power supply winter training

7/26/2019 Power Supply Winter Training

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INTRODUCTION

A power supply needs mainly two things, SOURCE of energy and a REGULATION

MECHANISM to make the power supply meet our needs. Linear Power supply,

taking into considerations the requirements, cost effectiveness, and its

complexity. The Linear supply will be made using mains as its source, and the

output will be regulated.

EAGLE (Easily Applicable Graphical Layout Editor) by Cadsoft is a flexible and

expandable EDA schematic capture, PCB layout, autorouter and CAM program

widely used since 1988. EAGLE is popular among hobbyists because of its

freeware license and rich availability of component libraries on the web.

Audacity is a free open source digital audio editor and recording computer

software application. In addition to recording audio from multiple sources,

Audacity can be used for post-processing of all types of audio, including podcasts

by adding effects such as normalization, trimming, and fading in and out.


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REGULATED POWER SUPPLY

Source is the first requirement for a power supply. The sources may include the

following:

1) Battery

2) Solar cell

3) Heat based Power supply

4) AC mains-220 volts after rectification

The characteristics of a good power supply include -a high energy /stable source

along with a good quality regulator which has a wide range of input voltage with

a small range of output voltage.

Types of regulators:

1) Stabilizers: AC stabilizers which use Autotransformers to regulate the

output with respect to the fluctuating input.

2) Linear Power supply (DC): This type of regulator works in the linear region

of transistor. It can only give the output in step down mode. It is less

efficient as quite a lot amount of power is wasted in this type of regulator.

3) Switching Su pp ly ( DC): Also kn ow n a s Swi tc hi ng M od e Po we r

S u p p ly (SMPS), it is the mode widely used type of regulator due to itsvarious advantages. It is power efficient as it only works in either the

saturation mode or cut-off mode of the transistor. In both the regions, the

ideal power output is zero. Although it keeps on switching, it still gives a

constant output voltage. Moreover, unlike a linear regulator, it can work

in both Buck and Boost modes where buck means step down mode ad

Boost means Step up mode.

Mobile phones use this kind of power supply. Mobiles work on a constant

voltage of 3.3 volts, whereas the battery voltage varies from 2.5 V to 4.2

V. Thus the regulator continuously works to provide the required voltage.

We have made a Linear Power supply, taking into considerations the

requirements, cost effectiveness, and its complexity. The Linear supply will be

using mains as its source, and the output will be regulated.


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LINEAR POWER SUPPLY

Schematic of basic AC-to-DC power supply, showing (from L-R) transformer, full-wave bridge rectifier, filtercapacitor and resistor load

Different stages of our power supply

included:

1. Stepping Down the AC Mains Supply

2. Rectification of the AC

3. Adequate filtering of the rectified output

4. Regulation of the output

5. Delivery of the output

Stepping Down the AC mains

The Ac Mains 220 V was stepped down through a step down transformer

of appropriate rating; lets say 0-12V, which can provide a maximum DC voltage

of 12 x 1.414 =16.97V.

Rectification of AC

There were a few options of rectifiers available like half wave, full wave, and

bridge. We went for a bridge as it does not require a center tapped transformer

and allows exploitation of the complete range of the transformer. This is the

rectified AC wave. We call this wave as DC but actually is Unipolar AC. This Wave

still did not meet our desired characteristics and needed to be filtered.


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Filter Action

The Unipolar AC needed to be filtered to convert it into usable DC. Thus a

filter circuit such as RC or LC or Chunks of LC circuit was required. We went

for a RC filter for its easy design, availability and low maintenance.

In spite of the filtering, we had some fluctuations of operating point due to the

non- ideal characteristics of the filter circuit and as a consequence, noise gets

added.

Regulation of the output

Let us consider the regulator as a Black Box, in which we give the filtered DC Vin

as the Input with Iin as the current, and get Regulated DC voltage Vo as the

output along with maximum current Imax.

This regulator also employs a short circuit protection which does not allow

the current to exceed Imax.

At all times, Imax will be less than Iin ,as some part of the entering current goes

into the biasing of the transistor. Let Iq be the current consumed in the circuit at

no load. Thus the power still consumed by the supply at no load is Vcc*Iq. This

power is wasted in the form of heat.

Regulated Output

The regulated output has to be delivered via some means to power some or

the other devices/appliances/circuits. This was done by installing a two pin

standard connector which was left open circuited. To keep an eye on the output

of the dc voltage, we installed a Led in parallel with the output.

