Proprietary and Confidential
? Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott i AC-DC Power Supply An engineering device completed as apart of certification which converts AC power into DC output
Presented to the Faculty by -
Jeremy H. Shum
President, CEO Cassie L. Stott
VP, Government Proprietary and Confidential ? Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott ii EXECUTIVE SUMMARY
The aim of this practical is:
?
To develop a power supply within six laboratory sessions ?
Test the power supply, collecting results ?
Comparing actual results against expected results (industry standard), understanding underlying theory ?
Understand the theory behind the circuit ?
Rectification of Alternative-Current signal into Direct-Current ?
Rectification through diode (single diode; diode bridge); capacitor bank; voltage regulator ?
Variability of voltage source through potentiometer ?
Voltage drop attributed to increasing current ?
Understand the underlying materials: diode bridge; diode; electrolytic capacitor; fuse; jumper; light emitting diode; PIC chip; potentiometer; resistor; and voltage regulator ?
Use the underlying measurement and production equipment; cathode ray oscilloscope; multimeter; and soldering station. The method used includes:
?
Soldering a pre-conceptualized kit ?
Modeling the electrical power supply in MultiSIM The results found demonstrated:
?
Unidirectional property of diodes ?
Rectification through capacitor bank ?
Rectification through diode bridge Proprietary and Confidential
?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott iii TABLE OF CONTENTS
Executive Summary ………………………………………………………………………………………………………………………………………………………………………. ii
Table of Contents ………………………………………………………………………………………………………………………………………………………………………….. iii
List of Figures ………………………………………………………………………………………………………………………………………………………………………………… iii
1 Introduction …………………………………………………………………………………………………………………………………………………………………………… 1
1.1 Theory …………………………………………………………………………………………………………………………………………………………………………….. 1
1.1.1 Rectification of Alternative-Current signal into Direct-Current ………………………………………………………………….. 1
1.1.2 Variability of voltage source through potentiometer …………………………………………………………………………………….. 2
1.1.3 Voltage drop attributed to increasing current ………………………………………………………………………………………………… 2
2 Method ……………………………………………………………………………………………………………………………………………………………………………………. 3
2.1 List of Tools …………………………………………………………………………………………………………………………………………………………………… 3
2.2 Setup Procedure …………………………………………………………………………………………………………………………………………………………… 3
3 Result Discussion ………………………………………………………………………………………………………………………………………………………………….. 4
3.1 Unidirectional property of diodes …………………………………………………………………………………………………………………………….. 4
3.2 Rectification through capacitor bank ………………………………………………………………………………………………………………………. 4
3.3 Rectification through diode bridge …………………………………………………………………………………………………………………………… 4
3.4 Load tests ………………………………………………………………………………………………………………………………………………………………………. 4
4 Conclusion ……………………………………………………………………………………………………………………………………………………………………………… 5
5 Appendices …………………………………………………………………………………………………………………………………………………………………………….. 6
5.1 Circuit design …………………………………………………………………………………………………………………………………………………………………. 6
5.2 Circuit diagram ……………………………………………………………………………………………………………………………………………………………… 6
5.3 Logbook …………………………………………………………………………………………………………………………………………………………………………… 8
5.3.1 Practical 1: MultiSIM Circuit Simulation …………………………………………………………………………………………………………… 8
5.3.2 Practical 2: Positive Variable Voltage Supply ………………………………………………………………………………………………….. 4
5.3.3 Practical 3: Negative Variable Voltage Supply ………………………………………………………………………………………………… 2
5.3.4 Practical 4: The Fixed +5V Output …………………………………………………………………………………………………………………….. 3
5.3.5 Practical 5: Finishing the Power Supply …………………………………………………………………………………………………………… 6
5.3.6 Practical 6: Demonstrating the Power Supply ………………………………………………………………………………………………… 7
5.5 SI Prefixes ………………………………………………………………………………………………………………………………………………………………………. 9
5.6 SI units for electronic components …………………………………………………………………………………………………………………………… 9
5.7 Safety considerations ………………………………………………………………………………………………………………………………………………… 10
LIST OF FIGURES
Figure 1.1: Circuit design …………………………………………………………………………………………………………………………………………………………….. 1
Figure 1.2: Circuit design …………………………………………………………………………………………………………………………………………………………….. 2
