Zener diode voltage regulator

    I.            Aim

 To construct a zener diode voltage regulator and measure its line and load regulation.

 II.            Apparatus

Zener diode, resistor, variable DC power supply, milliammeter, voltmeter, Rheostat and wire.

III.            Theory

 The Zener diode is like a general-purpose signal diode. When biased in the forward direction it behaves just like a normal signal diode, but when a reverse voltage is applied to it, the voltage remains constant for a wide range of currents.

                        

                                                                    Fig 1: Symbol for zener diode

Avalanche Breakdown: There is a limit for the reverse voltage. Reverse voltage can increase until the diode breakdown voltage reaches. This point is called Avalanche Breakdown region. At this stage maximum current will flow through the zener diode. This breakdown point is referred as “Zener voltage”.

 

The Zener Diode is used in its "reverse bias". From the I-V Characteristics curve we can study that the zener diode has a region in its reverse bias characteristics of almost a constant negative voltage regardless of the value of the current flowing through the diode and remains nearly constant even with large changes in current as long as the zener diodes current remains between the breakdown current IZ(min) and the maximum current rating IZ(max).

This ability to control itself can be used to great effect to regulate or stabilise a voltage source against supply or load variations. The fact that the voltage across the diode in the breakdown region is almost constant turns out to be an important application of the zener diode as a voltage regulator

      i.            Characteristics

                                            

Fig 2: Zener diode characteristic curve

Figure 2 shows the current versus voltage curve for a Zener diode. Observe the nearly constant voltage in the breakdown region.

The forward bias region of a Zener diode is identical to that of a regular diode. The typical forward voltage at room temperature with a current of around 1 mA is around 0.6 volts. In the reverse bias condition the Zener diode is an open circuit and only a small leakage current is flowing as shown on the exaggerated plot. As the breakdown voltage is approached the current will begin to avalanche. The initial transition from leakage to breakdown is soft but then the current rapidly increases as shown on the plot. The voltage across the Zener diode in the breakdown region is very nearly constant with only a small increase in voltage with increasing current. At some high current level the power dissipation of the diode becomes excessive and the part is destroyed. There is a minimum Zener current, Iz(min), that places the operating point in the desired breakdown. There is a maximum Zener current, Iz(max), at which the power dissipation drives the junction temperature to the maximum allowed. Beyond that current the diode can be damaged. Zener diodes are available from about 2.4 to 200 volts.

    ii.            Zener Diode as Voltage Regulators

The function of a regulator is to provide a constant output voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or the variation in the load current and the zener diode will continue to regulate the voltage until the diodes current falls below the minimum I_Z(min) value in the reverse breakdown region. It permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage. The Zener diode specially made to have a reverse voltage breakdown at a specific voltage. Its characteristics are otherwise very similar to common diodes. In breakdown the voltage across the Zener diode is close to constant over a wide range of currents thus making it useful as a shunt voltage regulator.

The purpose of a voltage regulator is to maintain a constant voltage across a load regardless of variations in the applied input voltage and variations in the load current. A typical Zener diode shunt regulator is shown in Figure 3. The resistor is selected so that when the input voltage is at V_IN(min) and the load current is at I_L(max) that the current through the Zener diode is at least I_z(min). Then for all other combinations of input voltage and load current the Zener diode conducts the excess current thus maintaining a constant voltage across the load. The Zener conducts the least current when the load current is the highest and it conducts the most current when the load current is the lowest.

                                               

                                                             Fig 3: Zener diode shunt regulator

If there is no load resistance, shunt regulators can be used to dissipate total power through the series resistance and the Zener diode. Shunt regulators have an inherent current limiting advantage under load fault conditions because the series resistor limits excess current.    

                            

 A zener diode of break down voltage V_z is reverse connected to an input voltage source V_i across a load resistance R_L and a series resistor R_S. The voltage across the zener will remain steady at its break down voltage V_Z for all the values of zener current I_Z as long as the current remains in the break down region. Hence a regulated DC output voltage V₀ = V_Z is obtained across RL, whenever the input voltage remains within a minimum and maximum voltage.

Basically there are two type of regulations such as:

a) Line Regulation

In this type of regulation, series resistance and load resistance are fixed, only input voltage is changing. Output voltage remains the same as long as the input voltage is maintained above a minimum value.

b) Load Regulation

In this type of regulation, input voltage is fixed and the load resistance is varying. Output volt remains same, as long as the load resistance is maintained above a minimum value.

  iii.            Design a Voltage Regulator

   

When selecting the zener diode, be sure that its maximum power rating is not exceeded.

