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Essay: Efficient Solar Power Inverter With Led Lighting

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Efficient Solar Power Inverter With Led Lighting

Solar Energy is most widely and easily available form of energy in world. Humans have been using this energy from years in form of heating and producing electricity. Electricity produced from solar energy costs very less per kW/h of other forms of electricity generation and also does not cause any kind of pollution.
Solar power , a free of cost reneawable energy source can be used by means of solar panels by converting it to electrical form.solar panels consists of photovoltaic cells,when exposed to light, can generate and support an electric current without being attached to any external voltage source, but do require an external load for power consumption.
Solar power is not continuous throught out the day as day light defers time by time. A charge controller prevents overcharging and may prevent against overvoltage, which can reduce battery performance or lifespan, and may pose a safety risk. It may also prevent completely draining or deep discharging of a battery or perform controlled discharges, depending on the battery technology, to protect battery life. The terms "charge controller" or "charge regulator" may refer to either a stand-alone device or to control circuitry integrated within a battery pack battery-powered device or battery recharger.
A power inverter,or inverter ,is an elecrtical power converter that changes direct current to alternating current;the converted AC can be at any required voltage and frequency with the use of appropriate transformers,switching,and control circuits.
LEDs ‘ultra efficient light-emitting diodes offer higher efficiency and reliability and are now widely adopted for illumination purpose.LED driver is required for using the output from inverter to supply constant current to LDE or string of LEDs.
LEDs connected as strings can be used as light source in the future replacement of fluroscent lamp as it gives better efficiency and long life.
INDEX

ABSTRACT
1.INTRODUCTION
WORLD ENRGY DEMAND:
1.1.1 POPULATION DEVELOPMENT:
1.1.2 ECONOMIC DEVELOPMENT:
1.1.3 ENERGY INTENSITY OF GDP:
1.1.4 PROJECTION OF POPULATION DEVELOPMENT
1.2 CONTRIBUTION OF RENEWABLE ENERGY
1.3 INTRODUCTION TO SOLAR ENERGY
1.4 TECHNOLOGY OF SOLAR PANEL:
2. CHARGE CONTROLLER
2.1 DIFFERENET TYPES OF SOLAR CHARGE CONTROLLER:
2.2 WHAT IS A SOLAR CHARGE CONTROLLER:
2.3 NECESSITY OF CHARGE CONTROLLER:
2.4 WORKING OF CHARGE CONTROLLER :
2.5 RECHARGABLE BATTERIES:
2.6 TYPES OF RECHARGEABLE BATTERIES

3. SOLAR POWER INVERTER
3.1 CLASSIFICATION
3.2 MOSFET
3.3 IC CD4047
3.3.1 FEATURES
3.4 CIRCUIT DIAGRAM
4. LED DRIVER
4.1 INTRODUCTION
4.2 WHAT IS LED DRIVER?
4.3 OFFLINE LED DRIVER:-
4.4 GENERAL REQUIREMENTS
4.5 IC-AL9910 FOR OFF LINE LED DRIVER
4.5.1 INTRODUCTION
4.5.2 PIN ASSIGNMENT
4.5.3 FEATURES
4.5.4 APPLICATIONS
4.5.5 TYPICAL APPLICATION CIRCUIT
4.5.6 PIN DESCRIPTION
4.6 DESIGN PARAMETERS:
4.6.1 SETTING THE LED CURRENT
4.6.2 SETTING OPERATING FREQUENCY
4.6.3 INPUT BULK CAPACITOR:
4.6.4 POWER FACTOR CORRECTION

4.7 HIGH POWER FACTOR LED REPLACEMENT FLUROSCENT TUBE USING AL9910
4.7.1 PASSIVE FACTOR CORRECTION STAGE DESIGN

4.8 CAPACITORS OF LED DRIVER
4.8.1 LIFETIME OF CAPACITOR VS. TEMPERATURE
4.8.2 LED DRIVER WITH CERAMIC CAPACITOR
4.8.3 HARDWARE IMPLEMENTATION AND TESTING:
5. LED