Proprietary and Confidential ?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 1 1 INTRODUCTION
The
The successful development of the circuit marked our success. The appearance of our circuit is rather
Figure 1.1: Circuit design
The production manual however, didn’t mandate a simple AC to DC signal conversion. The purpose of the extensiveness of conversion
objective of this project was to develop a power supply which converted AC into DC voltage. Of course, engineering development is never warranted without complementary testing and analytics. The scope of the practical was the use of a pre-designed board, in accordance with a guide by Everingham (2009). chic, as shown in the picture below. This AC to DC transformation is shown through the plugging of monitoring equipment into the green tri- and quart- units, as demonstrated below: 1, is so that students could make empirical observations, contrasting (1) a positive source versus a negative source; contrasting (2) various voltages; contrasting (3) rectification by a single diode (used in conjunction with analog electronics) versus a diode bridge (used in conjunction with digital electronics). With the digital logic switch and square wave generator, this production also provides a good foundation for students to transit into further studies in digital electronics from analog electronics. 1 They included (1) one positive, variable voltage source (1 to 12 volts); (2) one negative variable voltage source (-1 to -12 volts); (3) one fixed, regulated +5 source; (4) one TTL digital switch, , which allowed to change the output to either 0V or +5V (corresponding to digital low and digital high respectively); and (5) One alternative 0V/5V square wave output, with adjustable frequency
The concept of soldering is introduced, and various other electronic devices and circuit components are also introduced. As a result, the production of this power supply warrants as a powerful resource to introduce students into the world of electrical and electronics engineering.
1.1 Theory
The square wave generator and TTL logic switch has not been discussed, because it seems that discussion of these components fall outside the scope of this course, and are only incidental to the operation of the circuit.
1.1.1 Rectification of Alternative-Current signal into Direct-Current
In order to fulfill the core competency of converting AC into DC signal, the input sinusoidal wave must undergo numerous alterations to produce a signal that is linear, rather than sinusoidal. The optimal output DC signal would have a number of attributes, including: (1) adherence to expected voltage output; (2) linearity of wave as a DC signal; and (3) the sustainability of the signal under high current pressure.
1.1.1.1 Rectification through diode
Proprietary and Confidential ?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 2 1.1.1.1.1 Rectification through single diode
A single diode achieves half-wave rectification. This is possible through the chemical property of a diode, which allows current pass in uni-directionally. Subsequently, half the sinusoidal signal will disappear, as shown below.
Figure 1.2: Circuit design
By reversing the single diode, it is possible to achieve half-wave rectification in the opposite polarity, thus switching a positive variable supply into a negative variable supply.
1.1.1.1.2 Rectification through diode bridge
Whereas the variable sources are rectified through a single diode, the difference with the +5 source
2 is that the signal is rectified through a diode bridge. A diode bridge can deliver full-wave rectification (as contrasted with a single diode that delivers half-wave rectification), which differs to half-wave rectification because full-wave rectification utilizes the entire wave, flipping opposite polarities into the same polarity; whereas half-wave rectification omits half the entire polarity of a wave. As a result, less capacitors (two rather than three capacitors in the capacitor bank) can be used to achieve a nice, smooth DC signal. 2 Other differences are that it only has two capacitors in the filtration bank, a different model voltage regulator, and lack of variability.
3 The transient theory of capacitors is that between being fully charged or fully discharged (in “steady states”), it moves through transience.
