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Faculty of Engineering

Electrical Department

Name : ISKANDAR ZULKARNAIN

Matrix No : KEE!"#$%

&ear : '

Seme(ter : )Date : %# *une )!!$

E+,ERIMEN- )

,engu.uran ,aramiter -ran(i(tor

/y0ri12

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E+,ERIMEN- )

Theory

A filament of a lamp is make of tungsten. Therefore when a voltage apply to the lamp

the filament the current flow thought the filament and light emitted. The light intensity of thelamp will increase with increment in current from the threshold to the maximum value. Whilethe colour of the filament emitting light from deem red to white.

The Ohm's law gives a resistance of a common conductor by this euation!

Therefore a conductor Ohm will have a constant resistance ". The plotted current#voltage line is a straight line with a slope eual to ". $owever% the filaments material has a

positive temperature coefficient. Therefore% as the temperature raised by increasing in currentthought it% its resistance also increases as shown by the graph below.

&urposeThe purpose of this experiment is to!

1. Acuaint you with the Trainer and experiment procedures.

" ( resistance) ( voltage apply* ( current"

(

)*

+raph *#) for filament

*

)

,ilament

-onductor Ohm

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. emonstrate the effect of filament current on the intensity and /colour0 of theradiated light from an incandescent lamp.

. emonstrate the effect of tungsten2s positive temperature coefficient.

&rocedure!1. Wire the circuit shown in the schematic diagram 3,ig 1.14. Ad5ust "1to midrange.

. 6et your test euipment as follows!

7illiammeter to 188 milliammeter% -.

)oltmeter to a range greater then 1 volts.

1. Apply power to the breadboard and check the circuit wiring. The milliammeter shouldindicate roughly 8mA% the voltmeter should indicate 1 volt or less% and the lampfilament may glow dimly. When you are satisfied the circuit is wired properly% increasethe resistance of "1to its maximum value. This will be indicated by a decrease in boththe milliammeter and voltmeter indications.

. The voltage and the current of the lamp when "1is maximum had been recorded from themeter.

. "ecord the current when the voltage increases. Also note the light intensity and colour asyou progress through increasing the voltage.

A

V

MILLIAMMETER

+12v

3

2

1

R

1K

CONTROL

LAMP

VOLTMETER

1

,igure 1#1

"96:;T6!

When the "1is maximum!

*;( < mA 9;( 8.11 volts

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When the lamp filament 5ust begins to glow!

*;( < mA 9;( 1.== volts

This are the current reading and the "esistance calculated when the voltage increase!

3oltage4 EL536 7urrent4 IL5mA6 Re(i(tance4 RS5 6

1 8

>8 ?8

> ?< @

@ =8

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E+,ERIMEN- '

Theory;9 is a forward#biased B 5unction which emits visible light when energies in

forward biased. uring the conduction% the recombination of electron and the hole give upsome energy in heat and light. $ence the electron is 5umping from one valence to another this

will give up specific wave length 3emit one colour only4.The colour of the emitted light depends on the type of material used.

ex.

+aAs infrared radiation 3invisible4

+a& red or green light

+aAs& red or yellow 3amber4 light

;9 emit no light when reverse biased. The ;9 is operate at voltage between levels from1.?) to .)

&urposeThe purpose of this experiment is to demonstrate!

1. The selection of current limiting resistance in an ;9 circuit

. The relationship between forward current and ;9 intensity

. The differences in ;9 radiation patterns

>. That the colour of light emitted by an ;9 is not dependent upon lens colour

?. The effects of freuency on the visual appearance

@. The use of a diode as reverse voltage protection in an ;9 circuit

=. The use of inverse#parallel ;9s in a dual#polarity circuit

?

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A

V

MILLIAMMETER

+5V

3

2

1

R

CONTROL

VOLTMETEROR SCOPE

LED

S

200 ohm

,igure @#=

&urpose

The &urpose of this experiment was demonstrated!

1. The selection of current limiting resistance in an ;9 circuit.

. The relationship between forward current and ;9 intensity.

. The differences in ;9 radiation patterns.

>. That the color of light emitted by an ;9 is not dependent upon lens color.

?. The effects of freuncy on the visual appearance of ;9 indicators.

@. The use of diode as reverse voltage protection in an ;9 circuit.

=. The use of inverse#parallel ;9s in a dual#polarity circuit.

@

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&rocedure

1. The circuit shown in the schematic diagram 3,igure @#=4 is wired. The lead is solder to the

88 control. The short lead was connected to ground when installing the ;9. The "6is

ad5usted to midrange.

. The test euipment is set as follows.