5.1 INTRODUCTION
5.2 BENEFITS OF LED LIGHT BULBS
5.3 WHY LED LAMPS?
5.4 PROJECT ARRANGEMENT ON BOARD

6. CONCLUSION


LIST OF FIGURES PAGE NO.
1.Projection of population development 13
2. The photovoltaic effect in PV cells 16
3. solar panel construction 16
4. block diagram of project 17
5. charge controller block diagram 19
6. Circuit Diagram of Charge Controller 21
7. charging continues as battery voltage is not more
than supply voltage. 22
8. charging is stopped by charge controller as the battery
voltage is exceed the limit. 23
9. pin diagram of IC CD4047 28
10. circuit diagram of inverter 29
11. dc-dc one stage converter 34
12. AC-DC passive solution for driving LED arrangement 35
13. Ic-Al9910 Pin Diagram 36
14. LED driver circuit with AL9910/A 38
15. Functional block diagram 39
16.Constant off time configuration 41
17.Typical application circuit with passive PFC 42
18.electrical diagram of an offline 13W LED driver 43
19.Power factor correction circuit 44
20. Testing of LED driver 45
21 Capacitor lifetime vs. temperature 46
22. Comparison of wattage usage for same lumens output 49
23.project arrangment on board 54

List of tables

1.Pin discription of IC AL9910
2.component specification of LED driver
3. Equivalent wattages and light output of incandescent, CFL and LED bulbs
4. Comparing the features of incandescent, CFL and LED bulbs

CHAPTER-1
INTRODUCTION

1. FACTS ABOUT ENERGY AND ENVIRONMENT

1.1. WORLD ENERGY DEMANd

World Energy Consumption refers to the total energy used by all of human civilization. Typically measured per-year, it involves all energy harnessed from every energy source we use, applied towards humanity’s endeavors across every industrial and technological sector, across every country. Being the power source metric of civilization, World Energy Consumption has deep implications for humanity’s social-economic-political sphere. Various institutions such as the IEA, EIA, and EEA record and publish energy data periodically. Improved data and understanding of World Energy Consumption may reveal systemic trends and patterns, which could help frame current energy issues and encourage movement towards collectively useful solutions.
The development of future global energy demand is determined by three key factors:

1.1.1. POPULATION DEVELOPMENT
The number of people consuming energy or using energy services According to IEA data from 1990 to 2008, the average energy use per person increased 10% while world population increased 27%.

1.1.2. ECONOMIC DEVELOPMENT
For which gross domestic product (GDP) is the most commonly used indicator. In general an increase in GDP triggers an increase in energy demand.

1.1.3. ENERGY INTENSITY OF GDP
How much energy is required to produce unit of GDP. Energy conservation means the quantity of energy used without changing the amount of work gained. In other words, it means increasing the amount of work without changing the quantity of energy used. As a measure of energy conservation ,’Energy Intensity ‘,which is the amount of energy consumption per work unit , is often used .Although the term ‘ Energy Conservation ‘ often is used in relation to technological energy efficiency, there also in energy conservation based on consumer energy
saving behavior, or changes in industrial structure and in lifestyle, and there are needs for measuring entire energy conservation of a country, including all such technological, structural and behavioral factors. This is called as ‘Energy Intensity of GDP’.

1.1.4. PROJECTION OF POPULATION DEVELOPMENT:

Fig 1.Projection of Population Development
Following the United Nations population development projection, the world population will increase from 6.3 billion people now to 8.9 billion in 2050. The world’s population is expected to grow by 0.78% over the period 2003 to 2050.The population share for those countries classified now as ‘developing regions’ will increase from 76% to 82% by 2050.Satisfing the energy need of growing population in the developing regions in a key challenges for achieving global growth. This continuing growth put additional pressure on energy resources of the environment.
1.2. CONTRIBUTION OF RENEWABLE ENERGY
Renewable Energy currently provided 13% of the World’s energy need. The main sources of renewable energy at present are hydro electric power and geothermal power. Biomass provides 10% of the world’s primary energy need, mostly in developing countries, Where villages burn Cow dung on basis stoves. But the technology for producing electricity from biomass has not changed much in recent year. Solar and Wind energy already play an important part in few countries. Around 20% of Denmark’s electricity comes from wind and about 80% of China’s hot water from Solar energy but worldwide those two energy sources barely register. In the past they have flourished when oil crises pushed subsides and investment their way. At another time they have survived in a tiny niche, providing power to isolated communities. But now they are enjoying their biggest boom ever. Solar energy power has grown by an average of 41% a year over the past three years, while wind has grown by 18% a year.
1.3. INTRODUCTION TO SOLAR ENERGY
Solar energy has the greatest potential of all the sources of renewable energy and of only a small amount of this form of energy could be used, it will be one of the most important supplies of energy especially when other sources in the country have depleted. Energy comes to the earth from the sun. This energy keeps the temperature of the earth above that in colder space, causes current in the atmosphere and in ocean, causes the water cycle and generates photosynthesis in plants. The solar power where sun hits atmosphere is 1017 watts, whereas the solar power on the earth’s surface is 1016 watts. The total worldwide power demand of all needs of civilization is 1013 watts. Therefore, the sun gives us 1000 times more power than we need. If we can use 5% of this energy, it will be 15 times what the world will require.
1.4. TECHNOLOGY OF SOLAR PANEL:
Solar panels are devices that convert light into electricity. They are called solar after the sun. The sun is the most powerful source of the light available for us. They are sometimes called Photovoltaic which means ‘Light Electricity’. Solar cells or PV cells rely on the Photovoltaic effect to absorb the energy of the sun and cause current to flow between two oppositely charge layers.

