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Types of diodes and working
A diode is a two-terminal device, having two active electrodes, between which it allows the transfer of current in one direction only. Diodes are known for their unidirectional current property, wherein, the electric current is allowed to flow in one direction. Basically, diodes are used for the purpose of rectifying waveforms, and can be used within power supplies or within radio detectors. They can also be used in circuits where 'one way' effect of diode is required. Most diodes are made from semiconductors such as silicon, however, germanium is also used sometimes. Diodes transmit electric currents in one direction, however, the manner in which they do so can vary. Several types of diodes are available for use in electronics design. Some of the different types are:
Light Emitting Diode (LED): It is one of the most popular type of diodes and when this diode permits the transfer of electric current between the electrodes, light is produced. In most of the diodes, the light (infrared) cannot be seen as they are at frequencies that do not permit visibility. When the diode is switched on or forward biased, the electrons recombine with the holes and release energy in the form of light (electroluminescence). The color of light depends on the energy gap of the semiconductor.
Avalanche Diode: This type of diode operates in the reverse bias, and used avalanche effect for its operation. The avalanche breakdown takes place across the entire PN junction, when the voltage drop is constant and is independent of current. Generally, the avalanche diode is used for photo-detection, wherein high levels of sensitivity can be obtained by the avalanche process.
Laser Diode: This type of diode is different from the LED type, as it produces coherent light. These diodes find their application in DVD and CD drives, laser pointers, etc. Laser diodes are more expensive than LEDs. However, they are cheaper than other forms of laser generators. Moreover, these laser diodes have limited life.
Schottky Diodes: These diodes feature lower forward voltage drop as compared to the ordinary silicon PN junction diodes. The voltage drop may be somewhere between 0.15 and 0.4 volts at low currents, as compared to the 0.6 volts for a silicon diode. In order to achieve this performance, these diodes are constructed differently from normal diodes, with metal to semiconductor contact. Schottky diodes are used in RF applications, rectifier applications and clamping diodes.
Zener diode: This type of diode provides a stable reference voltage, thus is a very useful type and is used in vast quantities. The diode runs in reverse bias, and breaks down on the arrival of a certain voltage. A stable voltage is produced, if the current through the resistor is limited. In power supplies, these diodes are widely used to provide a reference voltage.
Photodiode: Photodiodes are used to detect light and feature wide, transparent junctions. Generally, these diodes operate in reverse bias, wherein even small amounts of current flow, resulting from the light, can be detected with ease. Photodiodes can also be used to generate electricity, used as solar cells and even in photometry.
Varicap Diode or Varactor Diode: This type of diode feature a reverse bias placed upon it, which varies the width of the depletion layer as per the voltage placed across the diode. This diode acts as a capacitor and capacitor plates are formed by the extent of conduction regions and the depletion region as the insulating dielectric. By altering the bias on the diode, the width of the depletion region changes, thereby varying the capacitance.
Rectifier Diode: These diodes are used to rectify alternating power inputs in power supplies. They can rectify current levels that range from an amp upwards. If low voltage drops are required, then Schottky diodes can be used, however, generally these diodes are PN junction diodes.
Small signal or Small current diode - These diodes assumes that the operating point is not affected because the signal is small
· Large signal diodes - The operating point in these diodes get affected as the signal is large.
Transient voltage supression diodes - This diode is used to protect the electronics that are sensitive against voltage spikes.
· Gold doped diodes - These diodes use gold as the dopant and can operate at signal frequencies even if the forward voltage drop increases.
· Super barrier diodes - These are also called as the rectifier diodes. This diodes have the property of low reverse leakage current as that of normal p-n junction diode and low forward voltage drop as that of Schottky diode with surge handling ability.
· Point contact diodes - The construction of this diode is simpler and are used in analog applications and as a detector in radio receivers. This diode is built of n – type semiconductor and few conducting metals placed to be in contact with the semiconductor. Some metals move from towards the semiconductor to form small region of p- tpye semiconductor near the contact.
