btec hnc - electronics - investigate types of amplifier

Investigate Types of AmplifierElectronics

By Brendan Burr

Brendan Burr BTEC Higher National Certificate in ElectronicsInvestigate Types of Amplifier

Table of Contents

TABLE OF CONTENTS - 2 -

TASK 1 - 4 -

1.1 A Class A power amplifier has a quiescent collector current of 750 mA from a 12 V DC supply. It produces 6 W of audio signal power delivered to a loudspeaker load of 8 Ω by transformer coupling. - 4 -

Solution (a):- - 4 -Solution (b):- - 4 -Solution (c):- - 4 -Solution (d):- - 5 -Solution (e):- - 5 -

TASK 2 - 6 -

2.1 A Class B power amplifier has a +/- 12 V DC supply. The load is a resistor of 10 k Ω It is to be supplied with an AC signal of frequency 1 kHz and amplitude of 5V. Run a circuit simulation using Croc Clips or Multisim and produce the following: - 6 -

Solution (a):- - 6 -Solution (b):- - 7 -Solution (c):- - 8 -Solution (d):- - 9 -

TASK 3 - 10 -

3.1 For a tuned collector amplifier that has a + 12 V DC supply run a circuit simulation using Croc Clips or Multisim and produce the following:- - 10 -

Solution (a):- - 10 -Solution (b):- - 11 -Solution (c):- - 12 -Solution (d):- - 13 -

TASK 4 - 15 -

4.1 Run a circuit simulation for the following circuit configurations using Croc Clips or Multisim:-- 15 -

Solution (a):- - 15 -Solution (b):- - 16 -

4.2 - 17 -Solution (a):- - 17 -Solution (b):- - 17 -

2


EVALUATION - 18 -

CONCLUSION - 18 -

BIBLIOGRAPHY - 19 -

Books - 19 -

Catalogues - 19 -

Websites - 19 -

3


Task 1

1.1 A Class A power amplifier has a quiescent collector current of 750 mA from a 12 V DC supply. It produces 6 W of audio signal power delivered to a loudspeaker load of 8 Ω by transformer coupling.

(a) Draw a circuit diagram (b) Calculate the DC Power.(c) Calculate collector power dissipation. (d) Calculate the efficiency(e) Calculate the transformer turns ratio if the reflected load is required to be 128Ω

Solution (a):-

Solution (b):-

Solution (c):-

4


Solution (d):-

Solution (e):-

5


Task 2

2.1 A Class B power amplifier has a +/- 12 V DC supply. The load is a resistor of 10 k Ω It is to be supplied with an AC signal of frequency 1 kHz and amplitude of 5V. Run a circuit simulation using Croc Clips or Multisim and produce the following:

(a) A circuit diagram(b) Typical input and output waveforms showing the cross over distortion(c) A circuit diagram of the Class B amplifier modified for Class AB(d) Typical output waveforms showing the cross over distortion removed.

Solution (a):-

6


Solution (b):-

7


Solution (c):-

8


Solution (d):-

9


Task 33.1 For a tuned collector amplifier that has a + 12 V DC supply run a circuit

simulation using Croc Clips or Multisim and produce the following:-

(a) A circuit diagram(b) Calculation of the resonant frequency.(c) A typical frequency response curve.(d) Calculation of the Gain-Bandwidth product.

Solution (a):-

Closed Switch

Open Switch

10


Solution (b):-

Closed Switch

Hz

Open Switch

Hz

11


Solution (c):-

See the Tuned Collector Amplifier Booklet for the results.

Switch Closed

33

36

39

42

45

48

51

54

15 15.25 15.5 15.75 16 16.25 16.5 16.75 17

Frequency of Vin (kHz)

Vo

lta

ge

Ga

in A

v (

dB

)

Switch Open

20

21

22

23

24

25

26

27

28

29

30

10 12 14 16 18 20

Frequency Vin (kHz)

Vo

lta

ge

Ga

in A

v (

dB

)

12


Solution (d):-

Closed Switch

Hz

dB

13


Open Switch

Hz

dB

14


Task 4

4.1 Run a circuit simulation for the following circuit configurations using Croc Clips or Multisim:-

(a) An Inverting Operational Amplifier with a closed loop gain of -10(b) A Non inverting Operational Amplifier with a closed loop gain of +11

Solution (a):-

15


Solution (b):-

16


4.2 For each of the circuits in 4.1 produce a table of measured values for Input and Output voltage levels and input current. Compare the results in terms of:-

(a) Open Loop v Closed Loop Voltage Gain(b) Open Loop v Closed Loop Input Resistance.