7iliammeter 188mA - "ange

)oltmeter to ) - "ange

. Trainer is powered and "6is ad5usted for an indication of >8mA on miliammeter. The ;9grows brightly. "ecord the voltage. "6 is ad5usted to obtain the following values of

forward current and record down the forward voltage at each point. 3The 1k control

is connected to obtain current level of 1?mA or less.4

>. The data collected is plot on the chart provided in ,igure @#@. raw a graph.

?. :sing the *, # ), curve from ,igure @#8mA of forward current. *nsert the

=

)"6

*"6

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control into the circuit% apply power to the Trainer% and observe the milliammeterindication. *f your curve and calculations are correct the milliammeter should indicatevery close to >8mA. "emove power from the Trainer. "epeat this procedure for 8mA%

8mA% and 18mA. 3*t may be necessary to use the 1kcontrol to obtain 18mA *,4.

"emove power from the Trainer.

"esultFor8ar1 current4 IF5mA6 For8ar1 9oltage4 3F536>8 .?@

? .>=

8 .8 .?@ .>>8 8.8@18

8 .< .@8 8.8

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8 1>.< 8.1>88

18 1#@>?4. Apply power to the Trainer and observe the colour emitted from the ;9. Boticethat it bears no relationship to the lens colour% but is solely a function of the chipmaterial. 6ince the lens of this ;9 is clear% observe also the magnification ualities ofthe lens. Observe the chip through the side of the dome and compare this to itsappearance when viewed from the top.

18. Ad5ust "6until the milliammeter indicates 8mA. Bow hold a piece of white paper over the;9% with the paper 5ust touching the lens. Bote the pattern of light produced on the top ofthe paper.

,igure @#

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"emove power from the Trainer and replace the clear ;9 with the original red ;9."eapply power to the Trainer and ad5ust "6for 8mA of forward current.

Again% hold the paper on top of the ;9 and observe the light pattern. 3Bote! *t may benecessary to reduce room lighting to observe this effect.4 -ompare the radiation patterns ofthese two ;9s.

Bow% reinstall the clear ;9 in your test circuit. -arefully vary "6so that *,varies slowlyfrom maximum to Dero. Bote the intensity of the ;9 at various values of forward current.

"esult

Observation for step .

"esult

,rom the oscilloscope% the voltage levels at T&1 switch between 8) to ?) at about 1 $D.

The voltage output at T& switch in between I1) and #1). The freuency is the same as

from T&1.

The ;9 is blinking on and off at about 1 $D 3same as the freuency at T&1 and T&4.

iscussion

*n this circuit% time ??? *- is the freuency oscillator. The freuency output can be change byad5usting "1. The output of the timer is "- coupled to a non#inverting couple to a comparatorcircuit follows the timer output freuency. The output from comparator is switching betweenI1) and #1). This provides a variable freuency A- signal.

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&rocedure 3continue4

1=. 6et oscilloscope controls as follows!

?)G division vertical deflection% - coupling.

? millisecondsGdivision horiDontal deflection.

6weep centered on screen with input grounded.

11. Ad5ust "1until the ;9 blinks rapidly on and off. Bow very carefully ad5ust "1 to the

point where the ;9 appears to 5ust stop blinking and starts to glows steadily.

1. -onnect oscilloscope to test point and ad5ust the scope control for a stable display of atleast one complete cycle. 37ake sure the vertical and horiDontal controls are in the/calibrated0 position4. etermine the time reuired for one cycle and convert this readingof freuency% using the euation!

freuency (time

1

The computed freuency should be somewhat less than ?8$D. 6lowly vary "1back andforth slightly while observing the ;9 and scope presentation. Botice that while the ;9appears to make a relatively sharp transition between flashing and steady operation% thescope reveals that only a smooth change of freuency is occurring.

8. Ad5ust "1until one cycle of the signal is displayed on your oscilloscope. "ecord thiswaveform on ,igure @#1A.

1. "emoves power from your Trainer and temporarily remove the ;9 from the circuit."eapply power to Trainer and record the oscilloscope display on ,igure @#1E."emove power from the Trainer.

. With the ;9 still removed% temporarily reverse the 1B>1> diode. Apply power to theTrainer and record the oscilloscope display on ,igure @#1-. "emove power from theTrainer. "eturn the test circuit to its original configuration by again reversing the diode3black band toward T&4 and reinstalling the ;9 in its proper position.

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"esult

When the ;9 stop blinking% time ( > ms

$ence% freuency (

( >1.=$D J ?8$D

When "1is ad5usted to obtain a full waveform% the graph from the oscilloscope is shown asfollows.

+raph A +raph E

+raph -

Figure "2)'

The voltage across ;9 gives a longer wave line compare to the 1B>1> diode.

