Emergency Lighting Fluorescent Lamp

Abstract:

An emergency light essentially consists of a source of electricity – a rechargeable

battery pack and an automatic sensing circuit to check the presence(or absence) of

mains supply.The sensing circuit connects a lamp (or a compact fluorescent tube

inverter) circuit in the event of mains failure and disconnects it when the mains

supply is restored.When ac mains supply is available,a charger circuit charges the

battery pack to keep it in top condition

Introduction:

 The 8w emergency lighting converter shown here can be constructed at a fraction of the cost of older 

to220 transistor based designs Using the ztx851 which has a saturation voltage of only 150mv at 4a 

(the cycle by cycle peak current seen with this design), the circuit runs with an efficiency of over 70%, a 

key feature for these battery operated circuits. Care with the transformer design and construction will 

allow the use of the higher gain ztx869 br>which will raise efficiencies even higher 

the ztx851 and ztx869 are available in the e-line (to92 style) package which has a 1.2w power rating for 

these device types. this permits significant space savings to be made since the bulky 

to220 transistors and corresponding heat sinks can be eliminated the operating frequency has been 

limited to around 25khz to minimize transformer losses, yet ensuring the converter is inaudible. 

Emergency lighting systems provide illumination in the event of mains failure and consist of a monitor 

circuit, a battery pack with trickle charging, and a dc-ac inverter the inverter is used with the existing 

fluorescent tubes or an additional smaller tube, and is enabled by the monitor circuit.

CIRCUIT:

This super simple design of an inverter circuit does not limit it in any way from providing a high output power and an efficiency of a good 75%. Learn how to build an inverter that will satisfy most of your power requirement at quite an affordable cost.

The article deals with the construction details of a mini inverter. Read to know how to build an inverter which can provide reasonably good power output and yet is very affordable and sleek.

There may be a huge number of inverter circuits available over the internet and electronic magazines. But these circuits are often very complicated and hi-end type of inverters. Thus we are left with no choice but just to wonder how to build an inverter that can be not only easy to build but also low cost and highly efficient in its working. Well your search for such a circuit ends here. The circuit of an inverter described here is perhaps the smallest as far its component count goes yet is powerful enough to fulfill most of your requirements.

Construction Procedure

This simple mini inverter circuit can be completed through the following easy steps:Cut two sheets of aluminum of 6/4 inches each.Bend one end of the sheet as shown in the diagram. Drill appropriate sized holes on to the bends so that it can be clamped firmly to the metal cabinet.Also drill holes for fitting of the power transistors. The holes are 3mm in diameter, TO-3 type of package size.Fix the transistors tightly on to the heatsinks with the help of nuts and bolts.Connect the resistors in a cross-coupled manner directly to the leads of the transistors as per the circuit diagram.Now join the heatsink, transistor, resistor assembly to the secondary winding of the transformer.

Fix the whole circuit assembly along with the transformer inside a sturdy, well ventilated metal enclosure.Fit the output and input sockets, fuse holder etc. externally to the cabinet and connect them appropriately to the circuit assembly.

Circuit Description

The functioning of this mini inverter circuit is rather unique and different from the normal inverters which involve discrete oscillator stage for powering the transistors.However here the two sections or the two arms of the circuit operate in a regenerative manner. Its very simple and may be understood through the following points:The two halves of the circuit no matter how much they are matched will always consist a slight imbalance in the parameters surrounding them, like the resistors, Hfe, transformer winding turns etc.Due to this, both the halves are not able to conduct together at one instant.Assume that the upper half transistors conduct first, obviously they will be getting their biasing voltage through the lower half winding of the transformer via R2.However the moment they saturate and conduct fully, the entire battery voltage is pulled through their collectors to the ground.This sucks out dry any voltage through R2 to their base and they immediately stop conducting.This gives an opportunity for the lower transistors to conduct and the cycle repeats.The whole circuit thus starts to oscillate.The base Emitter resistors are used to fix a particular threshold for their conduction to break, they help to fix a base biasing reference level.

