3 electronic components

8/2/2019 3 Electronic Components

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Resistors,

Capacitors,

Diodes


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Electronic Components

Resistors

Capacitors Diodes


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Resistors

Resistors resist the flow of electricityA resistor is used when we don't want a fullcurrent flowing through all parts of a circuit


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A resistor is a piece of material that

obeys Ohm's Law. R=V/I


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Uses for Resistors

Control the current flowing from one part of a circuit

to another.Convert electrical energy into heat or light.

For example:

Electric heaters.

Electric lamps.


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Resistance Summary

Resistance resists the flow of current.

Resistance is determined by a conductor'satoms, length and area.

A resistor is a component designed to reducethe flow of current.

Resistors are used to control the flow of currentthrough a circuit or to convert energy intoheat and light.


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Variable Resistors

Resistance increases withincreasing length. It ispossible to use this effectto build a variable resistor.

Resistance can be altered bychanging the length ofresistor in the circuit.

Rotating the knob alters thelength, and in turn theresistance.


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Variable Resistor Uses

Varying resistance in a circuit will

increase or decrease the current. Weuse this to control other components,for example:

Lamps - brighter or dimmerMotors - faster or slower


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Examples of Variable Resistors

a rheostat: a variable resistor with two

terminals, one fixed and one sliding. It isused with high currents, above watt.

a potentiometer: a common type of variableresistor. One common use is as volume

controls on audio amplifiers and other formsof amplifiers.


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Carbon Resistor

The most common

resistor is the Carbonresistor.

Inside a carbon resistoris a 'ceramic 'core' on

which is deposited aspiral carbon 'track'. Thetrack may have beenmachined, or 'burnt' awaywith a laser beam.

A carbon resistor with the paintremoved showing the spiral


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High-power Resistors

High-power "wire-wound" resistors have a spiral ofhigh-resistance wire wound around the ceramic core.


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Power Rating

The amount of heat a resistor can handle isindicated by its "power rating" or "wattage".

Common carbon resistors have a powerrating of half a watt.

Wire-wound resistors are able to handle

much higher currents and much more heat.They are physically much larger than Carbonand metal-film resistors.


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Variance

Most common carbon resistors are guaranteed to bewithin 5% of their marked value.

'Metal-oxide' resistors, with a blue body, areguaranteed to meet their marked value plus, orminus 1%.


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Color Coding

First Digit

SecondDigit

Number of Zeros

(Multiplier)

Tolerance

Color Digit Multiplier

Black 0 x1 (nozeros)

Brown 1 x10 (1 zero)

Red 2 x100 (2 zeros)

Orange 3 x1,000 (3 zeros)

Yellow 4 x10,000 (4 zeros)

Green 5 x100,000 (5 zeros)

Blue 6 x1,000,000 (6 zeros)

Violet 7 x10,000,000 (7 zeros)

Grey 8 --

White 9 --

Red -- 1% Tolerance

Gold -- 5% Tolerance

Silver -- 10% Tolerance

None -- 20% Tolerance


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Three Band Resistors (obsolete)

Three color-band resistors have a tolerance of 20% and

cost the same as 10% resistors, therefore most engineersare now specifying 10% tolerance resistors for newdesigns.


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Four Band Resistors

This is the type of resistor you will more than likelyencounter in today's modern electronic products.

Read the colors from left to right just like for three color-band resistors.

The fourth band is the tolerance band. Tolerance valuesfor four band resistors can only be 2%, 5%, or 10% (red,gold, or silver respectively).

Orange =3, red = 2, yellow = 4 zeros, gold =5%


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Tolerance

Calculate resistance range of 1k5 resistor with atolerance of 5%

1. Convert resistance to ohms1k5=1,500

2.Calculate 5% of 1,500

1,500 x 5/100 = 753. Calculate maximum & Minimum values

Max = 1500 + 75 = 1575

Min = 1500 75 = 1425

Resistor range is: 1425 to 1575


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Multiplier Band: Gold & Silver

Four-band resistors can have values less

than 10 by using Silver and Gold asmultiplier colors.

Gold = x10-1 and Silver = x10-2. Thenegative sign means move the decimal point

to the left.


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Five Band Resistors (rare)

Bands 1, 2, & 3 are digits

Band 4 is multiplier Band 5 is Tolerance

Tolerance values for five band resistors can only be 0.05%,0.1%, 0.25%, 0.5% or 1% (gray, violet, blue, green, brown).

Red, Red, Black, Gold, Brown

2, 2, 0, x10-1, 1% = 22.0


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Resistors in Series and Parallel

Tutorial


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Resistors In Series=resistance

Resistors in series = sum of resistance

If 2 resistors are in series then the total resistance is thesum of their resistance. (R1 + R2)

Total resistance = 3


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Calculate 2 resistors in parallel

If 2 resistors are in parallel then the total resistance isproduct over sum (Ohms Law).

R1xR2 / R1+R2


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3 or more resistors

If there are 3 or more resistorsin parallel then the total

resistance is the inverse ofthe sum of the inverses of theresisters.

1

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

1 1 1

--- + --- + ---

R1 R2 R3

Why?


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1. Voltage doesnt changeEach of the resistors must

have the same voltage.

So:


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1. Voltage doesnt changeEach of the resistors must

have the same voltage.