1>

1

>x18#

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iscussion

*n 6tep 1= and 18K negative. This will tend to lower the freuency at which the ;9 appears toglow steadily. Therefore% the freuency computed in 6tep 1 was probably between >8$D and?8$D.

*n 6tep 8 through % the effect of diode limiting on the test waveform.

+raph A shows the normal voltage levels across the ;9. The positive portionrepresents the froward voltage drop for ;9 3.?)4. The negative portion represents thefroward voltage drop for the 1B>1> diode 38.=)4.

+raph E shows the characteristic of the forward and reverse bias for the 1B>1>diode. Therefore the negative portion remain essentially unchanged. $owever the positive

portion has raise to I1) 3output from comparator4 and the diode cannot conduct in reversebiased. ,rom this we can see that the ;9 has a ),of 1) and )"of 8.=). The maximumreverse voltage rating of this ;9 is ?). Thus% the diode provides more than adeuate

protection to the ;9. The

+raph - shows the waveform of the voltage levels that would be developed across anunprotected ;9. 6ince the negative portion of this waveform is nearly #1)% which destroythe ;9% we simulated this condition by replacing the ;9 with the silicon diode 3reverse

voltage rating ( =?)4. Of course% with an ;9% the positive voltage level would be at aboutI) as indicated by the dotted line in ,igure @#1-% rather than the I8.=) observed. This isdue to the different in forward voltage drops between the two devices. Lou can then concludefrom this ,igure that an ;9 cannot be used in this circuit without some form of reversevoltage protection.

1?

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&rocedure 3continue4

. Apply power to the Trainer and again observe the waveform at T&. *t should be the sameas recorded in ,igure @#1A. "emove power from the Trainer and replace the diode3?@#?@4 with the green ;9 3>1#@>4% as shown in ,igure @#1>. 7ake sure the shortlead of the ;9 3the flat side4 is toward T&.

+_

TP3

LED $RED%LED $#REEN%

100ohm

>. Apply power to the Trainer. Eoth ;9s should light. Observe the waveform at T& andcompare it to the waveform recorded in ,igure @#1A. With identical ;9s% the

positive and the negative voltage levels would be eual but opposite. To observe this%remove power from the Trainer and replace the red ;9 with the amber ;9 3>1#@>14. The forward voltage characteristics of this ;9 are very similar to those of thegreen ;9. Apply power to the Trainer and note the positive and negative voltagelevels at T&. They should be approximately I) and #).

?. "emove power from the Trainer and replace the two ;9s with the single bicolour ;9%as shown in ,igure @#1?. *nstall the bicolour ;9 so that its shorter lead 3the flat side4is connected to T&. Apply power to the Trainer and ad5ust "1 for maximumresistance. The ;9 should alternate between red and green at slightly less than a 1 $D

rate. "emoves power from the Trainer and disconnect the 18, capacitor from pin ? of

the 1>?< comparator. 3"efer to ,igure @#184.

1@

,igure @#1>

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,igure @#1@

+_

TP3

LED $RED%LED $#REEN%

100ohm &ICOLOR LED

@. -onnect pin ? of the 1>?< to I1) and apply power to the Trainer. Observe the ;9.-onnect pin ? to #1) and observe the ;9. "emove power from the Trainer.

=. "everse the ;9 so that the shorter lead 3the flat side4 is toward ground and repeat 6tep@. The ;9 should now react in an opposite manner. This circuit is a simple polarityindicator in which the indications can be reversed by merely reversing the ;9."emove power from the Trainer.

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"esult

The output waveform at T& for 6tep > is as shown below.

When red ;9 is replaced with amber ;9% the graph change slightly as follow.

iscussion

*n this circuit% the 1B>1> diode acts as a polarity#sensitive switch that in fact insert or

removes the 1k resistor. When T& is positive% the diode is reverse biased and will not

conduct% current will flow through the green ;9 segment% the 1kresistor% and the 188k

resistor to the comparator output. Thus% the green segment is current limited by 11888 of

resistance.

On the other hand% when T& is at a negative potential% the switching diode is forwardbiased and the conduction diode resistance% and the red ;9 segment to ground. -urrent

limiting in this direction is only 188. Therefore% in this configuration% the red segment

conducts mush more current than the green segment. The opposite effect can be obtainedsimply by reversing the switching diode.

:sing the euations associated with ,igure #8E% we can experiment the variousresistance ratio 3make sure the forward current does not exceed >8mA.

-onclusion

The ;9 is a useful device. *t is use for display signal% rectification A- signal% shows

current direction etc. 6ince ;9 function in low levels 31.?) to .)4% it is useful as a high

sold stage devices.

iode protection is important for operating in high reverse voltage.

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