A Solar panel is a collection of solar cells. Although each solar cell provides a relative small amount of power, Many solar cells spread over a large area can provide enough power to be useful. To get the most power, Solar panels have to be pointed directly at the sun.

A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a packaged, connected assembly of photovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications. Each panel is rated by its DC output power under standard test conditions, and typically ranges from 100 to 450 watts. The efficiency of a panel determines the area of a panel given the same rated output – an 8% efficient 230 watt panel will have twice the area of a 16% efficient 230 watt panel. Because a single solar panel can produce only a limited amount of power, most installations contain multiple panels.

A photovoltaic system typically includes an array of solar panels, an inverter, and sometimes a battery and or solar tracker and interconnection wiring. To understand the operation of a PV cell, it is need to consider both the nature of the material and the nature of sunlight. PV cells consist of two types of material; p-type silicon and n-type silicon. Light of certain wavelengths is able to ionize the atoms in the silicon and the internal field produced by the junction separates some of the positive charges (holes) from the negative charges (electrons) within the PV device. The holes are swept into the p-layer and the electrons are swept into n-layer. Although these opposite charges are attracted to each other, most of them can only recombine by passing through an external circuit outside the material because of the internal potential energy barrier. Therefore if a circuit as shown in Fig. 1 is composed, power can be produced from the cells under illumination, since the free electrons have to pass through the load to recombine with the positive holes [14].The photovoltaic module is the result of associating a group of photovoltaic cells in series and parallel, with their protection devices, and it represents the conversion unit in this generation system

Fig.1 The photovoltaic effect in PV cells
fig.2 solar panel construction
BLOCK DIAGRAM
Fig.3 block diagram of project

CHAPTER-2

SOLAR CHARGE CONTROLLER

2.1 DIFFERENT TYPES OF SOLAR CHARGE CONTROLLER:
The solar charge controller is an essential element in photo-voltaic systems. The general block diagram of PV system comprising of PV panel, charge controller, battery and load is as follows:

fig.4 charge controller block diagram

WHAT IS A SOLAR CHARGE CONTROLLER:

A conventional solar charge controller limits the rate at which electric current is added to or drawn from electric batteries.
It prevents overcharging and also prevents batteries against overvoltage, which can reduce battery performance or lifespan, and may pose a safety risk. It also prevents completely draining or deep discharging a battery, or perform controlled discharges, depending on the battery technology, to protect battery life.
The conventional charge controller thus disconnects the supply from batteries when it is completely charged and connects the battery again when the battery voltage falls back again
.
NECESSITY OF CHARGE CONTROLLER:

A solar charge controller is needed in virtually all solar power systems that utilize batteries. The job of the solar charge controller is to regulate the power going from the solar panels to the batteries. Overcharging batteries will at the least significantly reduce battery life and at worst damage the batteries to the point that they are unusable.
The most basic charge controller simply monitors the battery voltage and opens the circuit, stopping the charging, when the battery voltage rises to a certain level. Older charge controllers used a mechanical relay to open or close the circuit, stopping or starting power going to the batteries.

2.4 WORKING OF CHARGE CONTROLLER:

The circuit of the conventional controller which we designed is as follows:
fig.5 Circuit Diagram of Charge Controller

Initially when the battery is under-charged, the relay contacts are in closed position as the relay used in the above circuit is of NC type and hence the power from PV panel flows to battery and charges the battery.
A fixed value is set by changing the ‘big preset’ value which is compared with the battery voltage all the time using zener diode and transistor configuration.
In solar charge controller circuit switching transistor is used to sense the overvoltage of battery. When battery is fully charged, the Zener diode which is connected to the base of the Transistor goes in breakdown mode, which triggers the base of the transistor resulting in switching ON the relay circuit, which cuts down the direct charging path of the battery from solar panel, so that the battery can be protected from the over current and heating.
A high resistance is connected between the contact of relay which allows very low current to pass through battery charging and this reduces self discharging rate of battery i n ideal mode.