%Load Regulation = / (())

LINE REGULATION: The ratio of change in output voltage to change in input voltage

at a constant load.

%Line regulation = / ((max ) (min ) )


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ZENER DIODE AS VOLTAGE REGULATOR

A Zener diode can be used as a voltage regulator. It is connected in reverse biasmode to act as a voltage regulator. The current-voltage (I-V) characteristics show

that the voltage remains constant over a range of input voltage and thus helps in

regulation. But the current drawn at any value of load is constant in case of Zener

diode and a part of current of the Zener diode flows in the load at any time. The

total current cannot exceed the max rating of the Zener diode. It is useful in case

where load requirements are significantly low.

To increase the load regulation by some amount in the Zener regulator, we usethe following configuration:

Zener with CC Amplifier configuration


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Moreover, When Rc is connected and needs 100 mA, (let =100), the base needs

1mA of current. If Zener diode had 20 mA flowing in it, and now 19mA will still be

flowing in it, thus suggesting that the change in Zener voltage will be very less and

the transistor has also increased the load capabilities of the this regulated supply.

Here the current is increased by times and thus voltage regulation is decreased

by times. For D3 to show the same drop as the T1, take another transistor andreplace D3 with it with its collector and base shorted. This makes sure that the

diode and base emitter junction are exactly identical.

Short Circuit Protection

Now consider the situation where the output is shorted. In this case, the whole

current will be diverted to base and the zener diode will become ineffective thus

increasing the power dissipation tremendously and may even damage the

appliance. Excessive heat may even melt the transistor, making the circuit

useless.

Thus we employ a short circuit protection mechanism in our regulator.

Here we can see that another transistor T2 has been

employed into the circuit. This acts as the short

circuit protector. The resistor R2 is connected

between the base and emitter of the T2. Let the

current flowing in T2 be Ix. If Vbe= Ix*R2 becomes

equal to 0.7 V i.e. the forward drop voltage of the B-

E junction of T2, the T2 starts conducting, thus taking

a major part of base current of base of T1, and

depriving T1 from base current, ultimately forcing T1

into the cut-off region.

Thus, Imax= Vbe/R2, even in the case of short

circuit. Thus we can independently set the value of

Imax on the basis of its deciding factor, i.e. the value

of R2.


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Characteristics of the output voltage w.r.t Current. We see that the at Imax , voltage becomes zero.


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USE OF OP-AMP

Op-Amps or operational amplifiers are a breakthrough in electronics. They have a

wide application in the field of electronics. Op-amps are amplifiers which have

characteristics that are very close to the characteristics of ideal amplifier. They

have very high input impedance and very low output impedance, which are the

basic desired characteristics of an amplifier. Although they have very high open

loop gain (ideally infinity), but their closed loop gain can be controlled very

precisely according to our needs just by using two resistors.

In op-amp has three terminals, mainly an Inverting

terminal, A Non-inverting terminal and An Output

terminal.

We had used op-amp in closed loop gain form to

achieve a controlled gain.

We can use the following rules while using an op amp in closed loop configuration.

1) The voltage difference between inverting and non inverting terminal is

zero.

2) The current going in/out of the inverting or non-inverting terminals of the

op- amp is zero.

This is the diagram of op-amp used as an

amplifier in non-inverting configuration.

The Vout can be calculated by using

Kirchhoffs voltage and current laws.

The total amplifier gain is found out to be:

A0=1+

.


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We provide Vin by the means of Zener diode. We used the second configuration

of zener for a wider range, stability and less deviation of the zener voltage, i.e.

this configuration , as explained earlier is very

useful.

Now, although the output we were getting was regulated, the current

requirements were still high. The average and maximum current provided by

an op-amp is very low, i.e. of the order of 20mA and thus needed to be

amplified further. Thus we used a Transistor in Common Collector

configuration to achieve the desired characteristics of the current without

any amplification in voltage.

The modified circuit diagram is as follows :

Although this configuration takes care of the current requirement but this

configuration leads to loss of voltage V developed at the output terminal of the op-

amp.


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The main objective of using an op-amp fails with this. Thus we make a further

modification to take care of the Vout developed at the end output across load

R6.

We took the feedback from the

emitter leg of transistor T1

instead of taking from the op-

amp. This took care of any

voltage drop that occurred

between Output terminal of op-

amp and load resistor R6.

The Modified Circuit is As follows:

Thus

Vout= Vout+ Vbe and

Vout should be well

within the limits of Vcc

sothat saturation does not

occur.

Now to make the Vout variable and achieve any value, we make one of the feedback

resistors variable.