REGULATED POWER SUPPLY:

The power supplies are designed to convert high voltage AC mains electricity to a suitable low

voltage supply for electronic circuits and other devices. A RPS (Regulated Power Supply) is the Power

Supply with Rectification, Filtering and Regulation being done on the AC mains to get a Regulated

power supply for Microcontroller and for the other devices being interfaced to it.

A power supply can by broken down into a series of blocks, each of which performs a

particular function. A d.c power supply which maintains the output voltage constant irrespective of a.c

mains fluctuations or load variations is known as “Regulated D.C Power Supply”

For example a 5V regulated power supply system as shown below:

Transformer:

A transformer is an electrical device which is used to convert electrical power from one Electrical 

circuit to another without change in frequency.

Transformers convert AC electricity from one voltage to another with little loss of power.

Transformers work only with AC and this is one of the reasons why mains electricity is AC. Step-up

transformers increase in output voltage, step-down transformers decrease in output voltage. Most power

supplies use a step-down transformer to reduce the dangerously high mains voltage to a safer low

voltage. The input coil is called the primary and the output coil is called the secondary. There is no

electrical connection between the two coils; instead they are linked by an alternating magnetic field

created in the soft-iron core of the transformer. The two lines in the middle of the circuit symbol

represent the core. Transformers waste very little power so the power out is (almost) equal to the power

in. Note that as voltage is stepped down current is stepped up. The ratio of the number of turns on each

coil, called the turn’s ratio, determines the ratio of the voltages. A step-down transformer has a large

number of turns on its primary (input) coil which is connected to the high voltage mains supply, and a

small number of turns on its secondary (output) coil to give a low output voltage.

An Electrical Transformer

Bridge Rectifier:

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve

full-wave rectification. This is a widely used configuration, both with individual diodes

wired as shown and with single component bridges where the diode bridge is wired

internally.

   A bridge rectifier makes use of four diodes in a bridge arrangement as shown in fig (a) to achieve full-

wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with 

single component bridges where the diode bridge is wired internally.

Fig (A)

Operation: During positive half cycle of secondary, the diodes D2 and D3 are in forward biased while D1 and D4 are in reverse biased as shown in the fig(b). The current flow direction is shown in the fig (b) with dotted 

arrows.

Fig (B)

During negative half cycle of secondary voltage, the diodes D1 and D4 are in forward biased while D2 

and D3 are in reverse biased as shown in the fig(c). The current flow direction is shown in the fig (c) with dotted 

arrows.       

             

                                         Fig(C)

Filter:

A Filter is a device which removes the ac component of rectifier output but allows the dc component 

to reach the load.

Capacitor Filter:

We have seen that the ripple content in the rectified output of half wave rectifier is 121% or that of 

full-wave or bridge rectifier or bridge rectifier is 48% such high percentages of ripples is not acceptable for most 

of the applications. Ripples can be removed by one of the following methods of filtering.

(a)  A capacitor, in parallel to the load, provides an easier by –pass for the ripples voltage though it due to low 

impedance. At ripple frequency and leave the D.C. to appear at the load.

(b) An inductor, in series with the load, prevents the passage of the ripple current (due to high impedance at 

ripple frequency) while allowing the dc (due to low resistance to dc).

(c) Various combinations of capacitor and inductor, such as L-section filter    section filter, multiple section 

filter etc. which make use of both the properties mentioned in (a) and (b) above. Two cases of capacitor filter, 

one applied on half wave rectifier and another with full wave rectifier.

Filtering is performed by a large value electrolytic capacitor connected across the DC supply to act as a 

reservoir, supplying current to the output when the varying DC voltage from the rectifier is falling. The capacitor 

charges quickly near the peak of the varying DC, and then discharges as it supplies current to the output. 

Filtering significantly increases the average DC voltage to almost the peak value (1.4 × RMS value). 

To calculate the value of capacitor(C),

C = ¼*√3*f*r*Rl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000µF hence large value of capacitor is placed to reduce ripples and to improve the DC component.

3.2Resistors:

A linear resistor is a two-terminal, linear, passive electronic component that implements

electrical resistance as a circuit element. The current through a resistor is in direct proportion to the

voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's terminals

to the intensity of current through the resistor is called resistance. This relation is represented by Ohm's

law:

Figure 3.2.1 Picture of Resistor

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the

constant of proportionality is the resistance (R).