Fig.6 charging continues as battery voltage is not more than supply voltage.

fig.7 charging is stopped by charge controller as the battery voltage is exceed the limit.

When the battery voltage increases than the preset value, the relay operates and the contacts get opened and LED glows. Thus the 50 ohm fusable resistor gets connected in the circuit and very small current now flows to the battery, thus preventing battery from overvoltage as well as complete discharge.
If in case the battery voltage decreases than the preset value, the relay contacts go to original position and the battery is again connected to PV panel and power again flows to battery and charging is resumed.
We can change the battery charging voltage limit by adjusting the value of variable resistor connected in circuit as per the type and capacity of battery.

2.5 RECHARGEABLE BATTERIES:
A rechargeable battery, storage battery, or accumulator is a type of electrical battery. It comprises one or more electrochemical cells, and is a type of energy accumulator. It is known as a secondary cell because its electrochemical reactions are electrically reversible. Rechargeable batteries come in many different shapes and sizes, ranging from button cells to megawatt systems connected to stabilize an electrical distribution network. Several different combinations of chemicals are commonly used, including: lead’acid, nickel cadmium (NiCd), lithium ion (Li-ion). Rechargeable batteries have lower total cost of use and environmental impact than disposable batteries. Some rechargeable battery types are available in the same sizes as disposable types. Rechargeable batteries have higher initial cost, but can be recharged very cheaply and used many times.

2.6 TYPES OF RECHARGEABLE BATTERIES
AUTOMOTIVE BATTERIES
JELL BATTERIES
Li-Ion BATTERIES
Ni-Cd BATTERIES

Chapter -3

SOLAR POWER INVERTER

3.1 classification
In the world of today there are currently two forms of electrical transmission ,direct current(DC) and Alternating Current(AC), each with its own advantages and disadvantages.DC power is simply the application of a steady constant voltage across a circuit resulting in a constant current.A battery is the most common source of DC transmission as current flows from one end of circuit to other.
V=IR
P=VI=I2R
As can be seen in the equations above,power loss can be derived from the elecrtrical current squared and the resistance of a transmission line. When the voltage is increased,the current decreases and concurrently the power loss decreases exponentially;therefore high voltage transmission reduces power loss.For this reasoning electricity was generated at power stations and delivered to homes through AC pwer.Alternating current, unlike DC,is easy to step up or down the voltage by transformer.

The adoption of AC power has created a trend where most devices adapt AC power from an outlet into DC power for use by the device.however,AC power is not always available and the need for mobility and simplicity has given batteries an advantage in portable power.Thus,for portable AC power ,inverters are needed.Inverters take a DC voltage from a battery or a solar panel as input,and convert it into AC voltage output.

Power inverters are devices which canconvert electrical energy of DC form into that of AC.The purpose of a DC/AC power inveter is typically to take DC power supplied by a battery,such as 12 volt batery,and transform it into a 120 volt AC power source operating at 50 hz,

There are three types of DC/AC inverters available in the market,which are classified by their output type:square wave,modified-sine wave or modified-sine wave.Pure sine wave inversion is accomplised by taking a DC voltage source and switching it across a load using an h-bridge.If this voltage needs to be boosted from the DC source,it can be accomplised either before AC stage by using a DC-DC boost converter,or after the AC stage by using a boost transformer.
3.2 MOSFET
MOSFET are voltage-controlled switches.Unlike triacs,MOSFETS have the capability of being turned on and turned off.They also switch much faster than triacs.As illustrated in figure,the MOSFET acts as a unidirectional switch between the drain and source terminals,and has an internal anti parallal diode.An applied gate-to-source voltage of approximately 4 to 5 is sufficient to turn on the mosfet.Faster turn on is achived by 12-18 volts applied.Then,when the gate to source voltage is set to zero,the mosfet turns off(i.e.,drain-to-source resistance becomes very large).
We are using MOSFET IRF540 in our inverter circuit.

fig. internal schematic diagram

TYPE VDSS RDS ID
IRF540 100 V <0.077 ‘ 22 A

Typical Rds =0.055′
Exceptional dv/dt capability
100% avalanche tested
Low gate charge
Application orientedis threfore suitable as primary witch in advanced high efficiency,high frequency isolated DC_DC converter for applications.
This MOSFET series realized with STMicroelectronics unique StripFET process has specifically been designed to minimize input capacitance and gate charge. It is also intended for low gate requirements.