· Peltier diodes - This diode is used as heat engine and sensor for thermoelectric cooling.
· Gunn diode - This diode is made of materials like GaAs or InP that exhibit a negative differential resistance region.
· Crystal diode - These are a type of point contact diodes which are also called as Cat’s whisker diode. This didoe comprises of a thin sharpened metal wire which is pressed against the semiconducting crystal. The metal wire is the anode and the semconducting crystal is the cathode. These diodes are obsolete.
· Avalanche diode - This diode conducts in reverse bias condition where the reverse bias volage applied across the p-n junction creates a wave of ionization leading to the flow of large current. These didoes are designed to breakdown at specific reverse voltage in order to avoid any damage.
· Silicon controlled rectifier - As the name implies this diode can be controlled or triggered to the ON condition due to the application of small voltage. They belong to the family of Tyristors and is used in various fields of DC motor control, generator field regulation, lighting system control and variable frequency drive . This is three terminal device with anode, cathode and third controled lead or gate.
· Vaccum diodes - This diode is two electrode vacuum tube which can tolerate high inverse voltages.
Diodes are used widely in the electronics industry, right from electronics design to production, to repair. Besides the above mentioned types of diodes, the other diodes are PIN diode, point contact diode, signal diode, step recovery diode, tunnel diode and gold doped diodes. The type of diode to transfer electric current depends on the type and amount of transmission, as well as on specific applications.
Light Emitting Diode (LED): It is one of the most popular type of diodes and when this diode permits the transfer of electric current between the electrodes, light is produced. In most of the diodes, the light (infrared) cannot be seen as they are at frequencies that do not permit visibility. When the diode is switched on or forward biased, the electrons recombine with the holes and release energy in the form of light (electroluminescence). The color of light depends on the energy gap of the semiconductor.
Avalanche Diode: This type of diode operates in the reverse bias, and used avalanche effect for its operation. The avalanche breakdown takes place across the entire PN junction, when the voltage drop is constant and is independent of current. Generally, the avalanche diode is used for photo-detection, wherein high levels of sensitivity can be obtained by the avalanche process.
Laser Diode: This type of diode is different from the LED type, as it produces coherent light. These diodes find their application in DVD and CD drives, laser pointers, etc. Laser diodes are more expensive than LEDs. However, they are cheaper than other forms of laser generators. Moreover, these laser diodes have limited life.
Schottky Diodes: These diodes feature lower forward voltage drop as compared to the ordinary silicon PN junction diodes. The voltage drop may be somewhere between 0.15 and 0.4 volts at low currents, as compared to the 0.6 volts for a silicon diode. In order to achieve this performance, these diodes are constructed differently from normal diodes, with metal to semiconductor contact. Schottky diodes are used in RF applications, rectifier applications and clamping diodes.
Zener diode: This type of diode provides a stable reference voltage, thus is a very useful type and is used in vast quantities. The diode runs in reverse bias, and breaks down on the arrival of a certain voltage. A stable voltage is produced, if the current through the resistor is limited. In power supplies, these diodes are widely used to provide a reference voltage.
Photodiode: Photodiodes are used to detect light and feature wide, transparent junctions. Generally, these diodes operate in reverse bias, wherein even small amounts of current flow, resulting from the light, can be detected with ease. Photodiodes can also be used to generate electricity, used as solar cells and even in photometry.
Varicap Diode or Varactor Diode: This type of diode feature a reverse bias placed upon it, which varies the width of the depletion layer as per the voltage placed across the diode. This diode acts as a capacitor and capacitor plates are formed by the extent of conduction regions and the depletion region as the insulating dielectric. By altering the bias on the diode, the width of the depletion region changes, thereby varying the capacitance.
Rectifier Diode: These diodes are used to rectify alternating power inputs in power supplies. They can rectify current levels that range from an amp upwards. If low voltage drops are required, then Schottky diodes can be used, however, generally these diodes are PN junction diodes.