4 The rectification through a capacitance bank based on the theoretical assumption that when a capacitor is charging, the charge exponentially increases until it hits its next steady state; and that when a capacitor is discharging, the charge exponentially decreases until it hits its next steady state. This is conjugated by the theoretical assumption that when the AC signal first approaches its positive slope, it is a rather steep increase, which as it turns into a negative slope, decreases in steepness at an increasing rate
1.1.1.2 Rectification through capacitor bank
Although a diode (particularly the single diode) provides half-wave rectification, the signal, even though either entirely positive or entirely negative, still lacks the linearity required for DC output. As a result, the transient theory of capacitors
Mathematically
3 provides a complementary characteristic, whereby if the power stored in the capacitor is combined with the half-rectified signal of the circuit, a rather linear wave can be created. The surplus of capacitors leads to increased ripple rejection. From an engineering perspective, the cost of increasing capacitors must thus be balanced against the quality conformance of a highly linearity signal. 4, when the capacitor is conjugated with the half-rectified AC signal, as the AC slowly approaches its negative slope, the capacitor will slowly increase its discharge of power; and as the AC slowly approaches its positive slope, the capacitor will slowly decrease its discharge of power. 1.1.1.3 Rectification through voltage regulator
The voltage regulators include: (1) LM317T (positive variable voltage supply); (2) LM337T (negative variable voltage supply); and (3) MC7805CT (+5V regulated supply). Post capacitor bank-rectification, these provide good voltage regulation.
1.1.2 Variability of voltage source through potentiometer
The variability of the voltage source can be attributed to the use of potentiometers, which is effectively a voltage divider circuit, that depending on the screw clock-face location, divides the voltage from the source between two different outputs at varying intensities.
1.1.3 Voltage drop attributed to increasing current
As the load (current) of the power supply increases, the power supply becomes overloaded, and the voltage drops away (and voltage variability
5 increases). This distinguishes the ideal from the real voltage values, from the V-I load characteristic graph. Proprietary and Confidential ?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 3 5 Voltage variability is also known as “ripple”
6 Diode bridge is similar to the diode, but has increased effectiveness, due to full wave rectification of an AC signal.
7 Diode only allows current to pass through it in one direction, not the other, useful due to its half-wave rectification of an AC signal.
8 Electrolytic capacitor stores energy in the form of an electric field.
9 Fuse is a low-cost switch, that “blows” when an unexpectedly large current passes through. This can potentially protect the circuit, which if “blown”, could cost more than the replacement of the low-cost fuse.
10 Jumpers are low-cost switches, that are used in this project to warrant quick (dis/)connection of the capacitors, for testing purposes. When attached (physically), jumpers will connect the two adjoining legs of the circuit together; but when disconnected, will keep the two adjoining legs disconnected.
11 The LED provides easy illumination and indicates current is passing through that phase of the circuit. This had to be used in conjunction with a resistor, as too little current (high resistance) led to dim glow; and too high current (little resistance) would cause the LED to “burn out”.
12 This is a programmable chip for the control of digital circuits.
13 Through the circuit of two resistances, the sum is a given value, combination dependent on the clock-face.
14 Resistors resist the flow of current, depending on their resistance, depending on the color of their bands.
15 Voltage regulators regulate voltage, ideally independent of current
16
Voltage between terminals of a CRO deflects an electron beam up or down, proportional to the magnitude of voltage (they are effectively complex voltmeters). An internal circuit sweeps this electron beam from left-to-right, proportional to a user-set time-based control. This results in a plot of voltage against time, on a phosphorescent screen. There are generally two painted divisions: (1) time per division (time/div), called the time base16; and (2) volts per division (volts/div), called the voltage scale16. The coupling switch may also be needed to switched to GND (or OFF) mode16; AC mode16; and DC mode16. DC mode is the most likely required setting. 17
18 Soldering is the systematic attachment of a component with the circuit board. Through a combination of physics and chemistry laws, a component can be easily attached to a circuit, in abidance with standards set by the peak electrical engineering associations, by soldering a component’s cut legs. In effect, the solder attaches to both the circuit and component, causing them to become adjoined. In practice however, this may not be an exact; what is warranted, is that since a metallic blob has been adjoined to the end of a metallic component (adjoined under high temperature, unwavering at lower temperatures, particularly room temperatures), the component is unable to be disconnected from the board due to the size of the component (on one side), size of the metallic blob (on the other side), and the relatively smaller size of the hole, which causes the component to remain coercively adjoined.