3.3 IC CD4047:
CD 4047 is a low power CMOS astable/monostable multivibrator IC. Here it is wired as an astable multivibrator producing two pulse trains of 0.01s which are .gate of Q1 and pin 11 is connected to gate of Q2. Resistors R3 and R4 prevents the loading of the IC by the respective MOSFETs.
When pin 10 is high Q1 conducts and current flows through the half of the transformer primary which accounts for the positive half of the output AC voltage.When pin 11 is high Q2 conducts and current flows through the lower half of the transformer primary in opposite direction and it accounts for the negative half of the output AC voltage.

fig.8 pin diagram of IC CD4047

The CD4047 is capable of operating in either the monostable or astable mode.It requires an external capacitor between pins 1 and 3 and an external resistor (between pins 2 and 3) to determine pulse width in the monostable mode, and the output frequency in the astable mode.
Astable operation is enabled by a high level on the astable input or low level on the astable input. The output frequency at Q and Q outputs is determined by the timing componenets. A frequency twice that of Q is available at the oscillator output, a 50 % duty cycle is not guaranteed.
Monostable operation is obtained when the device is triggerd by LOW-TO-HIGH transitition at +trigger input or HIGH-TO-LOW transition at ‘trigger input. The device can be triggered by applying a simultaneous LOW-to-HIGH transition to both the =trigger and retrigger inputs.
A high level on reset input reset the outputs Q to LOW, Qbar to high.

3.3.1 Features:
Wide supply voltage range : 3.0V to 15V
High noise immunity : 0.45 VDD
Low power consumption : special CMOS oscillator configuration
Only one external R and C required.

3.4 Circuit Diagram
fig.9 circuit diagram of inverter

CHAPTER 4

LED DRIVER

4.1 Introduction
Light emitting diodes (LEDs) are considered the future trend in lighting due to their high efficiency and high reliability.

There is need of design of the converters used to drive lighting devices. As a result, many well-known topologies have been optimized in order to be used in LED-lighting applications and many new topologies.

Light emitting diodes (LEDS) are spreading over all lighting applications (vehicles lights, home and street lighting traffic and commercial signs etc). In fact, they are considered as the future trend in lighting due to their outstanding advantages.

Their lifetime is very long, around 50,000 hours depending on the driving technique, operating temperature, etc

.They are environmentally friendly, as there are produced without mercury.

They are based on semiconductors. There for they are resistance to shock and vibrations.

They are easily turn-on and turn-off, which allows use in intelligent lighting.

With the rapid development in high brightness LED technologies, both the efficiency (light output per watt in) and the cost of phosphor converted white LEDs have improved significantly. The solid lighting (SSL) technology based on LED is a promising alternative for future lighting application.

Because the demands of LEDs regarding voltage and current are completely different from the rest of lighting devices. HB-LEDs Have a nominal DC current which may vary from 100mA to 1 or 2. Regarding the voltage, it depends on the number of LEDs connected in series, but the standard knee voltage of these devices is around 3-4V. Depending on the number of LEDs supplied by the driver and their specified way of association of the output voltage of the driver be as high as 140V or as low as 12V. Regarding the output current of the driver, it may be as low as 350mA or as high as 5A.

4.2 What is LED Driver?

A LED driver is an electrical device that regulates the power to an LED or strings of LEDs.

LED drivers control the amount of current and voltage supplied to light emitting diodes

Driver different from conventional power supplies is that an LED driver responds to the ever y changing needs of the LED, or circuit of LEDS, by supplying a constant amount of power to the led as its electrical properties change with temperature.

The LED is powered by DC current and its brightness is directly related to its forward current.

4.3 Offline LED driver

An ac to dc LED driver is required to convert the AC power of the grid to the DC power required by the LED lighting fixture.

This type of driver contain rectify circuit,power factor correction circuit,voltage controller.

Fig.11 AC-DC passive solution for driving LED arrangement

Instead of using a capacitor for limiting the maximum current driven by the LEDs,it may be possible to use a DC-DC converter in cascade with the rectifier in order to keep constant the current supplied to load.
Obviously,a capacitor between both is necessary in order to have available energy during the periods of time in which the line voltage is close to zero.