Short Circuit Protection

Here, transistor T2 acts as a short circuit protector and RC is the maximum current

deciding factor.


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Use of IC LM723

As we have seen above, the regulator circuit requires a lot of components to

work properly.

But, we have an IC LM723, which has most of the above components bundled in it.

The Zener Input configuration, Op-amp, and Short Circuit Protection is bundled in

itself, thereby reducing the size and labour and also increasing the reliability of the

circuit. The device can be connected to operate as a positive or negative voltage

regulator with an output voltage ranging from 2 V to 37 V, and output current

levels up to 150 m A. The maximum supply voltage is 40 V, and the line and

load regulations are each specified as 0.01%.

The rectified and filtered ac signal is used to power LM 723. The 6th pin of this IC is

Vref. It provides the reference voltage of 7.15V. The 5th and 4th pin are non-

inverting and inverting terminal of comparator respectively.


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Delivery of Output

Consider a situation with above circuit but with output delivery at a physically large

distance from the power supply. This will lead to high voltage drop across the long

conductors and thus the actual voltage delivered to the load will be less than that

of desired value. Thus we go for a 4 terminal solution.

The 4 Terminal solution suggests that the op-amp sensing terminals should be taken

along with the delivery wires at the load and must be connected very near to load,

which compensates for the voltage loss.

Use Of capacitors

In the above circuits, capacitors have been used at some places in parallel with load

resistor. These capacitors are known as frequency compensators. The transients

that may occur due to noise during the operation of power supply may also result

in phase change and the negative feedback could be changed to positive feedback.

To avoid that, capacitors are used.

Component Value Selection for Output Value

R1 & (R5+Rx1) form a potential divider at the 5th pin. Similarly, R2 & (R4+Rx2)

forms a potential divider at the inverting terminal. Voltage at +IN terminal =

Vref*(R1+RX)/(R1+R5+RX) Voltage at IN terminal = Vout*(R4+RY)/(R2+R4+RY) If

R2=R5=0, thenVout = Vref = 7.15V

If only R2=0, any voltage less can be made, if only R5=0, any voltage above 7.15V

can be achieved. For Vout=5V, we put, R2=0. Therefore, Voltage at -IN terminal =

5V.

We, therefore, choose R1, R5, RX such that (R1+RX)/(R1+R5+RX)=5/7.15.


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PCB FABRICATION

Printed circuit boards are electronic circuits boards created for mounting

electronic components on a nonconductive board, and for creating conductive

connections between them. The creation of circuit patterns is accomplishedusing both additive and subtractive methods. The conductive circuit is generally

copper, although aluminium, nickel, chrome, and other metals are sometimes

used. There are three basic varieties of printed circuit boards: single sided,

doublesided, and multilayered.

1. Single sided PCB: conductors on only one surface of a dielectric base.

2. Double sided PCB: conductors on both sides of a dielectric base, usually the

two layers are interconnected by platedthroughholes (PTHs).

3. Multilayer: conductors on 3 or more layers separ ated by dielectric material

and the layers are interconnected by PTH or pads 4 layer PCB is a sandwich of 2

double layered PCBs. Likewise 6 layer PCB is a sandwich of 3 double layered PCB.

This sandwiching is done by placing oxidizing material between double layered

PCBs. The spatial and density requirement, and the circuitry complexity

determine the type of board to be produced.

CAD System

Recommended software for the CAD system is EAGLE. This software has

enhanced features like improved interactive routing, user selectable track

width, internal routing loops, PCB routing completion detector, preserving track

angles while dragging, designing bottom layer layout just by flip and editing the

board etc.

Note: Minimum track width requirement is 0.2 mm and minimum spacing

between tracks is 0.2 mm.

We used a very simple and fast technique to make Printed Circuit Boards at Home.

This technique works reliably for thin tracks down to 10 mils, and is suitable for mostsurface-mount parts. Though this technique is not scalable but it is a very efficient

way to help learners bring their ideas into practicality. We use this technique to

make our Power Supply.


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COMPONENTS REQUIRED:

For PCB Fabrication

1) Laser Printer

2) Glossy Paper

3) Household Iron4) Copper Clad Laminate

5) Etching Solution (FeCl3 Solution)

6) Kitchen Scrubs

7) Thinner

For Power Supply

1) IC 723

2) 14 Pin IC Base

3) 1N5399

4) Resistors

5) Capacitors

6) Heat Sink

7) MJE3099

8) DC Power Jack

9) LED

PRINCIPLELaser printers and photocopiers use plastic toner, not ink, to draw images. Being

plastics, toner is resistant to etching solutions used for making PCBs. Like most

plastics, toner melts with heat, turning in a sticky, glue-like paste. So print the board

layout on paper as usual, place the sheet face-down on PCB copper, and melt toner

on copper applying heat and pressure. This can be achieved using household iron.