A combination of measurement devices in a single unit, which can read voltage, current, resistance, and possibly more (depending on multimeter). Some can also measure temperature! There may be more than two terminals, but only two of them are ever used at once. The terminal labeled “COM” (short for common) is where the ground/negative always goes. The positive terminal generally goes in a terminal labeled ” V?A”. The multimeter functions as a (a) voltmeter17; (b) ammeter17; and (c) ohmmeter17 2 METHOD
All relevant calculations have been appended.
2.1 List of Tools
The
The
In order to use the cathode ray oscilloscope, we put the coupling switch on to “DC mode”, where both AC and DC components of the input are shown on the CRO screen. We then attached the relevant Channel diodes to the respective test point, and using a television production camera, recorded the associated wave form. If the vertical and horizontal axis caused unease of view, knobs were subsequently turned to adjust for a ergonomic view.
In order to use the multimeter, the mode of operation was first set. Next, the ground/negative was attached to the “COM” terminal; and the positive lead into the V?A terminal.
materials used to develop the final product includes (1) diode bridge6; (2) diode7; (3) electrolytic capacitor8; (4) fuse9; (5) jumper10; (6) light emitting diode11; (7) PIC chip12; (8) potentiometer13; (9) resistor14; and (10) voltage regulator15. The features of these components have been appended and footnoted. equipment used to develop the final product includes (1) measuring equipment; and (2) production equipment. Measurement equipment used in this project include; (a) cathode ray oscilloscope16; and (b) multimeter17. Production equipment included the (a) soldering station18. 2.2 Setup Procedure
In order to develop the final product, the team went through the systematic process of soldering exclusively in
Even before starting the mandate to build the electrical power supply, to team took to the engineering design studio to model the circuit in
sequitar adherence with the manual. Furthermore, the team maintained the logbook with updates for every week to ensure that all concepts were pre-understood. As a step-by-step guide was provided, little thought had go into the development process, with the exception of ensuring that the guide was followed unerringly. As a result, there was particular emphasis on (1) component polarity; and (2) contrasting between similarly looking (but different) components. By following the guide, the need to identify color codes for resistors and resistors pre-LED were also quite straight-forward. MultiSIM, a computer aided design program used in conjunction with electrical engineering. The virtual oscilloscopes and multimeters provided useful expectation of values. Proprietary and Confidential ?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 4 3 RESULT DISCUSSION
Results
were empirically quantitatively measured from the (1) cathode ray oscilloscope; and (2) multimeter. The relevant graphs and readings (subsequently tabled and graphed) have been appended. Discussion
of the results begins with outlining the major headlines. This included: (1) the unidirectional property of diodes; (2) rectification through capacitor bank; (3) rectification through diode bridge; and (4) load tests. Although the (5) generation of square wave, was also a consideration in the practical, the handbook seems to indicate that its understanding is not critical in the scope of this course, thus is omitted from discussion. 3.1 Unidirectional property of diodes
By measuring the diode in the positive direction
19 we obtained a measurement of 6.36? In reverse, the negative direction20, we obtained 0? This was an expected result, and demonstrates the unidirectional property of diodes. This unidirectional chemical property is not exclusive to electrical engineering, and has many applications (even with other analogous materials) in other engineering areas, including optics. 19 Using H4 to H12
20 Using H4 to H12, once again
21 14.38-13.75=0.63V
22 1-(6.14/12.02)=48.9%
23 1-(9.6/12.01)=20.1%
24 1-(4.024/6)=32.9%
25 1-(5.936/6)=1.067%
26 1-(4.950/5.057)=2.12%
3.2 Rectification through capacitor bank
The CRO was used to observe the input AC voltage by circumventing the capacitor bank. It was found that as more capacitors were added through the connection of jumpers, the signal, qualitatively, became more and more flat. Quantitatively, we found the maximum voltage didn’t correspond with the expected maximum voltage, with a deviation of 0.6V
