make a voltage doubler circuit only two capacitors and two diodes are requiredcosting pennies each. The circuit diagram is displayed below:

Voltage TriplerA voltage tripler or other larger voltage multiplier can be built by extending thevoltage doubler circuit. One extra capacitor and a diode are required for each increase inmultiple - therefore a tripler has a total of three capacitors and three diodes as shownbelow.

Bridge Rectifier:-For most alternative energy applications, we require a direct current (DC) voltage to begenerated - for example to charge a bank of batteries. However wind turbines and wavepower generators create an alternating current (AC) voltage. This is where the BridgeRectifier comes in. The AC voltage generated is passed through a circuit of four diodesarranged as shown below and emerged converted into a more useful DC output.

Diodes allow electricity to flow in only one direction, but there is a small voltage lostacross the a diode of 0.7V called the forward voltage drop. If the diode is wired in thewrong direction then no current (actually a very tiny current) flows across the diode.However, if the voltage is too high and goes over the diode's maximum reversevoltage, the diode will breakdown and fail.

If you would like to make your own bridge rectifier then the 1N4001 diode is perfect formost low voltage circuits where the current is less than 1A. The 1N5401 diode is usedwhere the maximum current is 3A.
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A positive clipper circuit passes a positive input signal voltage below its threshold andoutputs a constant voltage for an input signal voltage above its threshold. A negativeclipper does the same thing for negative voltages.

It is often implemented with diodes.

It's effect on a sine wave is to flatten the peaks.Clipper circuit consist of a diode and a resistor.Depending upon the direction of the diode(forward of reversed biased),it acts as a openswitch(reversed biased) or closed switch(forward biased).Which can clipp the positive or

negative part of input signal at the output.It is used in wave shaping, basically a rectifier circuit...msg

Clipper (electronics)

In electronics, a clipper is a device designed to prevent the output of a circuit fromexceeding a predetermined voltage level without distorting the remaining part of theapplied waveform.

A clipping circuit consists of linear elements like resistors and non-linear elements like

junction diodes or transistors, but it does not contain energy-storage elements likecapacitors. Clipping circuits are used to select for purposes of transmission, that part ofa signal wave form which lies above or below a certain reference voltage level.

Thus a clipper circuit can remove certain portions of an arbitrary waveform near thepositive or negative peaks. Clipping may be achieved either at one level or two levels.Usually under the section of clipping, there is a change brought about in the wave shapeof the signal.

Clipping Circuits are also called as Slicers, amplitude selectors or limiters.

Zener Diode
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In the example circuits above, one or two zener diodes are used to clip the voltage VIN.In the first circuit, the voltage is clipped to the reverse breakdown voltage of the zenerdiode. In the second, it is limited to the reverse breakdown voltageplus the voltagedrop across one zener diode.

[edit] Application

It is used in television sets and FM receivers. It is also used for amplifiers and differenttypes of op-amps through which it is possible to perform mathematical operations.

[edit] Classification

Clippers may be classified into two types based on the positioning of the diode. [1]

Shunt Clippers, where the diode is in series with the load resistance, and Series Clippers, where the diode in shunted across the load resistance.

The diode capacitance affects the operation of the clipper at high frequency andinfluences the choice between the above two types. High frequency signals areattenuated in the shunt clipper as the diode capacitance provides an alternative path tooutput current. In the series clipper, clipping effectiveness is reduced for the samereason as the high frequency current passes through without being sufficiently blocked.

Clippers may be classified based on the orientation(s) of the diode. The orientationdecides which half cycle is affected by the clipping action.

Positive Diode Clipper Negative Diode Clipper

The clipping action can be made to happen at an arbitrary level by using a biasingelements (potential sources) in series with the diode.

Positively Biased Diode Clipper Negatively Biased Diode Clipper

The signal can be clipped to between two levels by using both types of diode clippers incombination. [2] This clipper is referred to as

Combinational Diode Clipper or Two-Level Clippers

The clamping network is the one that will "clamp" a signal to a different dc level. Thenetwork must have capacitor, a diode, and a resistive element, but it also employs anindependent dc supply to introduce an additional shift.
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SWITCHES

Question 1:

What is the purpose of the switch shown in this schematic diagram?

Question 2:

How is an electrical switch constructed? What goes on inside the switch that actually"makes" or "breaks" a path for electric current?

What difference will it make if the switch is located in either of these two alternatelocations in the circuit?

Does this switch (in the closed state) have a low resistance or a high resistance between

its terminals?

How might you use a meter (or a conductivity/continuity tester) to determine whetherthis electrical switch is in the open or closedstate?

Identify the following types of switches, according to the number of "poles" and"throws" each switch has:


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Identify the following types of switches, according to their style of actuation (how each

switch is physically operated):

What type of switch is represented by this schematic symbol?

What type of switch is represented by this schematic symbol?


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Question 10:

What positions do the switches have to be in for the light bulb to receive power?

Question 11:

Electric motors of thepermanent magnetdesign are very simple to reverse: just switchthe polarity of the DC power to the motor, and it will spin the other direction:

Complete this schematic diagram, showing how a DPDT switch may be placed in thiscircuit to reverse the motor's direction of rotation without the need to disconnect and re-connect wires:

Question 12:

What will the light bulb do when the switch is open, and when the switch is closed?


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Question 13:

Examine this schematic diagram:

Now, without moving the following components, show how they may be connectedtogether with wires to form the same circuit depicted in the schematic diagram above:

Question 14:

What does the normalstatus of an electrical switch refer to? Specifically, what is the

difference between a normally-open switch and a normally-closedswitch?

Question 15:

Identify the "normal" status of each switch, whether it is normally-open (N.O.) ornormally-closed(N.C.):

Based on the symbols shown, describe what physical condition results in the switchcontacts being open, and what condition results in the switch contacts being closed, foreach switch.


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Question 16:

Identify the "normal" status of each switch, whether it is normally-open (N.O.) ornormally-closed(N.C.):

Based on the symbols shown, describe what physical condition results in the switchcontacts being open, and what condition results in the switch contacts being closed, foreach switch.

1-This device is known as a switch, and its purpose in this circuit is to establish orinterrupt the electrical continuity of the circuit in order to control the light bulb.

2-Switches typically use metal contacts that are touched together or moved apart by

some sort of actuating lever, shaft, or other mechanical assembly.

This is a selectorswitch of the break-before-make variety.

This is a selectorswitch of the make-before-breakvariety

For the light bulb to be energized, both switches must either be in the p" position, or inthe "down" position.

Notes:DPDT switches are often used as polarity-reversal devices. No doubt your students willsee (or build!) this switch arrangement some time in their careers.


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When the switch is closed, the light bulb will receive full voltage from the battery. Whenthe switch is open, the light bulb will receive less voltage (and correspondingly, lesscurrent).

The "normal" status of a switch refers to the open or closed status of the contacts whenthere is no actuating force applied to the switch.

Temperature switch: cold= contacts closed, hot= contacts open

Pushbutton switch: unpressed= contacts closed,pressed= contacts open

Pressure switch: no applied pressure = contacts open,pressure applied= contactsclosed

Limit switch: untouched= contacts open, mechanical force = contacts closed

Flow switch: no fluid flow= contacts open, fluid flow= contacts closed

Level switch: dry (hanging in air) = contacts closed, submerged= contacts open

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Electronics Fundamentals - I.doc