PDF Department of Electrical and Electronic Engineering

The circuit drawn relates to a regular industrial project, showing how the batteries take control during an interruption in electrical supply or variation outside the normal limits of the voltage line, without interruption of the operation which provides a steady regulated output supplied (5 Volts at LM7805) ) and an unregulated supply (12 Volts). The input to the primary winding of the transformer (TR1) is 240V. This project report has a total of six chapters. The first chapter describes a brief idea about Preface, literature review, objectives of this work and work status. The second chapter contains theory of diode.

Diode [1]

History

Electronic symbols

Point-contact diodes

A block of n-type semiconductor is constructed, and a conductive tip contact made with a group-3 metal is placed in contact with the semiconductor. Some metal migrates into the semiconductor to make a small area of p-type semiconductor near the contact.

A point contact diode works the same as the junction diodes described below, but their construction is simpler. It is called the depletion region due to the absence of charge carriers (electrons and holes in this case).

Types of semiconductor diode

Laser diodes are commonly used in optical storage devices and for high-speed optical communication. The term step recovery is related to the shape of the reverse recovery characteristic of these devices.

Voltage Regulator[2]

Use IC 7805 voltage Regulator
Datasheet
Pin Diagram
Pin Description

The voltage source in a circuit may fluctuate and will not give a fixed voltage output.

Transformer[3]

The Power Transformer

A transformer should either step up or step down the AC supply voltage to meet the requirements of the solid state electronic devices and circuits powered by the DC power supply. One of the important features of a transformer is the electrical isolation between the primary and secondary. The voltages in the primary and secondary windings are directly proportional to the turns ratio of the two windings.

If V1 is the voltage applied to the primary, V2 is voltage induced in the secondary, N1 is the number of turns in the primary and N2 is the number of turns in the secondary, then the relationship between them is given by the expression

Turns ratio

Induction law

If the turns of the coil are oriented perpendicular to the magnetic lines, the current is the product of the magnetic flux density B and the area A it crosses. The area is constant and is equal to the cross-sectional area of the transformer core, while the magnetic field changes with time according to the excitation of the primary. If we take the ratio of the above two equations, we get the same voltage ratio and turns ratio shown above, that is,.

Nevertheless, it is impossible to eliminate all leakage currents, because they play an essential role in the operation of the transformer. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary.

Rectifier[4]

The Full Wave Rectifier

Full Wave Rectifier Circuit

This configuration results in each diode in turn conducting when its anode terminal is positive with respect to the transformer center point C giving an output during both half cycles twice as much as for the half wave rectifier, so it is 100% efficient as shown below. The peak voltage of the output waveform is the same as before for the half-wave rectifier provided that each half of the transformer windings has the same effective voltage value. The main disadvantage of this type of full wave rectifier circuit is that a larger transformer is required for a given power output with two separate but identical secondary windings which makes this type of full wave rectifier circuit expensive compared to the "Full Wave Bridge Rectifier" circuit equivalent.

The Full Wave Bridge Rectifier[5]

The Diode Bridge Rectifier[6]

The Positive Half-cycle[7]

During the negative half cycle of the supply, diodes D3 and D4 conduct in series, but diodes D1 and D2 switch "OFF" as they are now reverse biased.

The Negative Half-cycle

The Smoothing Capacitor[8]

Full-wave Rectifier with Smoothing Capacitor

The smoothing capacitor converts the full-wave ripple output of the rectifier to a smooth DC output voltage. However, they are two important parameters to consider when choosing a suitable smoothing capacitor and these are its Working Voltage, which should be higher than the no-load output value of the rectifier and its of capacitance, which determines the amount of ripple that will appear. superimposed on top of the DC voltage. Where: I is the DC load current in amperes, ƒ is the ripple frequency or twice the input frequency in Hertz, and C is the capacitance in Farads.

Therefore, the fundamental frequency of the ripple voltage is twice the frequency of the AC supply (100Hz) where for the half-wave rectifier it is exactly equal to the supply frequency (50Hz). The amount of ripple voltage superimposed on the DC supply voltage by the diodes can be practically eliminated by adding a highly improved π-filter (pi-filter) to the output terminals of the bridge rectifier.

Capacitor[9]

History

Daniel Gralath was the first to combine multiple jars in parallel into a "battery" to increase charging capacity. Benjamin Franklin examined the Leyden jar and came to the conclusion that the charge was stored on the glass, not in the water as others had assumed. He also adopted the term "battery", (denoting the increase in force by a series of similar units as in a battery of guns), subsequently applied to clusters of electrochemical cells.

