report electronic circuit 1 audio amplifier

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<b>Instructor: PhD Nguyen Vu Thang Student’s name: Pham Viet Hoang </b>

<b>Student’s ID: 20182951</b>

<b>AUDIO AMPLIFIER REPORT:</b>

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<b><small>--SCHOOL OF ELECTRONIC AND TELECOMUNICATION</small></b>

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4.2. Stage 1: Voltage amplifier...7

4.3. Stage 2: Current amplifier...10

4.4. Stage 3: Power amplifier...15

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<b>List of figures:</b>

Figure 1: Block

Figure 2: Audio- amplifying circuit sketch………7

Figure 3: Voltage- amplifying circuit sketch………8

Figure 4: Current- amplifying circuit sketch………9

Figure 5: Power- amplifying circuit sketch………..10

Figure 6: Circuit simulation on the Proteus software………11

Figure 7: Simulating result on Oscilloscope……….11

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<b>1. Introduction</b>

In term 2021.1,I learn about amplifiers and transistors, and now,I design the audio amplifier circuit using BJT for more understanding about its operation and its application.

<b>Non-functional requirements: </b>

Simple, easy to use. Easy to fix. Low cost. • Compact size

2.2. Description

The audio power amplifier, also known as the audio amplifier, is a type of electronic amplifier that amplifies low-power audio impulses to a level sufficient for driving loudspeakers (the frequencies of low-power signals are always between20Hz and 20KHz, which is the range of human hearing). A three-stage circuit mustbe designed to build a full circuit for the audio power amplifier.

2.3. Parameters

Power supply: 15VDC.

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Input signal: 100mV AC (The signal is supplied through the audio jack from our computer or smartphone).

Efficiency: Frequency response: Frequency response is the term used to describe the range of tones that a stereo system can reproduce. The range of frequency response should be wide enough (20Hz to 20 KHz). The frequency response should be flat (linear).

Amplifier gain: Combination of the pre-amplifier’s gain and the amplifier.

<b>power-3. Block diagram</b>

Our product is divided into 6 main parts: AC input signal, Power supply, Voltage amplifier, Current amplifier, Power amplifier and Speaker or Load.

<small>Figure 1: Block </small>

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<b>4. Block designing</b>

4.1. Circuit sketch

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We use:

• The NPN transistor, BC547 to amplify the small input signal because it is used asa small signal transistor for VHF (very high frequency) amplifier.

• TIP41C, TIP42C to amplify the power of signal because they are power BJT.

4.2. Stage 1: Voltage amplifier

We employ the Common-Emitter voltage-divider bias setup in the voltage amplifier circuit. The voltage-divider bias setup is less affected by temperature changes, which is why it is more stable than other biasing systems. The voltage gain is increased by using the bypass capacitor.

<small>Figure 2: Audio- amplifying </small>

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<b>DC Mode:</b>

<small>Figure 3: Voltage- amplifying </small>

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- Based on the data sheet of BC547, choose:+ The working point of Q is: = 6V ; = 12.5mA+ = 250

- Apply Kirchoff’s voltage law: = . + . + . +

+ + = = = 720

Since + is the emitter voltage at Q point.Choose: + = = 120 = 720 – 120 = 600 In reality: Choose = = 300 - = = 2.08

- Assume = 45

= 45 => = 45 = 11.25

= 11

- + = 120 => = 109 =110

= 91.2 = 91

- Since << => The circuit is stable. << (+ ) = 250 x 120 = 30000 = = 3k

- Apply Kirchoff’s voltage law: . = . + + +

= x + 0.7V + 1.5V = 16.34k

= 16k ; = 330

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<b>AC Mode:</b>

- = // // .( + ) = 16.34k // // 250x(2.08 + 11 ) = 1427.87

- =

= 600 - = 5.6

Choose = 100 - Similarly, choose = 100 Current of the output signal:- = =

= 0.07 mA-

=

15992

4.3. Stage 2: Current amplifier

I choose emitter – follower Darlington connection configuration to amplifier the current. Stage 1 does not amplify the current so much. At this configuration, the voltage gain is always approximately 1. I want to use this circuit to amplifier the small current with high gain to increase the Power.

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= = 0.07 mA

- Stage 2 need to amplify to the value of Current gain of stage 2 is:

= = = 640

- does not amplify the voltage, so assume that = 1 = .

= = 38.53 k Choose = 39 k

<b><small>DC MODE:</small></b>

<small>Figure 4: Current- amplifying </small>

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Because the output current of this stage will cause important effect on stage 3 (namely heat effect on T4 & T5), so based on the datasheet of TIP41, I choose the working point of T3 is ( = 6V, = 0.25A). At that point = 55.

= - = 15 – 6 = 9V

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- From the operation point of , assume that = 0.73V = 0.25 A

= = = 4.55 mA = = 4.55 mA

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- With = 4.55 mA, based on the datasheet of BC547, choose = 110.- Similarly, assume = 0.7V

= = = 41 -

= . + + + = = = 111.46 k = 112 k = =

= 36

<b>AC MODE:</b>

= = = 0.1

= // (// ) = 112 k // [110 x 55 x (36 // 60.2 )] = 61.5 k ( > = 39 k )

= 0.1 = = 0.13 Choose = 100

4.4. Stage 3: Power amplifier

The output stage of a Class AB amplifier combines the benefits of both a Class A and a Class B amplifier while reducing the drawbacks of each, such as low efficiency and distortion. It outperforms class A and has less distortion than class B. I employ a pair of normal forward biased diodes within the amplifier's biasing configuration to correct for any temperature-related change in the base-emitter voltage (VBE), as illustrated below.

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- The output device is an 4 – 3W speaker.

- To avoid damage the equipment, we have: = 4 , = = 2.5W

= = V

= = 3.16V x 4.5 VThe input voltage is 100mV

The maximum voltage gain of the system is: = =

= 45

- avoid signal distortion, choose 2 = 2 x 4.5 = 9V

<small>Figure 5: Power- amplifying </small>

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= 15V = = = 1.12 A

- Based on the datasheet of TIP41 and TIP 42, assume that = = 50 = = = = 22.4mA

Apply Kirchoff’s voltage law: = + + +

+ = - - = 15V – 0.7V – 0.7V = 13.6V= = = 6.8V

= = = = 303.57 = = 300 = 1.99

Choose = 2.2 mF = = = 0.023

Consider one half of this stage:

= // .( + ) = 300 // 50x(0.023 + 4 = 120.41 = = 60.2

= 0.023

Input current for this stage to get the maximum power of the speaker: = . = 1. = 30.1

= = = = 37.2 mA = + = 22.4mA + 22.4mA

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= 44.8 mA = = = 66

<small>Figure 6: Circuit- Simulation on the </small>

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5.2. Simulating result

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<b>6.Testing with breadboard</b>

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<b>7.Layout PCB circuit</b>

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<small>On the breadboard, the output sound is audible, however TIP41 and TIP42 are extremely hot.I learned how to construct electronic circuits and run simulations as a result of this assignment. I may have made a mistake during the procedure, and I am hoping that the teacher can assist me in correcting it. Thank you so much for everything.</small>

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