4.4 general requirements
High input power factor
No E-cap
Output voltage 24~34V(nominal 28v)
Output current 20mA~180mA (constant)
AC input voltage
High efficiency

4.5 IC ‘AL9910 for off line LED driver

4.5.1 Introduction:

The AL9910/A high voltage PWM LED driver-controller provides an efficient solution for offline high brightness LED lamps from rectified line voltages ranging from 85VAC up to 277VAC.
The AL9910 drives external MOSFETs at switching frequencies up to 300kHz, with the switching frequency determined by a single resistor. The AL9910 topology creates a constant current through the LEDs providing constant light output.
The output current is programmed by one external resistor and is ultimately determined by the external MOSFET chosen and therefore allows many low current LEDs to be driven as well as a few high current LEDs.
The LED brightness can be varied by both Linear and PWM dimming using the AL9910’s LD and PWM_D pins respectively. The PWM_D input operates with duty ratio of 0-100% and frequency of up to several kHz.
4.5.2 Pin Assignments :

Fig.12 IC-AL9910

4.5.3 Features
‘ >90% Efficiency
‘ Universal rectified 85 to 277VAC input range
‘ Input voltage up to 500V
‘ Internal voltage regulator removes start-up resistor
‘ 7.5V MOSFET drive ‘ AL9910
‘ Drives LED Lamps with both high and low current LEDs
‘ Internal Thermal Protection (OTP)

4.5.4 Applications
‘ LED offline lamps
‘ High voltage DC-DC LED Driver
‘ Signage and Decorative LED Lighting
‘ Back Lighting of Flat Panel Displays
‘ General purpose constant current source
4.6.5 Typical Application Circuit :
Fig.13 LED driver circuit with AL9910/A
4.6.6 Pin description:

Table 1 pin description of IC AL9910

Table 1 pin description of IC AL9910
Functional block diagram:

Fig .14 Functional block diagram
The AL9910 contains a high voltage LDO the output of the LDO provides a power rail to the internal circuitry including the gate driver.
When the voltage across Sense exceeds the current sense pin threshold the external MOSFET Q1 is turned off. The stored energy in the inductor causes the current to continue to flow through the via diode D1.
The AL9910’S LDO provides all power to the rest of the IC including Gate drive this removes the need for large high power startup resistors. This means that operate correctly also be used to supply up to 1mA to external circuits.
The AL9910 operates and regulates by limiting the peak current of the external MOSFET, THE peak current sense threshold is nominally set at 250mV.The sane basic operation is true for isolated topologies, however in these the energy stored in the transformer delivers energy energy to LEDs during the off-cycle of the external MOSFET.

4.7 Design Parameters

4.7.1 Setting the LED Current

In the non-isolated buck converter topology, figure 1, the average LED current is not the peak current divided by 2 – however, there is a certain error due to the difference between the peak and the average current in the inductor. The following equation
Accounts for this error:

4.7.2 Setting Operating Frequency
The AL9910 is capable of operating over a 25 and 300 kHz switching frequency range. T he switching frequency is Tosc=(Rosc+22)/25 programmed by connecting an external resistor between ROSC pin and ground.
The corresponding oscillator period is: The switching frequency is the reciprocal of the oscillator period. Typical values for ROSC vary from 75k?? to 1M?? When driving smaller numbers of LEDs, care should be taken to ensure that tON > tBLANK. The simplest way to do this is to reduce/limit the switching frequency by increasing the ROSC value. Reducing the switching frequency will also improve the efficiency. When operating in buck mode the designer must keep in mind that the input voltage must be maintained higher than 2 times the forward voltage drop across the LEDs. This limitation is related to the output current instability that may develop when the AL9910 operates at a duty cycle greater than 0.5. This instability reveals itself as an oscillation of the output current at a sub- harmonic (SBO) of the switching frequency.