I_max             Maximum current for Zener diode

V_Z          Zener Diode standard  voltage 

V_in          Input voltage(it is known)
V_s           Voltage across series resistance
V_L           Voltage across the load resistance
I_S            Current passing through the series resistance
I_Z            Current passing through the Zener diode
I_L            Current passing through the load resistance

  iv.            Calculating voltage and current 

The total current drawn from the source is the same as that through the series resistor 

The current through the load resistor is  

 

 and the zener diode current is 

If the voltage source is greater than Vz

  and  

 If the voltage source is less than Vz

    and    

IV.            Procedure

Using the circuit diagram, identify the connections in the given platform. Connections are made as shown in the below diagram.

i.                     Line regulation

1.      Choose the zener diode to start the experiment.

2.      Insert the series resistance value.

3.      Fix the load resistance value by using Load Resistance slider.

4.      Change the Rheostat value from maximum to 0 by the interval 100.

5.      Note down the corresponding input voltage and output voltage and tabulate it.

6.      Plot the graph in which V_IN at x-axis V_L at y-axis.

 

                                                Percentage of Line regulation =

ii.                   Load Regulation

1.      First 3 steps are same as above.

2.      Fix the Rheostat value, to get the 12 V at voltmeter across rheostat. 

3.      Change the load Resistance with the interval of 100 Ω/1000 Ω up to maximum range.

4.      Note  the reading and tabulate it.

5.      Plot the graph between V₀ along x-axis and R_L along y-axis.

                                           Percentage of Load regulation = 

 V.            Conclusion

The Zener diode, with its accurate and specific reverse breakdown voltage, allows for a simple, inexpensive voltage regulator. Combined with the right resistor, fine control over both the voltage and the supply current can be attained.

However, the low power ratings of standard Zener diodes and resistors make this solution impractical for high power devices.

                               Percentage of Line regulation ==

                               Percentage of Load regulation = =

VI.            Precautions

Ø  All connections  should be neat ,clean and tight

Ø  Key should be used in circuit and opened when the circuit is not being used.

VII.            Uses

Ø  Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits.

Ø  Zener diodes are also used in surge protectors to limit transient voltage spikes

Ø  Another notable application of the zener diode is the use of noise caused by its avalanche breakdown in a random number generator

VIII.            References

Ø  Gates, Earl. Introduction to electronics. Clifton Parks, NY: Delmar, 2011.

Ø  http://amrita.vlab.co.in

Ø  Comprehensive Practical Physics

Ø  Harrison, Linden. Current sources & voltage references. Amsterdam New York: Newnes, 2005.

Ø  http://www.reuk.co.uk/What-is-a-Zener-Diode.htm

.

Sample acknowledgment 1

                                         Acknowledgement

                         

                          I take this opportunity to express my profound gratitude and deep regards to my teachers Prof.____________________  and Prof_______________. for their exemplary guidance, monitoring and constant encouragement throughout the course of this project. The blessing, help and guidance given by them time to time shall carry me a long way in the journey of life on which I am about to embark.

                        

                          I also take this opportunity to express a deep sense of gratitude to,_________ Principal, Senior Secondary School for his cordial support, valuable information and guidance, which helped me in completing this task through various stages.

                      

                          I would also like to express my heartily gratitude to the lab assistants                                        for their support during the making of this project.

                          Lastly, I thank almighty, my parents and friends for their constant encouragement without which this project would not be possible.

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ANALYSIS OF VEGETABLES AND FRUIT JUICES

AIM

To analyse some fruits & vegetables juice for the contents present in them.

INTRODUCTION

Fruits and vegetable are always a part of balanced diet. That means fruits vegetables provide our body the essential nutrients, i.e. Carbohydrates, proteins, vitamins and minerals. Again their presence in these is being indicated by some of our general observations, like -freshly cut apples become reddish black after some time. Explanation for it is that iron present in apple gets oxidixed to iron oxide. So, we can conclude that fruits and vegetables contain complex organic compounds, for e.g., anthocin, chlorophyll, esters(flavouring compounds), carbohydrates, vitamins and can be tested in any fruits or vegetable by extracting out its juice and then subtracting it to various tests which are for detection of different classes of organic compounds. Detection of minerals in vegetables or fruits means detection of elements other than carbon, hydrogen and oxygen.