21 above the expected value. This is attributed to the use of a 12V input supply rather than a 10V supply. With the attachment of the diode, capacitor bank, and voltage regulator, we found ripple to be negligible, which is expected as linearity necessitates variance deficiency. 3.3 Rectification through diode bridge
Using the CRO to contrast the effect of a diode bridge against a single diode, we observed a blazing full-wave half-rectified signal, as supposed to the half-wave rectified signal. This a more sinusoidal result than the half-wave rectified signal, which means less capacitors need to be used to lineate the wave. As expected, ripple was negligible (despite the use of two, rather than three capacitors), showing the conceptual advantage of the diode bridge over the capacitor bank.
3.4 Load tests
(Additional) current was applied between 0A to 0.5A, to various voltage supplies. By the application of 0.5A, the variance (? of voltage was found to be (from the statistical mean, ?:
?
+12V supply: 49%22 drop ?
-12V supply: 20%23 drop ?
+6V supply: 33%24 drop ?
-6V supply: 1%25 drop ?
It seems as though depending on the initial voltage, the drop varies. It seems as though as the initial voltage is larger, the proportional drop is also larger. Furthermore, an interesting observation is that the negative supply seems to be less susceptible to load drop than the positive supply. Also, the use of the diode bridge shows great improvement in load drop.
+5 supply: 2%26 drop Proprietary and Confidential ?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 5 4 CONCLUSION
In this project, we felt we successfully applied the theoretical principles learnt in this course to the building of an electronic device, despite some problems that we had to overcome. In particular, in approaching the project, we had little understanding of modern testing and measurement equipment; as well as only preliminary soldering knowledge. Throughout the project, with the assistance of the University community, we learnt how to use such technologies.
The power supply was tested as fully functional (we have Appended a systematic manual to achieve this as well); have successfully drawn up this Project Report; as well as fully appended our Logbook. This was all done to a high level of quality conformance, and good practices guides provided by the Professor-in-charge.
In addition, with tests conducted on the Cathode Ray Oscilloscope and Multimeter, we found that empirical results corresponded with the theoretical (expected) results. This demonstrated the unidirectional property of diodes; rectification through a capacitor bank; and rectification through a diode bridge.
In the report, we felt we have also communicated well
27. This was in conjunction with the practical procedure, which included development of the practical resource, gathering data, interpreting the results against industry standards. 27 Especially in terms of structure, background theory, procedure, results and plots, discussion and conclusion, and use of technical jargon and referencing as per the requirements of Professional Engineering Certification.
28 Outlined in the Appendix.
29 Our production was ethical as we did not plagiarize; falsify or misrepresent academic records; without expressly stating so.
Furthermore, we went above and beyond the requirements of the course in including published information.
We felt that we worked well collaboratively as a team, as special considerations in the context of the wider society. This included considerations for safety
28, and ethics29. We felt that this project taught us the basic underlying framework for electrical engineering, which would be useful in further years. I also felt that the course was structured in such a way that allowed us to research beyond the scope of the practical, inspiring us of the different circuit possibilities that will be covered in subsequent subjects. Proprietary and Confidential ?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 6 5 APPENDICES
5.1 Circuit design
This is an additional perspective to the one provided in the main section of the report:
5.2 Circuit diagram
This circuit (Everingham, 2009) was provided in the development of the engineering solution. Proprietary and Confidential
?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 7 This is explained as (Everingham, 2009): Proprietary and Confidential
?Do Not Photocopy ©2009 Jeremy Shum & Cassie Stott 8 5.3 Logbook
Included in the Logbook are a series of regular entries created in conformance with the Best Practices Guide, following the requirements of the practical guide. Furthermore, tables, comments, and answers to questions were drawn out using systematic scientific empirical method.
