International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
Making LED Lights at Home
Vinay Kumar Ravi#1, Anil Kumar M*2
#
Department of ECE, K L University
Green Fields, Vaddeswaram P.O, Guntur Dt – 522502, Andhra Pradesh, India
*
Department of ECE, K L University
Green Fields, Vaddeswaram P.O, Guntur Dt – 522502, Andhra Pradesh, India
Abstract— This document gives how to make your house glow
with LED lights made by you and reduce the power consumption
for lighting up.
changes from high to low and low to high. This will generate
a square wave at both of the collector terminals. Fig. 2 shows
the multivibrator circuit.
Keywords— Main power supply, DC conversion, LEDs, Power
consumption, Surge protection.
I. INTRODUCTION
During festivals or occasions, all the surroundings are
beautifully decorated with different flashing lights, working
on ac. Here the lights are programmed such that the lights are
flashing, moving; blinking etc…This is what we see in our
daily life. But no one is bothered how it works, how to make it.
In this document I want to show how a simple LED flasher
circuit works with the use of ac power supply. Here
multivibrator circuit which works on dc power supply is used
to generate square wave for flashing of LEDs.
II. WORKING
To know how the LED lights work, we need to know
mainly two things, namely Rectifier and Multivibrator.
A. Rectifier
First there is a step down transformer which steps down the
input voltage to 15v from ac. The obtained wave is also a
sinusoid ally varying signal of RMS voltage 15v. This wave is
sent through a full wave rectifier, which converts the negative
peaks to positive. Then this wave is sent through a filter
circuit which converts the pulsating dc to almost dc. Then this
wave is sent through a regulator which converts into pure dc.
By using different regulators we can obtain different voltages.
Fig. 1shows block diagram of regulated power supply.
Fig. 1 Block Diagram of Regulated Power Supply
B. Multivibrator
By using the 5v dc obtained from the dc power supply
circuit , a astable multivibrator circuit is operated. In an
astable multivibrator circuit we can see that the both sides of
the circuit are same. Due to the noise effect one of the
transistors will be in ON state and the other in OFF state. This
causes the collector output of ON transistor high and the
other output to be low. In the next state the transistor which is
ON will turn OFF and the OFF one to ON. By this the output
ISSN: 2231-5381 http://www.ijettjournal.org
Fig. 2 Multivibrator Circuit
The values of R1, C1 chosen according to the desired
square wave time period and Rc is chosen so required
collector current flows through the transistor to make it ON.
This square wave is given to another transistor
which is connected to LEDs. During positive half cycle the
will be on and the LEDs connected to that transistor will glow.
Remaining LEDs will not glow. This will make the LEDs
glow alternately.
III. DESIGN SPECIFICATIONS
A. Transformer Selection:
Select transformer such that it gives voltage higher
than the required dc voltage you want. Here I require 12v so I
have to choose more than 12v transformer.
B. Diode Selection:
The diode should be selected such that they should
resist the current flow that flows across it. Initially the current
should be obtained from the voltage and the components that
we are placing.
C. Capacitor Selection (Filter) :
Capacitor should be selected such that the ripples
should be less. If you don’t know how to select, put the
maximum capacitance you have and make sure that its voltage
rating is higher than the applied voltage.
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013
D. Regulator Selection:
Regulator should be selected such that the desired dc
output voltage can be obtained. Make sure about the current
that is flowing through it.
E. R1, R2 & C1 selection in multivibrator:
The resistor and capacitor should be selected such
that the required time delays for ON & OFF of LEDs in the
circuit. The time period of the square wave is given by
T=1.386*R1*C1
The resistor R2 should be selected such that the
required current flows through the transistor to make the
operating point in saturation.
IV. CIRCUITS
A. Components Required
Components List:
1. Center tapped transformer: (12-0-12) (1Amp)
2. Diodes: IN4007
3. Capacitors: 1000 µF (25v)
10 µF (25v)
4. Regulators: L7812CV
L7805CV
5. Resistors: 470Ω (0.25w)
47kΩ(0.25w)
1kΩ (0.25w)
22Ω (0.5w)
6. LED’s: Red (20mA)
Green (20mA)
B. DC Power Supply Circuit:
Fig. 3 AC to DC Convertor Circuit
Fig. 3 shows a AC to DC convertor circuit and works better
with transformer rating of output voltage of greater than 15V.
Fig. 4 Multivibrator Circuit
D. Surge Protection:
In some cases there may be excess voltage generated,
which may affect the circuit. So we can place a protection
circuits like placing an MOV(Metal Oxide Varistor) or a
PPTC (Polymeric Positive Temperature Coefficient) or a
resettable fuse.
ACKNOWLEDGEMENT
A successful and satisfactory completion of any
significant task is the outcome of invaluable aggregate
combinations of different people in the radial direction,
explicitly and implicitly.
I would therefore take this opportunity to thank and
express my gratitude to all those without whom this
document wouldn’t be possible.
I would like to thank our project in-charges Mr. M Anil
Kumar for his unfailing encouragement invaluable
guidance and suggestions given to us.
REFERENCES
[1] J.B.Gupta, Electronic Devices and Circuits, 3rd
edition, Katson books, 2009
[2] A.Anand Kumar, Pulse and Digital Circuits, 2nd
edition, PHI Learning Private Ltd, 2008
C. Astable-Multivibrator Circuit:
Fig. 4 shows an astable-multivibrator circuit with a duty
cycle of 50%. Here we are placing a amplifier circuit at the
output of multivibrator circuit so that it can drive more
number of LEDs.
The power supply required for the multivibrator can be
taken from the above circuit shown in fig. 3.
ISSN: 2231-5381 http://www.ijettjournal.org
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