Small signal or Small current diode - These diodes assumes that the operating point is not affected because the signal is small
· Large signal diodes - The operating point in these diodes get affected as the signal is large.
Transient voltage supression diodes - This diode is used to protect the electronics that are sensitive against voltage spikes.
· Gold doped diodes - These diodes use gold as the dopant and can operate at signal frequencies even if the forward voltage drop increases.
· Super barrier diodes - These are also called as the rectifier diodes. This diodes have the property of low reverse leakage current as that of normal p-n junction diode and low forward voltage drop as that of Schottky diode with surge handling ability.
· Point contact diodes - The construction of this diode is simpler and are used in analog applications and as a detector in radio receivers. This diode is built of n – type semiconductor and few conducting metals placed to be in contact with the semiconductor. Some metals move from towards the semiconductor to form small region of p- tpye semiconductor near the contact.
· Peltier diodes - This diode is used as heat engine and sensor for thermoelectric cooling.
· Gunn diode - This diode is made of materials like GaAs or InP that exhibit a negative differential resistance region.
· Crystal diode - These are a type of point contact diodes which are also called as Cat’s whisker diode. This didoe comprises of a thin sharpened metal wire which is pressed against the semiconducting crystal. The metal wire is the anode and the semconducting crystal is the cathode. These diodes are obsolete.
· Avalanche diode - This diode conducts in reverse bias condition where the reverse bias volage applied across the p-n junction creates a wave of ionization leading to the flow of large current. These didoes are designed to breakdown at specific reverse voltage in order to avoid any damage.
· Silicon controlled rectifier - As the name implies this diode can be controlled or triggered to the ON condition due to the application of small voltage. They belong to the family of Tyristors and is used in various fields of DC motor control, generator field regulation, lighting system control and variable frequency drive . This is three terminal device with anode, cathode and third controled lead or gate.
· Vaccum diodes - This diode is two electrode vacuum tube which can tolerate high inverse voltages.
Diodes are used widely in the electronics industry, right from electronics design to production, to repair. Besides the above mentioned types of diodes, the other diodes are PIN diode, point contact diode, signal diode, step recovery diode, tunnel diode and gold doped diodes. The type of diode to transfer electric current depends on the type and amount of transmission, as well as on specific applications.
Transmission and distribution system
The ac power supply scheme can be broadly divided into two functional systems
1.transmission system
2.distribution system
1.transmission system :
At the generating station bulk electrical power is generated by 3 phase synchronous generator operating in parallel. The usual generating voltage is 11kv.it may be 6.6kv or even33kv in certain areas. In order to reduce line losses the generated voltage is stepped up upto 430kv and the power is transmitted with the help of 3phase transformers at the generating station itself. The transmission system can be divided into two sub systems.
PRIMARY TRANSMISSION
The electrical power of generating station at 230kva is transmitted by 3phase 3wire over head line system to the out skirts of the city. This forms the primary transmission. In India extra high voltage and lines(above 220kv upto 760kv ac) were introduced in India during 1974 and the primary transmission is now well established in our country.
SECONDARY TRANSMISSION :
the primary transmission line terminates at the receiving station which is usually situated at the outer parts of the city. At the receiving station. Eat the voltage is reduced to 110kv by step down transformer. From this receiving station electrical power is transmitted at 110kv phase 3wire over head system to various substation located at different points in the city. This forms the secondary transmission.
DISTRIBUTION SYSTEM :
It is a system through which power is distributed to various consumer for utilization.
The entire power distribution system can be divided into two sub systems 1.primary distribution
2.secondary distribution
Primary distribution
The secondary transmission line ends at the distribution substation where voltage is reduced from 110kv to 11kv 3phase 3wire the 11kv lines run along the importance road side of the city this forms the primary distribution. The bulk consumer (having demand more than 150kw) are generally supplied power at 11 know for further handing with their own substations.