FIG.15 CONSTANT OFF-TIME CONFIGURATION
The oscillator period equation above now defines the AL9910 off time, t OFF. When using this mode the nominal switching frequency is chosen and from the nominal input and output voltages the off-time can be calculated: TOFF= (1-VOUT (nom)) * 1
VIN (nom) fosc
From this the timing resistor, ROSC, can be calculated:
ROSC= (toff (??s)*25-22(k’))

4.7.3 Input Bulk Capacitor:

For Offline lamps an input bulk capacitor is required to ensure that the rectified AC voltage is held above twice the LED string voltage throughout
the AC line cycle. The value can be calculated from:

Where
DH : Capacity charge work period, generally about 0.2 to 0.25
FL : Input frequency for full range (85 to 265VRMS)
??VDC_MAX= should be set 10 to15% of ‘2VLINE_MIN

If the capacitor has a 15% voltage ripple then a simplified formula for the minimum

value of the bulk input capacitor approximates to:

CMIN= ILED * VLEDs*0.06
VIN2

4.7.4 Power Factor Correction:
If power factor improvement is required then for the input power less than 25W, a simple passive power factor correction circuit can be added to the AL9910 typical application circuit. Figure 4 shows that passive PFC circuitry (3 current steering diodes and 2 identical capacitors) does not significantly affect the rest of the circuit. Simple passive PFC improves the line current harmonic distortion and achieves a power factor greater than 0.85.
Fig.16 Typical application circuit with passive PFC

Each of these identical capacitors should be rated for half of the input voltage and have twice as much capacitance as the calculated CMIN of the buck converter circuit without passive PFC

4.8 High Power Factor LED Replacement T8 Fluorescent Tube using the AL9910 High Voltage LED Controller
AL9910 high power factor buck LED driver

Fig.17 The electrical diagram of an offline LED driver.
On the input side, CX1, CX2, CX3, CX4, L1 and L2 provide sufficient filtering for both differential mode and common mode EMI noise which are generated by the switching converter circuit.
The rectified AC line voltage from the bridge rectifier DB1 is then fed into a passive power factor correction or valley fill circuit which consists of 3 diodes and 2 capacitors. D1, D2, D3, C1, C2 improve the input line current distortion in order to achieve PF greater than 0.9 for the AC line input.
The constant current regulator section consists of a buck converter driven by the AL9910. Normally, the buck regulator is used in fixed frequency mode but its duty cycle limitation of 50% is not practical for offline lamp. This problem can be overcome by changing the control method to a fixed off-time operation.
The design of the internal oscillator in the AL9910 allows the IC to be configured for either fixed frequency or fixed off-time based on how resistor RT is connected. For fixed off-time operation, the resistor RT is connected between the Gate and ROSC pins, as shown in Figure 1. This converter has now a constant off-time when the power MOSFET is turned off.. This change allows the converter to work with duty cycles greater than 50%.
4.8.1 Passive factor correction stage design:
The purpose of the valley fill circuit (see Figure 2) is to allow the buck converter to pull power directly off the AC line when the line voltage is greater than 50% of is peak voltage. Fig.18 Power factor correction circuit
Once the line drops below 50% of its peak voltage, the two capacitors are essentially placed in parallel. The bus voltage VIN (min) is the lowest voltage value at the input of the buck converter. VIN (min) at the minimum AC line voltage Vac (min) is,
VIN (min) = 2 ??Vac(min) 2 = 2 ??85Vac 2 = 60V

Table 2 Component Specification

4.9 Capacitors of LED Driver:
In LED driver capacitors are placed at rectifier side and across the LED string. Capacitor is use for reducing the ripple contain and smoothing output voltage waveform. Capacitor used across LED string is used for maintaining constant voltage across LED string.
In LED Driver LEDs are having good efficiency and long lifetime. But capacitor used in LED driver is having fewer lifetimes lifetime of LED driver depends on capacitor lifetime.
Generally aluminum electrolytic capacitors are used in LED driver but this type of capacitor hass some disadvantages which are most reasonable reduce the life time of LED driver.
4.9.1 Lifetime of capacitor vs. temperature:
fig. 19 capacitor lifetime vs. temperature

Life time of electrolyte capacitor reduces drastically with increase in ambient temperature. We know that LED string emits heat when it is glowing. Output side capacitor is connected across LED string which is placed at very small distance from LED string. So this capacitor will be subjected to continue heat emitted from the LED string. So its life time will decrease due to increase in ambient temperature. Ultimately lifetime of LED driver will be decrease due to failure of capacitor.
Hardware implementation and testing:

fig.20 testing of LED driver

String of LEDs start glowing as the input alternating voltage is applied through auto transformer. We have to use more voltage for more no. of LEDs connected in string.

CHAPTER 5
LED

5.1 Introduction:

Light emitting diodes (LEDs) are considered the future trend in lighting due to their high efficiency and high reliability, chromatic variety, shock and vibration resistance, etc. Besides their behavior is completely different from the rest of lighting devices and, consequently, it should be also taken into account in the design of the converters used to drive them. As a result, many well-known topologies have been optimized in order to be used in LED-lighting applications and many new topologies.

