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D Class Amplifier Design

Final Report REVISION HISTORY AND APPROVAL RECORD

Revisio n 0 1

Date

Purpose

22/05/2019

Document creation Document revision

06/06/2019

DOCUMENT DISTRIBUTION LIST Name

E-mail

Maria Del Remei Toda Ribes

[email protected]

Javier Prieto Navarro

[email protected]

Aniol Oriol Tordera

[email protected]

Héctor Arroyo Recio

[email protected]

Ramon Bragos Bardia (teacher)

[email protected]

Miguel Jesus Garcia Hernandez (teacher)

[email protected]

Joan Sarda Ferrer (teacher)

[email protected]

WRITTEN BY:

REVIEWED AND APPROVED BY:

Maria Del Remei Toda Ribes, Javier Prieto Navarro, Aniol Oriol Tordera, Héctor Arroyo Recio

Date

22/05/2019

Date

29/05/2019

Name

Javier Prieto Navarro

Name

Héctor Arroyo Recio

Position

Docum. Resp.

Position

Project leader

0. CONTENTS 0. 1. 2. 3. 4. 5. 6.

Contents Document scope Project summary Time plan updated System design documentation System implementation documentation System characterization

3 4 5 6 7 8 9

7. 8. 9.

Costs Conclusions Reflection document

10 11 12

1. DOCUMENT SCOPE The goal of this document is to explain how we have done the project and which objectives we have achieved. In this document you can find details about all the obstacles this project has encountered as well as how we have managed and solved them. It also contains our experiences, different views for every stage and the final schematic linking all the stages and power supply.

2. PROJECT SUMMARY We have started the project making simulations with Matlab in order to test and see how every stage works and which design we will use in our project. On the one hand, we choose the PWM-Modulator B+ design that contains a PWM with high‐ speed op amps and comparator. We find several obstacles, but we have mostly resolved them. We have to choose different values for components to make the PWM work properly. On the other hand, we choose B class output stage was made so we didn’t have to made it. Filter B was also relatively easy to make and it needs few (but with high quality) components. We also have to choose different values for Filter components to make the LPF work properly. When we finally make every stage work separately, we try to make it work together. Firstly, we use different power supplies in order to avoid the Output stage effect on the PWM stage. We have a clear signal on the output of filter using a constant 1 kHz signal made by Function Generator. Then, we had to weld them all on the printed circuit board. We firstly welded the output stage and filter and checked its correctly behaviour. Then we weld the PWM-Modulator and connect it to the output stage, but when we made the first try we can find some problems on the PWM caused by the half-bridge potential stage and it transferred this problems by the shared power supply. Because of that, we have to add some capacitors to minimize this effect and the noise created by every stage. Finally, after solved some of this problems we check its correct behaviour with an audio input signal and connecting the speaker. We can hear the music with some noise and the output power it isn’t the expected one.

3. TIME PLAN UPDATED

Our actual Time Plan has several changes respect the previous one. We have no idea how much time we have to use in every stage and finally it was larger than we had supposed. Also, we have some problems on the Project Assembly. Firstly, we test everything before welding Output Stage and it works as fine as it could and had no relevant problems with noise or power supply, but we think than if we weld PWM Modulator we can achieve a better THD and increase Output Power, but we don’t know what had happened but welding Output Stage put ourselves in a trouble because we have the problems I mentioned previously. Next weeks we had been trying to solve this problems and we solved some of them, but we think it can be better if we left the project without welding it. Finally, we did the Final Test the last day, but previously we didn’t know exactly when we do this and that is why we have changed it now.

4. SYSTEM DESIGN DOCUMENTATION To start designing our amplifier first of all we take a look on a MatLab script that allow us to see the response of different parametres, so we can choose the best way to choose the values of our amplifier components of every stage.

So we experimented with different values and we concluded the results. This is what we get when we run matlab with specific frequency,

Q,

amplitude

etc.:

Once we have tested the script with the different parametres values we can start designing the different blocks.

