Design and Implementation of a 12V Regulated Power Supply

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A 12V power supply having fixed and regulated output is
being tested and analyzed in lab and final product is
prepared according to customer’s requirements.
Author Name [Publish Date] [Category]
UCK
Designing a Product Which Meets
Customer’s Requirements
DESIGNING
+12V
Fixed Power Supply

Table of Contents
.....................................................................................................................................1
Introduction..........................................................................................................................5
LO1 Preparation Of Design Specifications Laterally Design Plan.....................................5
Engineering Design Specifications..................................................................................5
Stakeholder Design Brief’s Influence on Design Specs..................................................5
Design Planning: Gantt Chart and Planning Techniques................................................6
Design Specifications vs Industrial Standard Designed Products...................................7
LO2 Analyzing and Evaluating Initial Prototypes...............................................................8
1st Prototype.....................................................................................................................8
2nd Prototype....................................................................................................................8
3rd Prototype.....................................................................................................................9
Industrial Standard Evaluation........................................................................................9
Prototyping Characterizes: Getting Towards Final Design...........................................10
Charisma of 1st Prototype...........................................................................................10
Charisma of 2nd Prototype..........................................................................................10
Charisma of 3rd Prototype..........................................................................................10
Modelling and Prototyping Role...................................................................................11
Software and Hardware Utilization...............................................................................11
Suggested Improvements...............................................................................................12
LO3 Analyzing and Evaluating Final Design Constraints................................................13
Design Constraints.........................................................................................................13
Potential Boundaries of Ultimate Design......................................................................14
Role of Design Specifications.......................................................................................14
Acquiescence, Safety and Hazard Management............................................................15
Author Name 2

Usefulness of Concluding Design.................................................................................15
Efficiency Standards..................................................................................................15
Standards of Load Regulation...................................................................................15
Standards of Line Regulation....................................................................................16
Simulation Results.....................................................................................................16
Temperature Stability Standards................................................................................16
LO4 Design Presentation and Clients Feedback Over it...................................................17
Presentation....................................................................................................................17
Communication Techniques..........................................................................................18
Analyzing Design Presentation......................................................................................18
Potential Improvements in Response of Client’s Feedback..........................................19
Conclusion.........................................................................................................................19
Annex1: PCB Layout.........................................................................................................20
Annex2: Case Design........................................................................................................21
Annex3: Schematics..........................................................................................................22
Table of Charts
Chart 1: Evaluating Prototypes..........................................................................................10
Chart 2: Roles Played by Prototyping...............................................................................11
Chart 3: Role of Design Specifications in Overall Design Procedure...............................15
Table of Figures
Figure 1: Gantt Chart: Project Planning..............................................................................6
Figure 2: PERT chart...........................................................................................................7
Figure 3: 1st Prototype Schematics......................................................................................8
Figure 4: 2nd Prototype Schematics......................................................................................9
Author Name 3

Figure 5: Block Diagram of Regulated 12v power supply................................................13
Figure 6: Smoothing Capacitor And Its Ripple Rejection Response................................14
Figure 7: Load Regulation Simulation Graph...................................................................16
Figure 8: Design Hardware Presentation...........................................................................18
Figure 9: Design Presentation Techniques........................................................................18
List of Tables
Table 1: Design Brief’s Influence........................................................................................6
Table 2: Contrast Design Specifications with Industrial Standards....................................7
Table 3: Presenting Findings.............................................................................................17
Author Name 4

Introduction
Power Supplies used to provide power to electronic devices and are being in use in many
laboratories for testing other devices. Usually regulated and un-regulated power supply is
designed but for fixed output, regulated linear power supply is used. In this report, we have
discussed the design process carried out in response to customer’s requirements and made a +12v
fixed power supply in return. We have utilized many design and planning techniques and tried to
make a fully compliant industrial product so that other prototypes can be tested using this supply.
Regulation and fixed output are two main features along with the cost-effectiveness model of the
final design.
LO1 Preparation Of Design Specifications Laterally Design Plan
Engineering Design Specifications
Client’s brief suggests that the power supply should take 230VAC in and Gives +12VDC
out. In order to provide this, relevant electronics components must be utilized efficiently,
especially regulator selection must be done to provide fully regulated and uninterrupted constant
output. Efficiency can be increased using IC’s and smoothing capacitors.
Our design team took a keen look at design brief and then after consulting IEC standards,
they have made a design brief which is prepared completely in relevance to the client’s brief.
Following are some design specs prepared in time;
 Input Voltage 220~230VAC
 Output Voltage +12VDC
 Efficiency Standards 75~85%
 Ripple Factor ≤ 300mV
 Regulation IC or Zener
 Dimensions 7 x 2 x 4in
 Ambient Temperature Range -8℃ ~ +90℃
Stakeholder Design Brief’s Influence on Design Specs
We have given our very first priority to what client is acquiring from us. In this context,
client’s brief has a very significant impact on final design specs. As the input output voltage is
same as what’s required along with the regulation is set to also comply with that. Here is the
influence shown in below table;
Author Name 5

Table 1: Design Brief’s Influence
Design Brief of Customer Influence
Fixed O/P
Ripple and Noise Minimum
Regulated
Design Planning: Gantt Chart and Planning Techniques
First we make a plan to get through the possible available design tasks which will lead us
towards efficient final designing. So we made some design tasks before preparing a gantt chart
and then assigned each task a start and end date. In this way we were able to make a design plan
using Gantt chart and critical path.
Gantt chart is being prepared in order to monitor regularly project’s progress. It also
helps the whole team work on track. Gantt chart helps professionals to carry out their projects
smoothly, either they are of designing any engineering product or not. Here is a gantt chart we
have prepared before starting project;
Figure 1: Gantt Chart: Project Planning
We also made a PERT chart by critical path analysis and figured out the most critical
path necessary to carry out projects. Here it is shown below;
Author Name 6