MATERIAL REQUIRED

• Test Tubes
• Burner
• Litmus paper
• Laboratory reagents
• Various fruits
• Vegetables juices

CHEMICAL REQUIREMENTS

• pH indicator
• Iodine solution
• Fehling solution A and Fehling solution B
• Ammonium chloride solution
• Ammonium hvdroxide
• Ammonium oxalate
• Potassium sulphocynaide solution

PROCEDURE

The juices are made dilute by adding distilled water to it, in order to remove colour and to make it colourless so that colour change can be easily watched and noted down. Now test for food components are taken down with the solution.

TEST, OBSERVATION & INFERENCE

Test	Observation	Inference
ORANGE TEST:
Test for acidity:
Take 5ml of orange juice in a test tube and dip a pH paper in it. If pH is less than 7 the juice is acidic else the juice is basic.	The pH comes out to be 6.	Orange juice is acidic.
Test for Startch:
Take 2 ml of juice in a test tube and add few drops of iodine solution. It turns blue black in colour than the starch is present.	Absence of blue black in colour.	Orange juice is acidic.
Test for Carbohydrates (FEHLING’S TEST):
Take 2 ml of juice and 1 ml of fehling solution A & B and boil it. Red precipitates indicates the presence of producing sugar like maltose, glucose , fructose & Lactose.	No red coloured precipitates obtained.	Carbohydrates absent.
Test for Iron:
Take 2 ml of juice add drop of conc. Nitric acid. Boil the solution cool and add 2-3 drops of potassium sulphocyanide solution .Blood red colours shows the presence of iron.	Absence of blood red colour.	Iron is absent.
Test for Calcium:
Take 2 ml of juice add Ammonium chloride and ammonium hydroxide solution. Filter the solution and to the filterate add 2 ml of Ammonium Oxalate solution. white ppt or milkiness indicates the presence of calcium.	Yellow precipitate is obtained.	Calcium is present.

CONCLUSION

From the table given behind it can be conducted that most of the fruits & vegetable contain carbohydrate & vegetable contain carbohydrate to a small extent. Proteins are present in small quantity. Therefore one must not only depend on fruits and vegetables for a balance diet

TO STUDY THE RATE OF EVAPORATION OF DIFFERENT LIQUIDS

INTRODUCTION

When a liquid is placed in an open vessel, it slowly escapes into gas phase, eventually leaving the vessel empty. This phenomenon is known as evaporation. Evaporation of liquids can be explained in terms of kinetic molecular model. Although there are strong inter-molecular attractive forces which hold molecules of a liquid together, the molecules having sufficient kinetic energy can escape into gas phase if such molecules happen to come near the surface. In a sample of liquid all the molecules do not have same kinetic energy. There is a small fraction of molecules which have enough kinetic energy to overcome the attractive forces and escape into gas phase.

Evaporation causes cooling. This is due to the reason that the molecules, which undergo evaporation, are high-energy molecules; therefore the kinetic energy of molecules which are left behind is less. Since the remaining molecules have lower average kinetic energy therefore, temperature must be lower. If the temperature is kept constant the remaining liquid will have the same distribution of molecular kinetic energies and the high-energy molecule will keep on escaping from the liquid into the gas phase. If the liquid is taken in an open vessel, evaporation will continue until whole of the liquid evaporates.

REQUIREMENTS

Apparatus:

• Three petridishes of diameter 10 cm with covers
• 10 ml pipette
• Stop watch

Chemicals:

• Acetone
• Benzene
• Chloroform

PROCEDURE

• Clean and dry the petridishes and mark them as A, B, C.
• Pipette out 10 ml of acetone to petridish A and cover it.
• Pipette out 10 ml of benzene in petridish B and cover it.
• Pipette out 10 ml of chloroform in petridish C and cover it.
• Uncover all the three petridishes simultaneously and start the stop-watch.
• Note the respective time when the liquids evaporate completely from each petridish.

OBSERVATIONS

Petridish Mark	Liquid Taken	Time taken for complete evaporation
A	Acetone	53 min
B	Benzene	42 min
C	Chloroform	30 min

CONCLUSION

The rate of evaporation of the given three liquids is in the order:

Chloroform > Benzene > Acetone

Paper Chromatography: Basic Version

Objective

The objective of this project is to use paper chromatography to analyze ink components in permanent black markers.

Introduction

Matter makes up everything in the universe. Our body, the stars, computers, and coffee mugs are all made of matter. There are three different types of matter: solid, liquid, and gas. A solid is something that is normally hard (your bones, the floor under your feet, etc.), but it can also be powdery, like sugar or flour. Solids are substances that are rigid and have definite shapes. Liquids flow and assume the shape of their container; they are also difficult to compress (a powder can take the same shape as its container, but it is a collection of solids that are very small). Examples of liquids are milk, orange juice, water, and vegetable oil. Gases are around you all the time, but you may not be able to see them. The air we breathe is made up of a mixture of gases. The steam from boiling water is water’s gaseous form. Gases can occupy all the parts of a container (they expand to fill their containers), and they are easily compressed.