System block diagram:

PWM stage: We use the next schematic to do the PWM stage:

We choose the components values using theses formulas, so we get the fm that we want:

fm=

R2 4 RC R1

Output stage: For the output stage we use a set-up based on a DRV8837 from Texas Instruments:

Low Pass Filter(LPF): We build the LPF establishing the Q value that we want, this value must be close to frequency to be 22kHz. We know that R will be 8 Ohms. C=Q/Rw0 L=R/Qw0 So we build the LPF like next schematic with C=470nF and L=68uH:

5. SYSTEM IMPLEMENTATION DOCUMENTATION

1 √❑

and the cut-off

In the picture we show the final circuit schematic for our prototype, we have to change a lot of elements in order to make the design easier and we change the values of the components for implement the specifications. In our final schematic we use 3 dierents chips to generate the PWM:

The red block is configured as a integrator with the non-inverting input is biased at Vcc/2, and the green block as a comparator with hysteresis. In the red block there are a virtual connection between the inverting and non-inverting inputs allows current (I= Vcc/2R) which charges the capacitor C, for this reason the

output increasseslinearly with time and when it reaches 0.75Vcc, the green block change to its maximum output voltage. When the output voltage decrease in the integrator until 1/4Vcc the comparador output changes to zero. In the blue block we use the MAX9005 chip, which incorporates an amplifier and a comparator. We use the amplifier part to amplify the input signal and we put a capacitor to filter it, and in the non-inverting input we put the proper offset for the signal. We use the red and green block to generate the triangular wave signal which with the amplified signal goes together to the comparator to generate the PWM. Then, the modulated signal enters to the yellow stage (LPF) which is the responsible of amplify our modulated signal.In our case we choose a symmetric H bridge so both outputs are connected to a LPF and then to the speaker.

We use this to separate the feeding voltage to avoid problems and noise we put a capacitor .

Triangular wave Generate

value

AO + PWM

value

AD826AR

-

MAX9005

-

LT171

-

C

1uF

C

1nF,1uF

R5,R6,R7, R8

1.3K, 100K, 1K, 12K

R, R1, R2, R3, R4

4.7k, 1k, 2k, 10k x2

Discharge Capacitor

100nF

Discharge Capacitor

100nF

Power stage DRV8837

value -

6. SYSTEM CHARACTERIZATION

Filter L

68uH

C

470nF

Parameter

Output Power

Instruments and measurement set-up

We use an oscilloscope and the function generator to put the input signal to 1kHz and set the amplitude that we see there is not a lot of distortion in the output signal (169mV). We measure each pin of the 8 Ohms resistance with each oscilloscope channel and we make the difference between them (that is a function that oscilloscope do). Then with the cursors we measure the peak to peak voltage (4,64V approx.).

Involved variables and measured values

Voltage and the 8 Ohms resistance which is known. Peak to peak voltage (4,64V).

Model (parameter formula and result) V = 4,64V peak to peak R=8Ω Result

Parameter

0,34 W

Power Efficiency

Specification

1 W (minimum)

Instruments and measurement set-up

Oscilloscope, function generator and the power supply. And the same setup done in output power verification stage.

Involved variables and measured values

Output power and the power delivered by the power supply. Voltage and current. Voltage=5,0 Current = 0,1

Model (parameter formula and result) Result

68%

Specification

80%

Parameter

Bandwidth

Instruments and measurement set-up

Oscilloscope and function generator. And same setup done in first verification stage.

Involved variables and measured values

We start with the maximum voltage that we have to 1kHz and measure the fall off on 3dB (3,28V), we put the cursors with a difference of this amplitude and we change the frequency to 20Hz and to 20kHz and we see when the signal is between the cursors. 16Hz-20kHz

Model (parameter formula and result)

BW=f2-f1

Result

16Hz-20kHz

Parameter

THD

Specification

20 Hz – 20 kHz (-3 dB)

Instruments and measurement set-up

Involved variables and measured values

Oscilloscope but the oscilloscope can’t do the FFT of the difference, it can only do one function at a time, so we can do the FFT of just one side, the result will not be the correct but it will be an approximate one. To get the most accurate result we will use a Spectrum Analyser which makes the THD of the signal that we need and gives it to us automatically.