Light emitting diodes (LEDS) are spreading over all lighting applications (vehicles lights, home and street lighting traffic and commercial signs etc). In fact, they are considered as the future trend in lighting due to their outstanding advantages.

5.2 Benefits of LED light bulbs:
Long-lasting – LED bulbs last up to 10 times as long as compact fluorescents, and far longer than typical incandescent.
Durable – since LEDs do not have a filament, they are not damaged under circumstances when a regular incandescent bulb would be broken. Because they are solid, LED bulbs hold up well to jarring and bumping.
Cool – these bulbs do not cause heat build-up; LEDs produce 3.4 buts’/hour, compared to 85 for incandescent bulbs. Common incandescent bulbs get hot and contribute to heat build-up in a room. LEDs prevent this heat build-up, thereby helping to reduce air conditioning costs in the home.
Mercury-free – no mercury is used in the manufacturing of LEDs.
More efficient – LED light bulbs use only 2-17 watts of electricity (1/3rd to 1/30th of Incandescent or CFL). LED bulbs used in fixtures inside the home save electricity, remain cool and save money on replacement costs since LED bulbs last so long. Small LED flashlight bulbs will extend battery life 10 to 15 times longer than with incandescent bulbs.
Cost-effective – although LEDs are initially expensive, the cost is recouped over time and in battery savings. LED bulb use was first adopted commercially, where maintenance and replacement costs are expensive. But the cost of new LED bulbs has gone down considerably in the last few years. and are continuing to go down. Today, there are many new LED light bulbs for use in the home, and the cost is becoming less of an issue. To see a cost comparison between the different types of energy-saving light bulbs,

5.3 Why LED lamps?
Because the demands of LEDs regarding voltage and current are completely different from the rest of lighting devices. HB-LEDs Have a nominal DC current which may vary from 100mA to 1 or 2. Regarding the voltage, it depends on the number of LEDs connected in series, but the standard knee voltage of these devices is around 3-4V. Depending on the number of LEDs supplied by the driver and their specified way of association of the output voltage of the driver be as high as 140V or as low as 12V. regarding the output current of the driver, it may be as low as 350mA or as high as 5A.

Light Output LEDs CFLs Incandescent
Lumens Watts Watts Watts
450 4 – 5 8 – 12 40
300 ‘ 900 6 – 8 13 – 18 60
1100 ‘ 1300 9 – 13 18 – 22 75 ‘ 100
1600 ‘ 1800 16 – 20 23 – 30 100
2600 ‘ 2800 25 – 28 30 – 55 150
TABLE3: Equivalent wattages and light output of incandescent ,CFL and LED bulbs

– Lumens – The unit of measurement of the flow of light, or ‘luminous flux’. With light bulbs, it provides an estimate of the apparent amount of light the bulb will produce.
LEDs CFLs Incandescent
Frequent On/Off Cycling no effect shortens lifespan some effect
Turns on instantly yes slight delay Yes
Durability durable fragile Fragile
Heat Emitted low (3 buts’/hr) medium (30 buts’/hr) high (85 buts’/hr)
Sensitivity to temperature no yes Some
Sensitivity to humidity no yes Some
Hazardous Materials none 5 mg mercury/bulb None
TABLE4: Comparing the features of incandescent, CFL and LED bulbs
Fig.21 comparision of wattage usage for same lumens output

Project arrangement on board:

Fig.22 project arrangement on board
6. CONCLUSION
A solar panel (also solar module, photovoltaic module or photovoltaic panel) is a packaged, connected assembly of photovoltaic cells and from solar panel we get a dc sypply and supply electricity in battery through charge controller. we also designed a solar charge controller which uses the PV panel as power source for charging of batteries. The solar charge controller controls the charging of batteries as well as gives protection to batteries from over-charging as well as deep discharging. We are also made inverter which convert dc into ac. That conventional ac supply used for LED lighting so that perpose we made LED driver which is more efficient for lighting.

REFRENCES:
WWW.MAXIM-IC.COM/APP-NOTES/INDEX.MVP/ID/4669
WWW.DIODES.COM
WWW.ELECTROSCHEMATICS.COM
WWW.IEEE.ORG/INVERTER/SINE_WAVE_INVERTER.PDF
WWW.NXP.COM/SEMICONDUCTORS/MPPT_CONTROLLER_HTM

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