Download 12 volt power supply

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FATIMA
JINNAH
RAWALPINDI
WOMEN
UNIVERSITY
ELECTRONIC CIRCUITS PROJECT
12 Volt POWER SUPPLY
SUBMITTED TO:
SIR AHSAN ILYAS
SUBMITTED BY:
ZAINAB EJAZ........................BSE-2014-027
BSE-II
GROUP-A
DATE OF SUBMISSION: 19/05/2015
TABLE OF CONTENTS
INTRO
02
APPLICATION
02
COMPONENTS
03
TOOLS
04
CIRCUIT DIAGRAM
05
CONSTRUCTION
05
TEST
09
FINISH
10
WORKING
11
REFERENCES
14
1
12 VOLT POWER SUPPLY:
INTRODUCTION:
A power supply is an electronic device that supplies electric energy to an electrical load. The
primary function of a power supply is to convert one form of electrical energy to another
and, as a result, power supplies are sometimes referred to as electric power converters.
Some power supplies are discrete, stand-alone devices, whereas others are built into larger
devices along with their loads. Examples of the latter include power supplies found
in desktop computers and consumer electronics devices.
Every power supply must obtain the energy it supplies to its load, as well as any energy it
consumes while performing that task, from an energy source. Depending on its design, a
power supply may obtain energy from various types of energy sources, including electrical
energy transmission systems, energy storage devices such as a batteries and fuel cells,
electromechanical systems such as generators and alternators, solar power converters, or
another power supply.
All power supplies have a power input, which receives energy from the energy source, and
a power output that delivers energy to the load. In most power supplies the power input and
output consist of electrical connectors or hardwired circuit connections.
APPLICATION:
Power supplies are needed for most every bit of electronics equipment with the exception of
battery-powered devices.
Regulated power supply is the main component of electrical,electronics and as well as
automation equipment. Mobile phone charger, oscilator, amplifier are needed the regulated
power supply.
Power supplies have wide uses in slectronic circuits.They are also used in computers.
Making a Power Supply:
Below
is
the
guideline
to
make
a
12
volt
power
supply.
2
COMPONENTS:
Following components are required:

Piece of veroboard

Four 1N4001 diodes

LM7812 regulator

Transformer that has an output of 14v - 35v AC with an output current between
100mA to 1A, depending how much power you will need. (I found a 16v 200mA
transformer in a broken alarm clock.)

1000uF - 4700uF capacitor

1uF capacitor

Two 100nF capacitors

Jumper wires (I used some plain wire as jumper wires)

Resistor

LED light
3
TOOLS:
Following tools are required to make this power supply circuit:

Soldering iron

Solder, rosin core

Wire cutters

Solder sucker

Wire strippers

Digital multimeter

A thing you can cut veroboard tracks.

screwdriver

Hot glue (To hold components down and make the power supply physically strong
and sturdy.)

And some other tools that you might find helpful.
4
CIRCUIT DIAGRAM:
CONSTRUCTION:
Now, make the circuit on veroboard according to circuit diagram step by step.
5
6
Make sure you get good solder joints and no solder bridges, otherwise your power supply
won't work!
7
TEST:
After you had built your power supply, test it with your multimeter to make sure they are no
solder bridges.
FINISH:
After you tested it, put it in a plastic box or something to protect you from shocks.
But do not operate the power supply when it is not covered, it is very dangerous because of
the mains voltage on the transformer, you will get badly shocked!
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9
WORKING:
A power supply is used to reduce the mains electricity at 240 volts AC down to some thing
more useable, say 12 volts DC.
Step Down Transformer
A step down transformer will step down the voltage from the ac mains to the required voltage
level. The output of the transformer is given as an input to the rectifier circuit.
Rectification
Rectifier is an electronic circuit
consisting of diodes which carries
out the rectification process.
Rectification is the process of
converting an alternating voltage or
current into corresponding direct
(dc) quantity. The input to a rectifier
is ac whereas its output is
unidirectional pulsating dc. Usually
a full wave rectifier or a bridge
rectifier is used to rectify both the
half cycles of the ac supply (full
wave rectification). Figure below
shows a full wave bridge rectifier.
10
A bridge rectifier consists of four p-n junction diodes connected in the above shown manner.
In the positive half cycle of the supply the voltage induced across the secondary of the
electrical transformer i.e. VMN is positive. Therefore point E is positive with respect to F.
Hence, diodes D3 and D2 are reversed biased and diodes D1 and D4 are forward biased. The
diode D3 and D2 will act as open switches (practically there is some voltage drop) and diodes
D1 andD4 will act as closed switches and will start conducting. Hence a rectified waveform
appears at the output of the rectifier as shown in the first figure. When voltage induced in
secondary i.e. VMN is negative than D3 and D2 are forward biased with the other two
reversed biased and a positive voltage appears at the input of the filter.
DC Filteration
The rectified voltage from the rectifier is a pulsating dc voltage having very high ripple
content. But this is not we want, we want a pure ripple free dc waveform. Hence a filter is
used. Different types of filters are used such as capacitor filter, LC filter, Choke input filter, π
type filter. Figure below shows a capacitor filter connected along the output of the rectifier
and the resultant output waveform.
As the instantaneous voltage starts increasing the capacitor charges, it charges till the
waveform reaches its peak value. When the instantaneous value starts reducing the capacitor
starts discharging exponentially and slowly through the load (input of the regulator in this
case). Hence, an almost constant dc value having very less ripple content is obtained.
Regulation
This is the last block in a regulated DC power supply. The output voltage or current will
change or fluctuate when there is change in the input from ac mains or due to change in load
current at the output of the regulated power supply or due to other factors like temperature
changes. This problem can be eliminated by using a regulator. A regulator will maintain the
11
output constant even when changes at the input or any other changes occur. Transistor series
regulator, Fixed and variable IC regulators or a zener diode operated in the zener region can
be used depending on their applications. IC’s like 78XX and 79XX are used to obtained fixed
values of voltages at the output. With IC’s like LM 317 and 723 etc we can adjust the output
voltage to a required constant value. Figure below shows the LM317 voltage regulator. The
output voltage can be adjusted with adjusting the values of resistances R1 and R2. Usually
coupling capacitors of values about 0.01µF to 10µF needs to be connected at the output and
input to address input noise and output transients. Ideally the output voltage is given by
Figure below shows the complete circuit of a regulated +5V DC power supply using
transformer, bridge rectifier, filter (smoothing) and a fixed +5 V voltage regulator. Here we
can use IC 7803(for 3V),7809(for 9 V),7812(for 12V) etc.
…………..………………….…THE END………………………………………
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REFERENCES;
http://en.wikipedia.org/wiki/Power_supply
http://www.instructables.com/id/Make-a-simple-12-volt-powersupply/?ALLSTEPS
http://www.instructables.com/id/How-to-solder/
http://www.instructables.com/id/Choosing-The-Resistor-To-Use-With-LEDs/
http://www.instructables.com/id/HOW-TO-READ-CIRCUIT-DIAGRAMS/
http://www.electrical4u.com/regulated-power-supply/
http://www.hardwaresecrets.com/article/Everything-You-Need-to-KnowAbout-Power-Supplies/181/2
https://www.kitronik.co.uk/blog/how-a-power-supply-works/
http://computer.howstuffworks.com/power-supply1.htm
http://vr-zone.com/articles/how-power-supplies-work/11366.html
http://www.britishtelephones.com/howpowr.htm
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