Variable Power Supply Design Project: Meeting Stakeholder Requirements

Desklib provides past papers and solved assignments for students. This project details the design of a variable power supply.

DESIGNING A
PRODUCT THAT
MEETS CUSTOMER
REQUIREMENTS
ABSTRACT
Report on designing and building +5V ~ +15V
variable power supply according to stakeholder
specifications.
Student Name
Roll Number

Contents
LO1 Plan a design solution and prepare an engineering design specification in response to a
stakeholder’s design brief and requirements..........................................................................................4
1. Produce a design specification from a given design brief...........................................................4
2. Explain the influence of the stakeholder’s design brief and requirements in the preparation
of the design...........................................................................................................................................4
3. Design requirements according to user’s specification...............................................................5
4. Design process of power supply....................................................................................................6
5 Benchmarking................................................................................................................................8
LO2 Formulate possible technical solutions to address the student-prepared design specification
specifications..............................................................................................................................................9
1 Developing conceptual designs......................................................................................................9
1.1 Conceptual design 1...............................................................................................................9
1.2 Conceptual design 2.............................................................................................................10
1.3 Conceptual design 3.............................................................................................................11
2 Analysis of designs.......................................................................................................................11
3 Final selection of design...............................................................................................................12
4 Tools use for design development...............................................................................................12
5 Design improvement....................................................................................................................12
LO3 Prepare an industry-standard engineering technical design report............................................13
1. Final design..................................................................................................................................13
2. Design constraint.........................................................................................................................14
3. Role of design specification in producing final product............................................................14
4. Issues of compliance, safety, and risk management in selected design....................................14
5. Evaluation of effectiveness of selected design............................................................................15
5.1 Line regulation.....................................................................................................................15
5.2 Load regulation....................................................................................................................15
5.3 Cost effectiveness.................................................................................................................15
5.4 Efficiency..............................................................................................................................15
LO4 Present to an audience a design solution based on the design report and evaluate the
solution/presentation...............................................................................................................................15
1. Presentation of design..................................................................................................................15
2. Feedback of stakeholder..............................................................................................................16
3. Suggested design improvement...................................................................................................16

Conclusion................................................................................................................................................16
Appendix 1: Schematic of variable power supply.................................................................................17
Appendix 2: PCB layout..........................................................................................................................19
Appendix 3: Power supply 3d case.........................................................................................................19

List of figures
Figure 1 Block diagram of desired power supply............................................................................5
Figure 2 Design flow chart..............................................................................................................5
Figure 3 Conceptual design 1..........................................................................................................8
Figure 4 Conceptual design 2..........................................................................................................8
Figure 5 Final design elements......................................................................................................10
Figure 6 Importance of each specification in design.....................................................................11
List of tables
Table 1 User's specification.............................................................................................................3
Table 2 Stakeholder feedback form...............................................................................................12

LO1 Plan a design solution and prepare an engineering design specification in response to
a stakeholder’s design brief and requirements.
1. Produce a design specification from a given design brief.
Table 1 User's specification
Power supply category Variable
Ripple voltage Very low output ripple voltage
Output voltage +5 v ~ +15, variable output voltage
Voltage regulator Zener diodes, transistor
Function Variable power supply for testing another
prototype
2. Explain the influence of the stakeholder’s design brief and requirements in the
preparation of the design
 Importance scale: 1 - 50
 Feature rank: 1 – 5
Very low ripple in output
voltage Zener diodes Transistor variable output
0
5
10
15
20
25
30
35
40
45
50
Importance of design requirments
Importance

Very low ripple in output
voltage Zener diodes Transistor Variable output
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Feature ranking
Portable User Friendly Durable Flexible
3. Design requirements according to user’s specification
 Input voltage: 18 V AC/DC
 Output voltage: 1.2V ~ 15V
 Output current: 3A
 Ripple: ≤ 1 mV r.m.s
 Temperature: -40 °C ~ 125°C for 1000 hr
 Dimension: 29  15  13 cm
 LED display: No
 Capacitor: 2200/0.1/47 uF
 Dropout voltage: 1.3V ~ 1.5V
4. The design process of power supply
There are four major stages to build to gain variable output DC voltages.
 Input transformer: A step-down transformer is selected which will lower higher AC
voltage to the desired voltage level (Zhang et al, 2016).
 Rectifier: Full wave rectification is selected to convert AC voltage to DC voltage.
 Smoothing: Process of stabilizing output DC voltage

 Voltage regulation: Process to obtain DC output at the desired voltage.
4.1 Block diagram
Taking into account the design process components of power supply, figure 1 illustrates the
block diagram of the desired power supply design;
Figure 1 Block diagram of the desired power supply
4.2 Design flow chart
Figure 2 Design flow chart
4.3 Scheduling of the design process

