16 March 2010

AF AND RF CHOKES(COIL)

There are two types of chokes mostly used ratio.

   1. Audio-Frequency chokes
   2. Radio-Frequency chokes



AUDIO-FREQUENCY CHOKES:
                                                                                       The Importance offered by an inductance is directly proportional to the frequency,and in the audio range of 20 Hz to 10 KHz,the value of inductance required is relatively high.So,in order to increase the inductance at audio frequencies,the coils are wound on a core of ferromagnetic material.The losses due to eddy currents are minimized by making the core from number of very thin sheets which are insulated from each other.These are called lamination or stampings and may be in number of standard shapes and sizes.




                                                                  AF Choke

RADIO-FREQUENCY CHOKES: 
                                                           These are designed to operate at high frequencies above audio range and are referred to either as intermediate frequency chokes or radio frequency chokes.In this type of inductor it is desirable that the coil should have as high an inductance as possible to a wide band of frequencies.The losses are not so important as in tuning coils, but in order to keep the self capacitance low,two types of winding are used,one of which is the single layer solenoid,but made very thin to keep the capacitance small.to single layer winding is used for high radio frequencies other winding is multilayer which is used for low radio frequencies.

 

04 March 2010

How to make Simple Relay Work

 


How To make Simple Relay

Things Which Are Needed
1.Transformer
2.A Ferromagnetic Core
3.Two Springs
4.Electrical Contacts
5.Two Light Bulbs

RECTIFIERS

RECTIFIERS :
Now we come to the most popular application of the diode: rectification. Simply defined, rectification is the conversion of alternating current (AC) to direct current (DC). This involves a device that only allows one-way flow of electrons. As we have seen, this is exactly what a semiconductor diode does. The simplest kind of rectifier circuit is the half-wave rectifier. It only allows one half of an AC waveform to pass through to the load. 

Half-wave rectifier circuit.
For most power applications, half-wave rectification is insufficient for the task. The harmonic content of the rectifier's output waveform is very large and consequently difficult to filter. Furthermore, the AC power source only supplies power to the load one half every full cycle, meaning that half of its capacity is unused. Half-wave rectification is, however, a very simple way to reduce power to a resistive load. Some two-position lamp dimmer switches apply full AC power to the lamp filament for “full” brightness and then half-wave rectify it for a lesser light output.

Half-wave rectifier application: Two level lamp dimmer.
In the “Dim” switch position, the incandescent lamp receives approximately one-half the power it would normally receive operating on full-wave AC. Because the half-wave rectified power pulses far more rapidly than the filament has time to heat up and cool down, the lamp does not blink. Instead, its filament merely operates at a lesser temperature than normal, providing less light output. This principle of “pulsing” power rapidly to a slow-responding load device to control the electrical power sent to it is common in the world of industrial electronics. Since the controlling device (the diode, in this case) is either fully conducting or fully nonconducting at any given time, it dissipates little heat energy while controlling load power, making this method of power control very energy-efficient. This circuit is perhaps the crudest possible method of pulsing power to a load, but it suffices as a proof-of-concept application.
If we need to rectify AC power to obtain the full use of both half-cycles of the sine wave, a different rectifier circuit configuration must be used. Such a circuit is called a full-wave rectifier. One kind of full-wave rectifier, called the center-tap design, uses a transformer with a center-tapped secondary winding and two diodes, as in Figure.

Full-wave rectifier, center-tapped design.
This circuit's operation is easily understood one half-cycle at a time. Consider the first half-cycle, when the source voltage polarity is positive (+) on top and negative (-) on bottom. At this time, only the top diode is conducting; the bottom diode is blocking current, and the load “sees” the first half of the sine wave, positive on top and negative on bottom. Only the top half of the transformer's secondary winding carries current during this half-cycle as in Figure.

Full-wave center-tap rectifier: Top half of secondary winding conducts during positive half-cycle of input, delivering positive half-cycle to load..
During the next half-cycle, the AC polarity reverses. Now, the other diode and the other half of the transformer's secondary winding carry current while the portions of the circuit formerly carrying current during the last half-cycle sit idle. The load still “sees” half of a sine wave, of the same polarity as before: positive on top and negative on bottom. 

Full-wave center-tap rectifier: During negative input half-cycle, bottom half of secondary winding conducts, delivering a positive half-cycle to the load.
One disadvantage of this full-wave rectifier design is the necessity of a transformer with a center-tapped secondary winding. If the circuit in question is one of high power, the size and expense of a suitable transformer is significant. Consequently, the center-tap rectifier design is only seen in low-power applications.
The full-wave center-tapped rectifier polarity at the load may be reversed by changing the direction of the diodes. Furthermore, the reversed diodes can be paralleled with an existing positive-output rectifier. The result is dual-polarity full-wave center-tapped rectifier in Figure. Note that the connectivity of the diodes themselves is the same configuration as a bridge.