SECONDARY DISTRIBUTION :
the electrical power from primary distribution line 11kv is delivered to distribution substation. These substation are located near the consumer localities and step down the voltage to 400v 3phase 4wire for secondary distribution. The Voltages between any two phases is for 400v and between any phase and neutral is 230v.the single phase residential lighting load is connected between any one phase and neutral whereas 3 phase loads connected across 3 phase lines directly. The secondary distribution system consists of feeder, distributor, service mains.
SULPHUR HEXA FLUORIDE CIRCUIT BREAKERS(SF6)
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UNIVERSAL MOTOR WORKING
UNIVERSAL MOTOR;
CONSTRUCTION;
Universal motor can be operated either on ac and dc supply.the construcation of universal is same as that of dc series motor.the stator and rotor are made up of laminated silicon steel, to reduce eddy current and hysteresis loss,when the motor is operated on ac supply.the field winding is placed in the stator and the armature winding is housed in the rotor. the field winding has a few number of turns of turns t reduce the reactance.
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CONSTRUCTION;
Universal motor can be operated either on ac and dc supply.the construcation of universal is same as that of dc series motor.the stator and rotor are made up of laminated silicon steel, to reduce eddy current and hysteresis loss,when the motor is operated on ac supply.the field winding is placed in the stator and the armature winding is housed in the rotor. the field winding has a few number of turns of turns t reduce the reactance.
the field winding is connected in series with armature winding
OPERATION;
when the motor is connected to an ac supply,the same ac current fluxes through the field and armature winding.the field winding produces an alternating flux that reacts with the armature current and produces a torque.since both the armature current and field fluxes are reversed simultaneously,the torque always in the same direction.
CHARACTERISTICS;
the speed torque characteristics of universal motor are similar to that of dc series motor.
the speed increases with decreasing of load.at no load the speed of the motor is very high.however in a dc series motor the speed at no load is dangerously high value.
ADVANTAGES;
1.it is speed is high
2.ac and dc supply will be working
3.starting torque is high
APPLICATION;
1.vacuum cleaners
2.sewing machine
3.food mixers
4.machine tools
5.portable drilling machines
DISADVATAGES;
1.the speed at no load is dangerously high value.
REPULSION INDUCTION MOTOR WORKING
REPULSION INDUCTION MOTOR
construction;
THIS motor is a combination of repulsion and induction motor.the stator of this is made with non salient pole with single phase winding.
THE rotor is provided with two separate windings in common slots.one winding is armature winding with commutator and short circuited brushes (just like dc motor) the other winding is of squirrel cage type.the inner winding is a squirrel cage winding and the outer winding is commutated winding.repulsion induction motor the reactance
of the squirrel cage winding is very high.
working;
at the time of starting the frequency of rotor emf is more
(f=sf at starting slip (s)=1).hence the reactance of inner cage winding is high XL.therfore very little current flows through
the inner cage winding.when the rotor picks up speed the frequency
of the rotor emf is reduced and therefore the reactance of the rotor
will decrease now the squirrel cage winding takes up a larger portion of the current.
the brushes are short circuited and ride on the commutator continuously.the speed torque characteristics of repulsion inducation motor.the starting torque is high.the speed regulation is also good.
it can develop torque sudden heavy loads.
APPLICATION;
1.it is used to drive compressors.
2.petrol pumps
3.air pump
4.mixing machines
5.machine tools
6.hoists
ADVANTAGES;
1.starting torque high
2.speed regulation good
3.it can develop torque sudden heavy loads
4.starting current reduced
construction;
THIS motor is a combination of repulsion and induction motor.the stator of this is made with non salient pole with single phase winding.
THE rotor is provided with two separate windings in common slots.one winding is armature winding with commutator and short circuited brushes (just like dc motor) the other winding is of squirrel cage type.the inner winding is a squirrel cage winding and the outer winding is commutated winding.repulsion induction motor the reactance
of the squirrel cage winding is very high.
working;
at the time of starting the frequency of rotor emf is more
(f=sf at starting slip (s)=1).hence the reactance of inner cage winding is high XL.therfore very little current flows through
the inner cage winding.when the rotor picks up speed the frequency
of the rotor emf is reduced and therefore the reactance of the rotor
will decrease now the squirrel cage winding takes up a larger portion of the current.
the brushes are short circuited and ride on the commutator continuously.the speed torque characteristics of repulsion inducation motor.the starting torque is high.the speed regulation is also good.
it can develop torque sudden heavy loads.
