Using a Combination of a Group of High Efficiency White LEDs and a Unique Voltage Controller Circuit

8/4/2019 Using a Combination of a Group of High Efficiency White LEDs and a Unique Voltage Controller Circuit

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Using a combination of a group of high efficiency white LEDs and a unique

voltage controller circuit, almost an ideal LED emergency lights circuit can be

constructed. We will see the procedure here.

Introduction

We are all aware of the ill effects of the global warming that is gripping the world

strongly with each passing day. Though the major cause of this phenomenon is

the use of fossil fuels as the main source ofenergyby many countries, yet the

contribution of lights to the problem in different forms cannot be entirely ignored

too. The age old incandescent bulbs have become obsolete, but even the

modern CFLs emit quite a bit of heat. White LED lamps today are getting popular

due to their rather "cool" nature and high efficiency.

We will learn in this article how simple it is to construct a versatile LED

emergency lights circuit using a handful of white LEDs and a unique circuit

design that helps to increase the overall efficiency of the unit.

Principle of Functioning of the Present Circuit

The functioning of the present circuit may be understood as follows:
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We know that to illuminate a white LED we need a minimum of 3.6 volts and a

maximum of 20 mA of current. The latter being the forward voltage drop of a

white LED.

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In the present circuit we use a 6 volt battery as the power source. So what's the

big deal in illuminating a group of white LEDs with this battery? That's true, at the

first glance the circuit pretty ordinary - connecting a group of LEDs in parallel to a

battery. But something's special about this circuit. It's the inclusion of four diodes

in series with the LEDs and off course the addition of S1.

We know that according to Ohms law voltage is directly proportional to the

current, implies that if the 6 volt supply is directly applied to the LEDs, they will

start drawing excessive current, resulting in unnecessary dissipation of heat

through the resistors and the LEDs and will discharge the battery very fast,

decreasing the efficiency of the circuit.

This will happen because a potential difference of 6 volts is simply too high than

the forward voltage of the LEDs which is 3.6 volts (as discussed above).

By adding 4 diodes we are able to drop the voltage to exactly the forward voltage

of the LEDs (since each diode will drop a voltage of approx. 0.6 volts).

Thus, when the battery is fully charged at about 6 volts, the LEDs will be

receiving 3.6 volts, just enough to make them glow brightly without dissipating

extra power.

Now suppose the battery voltage drops to an extent when you see the LEDs

become weaker in their intensity, you can simply adjust the switch S1 a step

ahead by-passing one of the diodes. This will immediately restore the brightness

of the LEDs, may be for another couple of hours. After that the procedure may be

repeated by by-passing the next diode.
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Thus you are able to get multiple back-ups using the same battery which

wouldnt be possible if the LEDs were connected directly.

Parts List

You will require the following parts for this plug & play emergency lights circuit:

R1 = 1M, Watt, 5%, CFR,

R2 = 10K, Watt, 5%, CFR

R3 = 10 Ohms 1Watt,

ALL LED RESISTORS ARE = 22 Ohms, Watt,

C1 = 205/400V, PPC,

C2 = 100uF, 25V,

Z1 = 9 V, 1 WATT,

T1 = BD 140,

ALL DIODES = 1N4007,

S1 = SINGLE POLE 3-WAY SWITCH,

BATTERY = 6 VOLTS 4 AH,

LEDS = WHITE, 5mm, HIGH EFFICIENCY.

Why the Present Circuit is Unique?
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Connect a group of white LED s with a few series resistors to a 12 volt battery,

and here we go, a LED emergency light circuit is ready! You will find many such

trivial circuits in many other websites.

The present LED emergency light circuit is different from them because itconsumes very little battery power (6 Volts) and thus remains illuminated for at

least 40% more time than its ordinary counterparts.

It will be interesting for the readers to know that it is the voltage and not the

current that matters to keep the white LED s glowing. This property of white

LEDs has been exploited here.

Construction Clues

CAUTION: THE WHOLE CIRCUIT MAY CONTAINDANGEROUSFLOATING

AC MAINS WHEN SWITCHED ON, SO BE EXTREMELY CAREFUL WHILE

HANDLING AND TESTING THE DEVICE.

The construction procedure is as follows:

Finish the emergency light board assembly by soldering the white LED sand the other parts properly with the help of the given diagram.

Placement and spacing of the white LED s will depend on the cabinet sizeand structure, which may be home built or may be obtained ready-made.

Next, insert and solder the remaining passive components and also thetransistors and the diodes. Be careful with the transistor pin-outs and thediode orientations.

Inter-link correctly each component lead by bending and soldering thecomponent leads together with the help of the circuit schematic.

Clamp the battery and the transformer tightly in the cabinet with only themains cord coming out of it.

Automatic Switch-Over and Battery Charging

This plug and play emergency lights circuit is completely automatic and may be

kept connected to the AC mains permanently.

As long as mains power is alive, T1 receives a direct positive rectified potential

through D1 and thus is unable to conduct. This keeps the LEDs shut off and they

are not able to light up.
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In the meantime, the battery gets slowly trickle charged through D1 and D2.

The moment AC supply fails, the positive potential from the T1's base is

removed, so that now it gets biased through R2 and starts conducting, instantly

illuminating the whole LED array.

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Using a Combination of a Group of High Efficiency White LEDs and a Unique Voltage Controller Circuit

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