Figure 2: PERT chart
Design Specifications vs Industrial Standard Designed Products
Industrial design parameters are being set as criteria to judge if we have set standards
right or not. So we have taken two industrial products and take a contrast look over them by
writing in front of our design specs. Analysis is also carried out then to make some concluding
remarks over how much its matching and how much its different from industrial standards. 0 for
no match, 5 for medium, and 10 for fully complying. Analysis suggests that our product
specifications are 44.44% complying with industrial standards.
Table 2: Contrast Design Specifications with Industrial Standards
Terms Engineering Design
Specs
PPK 12V Power
Supply
Standardization
Analysis
VAC 220 ~ 230
50Hz
80 ~ 245
48 ~ 64Hz 5
VDC +12 +12 10
Efficiency Standards 75 ~ 85% 85 ~ 87% 5
Current (rated) 4 ~ 5A 2A 0
Ripple Factor ≤ 300mV 200mV 5
Regulatory Requirements IC’s or Zener Diode LM7812 5
Author Name 7

W x H x L 7 x 2 x 4in 1.5 x 3 x 6 in 5
Operating Temperature Range -8 ~ +90℃ ℃ -11℃ ~ +75℃ 5
Over_Voltage Guard   0
LO2 Analyzing and Evaluating Initial Prototypes
1st Prototype
First we’ve developed an easy prototype but its giving 12v output efficiently. We’ve also
used a fuse of 0.5A at input for overvoltage guard. T1 transformer is 220~15 VAC step down
transformer. Bridge rectifier is used at the output of transformer and thus it smooth out and
rectifies the ac input 15v into 15VDC but there are some fluctuations observed which are being
ripped out by a smoothing capacitor ahead. But after smoothing 20V present at this point shown
in yellow circle in below diagram. 7812 IC was used to limit and regulates those 20V at input
pin. One pin is grounded and one is at out point. This regulated output is then again smoothen
out using C2 and hence this way we got 12A output.
Figure 3: 1st Prototype Schematics
2nd Prototype
As the output was still fluctuating of above design and current was not upto the design
specs, so we have made some changes in circuit shown below. In order to linearize output and
increase the current to 5A, we have used two transistors to increase the current upto 5A. resistors
are used to protect transistors from getting saturated and also provide bias current.
Author Name 8

Figure 4: 2nd Prototype Schematics
3rd Prototype
As we have got desired current and voltage output, but regulation is still not set. So we
have made a design circuit in which we used a completely different method to regulate power
supply. We also replace LM7812 with LM338 IC and thus we have got our desired ripple factor
while testing output voltage in response to input voltage fluctuations and output current.
Industrial Standard Evaluation
Considering industrial standards and design specifications prepared before, this
evaluation is carried out and suggests possible problems in each circuit. While taking industrial
standards into account, we realize some important factors to include and discuss them in safety
hazards management points. But these safety points are what we have also considered here to
evaluate initial prototypes also. IEC standards suggest that there must be over voltage and over
current protection along with the short circuit protection circuits. This was little confusing
because for this much low voltages, and also looking at client’s brief, it was not required.
Anyhow, we have tested above designs overlooking these standard constraints, provided some
high voltages first prototype burned out but the third one remained intact against. Below is the
graph showing assumptions made after evaluation.
Author Name 9

1st Prototype 2nd Prototype 3rd Prototype
4.3
2.5 2
2.4
5
6
2
4
4
1.5 3 5
Evaluation of Prototypes
Chart 1: Evaluating Prototypes
Prototyping Characterizes: Getting Towards Final Design
Charisma of 1st Prototype
As we tested final design, output was carried out on DMM and it was observed as
continuously fluctuating worsening situation in response to stakeholder’s design brief. This
implies LM7812 is not getting good fit in this circuit. Also we used a transformer of 1A while
customer suggests 5A output rated current.
Charisma of 2nd Prototype
We made second prototype to increase current to 5A. for this purpose, we used transistors
across which a great loss of voltage was observed. So in order to manage one design
specification, we got imbalanced in the second one. We have tested this power supply to run
another circuit over that. It provided us with the fact that we should replace some components
and make a completely new design.
Charisma of 3rd Prototype
We again tested our 3rd prototype in lab to run other electronics over that. Its efficiency of
providing constant output was really acceptable. So this prototype made us clear our way in
getting finalize the design.
Author Name 10

64%
25%
11%
Role of Test Setups in Formulating
a Final Design
3rd Prototype
2nd Prototype
1st Prototype
Chart 2: Roles Played by Prototyping
Modelling and Prototyping Role
We have tried different software’s regarding simulation and modelling of initial
prototypes. In this way, we got the opportunity to learn the different behaviors of simulators
towards power supply circuit. Some were really fast with minimum run time, but some stopped
working due to extensiveness of transformer and regulator IC. Following key points regarding
role of modelling and prototyping, were detected;
 Prototyping helps initial evaluation of design constraints instead of direct finalizing
requirements. Confidence of design team developed over their product designing
procedure. But again and again testing disturbs the project timeline and also make it
more expensive.
 This experience gained from initial testing helps team present it more efficiently and
effortlessly but their focus may get loose while trying it again and again so they
accidently made first prototype for 1A output current.
Software and Hardware Utilization
 Software for Simulation: Eagle
 Software for PCB Design: Eagle PCB
 Software for Case Design: AutoCAD
 Hardware PCB: Ordered from PCB Way
Author Name 11

Suggested Improvements
While dealing with high main voltages in any electronics design, one must integrate all
possible overvoltage, overcurrent, and short circuit protections.
Author Name 12