APPLICATION;
1.it is used to drive compressors.
2.petrol pumps
3.air pump
4.mixing machines
5.machine tools
6.hoists
ADVANTAGES;
1.starting torque high
2.speed regulation good
3.it can develop torque sudden heavy loads
4.starting current reduced
Bipolar Stepper Motor working
Bipolar Stepper Motor
Stepper motors are available in three basic configurations:
1) Universal Stepper Motor
A universal stepper motor can be connected as a bipolar or a uni-polar stepper motor.
A universal stepper motor can be connected as a bipolar or a uni-polar stepper motor.
2) Uni-polar Stepper Motor
A Uni-polar stepper motor can be used as uni-polar or a bipolar stepper motor.
A Uni-polar stepper motor can be used as uni-polar or a bipolar stepper motor.
3) Bipolar stepper Motor
A bipolar stepper motor can only be used as a bipolar.
A bipolar stepper motor can only be used as a bipolar.
Bipolar Stepper Basics
A bipolar stepper motor has one winding per stator phase. A two phase bipolar stepper motor will have 4 leads. In a bipolar stepper we don’t have a common lead like in a uni-polar stepper motor. Hence, there is no natural reversal of current direction through the winding.
A bipolar stepper motor has easy wiring arrangement but its operation is little complex. In order to drive a bipolar stepper, we need a driver IC with an internal H bridge circuit. This is because, in order to reverse the polarity of stator poles, the electric current needs to be reversed. This can only be done through a H bridge.
There are two other reasons to use an H Bridge IC
1) The current draw of a stepper motor is quite high. The micro-controller pin can only provide up to 15 mA at maximum. The stepper needs current which is around ten times this value. A external driver IC is capable of handling such high currents.
2) Another reason why H Bridge is used is because the stator coils are nothing but inductor. When coil current changes direction a spike is generated. A normal micro-controller pin cannot tolerate such high spikes without damaging itself. Hence to protect micro-controller pins, H bridge is necessary.
The most common H Bridge IC used in most Bipolar stepper interfacing projects is L293D.
Interfacing to Micro-Controller
4 micro-controller pins are required to control the motor. We need to provide the L293D with 5 V supply as well as the voltage at which the motor needs to operate. Since we will be using both the drivers of the IC, we will assert the enable pin for both of them.
Interfacing Diagram
There are three different ways in which we can drive the bipolar stepper motor-
1) Only one of the phase winding are energized at a time. That is, either AB or CD is energized. Of course the coils will be energized in such a way that we get correct polarity. But only one phase is energized. This type of stepping will give less holding torque because only one phase is energized.
2) In this method, both the phases are activated at the same time. The rotor will align itself between two poles. This arrangement will give higher holding torque than the previous method.
3) The third method is used for half stepping. This method is used generally to improve the stepping angle. Here, in step 1 only 1 phase is ON, then in step 2, 2 phases are ON, then again only one phase is ON and the sequence continues.
Bipolar Stepper Drives
Many companies have started assembling their own bipolar stepper drives. Care must be taken that you connect the stepper motor correctly to the drive. Also the drive must be able to supply sufficient current for you stepper. The micro-controller must only provide the step and direction signal to the drive. This method will occupy only two micro-controller pins and is very helpful in projects that require large number of micro-controller pins for other functions.
Unipolar Stepper v/s Bipolar Stepper
Both uni-polar and Bipolar steppers are used widely in projects. However, they have their own advantages and disadvantages from the application point of view. The advantage of a uni-polar motor is that we do not have to use a complex H bridge circuitry to control the stepper motor. Only a simple driver like ULN2003A will do the task satisfactorily. But, there is one disadvantage of uni-polar motors. The torque generated by them is quite less. This is because the current is flowing only through the half the winding. Hence they are used in low torque applications.
