24 led dancing light

PHYSICS INVESTIGATORY PROJECT SEMICONDUCTOR DEVICES

NAVNEET KUMAR, XII BROLL NO 12238

KENDRIYA VIDYALAYA NO 2 COLABA, MUMBAI

PROJECT MADE BY

MRS.MANJU RANI RAWAT, PGT PHYSICS

KENDRIYA VIDYALAYA NO 2 COLABA, MUMBAI

GUIDED BY

C E R T I F I C A T E

Date: February 2015

This is to certify that NAVNEET KUMAR , a student of class XII ‘B’ studying in this school has completed the project named “24 LED Dancing Light” in the academic year 2014-2015

______________ ___________ ____________ Head of the department External Examiner Principal [PGT, Physics] K.V.No-2, Colaba, K V No 2 Colaba, Mumbai Mumbai

Place: Mumbai

1

A C K N O W L E D G E M E N T

It gives me great pleasure to express my gratitude towards Mrs. Manju Rani Rawat, PGT, Physics for her untiring help and encouragement throughout the duration of the project. Without her motivation and help, successful completion of the project would not have been possible.

Lastly, I would like to thank my parents and people those who provided me all the material required so as to finish the project within the allotted time period.

Navneet Kumar,

XII B

2

I N D E X 1. AIM OF THE

PROJECT2. THEORY3. MATERIALS AND

EQUIPMENTS USED4. PROCEDURE5. WORKING OF THE

CIRCUIT6. BIBLIOGRAPHY

3

1. AIM OF THE PROJECT TO CONSTRUCT A CIRCUIT OF 24 LED DANCING LIGHT

2. THEORYSEMICONDUCTORA semiconductor material has an electrical conductivity value between a conductor, such as copper, and an insulator, such as glass. The modern understanding of the properties of a semiconductor relies on quantum physics to explain the movement of electrons and holes in a crystal lattice. The electrical conductivity of a semiconductor material increases with increasing temperature, which is behavior opposite to that of a metal. Because the electrical properties of a semiconductor material can be modified by controlled addition of impurities, or by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, and energy conversion. Current conduction in a semiconductor occurs through the movement of free electrons and "holes", collectively known as charge carriers. Adding impurity atoms to a semiconducting material, known as "doping", greatly increases the number of charge carriers within it. When a doped semiconductor contains mostly free holes it is called "p-type", and when it contains mostly free electrons it is known as "n-type". The semiconductor materials used in electronic devices are doped under precise conditions to control the location and concentration of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions; the p–n junctions between these regions are responsible for the useful electronic behavior. Although some pure elements and many compounds display semiconductor properties, silicon, germanium, and compounds of gallium are the most widely used in electronic devices.

4

A large number of elements and compounds have semiconducting properties, including Certain pure elements are found in Group XIV of the periodic table; the most

commercially important of these elements are silicon and germanium. Silicon and germanium are used here effectively because they have 4 valence electrons in their outermost shell which gives them the ability to gain or lose electrons equally at the same time.

Binary compounds, particularly between elements in Groups III and V, such as gallium arsenide, Groups II and VI, groups IV and VI, and between different group IV elements, e.g. silicon carbide.

Properties

1. Variable conductivityA pure semiconductor is a poor electrical conductor as a consequence of having just the right number of electrons to completely fill its valence bonds. Through various techniques (e.g., doping or gating), the semiconductor can be modified to have an excess of electrons (becoming an n-type semiconductor) or a deficiency of electrons (becoming a p-type semiconductor). In both cases, the semiconductor becomes much more conductive (the conductivity can be increased by one million fold or more). Semiconductor devices exploit this effect to shape electrical current.2. DepletionWhen doped semiconductors are joined to metals, to different semiconductors, and to the same semiconductor with different doping, the resulting junction often strips the electron excess or deficiency out from the semiconductor near the junction. This depletion region is rectifying (only allowing current to flow in one direction), and used to further shape electrical currents in semiconductor devices.3. Energetic electrons travel farElectrons can be excited across the energy band gap of a semiconductor by various means. These electrons can carry their excess energy over distance scales of micrometers before dissipating their energy into heat – a significantly longer distance than is possible in metals. This property is essential to the operation of, e. g., bipolar junction transistors and solar cells.4. Light emissionIn certain semiconductors, excited electrons can relax by emitting light instead of producing heat. These semiconductors are used in the construction of light emitting diodes and fluorescent quantum dots.5. Thermal energy conversionSemiconductors have large thermoelectric power factors making them useful in thermoelectric generators, as well as high thermoelectric figures of merit making them useful in thermoelectric coolers