Matter is often a mixture of different substances. A heterogeneous mixture is when the mixture is made up of parts that are dissimilar (sand is a heterogeneous mixture). Homogeneous mixtures (also called solutions) are uniform in structure (milk is a homogeneous mixture). A sugar cube floating in water is a heterogeneous mixture, whereas sugar dissolved in water is a homogeneous mixture. You will determine whether the ink contained in a marker is a heterogeneous or homogeneous mixture, or just one compound.

In a mixture, the substance dissolved in another substance is called the solute. The substance doing the dissolving is called the solvent. If you dissolve sugar in water, the sugar is the solute and the water is the solvent.

For this project, you will be making a small spot with an ink marker onto a strip of paper. The bottom of this strip will then be placed in a dish of water, and the water will soak up into the paper.

The water (solvent) is the mobile phase of the chromatography system, whereas the paper is the stationary phase. These two phases are the basic principles of chromatography. Chromatography works by something called capillary action. The attraction of the water to the paper (adhesion force) is larger than the attraction of the water to itself (cohesion force), hence the water moves up the paper. The ink will also be attracted to the paper, to itself, and to the water differently, and thus a different component will move a different distance depending upon the strength of attraction to each of these objects. As an analogy, let’s pretend you are at a family reunion. You enjoy giving people hugs and talking with your relatives, but your cousin does not. As you make your way to the door to leave, you give a hug to every one of your relatives, and your cousin just says “bye.” So, your cousin will make it to the door more quickly than you will. You are more attracted to your relatives, just as some chemical samples may be more attracted to the paper than the solvent, and thus will not move up the solid phase as quickly. Your cousin is more attracted to the idea of leaving, which is like the solvent (the mobile phase).

Chromatography is used in many different industries and labs. The police and other investigators use chromatography to identify clues at a crime scene like blood, ink, or drugs. More accurate chromatography in combination with expensive equipment is used to make sure a food company’s processes are working correctly and they are creating the right product. This type of chromatography works the same way as regular chromatography, but a scanner system in conjunction with a computer can be used to identify the different chemicals and their amounts. Chemists use chromatography in labs to track the progress of a reaction. By looking at the sample spots on the chromatography plate, they can easily find out when the products start to form and when the reactants have been used up (i.e., when the reaction is complete). Chemists and biologists also use chromatography to identify the compounds present in a sample, such as plants.

Terms, Concepts and Questions to Start Background Research

• adhesion, cohesion forces
• capillary action
• stationary phase, mobile phase
• hydrophilic, hydrophobic
• R_f value
• paper chromatography
• solvent
• solution

Questions

• Why do different compounds travel different distances on the piece of paper?
• How is an R_f value useful?
• What is chromatography used for?

Bibliography

• Basic chemistry concepts:
  http://www.chem4kids.com
• Overview of liquids and capillary action:
  http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761571486&sec=18#s18
• Chromatography:
  http://www.doggedresearch.com/chromo/chromatography.htm
• BSE Blog:
  http://cbse-sample-papers.blogspot.com

Materials and Equipment

• water
• at least 15 identically sized strips of paper (5 for each pen)
  Note: chromatography paper or laboratory filter paper is preferable, but you can use a paper towel. The problem with paper towels is that they may be too absorptive and smear the ink. For more information on which papers work and which don’t.
• ruler
• pencils
• at least three different types of black markers (including one permanent marker), or at least three different colors of marker (including one permanent marker)
• a wide-mouth jar for the solvent

Experimental Procedure

Note: To make sure you can compare your results, as many of your materials as possible should remain constant. This means that the temperature, type of water used, size of paper strips, where the ink is placed onto the paper etc. should remain the same throughout the experiment.

1. Cut paper strips about one by four inches in area (they must all be the same size).
2. Take one of the paper strips and use a ruler and pencil to draw a line across it horizontally two cm from the bottom. This is the origin line (see illustration, below).
   
3. Pour a small amount of water into your glass (there should be barely enough for the paper strip to hang inside of the jar and just touch the water).
4. Using one of the markers, place a small dot of ink onto the line (see illustration, above).
5. Use the pencil to label the strip, so that you know which marker it represents.
6. Tape the paper to a pencil and hang it into the jar of solvent so that the bottom edge is just barely touching (see illustration, below).
   