Now when we remove paper from copper clad we are left with copper clad with

tracks of toner on it. When we etch it a FeCl3 solution, the result is a board with

black tracks of toner on it. Remove the toner using Scrub. And the Printed CircuitBoard is ready.


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STEPS INVOLVED

Step 1: Creating PCB layout of your circuit

This is done by converting your circuit's schematic diagram into a PCB layout

using PCB layout software like EAGLE.

Step 2: Take printout of PCB layout

Take a print out of your PCB layout using the laser printer and the A4 photo

paper/glossy paper.Keep in mind the following points:

1. You should take the mirror print out.

2. Select the output in black both from the PCB design software and printer

driver settings.

3. Make sure that the printout is made on the glossy side of the paper.

Step 3: Cutting the copper plate

Cut the copper board according to the size of layout.

Step 4: Make it smooth

Rub the copper side of PCB using steel wool or abrasive spongy scrubs. This

removes the top oxide layer of copper as well as the photo resists layer.

Sanded surface allow image to stick better

Step 5: Iron on Glossy paper method

Transfer the printed image from the photo paper to the board. Make sure to

flip top layer horizontally. Put the copper surface of the board on the printed

layout. Ensure that the board is aligned correctly along the borders of the

printed layout. Put tape along the two sides of the board non-copper side.

This will help to hold the board and the printed layout in position.

Step 6: Iron it!

After printing on glossy paper we iron it image side down to copper side.

Heat up the Electric iron to the maximum temperature.

Put the board and photo paper arrangement on a clean wooden table and

clothes with the back of the photo paper facing you.


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Hold one end of it by the Towel and put the hot iron on the other end for

about 10 seconds. Now, iron the photo paper all along using the tip and

applying little pressure for about 5 to 15 mins.

Pay attention towards the edges of the board you need to apply pressure,

do the ironing slowly. Long hard press seems to work better than moving iron around.

Here iron heat melts ink printed on glossy paper and get transfer to copper

plate.

CAUTION: Do not directly touch copper plate because it is very hot due to ironing.

Step 7: Peeling

After ironing, place printed plate in Luke warm water for around 10 minutes.

Paper will dissolve and remove paper gently. Remove the Paper off at lowangle & traces.

Step 8: Etching

1. Take a plastic box and fill it up with some water.

2. Dissolve 2-3 tea spoon of ferric chloride power in the water.

3. Dip the PCB into the Etching solution (Ferric chloride solution, FeCl3) for

approximately 30 mins.

4. The FeCl3 reacts with the unmasked copper and removes the unwantedcopper from the PCB.

5. This process is called as Etching. Use pliers to take out the PCB and check

if the entire unmasked area has been etched or not. In case it is not etched

leave it for some more time in the solution.

Gently move plastic box to and fro so that etching solution react with exposed

copper and form iron and copper chloride.

After every 2-3 minutes check whether all copper is etched or not.

Step 9: Spray with anti-oxidant

Spray an anti-oxidant on it so as to prevent copper from oxidation. Now we

have our PCB complete.

Step 10: Dry

Let PCB dry for 15 mins.


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Step 11: Drilling

Drill holes in PCB with suitable drills.

Step 12: Finishing

Smooth the edge of PCB to prevent cutting, clean any dust present on PCBby blowing air without touching copper. Screw corner holes

Step 13: Soldering

Put the soldering station on your right hand for soldering without

hindrance.

Use mildly wet sponge for cleaning soldering iron.

For easy soldering make right angle between body base and leg and

insert in PCB.

First warm the legs of component then apply soldering wire.

Remove extra metal with clipper.

Clean soldering iron again.

Repeat above method for soldering every component.

You can also repair any broken circuit route with soldering wire.

Step 14: Take the Reading

Test the power supply for various load voltages and currents.

Note down the readings.