Inverting Amplifier Closed Loop Non-Inverting Amplifier Closed LoopVIN VOUT IIN RIN AV VIN VOUT IIN RIN AV

10 V -100 V 9.99 mA 1 KΩ -10 dB 10 mV 0.11 V 0 A Ω 11 dB1 V -10 V 999 uA 1 KΩ -10 dB 100 mV 1.1 V 0 A Ω 11 dB

0.1 V -1 V 99.9 uA 1 KΩ -10 dB 1 V 11 V 0 A Ω 11 dBInverting Amplifier Open Loop Non-Inverting Amplifier Open Loop

VIN VOUT IIN RIN AV VIN VOUT IIN RIN AV

1 mV -10 V 0 A Ω -20000 dB 10 uV 0.2 V 0 A Ω 20000 dB10 mV -100 V 0 A Ω -20000 dB 100 uV 2 V 0 A Ω 20000 dB0.1V -1000 V 0 A Ω -20000 dB 1 mV 20 V 0 A Ω 20000 dB

Solution (a):-

The Voltage Gain between the Open Loop and Closed Loop circuits is significantly different. For the Closed Loop circuits the gain is -10db’s for the Inverting Amplifier, this means that the Input Voltage will be increased by a factor of 10 and then inverted by 180 degrees, resulting in it becoming a negative in the cases above.For the Non-Inverting Amplifier there is a Voltage Gain of +11dB’s, which means the Input Voltage is increased by a factor of 11 and not inverted by 180 degrees.Comparing this to the Open Loop circuits shows that the waveform is inverted by 180 degrees in the Inverting Amplifier, however the gain in decibels is significantly greater.The same can be said about the Non-Inverting Amplifier, where the Voltage Gain significantly increases the Voltage input to 20,000 times.

Solution (b):-

The Input Resistance in the Closed Loop Inverting Amplifier is 1,000 Ohms and allows for the calculation of the Voltage Gain. On all of the other circuits the Power Supply is fed directly into and is only driving the Op Amp, which means there is theoretically infinite resistance as the wire in the simulation does not have a natural material resistivity.

17


EvaluationI was forced to rush this assignment as I mistakenly recorded the incorrect hand in date on my tracker as 18th of May and not the 18th of March. Fortunately I found the assignment relatively straight forward which meant I was able to get the bulk of the assignment complete by the end of the weekend.For Task 1, I managed to use the notes which I had taken in the lessons to work out the DC Power, Collector Power Dissipation, Efficiency and the Transformer Turns Ratio. I also had a Class A circuit built in Croc Clips so with a bit of editing in Microsoft Paint, I had my circuit diagram too.I suffered a little bit of difficulty with Task 2, as the circuit I had developed in Croc Clips matched the required specifications, however the sinusoidal waveform had a peak voltage which was into the Mega-Volts. Due to the Transistors supply only being +/- 12V, the waveform appeared as more of a square wave than sinusoidal. The problem was related to the Probes, it seemed that if referenced to 0V it would successfully produce the necessary waveform.My Class AB Amplifier worked well and did not require any tweaking to perfect.Moving on to Task 3 in such little time gave me confidence to complete the assignment in time so I continued. It was once I was on to part (C) that I realised I needed to generate a bulk of data to produce the Frequency Response Curve. I then began to work my way through the Tuned Amplifier handout that was supplied in class. It took a long time to change the frequency and the graph to enable me to read it, then calculating the Gain. I moved this data into Microsoft Excel and produced two waveforms, one for the switch whilst it was open and one whilst the switch was closed.Task 4 presented the calculating of the correct component values to generate the required Gain in closed loop circuits. I found this relatively simple as it was just a choice of one resistor value divided by the required Gain, giving you the value for the remaining resistor.

ConclusionOverall I feel that I have adequately completed this assignment, considering the time constraints imposed by myself. It was fortunate that I had done so much circuit design work towards it in class, so it was simply a case of modifying the circuits slightly to meet the question criteria.I have learnt from this assignment to double check the hand in dates for the remaining assignments as it is quite clearly a potential problem.This assignment has tested my competency of creating and modifying circuits and also manipulating the waveforms, taking into account the effect that changes has on them.

18


Bibliography

Through guidance from my lecturer, the following text books, catalogues and websites I was able to complete this assignment:

Books

BTEC National Engineering (Mike Tooley & Lloyd Dingle) ISBN: 978-0-7506-8521-4Success in Electronics (Tom Duncan & John Murray)ISBN: 0-7195-4015-1Higher Engineering Mathematics (John Bird) ISBN: 0-7506-8152-7

Catalogues

N/A

Websites

N/A

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btec hnc - electronics - investigate types of amplifier

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