7. Let the water rise up the strip until it is almost at the top.
8. Remove the strip from the jar and mark how far the solvent rose with a pencil.
9. Analyze the ink component(s):
   Measure the distance the solvent and each ink component traveled from the starting position, then calculate the R_f value for each component (some of the ink components might not have moved at all!).
10. Repeat this experiment for each brand or color of marker five times.

Questions

• Did the different inks separate differently? By looking at the R_fvalues, can you tell if any of the ink components from the different markers are the same?
• If the ink components separated differently for each marker, why did this happen (think about the strength of attractions)?

What’s the Point of Boiling?

Objective

The goal of this project is to separate pure water from fruit juice using a simple stovetop distillation apparatus.

Introduction

This project uses the technique of distillation. Distillation is when you boil a liquid, and then capture the vapor that escapes from the liquid and cool it. The cooled vapor condenses back into liquid. The condensed liquid is called the distillate. Do you think this process changes the liquid?

What if the liquid you boil has substances dissolved in it? For example, what if you started with a solution of sugar water? If you boiled the sugar water, you know from experience that there would be steam rising up from the pot on the stove. If you condensed that steam back into liquid, do you think the condensed liquid (the distillate) would contain sugar or not?

In this project, you will learn how to build a simple stove top distillation apparatus with stuff that you probably have in your kitchen right now. All you need is a deep pot with a sloping lid, a coffee cup, a bowl, some ice, and a stove. Of course, you’ll also need a liquid to distill. Colored fruit juice will work fine, or you could make a solution of sugar water. Add food coloring to it if you like. The Experimental Procedure section, below, shows you how to put it all together to find out what happens.

Terms, Concepts and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

• Boiling point
• Phases of matter:
  • Solid
  • Liquid
  • Vapor
• Condensation
• Solvent
• Solute
• Distillate

Questions

• What happens to solute molecules when the solvent evaporates or boils?
• How will the distillate compare to the original juice for:
  • color?
  • taste?
  • pH?

Bibliography

• For information on phase changes of water, see:
  Nave, C.R. 2005. “Phase Changes,” HyperPhysics, Department of Physics and Astronomy, Georgia State University [accessed April 26, 2007] http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html.
• Chamot, E. and B. Chamot, 2003. “Molecular Level Motion of Different Phases,” Chamot Laboratories, Inc. [accessed April 26, 2007] http://www.chamotlabs.com/Phases.html.
• For information on the water cycle, see: USGS, 2006. “The Water Cycle,” USGS Water Science Basics [accessed April 26, 2007]http://ga.water.usgs.gov/edu/watercycle.html.
• Cbse Blog : http://cbse-sample-papers.blogspot.com

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• Stove
• Deep cooking pot with sloped lid
• Ceramic coffee cup
• Ceramic bowl
• Ice
• Hot mitts
• Colored fruit juice (e.g., orange juice, grape juice, cranberry juice, etc.)

Experimental Procedure

1. Do your background research so that you are familiar with the terms, concepts, and questions, above. For more information on distillation methods.
2. The line drawing below is an illustration of the stove-top distillation apparatus used in this experiment.
   

   Line drawing of a stove top distillation apparatus. The text explains how to use it.

3. Here are the steps for using the distillation apparatus.
   1. Pour the colored fruit juice into the bottom of the pot. Save at least 200 ml of the original juice for comparison to the distillate.
   2. Place the ceramic coffee cup, open side up, in the center of the deep pot. (That’s correct, right in the juice!)
   3. Place a bowl on top of the coffee cup. (The bowl will catch the condensed liquid that drips down from the lid.)
   4. Put the cover on the pot, upside down.
   5. Put ice in the cover of the pot.
   6. Turn on the burner to medium heat. You want the juice to boil moderately (not a rolling boil).
   7. Allow the pot to boil for 10 minutes or so (enough time to collect a sufficient amount of distillate for testing).
   8. When done, turn off the burner. Allow the pot to cool for a few minutes.
   9. Put on hot mitts and carefully remove the cover from the pot.
   10. Still wearing hot mitts, lift the bowl off of the coffee cup and set it down on a heat-resistant surface.
   11. Remove the coffee cup.
   12. After it cools, pour the remaining juice from the pot into a clear container.
4. How do the original juice, the remaining juice from the pot, and the distillate compare in terms of color?
5. Ordinarily in a chemistry experiment, you would not taste any of the solutions. In this case, since you are using clean kitchen utensils, and edible fruit juice, a taste test is OK. Let the liquids cool to room temperature before tasting them! How do the three different liquids compare for taste?
   1. Which liquid is sweetest?
   2. Which is least sweet?
   3. You should be able to explain why.