Dual polarity full-wave center tap rectifier
Another, more popular full-wave rectifier design exists, and it is built around a four-diode bridge configuration. For obvious reasons, this design is called a full-wave bridge. Figure 

Full-wave bridge rectifier.
Current directions for the full-wave bridge rectifier circuit are as shown in Figure  for positive half-cycle and Figure for negative half-cycles of the AC source waveform. Note that regardless of the polarity of the input, the current flows in the same direction through the load. That is, the negative half-cycle of source is a positive half-cycle at the load. The current flow is through two diodes in series for both polarities. Thus, two diode drops of the source voltage are lost (0.7·2=1.4 V for Si) in the diodes. This is a disadvantage compared with a full-wave center-tap design. This disadvantage is only a problem in very low voltage power supplies.

Full-wave bridge rectifier: Electron flow for positive half-cycles.

Full-wave bridge rectifier: Electron flow for negative half=cycles.
Remembering the proper layout of diodes in a full-wave bridge rectifier circuit can often be frustrating to the new student of electronics. I've found that an alternative representation of this circuit is easier both to remember and to comprehend. It's the exact same circuit, except all diodes are drawn in a horizontal attitude, all “pointing” the same direction. Figure.

Alternative layout style for Full-wave bridge rectifier.
One advantage of remembering this layout for a bridge rectifier circuit is that it expands easily into a polyphase version in Figure.

Three-phase full-wave bridge rectifier circuit.
Each three-phase line connects between a pair of diodes: one to route power to the positive (+) side of the load, and the other to route power to the negative (-) side of the load. Polyphase systems with more than three phases are easily accommodated into a bridge rectifier scheme. Take for instance the six-phase bridge rectifier circuit in Figure.

Six-phase full-wave bridge rectifier circuit.
When polyphase AC is rectified, the phase-shifted pulses overlap each other to produce a DC output that is much “smoother” (has less AC content) than that produced by the rectification of single-phase AC. This is a decided advantage in high-power rectifier circuits, where the sheer physical size of filtering components would be prohibitive but low-noise DC power must be obtained. The diagram in Figure  shows the full-wave rectification of three-phase AC.

Three-phase AC and 3-phase full-wave rectifier output.
In any case of rectification -- single-phase or polyphase -- the amount of AC voltage mixed with the rectifier's DC output is called ripple voltage. In most cases, since “pure” DC is the desired goal, ripple voltage is undesirable. If the power levels are not too great, filtering networks may be employed to reduce the amount of ripple in the output voltage.
Sometimes, the method of rectification is referred to by counting the number of DC “pulses” output for every 360o of electrical “rotation.” A single-phase, half-wave rectifier circuit, then, would be called a 1-pulse rectifier, because it produces a single pulse during the time of one complete cycle (360o) of the AC waveform. A single-phase, full-wave rectifier (regardless of design, center-tap or bridge) would be called a 2-pulse rectifier, because it outputs two pulses of DC during one AC cycle's worth of time. A three-phase full-wave rectifier would be called a 6-pulse unit.
Modern electrical engineering convention further describes the function of a rectifier circuit by using a three-field notation of phases, ways, and number of pulses. A single-phase, half-wave rectifier circuit is given the somewhat cryptic designation of 1Ph1W1P (1 phase, 1 way, 1 pulse), meaning that the AC supply voltage is single-phase, that current on each phase of the AC supply lines moves in only one direction (way), and that there is a single pulse of DC produced for every 360o of electrical rotation. A single-phase, full-wave, center-tap rectifier circuit would be designated as 1Ph1W2P in this notational system: 1 phase, 1 way or direction of current in each winding half, and 2 pulses or output voltage per cycle. A single-phase, full-wave, bridge rectifier would be designated as 1Ph2W2P: the same as for the center-tap design, except current can go both ways through the AC lines instead of just one way. The three-phase bridge rectifier circuit shown earlier would be called a 3Ph2W6P rectifier.
Is it possible to obtain more pulses than twice the number of phases in a rectifier circuit? The answer to this question is yes: especially in polyphase circuits. Through the creative use of transformers, sets of full-wave rectifiers may be paralleled in such a way that more than six pulses of DC are produced for three phases of AC. A 30o phase shift is introduced from primary to secondary of a three-phase transformer when the winding configurations are not of the same type. In other words, a transformer connected either Y-Δ or Δ-Y will exhibit this 30o phase shift, while a transformer connected Y-Y or Δ-Δ will not. This phenomenon may be exploited by having one transformer connected Y-Y feed a bridge rectifier, and have another transformer connected Y-Δ feed a second bridge rectifier, then parallel the DC outputs of both rectifiers. Figure  Since the ripple voltage waveforms of the two rectifiers' outputs are phase-shifted 30o from one another, their superposition results in less ripple than either rectifier output considered separately: 12 pulses per 360o instead of just six:

Polyphase rectifier circuit: 3-phase 2-way 12-pulse (3Ph2W12P)
  • REVIEW:
  • Rectification is the conversion of alternating current (AC) to direct current (DC).
  • A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load, resulting in one non-alternating polarity across it. The resulting DC delivered to the load “pulsates” significantly.
  • A full-wave rectifier is a circuit that converts both half-cycles of the AC voltage waveform to an unbroken series of voltage pulses of the same polarity. The resulting DC delivered to the load doesn't “pulsate” as much.
  • Polyphase alternating current, when rectified, gives a much “smoother” DC waveform (less ripple voltage) than rectified single-phase AC.

