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The Common -Collector AmplifierName: Mahfuz Alam EMT-1255 – D452 laboratory. Experiment # 9 Prof. Raymond YapDate : 04 – 21 -Table of contents Title page Objectives page Summary of theory page 3- Calculation page 4- Material needed page Procedure page Diagram of simulation page 7- Data table page 12...

Description

The Common -Collector Amplifier

Name: Mahfuz Alam EMT-1255 – D452 laboratory. Experiment # 9 Prof. Raymond Yap Date : 04 – 21 -2020

Table of contents 1

Title

page 1

Objectives

page 3

Summary of theory

page 3-4

Calculation

page 4-5

Material needed

page 5

Procedure

page 6

Diagram of simulation

page 7-11

Data table

page 12-13

Questions

page 13

Conclusion

page 14

2

Objectives : The purposes of this lab was to compute the dc and ac parameters for a common -collector amplifier by using “ Multisim” online tools. In addition, build the amplifier from objective 1 and measure the dc and ac parameters including input resistance and power gain. We also test the effect of different load resistors on the ac parameters. Lastly we predict the effect of faults in a common- collector amplifier.

Summary of Theory:

The common-collector (CC) amplifier also called the emitter-follower has the input signal applied to the base and the output is taken from the emitter. Below figure illustrates a CC amplifier using a pnp transistor with voltage-divider bias. The ac output voltage almost perfectly duplicates the input voltage waveform. While this implies that the voltage gain is approximately 1, the current gain is not; hence, it can deliver increased signal power to a load. The CC amplifier is characterized by a high resistance and a low output resistance..

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Frequently, a CC amplifier follows a voltage amplifier. Instead of having separate bias resistors, bias may be obtained through a dc path connected from the previous stage as illustrated in above figure. This technique is common in power amplifiers.

The ac parameters for the amplifier can be analyzed from the information given in the summary. The equivalent ac circuit illustrated in below figure and also we compute the ac resistance of the emitter, the amplifier’s voltage gain, total input resistance seen by the ac signal and lastly compute the amplifier’s power gain by using formula.

Calculation : 1. Compute the ac resistance of the emitter: VB = 12∗

( 1010+ 33 )

=2.79 V VE =2.79+0.7 =3.49 V IE =

12 −3.49 1k

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=8.51 mA Now the ac resistance of the emitter is , r. e =

25 mV ( 8.51mA )

=2.937 Ω 2. The amplifier’s voltage gain, AV =

Vout Vin

= (ℜ∨¿ RL )/(ℜ+ ℜ∨ ¿ RL ) =

2.937+(1 k∨|1 k ) ) (1 k∨¿ 1 k )/¿

=0.994 3. The total input resistance seen by the ac signal By using the formula given in the manual , Rin (total) = R1 || R2 || (ßac (re +RE || RL ) = (33 k || 10 k) || (100* ( 502.94 ) = 6658.41 Ω 4. The amplifier’s power gain, AP = (Rin ( total ))/ RL ¿ =

( 6658.41 1k )

= 6.68

Material needed : 

Resistors : 1. Two 1.0 K Ω 2. One 10 KΩ 3. One 33 KΩ 5



Capacitors : 1. One 1.0 µF 2. One 10 µF



One 10 KΩ potentiometer



One 2N3906 pnp transistor (or equivalent )

Procedure :

1. Since we use Multisim online tool for this lab experiment we did not have option to physically check the resistance of the resistors that listed in the table of lab manual.

2. However we did the calculation part where we compute the Base voltage, emitter voltage, emitter current, ac resistance of the emitter and so on. 3. When it come to construct the circuit we follow the diagram from the lab manual by using Multisim Live online tools.

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Figure from the Multisim online tools :

Current of input and output of part 1

7

Graph of following current :

8

Voltage of input and output part1 :

Graph of the voltage input and output for part1 :

9

Part 2 of the experiment with input and output :

Current of input and out for part 2 :

10

Current graph of part 2 ;

Voltage of part 2 : 11

Voltage graph for part 2

Data table : 1 12

DC parameter VB VE IE VCE

Computed value 2.79 V 3.49 V 8.51 mA -3.49 V

Measured value 2.94 V 3.77 V 8.49 mA -3.45 V

Computed value

Measured value

Ve

298 Vpp

299 Vpp

re

2.94 Ω

Av

0.99

Rin(total)

6658 Ω

Ap

6.6

Data table 2 :

Ac parameter Vb

0.98

Evaluation and review questions : 1. The output inversion and amplification between the input and output waveforms are same for an npn transistors circuit. 13

2. The circuit in this experiment was used voltage-divider bias. 3. A) the advantage of using voltage-divider bias compared to base bias is that it is independent of ß . B) The disadvantage of the voltage-divider bias circuit is that output voltages decreases when a load resistor is added due to loading effect. 4. Although the common -collector amplifier does not have a voltage gain it provides a very current gain which in turns provides a power gain. 5. VB = 13.20 V

re = 20 Ω

VE =12.50 V

Av =0.998

IE =1.25 mA

Rin =…

VCE =7.50 V

Ap = …

Conclusion In this experiment we have learned how to construct a Common Collector (CC) amplifier circuit by using online tool Multisim. However, I cannot find ohmmeter to measure the resistance of the component and the total resistance. Because I am unable to find ohmmeter or multimeter in “Multisim Live “ . So I compare the current and voltage result observed from Multisim with another online tool name “Falstad “ . From the both observation we can say that the hypothesis of our experiment is not fully satisfied. It would be great experience for us if we were able to do this lab physically.

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