So:


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2. Kirchhoff's Current Law

The sum of currents entering and

leaving any point in a circuitmust equal zero. So:


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3.Ohms Law (I=V/R)

By Ohm's Law,

is equivalent to:

Since all the voltages are equal, the V's cancel out,

and we are left with


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Formula For Any Number Of Resistors


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With Just 2 Resistors

1/RT = 1/R1 + 1/R2

RT = 1/ (1/R1+ 1/R2)RT = 1/((R2/R1R2) + (R1/R2R1))

RT = 1/(R1 + R2)/ R1 R2)

RT = (R1 R2)(R1 + R2)


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Practice


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Part 1

What is the resistance between A and B?

4

1 +3


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1

The 2 is shorted out


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10

10 = 4 +((10 x15 )/(10 +15 )


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17

17=5+(30x20)/30+20)


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11

1)7 resistor is shorted out

2) 4 and 2 resistors are

in series, making 6

3) 6 resistance is in

parallel with the 3 resistor,

making 2 (6*3)/(6+3)

3). Finally, the 2 resistance

is in series with the 9

resistor, making 11


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What is the total resistance between A & B?

Each resistor is 39 ohms.


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Hint

One end of each resistor is connected to A

The other end of each resistor is connected to B


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Circuit Redrawn

Schematics are often drawn in a way that makes itdifficult to follow current paths and voltage drops.Sometimes, redrawing part of the diagram in adifferent form helps to understand the circuit.

Total resistance is 13 ohms


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What is the resistance of R3?

R3=25k

Since R3 has acurrent of 40mA itis 4x R2, soresistance mustbe


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How much current does the meter read?

12mA

(160k x 40k)/(160k+40k)=32k15mA x 32k=480V

480V/40k=12mA

Or since 160 is 4x 40, the current across the 40k must be4 times that of current across 160k


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How much current does the meter read?

4mA

30V-22V=8V8V/2k = 4mA

What is the resistance of R1?


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R1 has a resistance of 5500

22V/4mA= 5500


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A =10mA

800+((3000x2000)/(3000+2000))+1000 =300030/3000=10mA


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B=5mA

3750+((2500x2500)/2500+2500))+1000=600030/6000=5mA


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C=20mA50+((500*4500)/500+4500))+1000=

150030/1500=20mA


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Capacitor

A capacitor is a passive electronic component thatstores energy in the form of an electrostatic field.

In its simplest form, a capacitor consists of twoconducting plates separated by an insulatingmaterial called the dielectric.

Capacitance is directly proportional to the surfaceareas of the plates, and is inversely proportional tothe plates' separation.

Capacitance also depends on the dielectric constantof the dielectric material separating the plates.


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The standard units of Capacitance

farad: F

microfarad: F (1 F = 10-6 F) nanofarad: nF (1 nF = 10-9 F)

picofarad: pF (1 pF = 10-12 F)


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Capacitors in Parallel Configuration

Capacitors in a parallel configuration each have thesame potential difference (voltage). Their totalcapacitance (Ceq) is given by:

The reason for putting capacitors in parallel is toincrease the total amount of charge stored. In otherwords, increasing the capacitance we also increasethe amount of energy that can be stored as itsexpression is


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Capacitors in Series Configuration

The current through capacitors in seriesstays the same, but the voltage across eachcapacitor can be different. The sum of thepotential differences (voltage) is equal to thetotal voltage. Their total capacitance is given

by


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Diode - Rectifier

A Diode is a small signal device with currenttypically in the milliamp range

A Rectifier is a power device, conducting from1to 1000 amps or even higher.

Many diodes or rectifiers are identified as

1NXXXX ..


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A Semiconductor Diode

A semiconductor diode consists of a PNjunction and has two(2) terminals, ananode(+) and a cathode(-). Current flowsfrom anode to cathode within the diode. Adiode and schematic representation are

shown below


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Diodes are unidirectional

Diodes are unidirectional, i.e. current flows inonly one direction (anode to cathodeinternally).

When a forward voltage is applied, the diodeconducts; and when a reverse voltage is

applied, there is no conduction.


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The direction of the diode symbol's"arrowhead" points againstthe direction of

electron flow.

This is because the diode symbol was invented byengineers, who predominantly use conventional flow

notation in their schematics, showing current as aflow of charge from the positive (+) side of thevoltage source to the negative (-).

This convention holds true for all semiconductorsymbols possessing "arrowheads:" the arrow points

in the permitted direction of conventional flow, andagainst the permitted direction of electron flow.


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Zener diodes

Diodes that can be made to conduct

backwards. This effect, called Zenerbreakdown, occurs at a preciselydefined voltage, allowing the diode tobe used as a precision voltagereference.


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Rectifier circuits

Rectification is the most popular applicationof the diode: rectification.

Rectification is the conversion of alternatingcurrent (AC) to direct current (DC).


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Half-wave Rectifer

The simplest type of rectifier circuit is the half-waverectifier which only allows one half of an AC

waveform to pass through to the load


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Half-wave rectification is a very simple way toreduce power to a resistive load. Some two-

position lamp dimmer switches apply full ACpower to the lamp filament for "full"brightness and then half-wave rectify it for alesser light output:


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Full-wave Bridge

A popular full-wave rectifier design it is builtaround a four-diode bridge configuration.


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Current directions for 1st half-cycle of

the AC waveform


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Current directions for 2d half-cycle of

the AC waveform

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