5.3.1 Practical 1: MultiSIM Circuit Simulation
1. Find the voltage drops across R1 and R2 in Figure 1, if
????1=26.3????, ????2=15.7????and ????????????=6????. The first note is that the resistors are in series (therefore current is same throughout circuit)
Circuit wide,
????????=????????????????????=????????????????1+????2 (Ohm’s law; adding of two resistors) Since we are given that
????????????=6????; ????1=26.3????; ????2=15.7?????????????=????????????????1+????2=626.3+15.7=642=17[A] For each individual ,
????????=????????.????(Ohm’s law) For
????1, ????=26.3????; and ????=17[????] (current is global) ?????1=????.????1=17?26.3?3.76[????] For
????2, ????=15.7????; and ????=17[????] (current is global) ?????2=????.????2=17?15.7?2.24[????] Kirchhoff’s Voltage Law states that based on the conservation of energy, that the vector addition of voltages around a circuit must equal to zero (or that input voltage must equal output voltage). Adding up
????1 and ????2, 26.3+15.7=6?, which is the input voltage. 2. Find the voltages VAB, VBC and VAC for Figure 1 if
????1=50????, ????2=34.2????and ????????????=5????. Making the same assumptions as in Question 1 (above):
?????????=????????????????1+????2=550+34.2=25421=0.0594 ?????????1=????1.????=25421?50?2.97[????] ?????2=????2.????=25421?34.2?2.03[????] These two voltages add up to 5V, as per KVL too.
????????????
is the voltage over ????1. This was calculated to be 2.97[V] ????????????
is the voltage over ????2. This was calculated to be 2.03[V] ????????????
is the voltage over ????1 and ????2. This is global voltage, 5[V] 3. Given that
????????????=?????????????????, where X and Y are any points in a circuit, and that ????????????=3????, find ????????????. If
????????????is 3V; ????????????represents a voltage of the same magnitude, in the opposite direction, thus would be -3V rather than 3V. 4. In Figure 1, if
????????????=2????, and ????????????=3????so that ????????????=2+3=5????, find a possible combination of resistances ????1 and ????2. Use Ohm’s Law to find the current which flows through your choice of ????1 and ????2. If
If
If
Because the resistors are plugged in series, the current is same throughout the circuit, using say
As in question 1,
????????????=2????, this means that the voltage through ????1 is 2V. ????????????=3????, this means that the voltage through ????2 is 3V. ????????????=5????, this means that ????????????=5????. ????to denote. ????????=????????????????1+????2=5????1+????2[????] Because current is global
?????1=????.????1=5????1+????2?????1=2 ?????5????1=2????1+2????2 ?3????1=2????2 Or:
?????2=????.????2=5????1+????2?????2=3 ?????5????2=3????1+3????2 ?2????2=3????1 Therefore, as long as
2????2=3????1 or ????2=32.????1 Current then,
????????=????????????????1+????2=5????1+32????1=105????1
| Obviously, there would be zillions of possibilities, but I have used Microsoft Excel to graph 10 different combinations:
????
????[? |
????
????[? |
I [A]
|
| 1.00
|
1.50
|
2.00
|
| 2.00
|
3.00
|
1.00
|
| 3.00
|
4.50
|
0.67
|
| 4.00
|
6.00
|
0.50
|
| 5.00
|
7.50
|
0.40
|
| 6.00
|
9.00
|
0.33
|
| 7.00
|
10.50
|
0.29
|
| 8.00
|
12.00
|
0.25
|
| 9.00
|
13.50
|
0.22
|