5

SEMICONDUCTOR DEVICESSemiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices (vacuum tubes) in most applications. They use electronic conduction in the solid state as opposed to the gaseous state or thermionic emission in a high vacuum. Semiconductor devices are manufactured both as single discrete devices and as integrated circuits (ICs), which consist of a number—from a few (as low as two) to billions—of devices manufactured and interconnected on a single semiconductor substrate, or wafer. Semiconductor materials are useful because their behavior can be easily manipulated by the addition of impurities, known as doping. Semiconductor conductivity can be controlled by introduction of an electric or magnetic field, by exposure to light or heat, or by mechanical deformation of a doped monocrystalline grid; thus, semiconductors can make excellent sensors. Current conduction in a semiconductor occurs via mobile or "free" electrons and holes, collectively known as charge carriers. Doping a semiconductor such as silicon with a small amount of impurity atoms, such as phosphorus or boron, greatly increases the number of free electrons or holes within the semiconductor. When a doped semiconductor contains excess holes it is called "p-type", and when it contains excess free electrons it is known as "n-type", where

p (positive for holes) or n (negative for electrons) is the sign of the charge of the majority mobile charge carriers. The semiconductor material used in devices is doped under highly controlled conditions in a fabrication facility, or fab, to control precisely the location and concentration of p- and n-type dopants. The junctions which form where n-type and p-type semiconductors join together are called junctions. There are two main categories of

semiconductor devices-Diodes and Transistors

6

DiodeThe diode is a device made from a single p–n junction. At the junction of a p-type and an n-type semiconductor there forms a region called the depletion region which blocks current conduction from the n-type region to the p-type region, but allows current to conduct from the p-type region to the n-type region. Thus, when the device is forward biased, with the p-side at higher electric potential, the diode conducts current easily; but the current is very small when the diode is reverse biased. Exposing a semiconductor to light can generate electron–hole pairs, which increases the number of free carriers and its conductivity. Diodes optimized to take advantage of this phenomenon are known as photodiodes. Compound semiconductor diodes can also be used to generate light, as in light-emitting diodes and laser diodes.

7

TransistorBipolar junction transistors are formed from two p–n junctions, in either n–p–n or p–n–p configuration. The middle, or base, region between the junctions is typically very narrow. The other regions, and their associated terminals, are known as the emitter and the collector. A small current injected through the junction between the base and the emitter changes the properties of the base-collector junction so that it can conduct current even though it is reverse biased. This creates a much larger current between the collector and emitter, controlled by the base-emitter current. Another type of transistor, the field-effect transistor, operates on the principle that semiconductor conductivity can be increased or decreased by the presence of an electric field. An electric field can increase the number of free electrons and holes in a semiconductor, thereby changing its conductivity. The field may be applied by a reverse-biased p–n junction, forming a junction field-effect transistor (JFET) or by an electrode isolated from the bulk material by an oxide layer, forming a metal–oxide–semiconductor field-effect transistor (MOSFET).The MOSFET, a solid-state device, is the most used semiconductor device today. The gate electrode is charged to produce an electric field that controls the conductivity of a "channel" between two terminals, called the source and drain. Depending on the type of carrier in the channel, the device may be an n-channel (for electrons) or a p-channel (for holes) MOSFET.

8

Although the MOSFET is named in part for its "metal" gate, in modern devices polysilicon is typically used instead.

RESISTORSA resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits. In electronic circuits resistors are used to limit current flow, to adjust signal levels, bias active elements, terminate transmission lines among other uses. High-power resistors that can dissipate many watts of electrical power as heat may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity. Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds and forms. Resistors are also implemented within circuits. The electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. The nominal value of the resistance will fall within a manufacturing tolerance.

9

CAPACITORSA capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e. insulator). The conductors can be thin films, foils or sintered beads of metal or conductive electrolyte, etc. The "nonconducting" dielectric acts to increase the capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, vacuums, paper, mica, oxide layer etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates. When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if a time-varying voltage is applied across the leads of the capacitor, a displacement current can flow. An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is expressed as the ratio of the electric charge Q on each conductor to the potential difference V between them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F). The capacitance is greater when there is a narrower separation between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates passes a small amount of leakage current and

also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired inductance and resistance. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow.

10

3. MATERIAL AND EQUIPMENTS

1. Light Emitting Diodes 12×RED + 12×GREEN2. Capacitors 02×10µF/16 V3. Resistors 02× 68KΩ + 01×100Ω 4. Transistors 02 × BC 1485. PCB board 6. Wires 7. 12 V battery / 12 V Adapter with adapter point for

supply8. Soldering heater and lead tin solder

11

4. CONSTRUCTION PROCEDURE

1. Collect all the material as per required 2. Check whether all the LED’s are functioning

or not3. Solder all the LED’s in the circuit board.4. Solder all the capacitors, resistors and

transistors to the circuit board5. Check whether the circuit formed is working

or not by connecting to 12 v battery/adapter

12

5. WORKING

CIRCUIT DIAGRAM FOR 24 LED DANCING LIGHT

It works on the principle of charging and discharging of capacitors C1 and C2. Current from the positive of battery flows through first set of LEDs D1-D23 to the collector of Transistor1 through resistor R1. Resistor R1 limits current through the LEDs to protect them. The current through R1 charges capacitor C2. It then discharges through the base of T2. This gives base current to T2 which is emitted to base of T1 again via R2 which instead of passing to T1, moves to R3. As a result second set of LEDs D2-D24 lights as the current flows through R3.Capacitor C2 again charges and the cycle repeats.

13

6. BIBLIOGRAPHY

1. INTERNET

a. www.wikipedia com

b. www.instructables.com

c. www.google.co.in [images]

2. Instruction Manual [Provided with the ‘do it yourself’ assembling kit]

14