The amount of resistance offered by a resistor is determined by its physical construction. A

carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a carbon film

resistor consists of a similar ceramic tube, but has conductive carbon film wrapped around the outside.

Metal film or metal oxide resistors are made much the same way, but with metal instead of carbon. A

wire wound resistor, made with metal wire wrapped around clay, plastic, or fiberglass tubing, offers

resistance at higher power levels. For applications that must withstand high temperatures, materials such

as cermet, a ceramic-metal composite, or tantalum, a rare metal, are used to build a resistor that can

endure heat.

A resistor is coated with paint or enamel, or covered in molded plastic to protect it. Because

resistors are often too small to be written on, a standardized color-coding system is used to identify

them. The first three colors represent ohm value, and a fourth indicates the tolerance, or how close by

percentage the resistor is to its ohm value. This is important for two reasons: the nature of resistor

construction is imprecise, and if used above its maximum current, the value of the resistor can alter or

the unit itself can burn up.

Every resistor falls into one of two categories: fixed or variable. A fixed resistor has a

predetermined amount of resistance to current, while a variable resistor can be adjusted to give different

levels of resistance. Variable resistors are also called potentiometers and are commonly used as volume

controls on audio devices. A rheostat is a variable resistor made specifically for use with high currents.

There are also metal-oxide varistors, which change their resistance in response to a rise in voltage;

thermistors, which either raise or lower resistance when temperature rises or drops; and light-sensitive

resistors.

One of the most important considerations circuit designers have to make when allocating

resistors in their designs is the appropriate power rating for components. The resistor power rating is

based on the amount of thermal loading a component will be able carry on a continuous basis and are

expressed in watts. There are a good range of standard watt resistors with many more supplemental

ratings made to order for specific applications.

Typical, off-the-shelf power ratings range from 1/8 watt to 50 watts although far larger examples

are regularly custom built. Generally a resistor power rating up to two watts will be of a linear carbon

design; larger examples include ceramic base, wire wound components. In our project we used a 1/4 th

power rated resistor.

Figure 3.2.2 Different power rated resistors

Types of resistors:

There are five main types of resistors, each drawn differently on a schematic. Fixed-value

resistors are represented by a simple zigzag, variable resistors are a zigzag with an arrowed line through

it at a diagonal angle, potentiometers are a zigzag perpendicular to an arrowed line, thermistors are a

zigzag with a line moving through diagonally and ending in a flat line, and photo resistors are

represented by two angled and arrowed lines pointing towards a zigzag. Fixed and variable resistors have

the widest applications, and they are seen in most electronic devices.

Fixed resistors are simply basic resistors with a resistor value which cannot be changed. A

variable resistor is a simple resistor, but its value may be adjusted by means of a control. A

potentiometer is a type of variable resistor. Thermistors have a variable resistance value which adjusts

based on the temperature; they may be used in electronic thermostats and also in many televisions. Photo

resistors adjust their resistance based on how much light comes into contact with them and are useful for

light-activated switches.

Resistor value calculation:

The value of a resistor is usually given by a series of colored bands on the surface of the resistor

itself. In most resistors, there are four bands of color. The first two bands represent the base-value of the

resistance as a two-digit number, the third band gives a multiplier, and the fourth band indicates the

tolerance. Resistors which require more precision in their value have five bands, with the first three

representing the resistance as a three-digit number, and the fourth and fifth lines representing multiplier

and tolerance respectively.

Reading a resistor may seem complex at first, but it is actually quite easy. First, we need to know what

the colors mean. As resistance-value numbers they are:

● Black 0

● Brown 1

● Red 2

● Orange 3

● Yellow 4

● Green 5

● Blue 6

● Violet 7

● Grey 8

● White 9

The remaining colors, gold and silver, are not used for resistance values. As multipliers, the colors

represent:

● Black x1

● Brown x10

● Red x100

● Orange x1,000

● Yellow x10,000

● Green x100,000

● Blue x1,000,000

● Violet x10,000,000

● Gold x0.10

● Silver x0.01

Lastly, tolerance values are:

● Brown 1%

● Red 2%

● Green 0.5%

● Blue 0.25%

● Violet 0.10%

● Grey 0.05%

● Gold 5%

● Silver 10%

No color represents 20%.