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SCHEMATIC

Board Layout


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Component used in PCB fabrication


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Print-out of board layout on a Glossy Magazine paper

Cleaned surface of copper clad

Iron used on a wooden block for transferring glossy magazine paper tone to copper clad

FeCl3 solution for removing exposed copper from copper clad


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Drill used for making 3mm holes

PCB before installing components

Soldering Station

Completed Power Supply


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OBSERVATIONS

The Power Supply when tested gave the following readings when connected to an

electronic load

S.NO. Current(mA) Voltage(V)

1. 88.59 11.99

2. 197.8 11.98

3. 223.25 11.95

4. 250.62 12.00

5. 285.23 11.97

6. 305.62 11.93

7. 332.35 11.91

8. 425 11.45

9. 545 1.35

10. 565.3 0.53

11. 599.36 0.32

Graph between Current and Voltage


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EAGLE CAD

EAGLE (Easily Applicable Graphical Layout Editor) by Cadsoft is a flexible andexpandable EDA schematic capture, PCB layout, autorouter and CAM program

widely used since 1988. EAGLE is popular among hobbyists because of its

freeware license and rich availability of component libraries on the web.

Schematic Editor

In this we can create circuit schematics in the symbolic form. The various

commands used in this are:

INFO Shows information about an object (component, signal, trace, etc.)

MOVE Allows components to be moved (same as schematic.)

GROUP Groups a collection of objects into a "group" that can be

manipulated.

DELETE Delete an object. Items created in schematics need to be deleted there.

SMASH Separate the text labels of a part from the part itself, so they can be

moved independently.

BREAK Add a corner to a line (or trace.)

ROUTE Turn an air wire into a trace

LINE Draw lines (usually in non-copper layers. ROUTE is for drawing copper.

VIA Create a hole and pad associated with some signal

HOLE A hole that isn't associated with a signal, i.e. for mounting.

RATSNEST Recomputes air wires and polygons, example after components

have been moved.

CHANGE Changes an object's properties.

RIPUP Changes a routed trace back to an air wire.TEXT Add text

POLYGON Create a polygon (actually, we'll use a text command.)

DRC Invoke the Design Rule Check and parameter setting.


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Board Layout Editor

Up in the file menu, there's a "Switch to board" selection. If we do that from a

bare schematic, it will offer to create the board from the schematic for us (say

"yes"), and then leave us sitting in the Board Editor.

The various commands used in board layout editor are:

AIR WIRES All the signals you created in the schematic are currently airwires;

thin yellow lines that are drawn in the shortest possible way, crossing each

other as needed. They stay connected to component pins even when you move

the component around.

RATSNEST Recomposes and redraws these after you move things around

(and, say, make two connected pins closer together than they used to be.)

ROUTING A signal consists of turning an air wire into an actual copper trace

on some layer(s) of the board, and positioning that trace so that it doesn't short

against other traces on the same layer of the board.

AUTOROUTE Invokes the auto router.

POWER PLANES are large areas of copper that carry an actual signal, usually

power and ground. On multi-layer boards, it's common to have entire layersmostly dedicated to such a power plane. Even on a single layer board there are

some advantages to doing something similar:

1) Use less etchant

2) Carries heavier current, just in case

3) Makes it easier to attach test leads


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AUDACITY

Audacity is a free open source digital audio editor and recording computer

software application. In addition to recording audio from multiple sources,

Audacity can be used for post-processing of all types of audio, including podcasts

by adding effects such as normalization, trimming, and fading in and out.

Features

Audacity can record live audio through a microphone or mixer, or digitize

recordings from other media. With some sound cards, and on any recent

version of Windows, Audacity can also capture streaming audio.

Import sound files, edit them, and combine them with other files or new

recordings. Export your recordings in many different file formats, including

multiple files at once.

Supports 16-bit, 24-bit and 32-bit (floating point) samples (the latter

preserves samples in excess of full scale).

Sample rates and formats are converted using high-quality resampling and

dithering.

Tracks with different sample rates or formats are converted automatically in

real time. Adjusting audio pitch while maintaining speed and adjusting audio speed

while maintaining pitch

Conversion of cassette tapes or records into digital tracks by automatically

splitting the audio source into multiple tracks based on silences in the source

material

Cross-platform operation Audacity works on Windows, Mac OS X, and

Unix-like systems (including Linux and BSD)

Audacity uses the wxWidgets software library to provide a similar graphical

user interface on several different operating systems


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Lissajous Curve

Lissajous curves are the family of curves described by the parametric equations

sometimes also written in the form

They are sometimes known as Bowditch curves after Nathaniel Bowditch, who

studied them in 1815. They were studied in more detail (independently) by Jules-

Antoine Lissajous in 1857. Lissajous curves have applications in physics, astronomy,

and other sciences. The curves close if is rational. Lissajous curves are a

special case of the harmonograph with damping constants

power supply winter training

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