On the other hand, bipolar stepper motors are a little complex to wire as we have to use a current reversing H bridge driver IC like an L293D. But the advantage is that the current will flow through the full coil. The resulting torque generated by the motor is larger as compared to a uni-polar motor.
Electric Lamp Types of Electric Lamp
Electric Lamp | Types of Electric Lamp
An electric lamp is a conventional light emitting component used in different circuits, mainly for lighting and indicating purposes. The construction of lamp is quite simple, it has one filament surrounding which, a transparent glass made spherical cover is provided. The filament of the lamp is mainly made of tungsten as it has high melting point temperature. A lamp emits light energy as the thin small tungsten filament of lamp glows without being melted, whileelectric current flows through it.
Uses of Electric Lamps
These lamps mainly get used for lighting and indicating purpose. Although, now days use of light emitting diodes for these two purposes dominates uses of conventional lamps. But still they are in use although at maximum places they are replaced by LEDs.
Rating of Electric Lamps
There are mainly three things that must be known before selecting a lamp for a specific purpose.
- Voltage across which the lamp to be connected for getting normal brightness of light. This voltage rating of electric lamp must be marked on the lamps. If the supply of voltage across the lamp is lower than rated value, the lamp will not glow properly aselectric current flowing through it will be insufficient. Again if the voltage across the lamp crosses the rated value, the filament may not be able to sustain the over currentand it will blow out.
- Power rating or current rating of electric lamp: When an electric lamp is connected across its rated voltage, its filament will carry an electric current depending upon the electrical resistance offered by the lamp. The filament of the lamp is so designed, that it must give most optimized brightness for that current. This electric current rating of electric lamp is very important parameter, as it determines the power consumption of the lamp. As a filament of lamp is considered as 100% resistive, the power consumption is nothing but the product of voltage and current rating of the lamp. Consumption of power is nothing but power rating of the lamp. Hence, if voltage rating of a lamp is known to us, then it is enough to know either current rating or power rating of that lamp, as power rating can be calculated from current rating and current rating can be calculated from power rating since electric power is product of voltage and electric current. It is normal practice that small rated lamps are rated by currentand higher rated electric lamps are rated by power.
Types of Electric Lamps
Another thing must be considered during selecting a lamp for a circuit. What types of electric lamp is suitable for specific circuits? Types of lamp depend upon designing pattern of the lamps. According to variation of deigns there are verities types of lamps are listed below,
Edison Screw type Lamps
The main feature of this type of lamp is that it has one contact in the base and other contact on the metallic body of the lamp. This metallic body of the lamp is of screw shaped. Commonly two types of Edison Screw lamps are available in market –- Miniature Edison Screw Lamp (MES) its bulb diameter is 10 mm (approx).
- Lilliput Edison Screw Lamp (LES) its bulb diameter is 5 mm (approx).
Miniature Center Contact type Lamps
Like MES and LES, it has one contact in the base and other contact on the metallic body of the lamp. But main difference is that this metallic body of the lamp is not screw shaped-it has bayonet style fittings. Its bulb diameter is 10 mm (approx).Small Bayonet Cap Lamps
It has also bayonet style fitting but has both contacts on the base of the lamp, hence there is no electrical connection with the body of the lamp. The standard bulb diameter is about 40 mm. It may have horizontal as well as vertical filament arrangements as shown. The power rating of the bulb can be up to 24 watt.Wire Ended Lamps
These are very small size lamps of about 6 mm long and has 3 mm diameter. The design is very simple; here contact wires directly come out from the glass cashing. Wire ended lamps are mainly designed for very low power rating and are also available in the market in very cheap rate. This lamp does not need any lamp holder; it can be soldered directly to the circuit board with the help of the contact wires come out from the glass cashing.