We measure the amplitude of the fundamental tone and the 5 next to it and apply the formula (this is if we use the oscilloscope, the Spectrum Analyser gives us the THD).

Model (parameter formula and result) Result

9.4 %

Specification

1%

7. COSTS First of all we have done a prototype cost, putting all the material of the circuit. Later we have done a table with the material we have used on the laboratory to do that prototype.

Prototype material cost: Components

Units (1 Product)

Price/Component

Total cost (1 product)

AD826AR

1

6,52 €

6,52 €

LT1711

1

4,96 €

4,96 €

R

1

0,05 €

0,05 €

R1

1

0,05 €

0,05 €

R2

1

0,05 €

0,05 €

R3 & R4 (voltage divider)

2

0,05 €

0,10 €

Capacitor

4

0,30 €

1,20 €

PWM (Triangular wave generator)

PWM (offset circuit / comparator)

R5

1

0,05 €

0,05 €

R6

1

0,05 €

0,05 €

R7

1

0,05 €

0,05 €

R8

1

0,05 €

0,05 €

Capacitor

2

0,25 €

0,50 €

MAX9005

1

2,05 €

2,05 €

1

7,20 €

7,20 €

L1

1

6,56 €

6,56 €

L2

1

6,56 €

6,56 €

C5

1

1,37 €

1,37 €

C1

1

1,37 €

1,37 €

R5

1

0,05 €

0,05 €

C9

1

0,20 €

0,20 €

Power Stage DRV8837 Low Pass Filter

Extra

TOTAL

40,79 €

Prototype equipment cost: Investments Equipment

Acquisition price

Years of amortization

%Residual value

Amortization per year

Oscilloscope

300 €

5

15

51

€

0.14

Power Supply

380 €

5

15

65

€

Frequency counter

400 €

5

15

68

€

2700 Multimeter

2000 €

5

15

340

pc

1200 €

8

25

113

TOTAL

4280 €

Salaries: Salaries

Amortization per day

Days of use

Amortization

€

12

1,68 €

0.18

€

12

2,12

€

0.19

€

12

2,24

€

€

0.93

€

12

11,18

€

0.31

€

5

1,54

€

€

18,76 €

Salary Employees

Salary (Euros/h)

Hours

total of one employee

Class work

7€

39

273

€

Design work outside of class

8€

20

160

€

TOTAL

Employees

Students

433 €

Number of employees

Salary employee

Total salaries

%Social Security

Social security charge

total cost employees

4

433 €

1732 €

35

606,20 €

2338,20 €

Payments and Expenses: Payments Cost Employees

2338,20 €

Investments

4280 €

Coworking place

150 €

Material Cost

40,79 €

TOTAL

6808,99 €

Expenses Cost Employees

2338,20 €

Expenses due to amortization

19,67 €

Coworking place

150 €

Material Cost

40,79 €

TOTAL

2548,66 €

We have differentiated what we really pay (6808,99 €) and the expense (2.548,66€) of making a product. The reason of this difference is that we divide the cost of the investments in the time of amortization taking into account the residual value of the investment so that we only consider the expense associated with the time we use it.

8. CONCLUSIONS We have learned some important things about how to work in team and solve the problems we had found. We also realize about the importance of keep the design that works, because firstly we have a good behaviour and few distortion and noise before we had welded it and then we find a lot of problems after this without knowing why it is caused. We probably can duplicate this design in order to avoid this kind of problems.

On the other hand we learn to choose the differents components and values like the process of research, and read and understand the different datasheets about them. We consider that this work is a good way to learn, because it’s a practical lessons about differents problems can you find with electronics devices, specifically with audio amplifiers.

9. REFLECTION DOCUMENT We have performed very well as a team and we have not any intern conflict. We know that when we welded the circuit in the printed circuit board we had some problem and the signal don’t work with all the requisites. We should not have disassembled the proto-board prototype to build the welded one because this prototype worked well and the most of the specifications were verified. We consider our organization very well and we have a balanced distribution with the work, all of the members have a good communication....