ELECTRON THEORY

INTRODUCTION:
            The operation of many Electronics devices depended upon the movement of charged particles i.e.electrons with in them.Therefore, it is very necessary to study the structure and arrangement of atoms is solids.The objective of this chapter is to present elementary knowledge about the physical structure of solid.
           This chapter also help to understand the energy bands with reference to conductors, insulators and semiconductors.Certain substance such as germanium,silicon,carbon etc.are neither good conductors like copper nor insulators like glass.In other words between the insulators and conductors there is another substance is called semiconductors.A semiconductor is a material whose conductivity lies somewhere that of a conductor and an insulator.Typical value of conductivity is 100 ohm's/cm3.Semiconductors are being extensively used in electronics circuits.Diodes,transistor and integrated circuits (IC) are also a semiconductor devices.Gallium arsenide is another semiconductors material becoming increasingly popular for microwave and solid state devices.



ELECTRONICS:

                                            "The most important branch of physics which deals with the flow of electrons through a gas,vacuum or semiconductor is known is "ELECTRONICS"

Electronics essentially deals with the electronics devices or equipments which are used to production,propagation and reception of electromagnetic waves.such devices are being used in almost all the industries for increasing production,efficiency and quality control.

ATOM:

                    In the universe,everything have its existence,make up the matter.Matters exist in the three forms solid liquid gas.There are 109 elements divided in to several groups according to their chemical properties and atomic number.The smallest particle having independent existence and which cannot be further divided is known as an atom.

03 March 2010

AC Circuits

AC THROUGH RESISTORS:
                                                                          When only a resistance connected in series with an alternating source as shown in fig 11.1(a),both current and voltage are zero at same instant.Similarly they both reach maximum at the same instant.for this reason they are said to be"in phase".





                                                                  (a)Circuit Diagram




                                                    (b)Current and voltage waveform

                   
                                                Fig.11.1 AC Through resistive circuit




                                                       


      If the voltage rises, the current rises and if the voltage falls,the current falls and so on.It means that both the voltage and current pass their maximum and minimum values at the same instant and their instantaneous values are said to be in phase.This behavior is shown Fig.11.1(b).
                                           




  
Power In A Resistive Circuit:
                                                  In a circuit containing resistance,only the current is in phase with the voltage and power at any instant is equal to {(i power 2)Multiply by R} (v Multiply i) Where v and i are instantaneous values.The voltage and current waveform are shown in fig.11.2.



 
Fig.11.2 Power waveform

                                                                                                                                                                                                              

                  During  the first half cycle the instantaneous values of voltage and current are both positive, so that the power given by v Multiply i is positive.On the sound half cycle both v and i are negative,so that the product of -v and -i is also positive. The power waveform is shown shaded,it is sinusoidal and has a frequency of twice that of the supply.Thus power is absorbed form the supply on both positive and negative half cycles.

AC Through Inductance:
                                            When only a inductor connected is series with an alternating source as shown in fig.11.3(a),then the current lags the applied voltage by 90` or voltage leads the current by 90`.Because the voltage and current are not zero at the same instant or maximum at the same instant, they are said to be out of phase.The phase.The phase difference corresponds to maximum value 90` after the voltage,the current reaches to maximum value 90`after the voltage,the current is said to lag the voltage by 90`.The behavior is shown in Fig.11.3(b).



                                             Fig.11.3 AC through inductive circuit 

02 March 2010

C P U Troubleshooting Procedures

PROCEDURE:
This is a simple Procedure.you want Problem Found in your Personal Computer?Look This guide

*First Connect Power Supply.Not Given Display?
*Disconnect Power Supply.
*Open Left Cover CPU.
*Hard disk & CD Rom Power Supply Remove And Clean.
*Hard Disk & CD Rom Data Cable Remove And Clean.
*Ram Remove his slot and Clean with Cloth.Check...Not Display...another Ram connect your PC and check...Not Display...Your old Ram check another computer is alright.
*Open Processor And check other computers.his alright.
*Replace Data cables in CPU.
*Check Your Jumpers Setting.
*Computer is ON and ok
*Start And Enter The BIOS Setup And Detect Hard Disk.And Set First Boot CD Rom Save And Exit.
*Enter Your Operating System Compact Disk And Start Windows Installation.Good Luck!

You Are Connect Double Hard Disk in a CPU?

*First Your Old Hard disk is Disconnect.
 *Set Old Hard Disk Jumper Setting.Old Hard Disk Jumper is Only MASTER.
*New Hard disk Jumper is Only SLAVE.
*Connect Cables & Start CPU.
*Enter BIOS Setup And Detect Hard Disk BIOS Show Two Hard Disk.Enjoy