Introduction to Electronic Components

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Experiment 3

INTRODUCTION TO ELECTRONIC COMPONENTS


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Component classificationsComponent classifications

Passive devicesPassive devices

- All electrical devices whichconsume energy are calledpassive devices, like resistors,

inductors and capacitors.

Active devicesActive devices

- Active devices produceenergy that can be used to

provide power gain in anelectronic circuit . This meansthat the power of their outputsignal may be more than


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Introduction to DiodesIntroduction to Diodes

A diode is an electrical deviceallowing current to movethrough it in one directionwith far greater ease than inthe other.

Most diodes are similar inappearance to a resistor andwill have a painted line onone end showing thedirection or flow (white side isnegative). If the negative sideis on the negative end of thecircuit, current will flow. If thenegative is on the positiveside of the circuit no current

will flow.


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N-type and P-typeN-type and P-type

semiconductorssemiconductors

Example: Adding other atomswith 5 valence electrons suchas Antimony(Sb),Arsenic(As)

and Phosporous(P) to Siliconto increase the free electrons.

Example: Adding other atomswith 3 valence electrons suchas Boron(B), Gallium(Ga) andIndium(In) to Silicon to createa deficiency of electrons or

hole charges.

Donor atom

Acceptor atom


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Diode biasingDiode biasing

A forward-biased diodeconducts current and drops asmall voltage across it,

leaving most of the batteryvoltage dropped across thelamp.

If the battery's polarity isreversed, the diode becomesreverse-biased, and drops allof the battery's voltageleaving none for the lamp


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Reverse BiasReverse Bias

If no voltage applied is acrossa semiconductor diode, a thindepletion region existsaround the region of the P-Njunction, preventing currentflow.

If a reverse-biasing voltage isapplied across the P-N

junction, this depletion regionexpands, further resisting anycurrent through it


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Forward BiasForward Bias

If a forward-biasing voltage isapplied across the P-Njunction, the depletion regioncollapses becoming thinner.The diode becomes lessresistive to current through it.

In order for a sustainedcurrent to go through the

diode; though, the depletionregion must be fully collapsedby the applied voltage. Thistakes a certain minimumvoltage to accomplish, calledthe forward voltage.


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I-V characteristicsI-V characteristics

A reverse-biased diodeprevents current from goingthrough it, due to theexpanded depletion region. Inactuality, A very small

amount of current can anddoes go through a reverse-biased diode, called theleakage current, but it can beignored for most purposes.

The ability of a diode towithstand reverse-biasvoltages is limited, as it is forany insulator. If the appliedreverse-bias voltage becomestoo great, the diode willexperience a condition known


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ReviewReview

1. A diode is an electrical component acting as a one-wayvalve for current. When voltage is applied across adiode in such a way that the diode allows current, thediode is said to be forward-biased.

2. When voltage is applied across a diode in such a waythat the diode prohibits current, the diode is said to bereverse-biased.

3. The voltage dropped across a conducting, forward-biased diode is called the forward voltage. Silicon

diodes have a forward voltage of approximately 0.7volts. Germanium diodes have a forward voltage ofapproximately 0.3 volts.

4. The maximum reverse-bias voltage that a diode canwithstand without breaking down


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Introduction to transistorsIntroduction to transistors

A transistor is asemiconductor device,commonly used as anamplifier or an electricallycontrolled switch. The

transistor is the fundamentalbuilding block of the circuitrythat governs the operation ofcomputers, cellular phones,and all other modernelectronics

This section will be mainlyconcerned with the bipolarjunction transistor (BJT).Bipolar junction transistors aresimilar to junction diodes, butone more junction is included.


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Transistor NPN and PNPTransistor NPN and PNP

How to determined NPN orPNP transistor?

When forward biased, the

resistance is low. Duringreverse bias, the resistance ishigh.

PNPNPN

Reference Ohmmeter for Transistors Checking

... RBE REB RBC RCB RCE REC

pnp high low high low high high

npn low* high** low high high high


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Transistor as a switchTransistor as a switch

Transistors can be used ascurrent-controlled switch. Thisis because, a relatively smallflow of electrons sent throughthe base of the transistor hasthe ability to exert controlover a much larger flow ofelectrons through thecollector.

Suppose we had a lamp thatwe wanted to turn on and offby means of a switch.

We need to add somethingmore so that we can havebase current.


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Transistor as a switchTransistor as a switch

Consider this example,where a solar cell is used tocontrol the transistor, whichin turn controls the lamp:

Or, we could use athermocouple to provide thenecessary base current toturn the transistor on:


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Transistors may be used asswitching elements to controlDC power to a load.

The switched (controlled)current goes between emitterand collector, while thecontrolling current goesbetween emitter and base.

When a transistor has zerocurrent through it, it is said to

be in a state ofcutoff(fullynonconducting).

When a transistor hasmaximum current through it,it is said to be in a state of

saturation (fully conducting).

Review


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How does a transformerHow does a transformer

work?work?

A transformer is based on avery simple fact aboutelectricity: when a fluctuatingelectric current flows througha wire, it generates a

magnetic field (an invisiblepattern of magnetism) or"magnetic flux" all around it.

The strength of themagnetism (which has therather technical name ofmagnetic flux density) isdirectly related to the size ofthe electric current. So thebigger the current, the

stronger the magnetic field.


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work?work?

Now there's anotherinteresting fact aboutelectricity too. When amagnetic field fluctuatesaround a piece of wire, it

generates an electric currentin the wire. So if we put asecond coil of wire next to thefirst one, and send afluctuating electric current

into the first coil, we willcreate an electric current inthe second wire.

Faraday's Law:

A changing magetic flux through a

loop of wire induces anelectromotive force (emf : voltage) and

push the current around the circuit.


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work?work?

The current in the first coil isusually called the primarycurrent and the current in thesecond wire is (surprise,surprise) the secondary

current. What we've donehere is pass an electriccurrent through empty spacefrom one coil of wire toanother. This phenomenon is

called electromagneticinduction. We can makeelectrical energy pass moreefficiently from one coil to theother by wrapping them

around a soft iron bar(sometimes called a core):


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Step-down transformerStep-down transformer

If the first coil has more turnsthat the second coil, thesecondary voltage is smallerthan the primary voltage:

This is called a step-downtransformer. If the second coilhas half as many turns as thefirst coil, the secondaryvoltage will be half the size ofthe primary voltage; if the

second coil has one tenth asmany turns, it has one tenththe voltage.

V2/V1 = N2/N1

I2/I1 = N1/N2


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Step-up transformerStep-up transformer

Reversing the situation, wecan make a step-uptransformer that boosts a lowvoltage into a high one:

In a step-up transformer, weuse more turns in thesecondary than in theprimary to get a bigger

secondary voltage and asmaller secondary current.

V2/V1 = N2/N1

I2/I1 = N1/N2


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Transformer at homeTransformer at home

Electronic devices such aslaptop computers andchargers for MP3 players andmobile phones use relativelytiny voltages:

a laptop needs about 15volts,

an iPod charger needs 12volts,

a cellphone typically needs

less than 6 volts when youcharge up its battery.

So electronic appliances likethese have smalltransformers built into them

(often mounted at the end of


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Transformer applicationTransformer application

IronAutomobile Ignition System


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Output power = IV

--------------------

Why is output at low

current and high

voltage, and not

high current and

low voltage?--------------------

Introduction to Electronic Components

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