As the task assigned to me, the first thing will be to hold a meeting with stakeholder to get a
better understanding of the product. At meeting my goal is to gather stakeholder
requirements and fully understand the desired product. Next task is to develop conceptual
designs of the product and analyze them on their performance. When the design is final then
product modelling and develops prototype will begin. A prototype of the product will be sent
to the stakeholder and ask for his feedback about the product. If the feedback comes with
changes then new prototype develops and send to stakeholder. This process will continue
unless positive feedback does not receive. When stakeholder stratified with prototype then
the final product will be developed. After that, a meeting with the meeting will be held with
stakeholder and present him product with its details.
4.4 Critical path analysis

5 Benchmarking
Specificatio
n
User’s
desired
power
supply
VAR
Tech –
1500
Single
output
YIHUA –
1502DD
PeakTech
6085
BEST 1502S
mini
Input
voltage 18V 220V 220V 115V ~ 230V 110V ~ 220V
Output
voltage 1.2 ~ 15A 0 ~ 15A 0 ~ 15A 0 ~ 15A 0 ~ 15A
Output
current 3A 0 ~ 2A 0 ~ 1A 0 ~ 2A 0 ~ 2A
Ripple ≤ 1 mV r.m.s ≤ 0.5 mV
r.m.s ≤ 3 mV r.m.s ≤ 1 mV r.m.s ≤ 1 mV r.m.s
Module
dimensions 291513cm 23x16x9.
5 cm
17x21x16.5c
m
95x16x22.5c
m
7.4x13.5x13.1c
m

Dual LED
display No Yes Yes No No

LO2 Formulate possible technical solutions to address the student-prepared design
specification specifications.
1 Developing conceptual designs
To design a product according to the desired specification, 10 conceptual designs were
developed in the lab. Out of 10, 3 conceptual designs are selected for final design development.
These 3 conceptual designs are formally briefed in section 1.1, 1.2, and 1.3.
1.1 Conceptual design 1
The first design developed for power supply uses a step-down transformer is used. The input
supply voltage is 220V ~ 230V AC, which needs to be lower to the desired level of 15V. For the
required output current of 1A, a step-down transformer of 18V-0-18V/2A installed. For DC
output voltage, AC voltage converted through rectification. A full-wave rectification bridge is
used to the 36V AC to 36V DC. For full-wave rectification, four diodes (1N4007  4) were
installed and are connected in a way that current flow in one direction to produce DC voltage at
the output. After full-wave rectification output DC voltage is not stable. For stabilizing DC
voltage, a capacitor (470 uF, 50V) is installed. Smoothing ripples in frequency, the capacitor
needs to be installed in parallel to full-wave rectification output. Now, a linear regulator
(LM317) is installed to gain constant voltage without fluctuation. The purpose of the regulator is
to maintain the output voltage at the desired level of 0A~15A and capable of providing 1A
current. As LM317 minimum output is 1.25V, two diodes of 1N4007 with 1K resistor are
connected in series to obtain output voltage near to 0V. When final testing of design is
conducted, it is observed that output voltage decreases as the demand for current increases and
LM317 started to heat up. From experiments, it is found that dissipation of power through
LM317 is greater than its limit.

Figure 3 Conceptual design 1
1.2 Conceptual design 2
The second design which considered in final design development is to use 18V/1.5A step-down
transformer. Which lowers 220V~230V to the desired level of 15V and output current of 1A. As
we required DC voltage at the output, full-wave bridge rectification needed to convert AC to DC
voltage. For this purpose 41N4007 diodes are installed in the circuit. To obtain DC voltage,
current flow is in one direction and one couple of diodes work as forward biased and second as
reverse biased at a time. As a result, the fluctuating DC voltage is obtained. To reduced
fluctuation, a capacitor (2200uF, 35V) is installed. This capacitor produced voltage has ripples
and to smooth ripples regulator (56 ohms, 2W) installed in the circuit. The decrease in ripples is
seen but not a better result. To more reduction of ripples in voltage, circuit attached with Zener
diode (18V, 1.5W), capacitor (100uF, 35V), and regulator (330 ohms) connected in parallel with
each other. Now to maintain the output voltage at the desired level three more parallel capacitors
(10uF 25V, 220uF 25V, 100uF 100V) and power transistor (2N3055) in series connected to the
circuit. After finalizing the circuit experiments are performed on this design. Experiment results
show that when designed power supply works in the biggest current, its power transistor heated
up (Mashhadi et al, 2016)