Leyden jars were later made by covering the inside and outside of jars with metal foil, leaving a space near the mouth to prevent sparks between the foils. The term was first used for this purpose by Alessandro Volta in 1782, referring to the device's ability to store a higher density of electrical charge than a normal insulated conductor.

Theory of operation

The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar after the University of Leiden where he worked. He was also impressed by the force of the shock he received, and wrote: "I would not endure another shock to the French royalty." Leyden jars or more powerful devices using flat glass plates alternating with foil conductors were used exclusively until about 1900, when the invention of the wireless (radio) created a demand for standard capacitors, and the steady transition to higher frequencies required capacitors with lower inductance.

A more compact construction began to be used from a flexible dielectric sheet such as oiled paper sandwiched between sheets of metal foil, wrapped or folded into a small package.

Hydraulic analogy

Energy of electric field

Current–voltage relation

DC circuits See also: RC circuit

A series circuit containing only a resistor, a capacitor, a switch, and a constant DC source of voltage V0 is known as a charging circuit.[16] If the capacitor is initially uncharged while the switch is open, and the switch is closed at t0, from Kirchhoff's voltage law it follows that. At t = 0, the voltage across the capacitor is zero and the voltage across the resistor is V0. As the capacitor reaches equilibrium with the source voltage, the voltages across the resistor and the currents through the entire circuit decay exponentially.

The example of discharging a charged capacitor also shows an exponential decay, but with the initial capacitor voltage replacing V0 and the final voltage being zero.

AC circuits

Impedance, the vector sum of reactance and resistance, describes the phase difference and amplitude ratio between a sinusoidally varying voltage and a sinusoidally varying current at a given frequency. Fourier analysis allows any signal to be constructed from a frequency spectrum, from which the response of the circuit to different frequencies can be found. The −j phase indicates that the AC voltage V = ZI lags the AC current by 90°: the positive current phase corresponds to the voltage increase as the capacitor charges; zero current corresponds to constant instantaneous voltage, etc.

Conversely, at very low frequencies the reactance will be high, so the capacitor is almost an open circuit in AC analysis, these frequencies have been "filtered out". Capacitors differ from resistors and inductors in that the impedance is inversely proportional to the defining characteristic; i.e. capacitance.

Capacitor types

Dielectric materials

Electrolytic capacitors break down naturally if left unused for a period of time (about a year), and if used at full power can short circuit, permanently damaging the capacitor and usually blowing a fuse or destroying the rectifier diodes (e.g. in older equipment, sparks in rectifier tubes). They can be repaired before use (and damage) by gradually turning on the operating voltage, often done on antique vacuum tube equipment over a period of 30 minutes by using a variable transformer to provide alternating current. Supercapacitors made of carbon airgel, carbon nanotubes or highly porous electrode materials, offer extremely high capacitance (up to 5 kF as of 2010) and can be used in place of rechargeable batteries in some applications.

AC capacitors are specially designed to operate in AC electrical circuits with mains (mains) voltage. They are usually robustly packaged, often in metal enclosures that can be easily grounded.

Structure

They are commonly used in electric motor circuits and are often designed for large currents, so they are usually physically large. To reduce series resistance and inductance for long boards, the boards and dielectric are staggered so that the connection is made at the common edge of the rolled boards, not at the ends of the foil or metallized film strips that make up the boards. 34;Axial' means that the conductors are on a common axis, usually the axis of the cylindrical body of the capacitor - the cables extend from opposite ends.

Radial bullets can more accurately be called tandem; they are rarely aligned along the radii of the body circumference, so the term is imprecise, though universal. The plates (up to the bend) are usually in planes parallel to that of the flat body of the capacitor and lie in the same direction; they are often parallel as manufactured.

Capacitor markings

Cost comparison

The rectified signal is attenuated by capacitor C1. When mains supply is available, the battery will be charged via diode D3 and the regulator IC receives supply via diode D5. All thanks to our thesis supervisor, Md.Dara Abdus Satter, Assistant Professor, Department of Electrical and Electronic Engineering, Daffodil International University for his valuable suggestions and guidance throughout this thesis. He always helps us in our working day in electronics lab and we find our project wrong. at the end he advises how the project was done.

We are grateful to our honorable Vice Chancellor, Professor Dr.M.Lutfar Rahman, Daffodil International University for providing a golden opportunity to achieve our B.Sc. Dr.Samsul Alam, Head of Department of Electrical and Electronics Engineering, Daffodil International University for his valuable suggestions.