So, if a resistor's bands are orange-green-orange-gold, then we know that its resistance is 35,000

ohms with a tolerance of plus or minus 5%. Similarly, if the resistor is banded as brown-red-yellow-

brown-blue, we know the resistance is 1,240 ohms with a tolerance of plus or minus 0.25%. More and

more frequently these days, resistors have the numerical values given for their resistance and tolerance in

addition to, or in place of, the color code. The two above examples would be written as 35k 5% and

1.24k .25%, respectively. Some European resistors use the 'k' instead of a decimal place, rendering the

second example instead as 1k24 .25%.

3.6 Light Emitting Diode:

A Light-Emitting Diode (LED) in essence is a P-N junction solid-state semiconductor diode that emits light when a current is applied though the device. By scientific definition, it is a solid-state device that controls current without the deficiency of having heated filaments. LED is the only semiconductor light source that exists till date. Like other semiconductors, LEDs also consume little power compared to conventional light sources.

The positive power is connected to one side of the LED semiconductor through the anode and a whisker and the other side of the semiconductor is attached to the top of the anvil or the negative power lead (cathode). It is the chemical composition or makeup of the LED semiconductor that determines the colour of the light that the LED produces as well as the intensity level. The epoxy resin enclosure allows most of the light to escape from the elements and protects the LED making it virtually indestructible. Furthermore, a light-emitting diode does not have any moving parts, which makes the device extremely resistant to damage due to vibration and shocks. These characteristics make it ideal for purposes that demand reliability and strength. LEDs therefore can be deemed invulnerable to catastrophic failure when operated within design parameters.

Figure 3.10 Light emitting diode

Salient features of LEDs

● High-levels of brightness and intensity

● Low radiated heat

● High-efficiency

● Can be easily controlled and interfaced to other devices

● Low-voltage and current requirements

● Long source life

● High reliability (resistant to shock and vibration)

● No UV Rays

● Applications of LED fall into three major categories:

1. Visual signal application where the light goes more or less directly from the LED to the human eye, to convey a message or meaning.

2. Illumination where LED light is reflected from object to give visual response of these objects.

3. Generate light for measuring and interacting with processes that do not involve the human visual system.

In our project and the prototype, we have used red LED.

BATTERY:

Battery (electricity), an array of electrochemical cells for electricity storage, either individually

linked or individually linked and housed in a single unit. An electrical battery is a combination of one

or more electrochemical cells, used to convert stored chemical energy into electrical energy.

Batteries may be used once and discarded, or recharged for years as in standby power applications.

Miniature cells are used to power devices such as hearing aids and wristwatches; larger batteries

provide standby power for telephone exchanges or computer data centers.

Figure 2.4: Lead-Acid Battery

Lead-acid batteries are the most common in PV systems because their initial cost is lower and

because they are readily available nearly everywhere in the world. There are many different sizes and

designs of lead-acid batteries, but the most important designation is that they are deep cycle batteries.

Lead-acid batteries are available in both wet-cell (requires maintenance) and sealed no-maintenance

versions. Lead acid batteries are reliable and cost effective with an exceptionally long life. The Lead

acid batteries have high reliability because of their ability to withstand overcharge, over discharge

vibration and shock. The use of special sealing techniques ensures that our batteries are leak proof and

non-spoilable. The batteries have exceptional charge acceptance, large electrolyte volume and low self-

discharge, Which make them ideal as zero- maintenance batteries lead acid batteries Are

manufactured/ tested using CAD (Computer Aided Design). These batteries are used in Inverter & UPS

Systems and have the proven ability to perform under extreme conditions. The batteries have

electrolyte volume, use PE Separators and are sealed in sturdy containers, which give them excellent

protection against leakage and corrosion.

Features:

Manufactured/tested using CAD

Electrolyte volume

PE Separators Protection against leakage