ET Lesson No 11: Resistors & Working Principles

ET Lesson No 11: Resistors & Working Principles


A resistor is a passive component in a circuit that provides resistance to the flow of current. There are many different types of resistors. These resistors vary in their construction, power dissipation capacities, and tolerance to various parameters (such as temperature and light). 
The types of resistors include:

1. Light Dependent Resistor (LDR)
2. Variable Resistor (VR)
3. Non-Linear Resistor or Varistor
4. Metal Film Resistor and Carbon Film Resistor
5. Wire Wound Resistor
6. Thermistor
7. Carbon Composition Resistor

1. Light Dependent Resistor (LDR)


A Light Dependent Resistor (or LDR) will vary in resistance depending on the intensity of light falling on it. This is made of cadmium sulfide which contains a small number of electrons when it is not illuminated. When a light ray falls on it, electrons get ejected and hence the conductivity of it increases. Hence, it offers low resistance when light falls on it and offers high resistance in the dark.


What is a Light Dependent Resistor or a Photo Resistor?

A Light Dependent Resistor (LDR) or a photo resistor is a device whose resistivity is a function of the incident electromagnetic radiation. Hence, they are light sensitive devices. They are also called as photo conductors, photo conductive cells or simply photocells.
They are made up of semiconductor materials having high resistance. There are many different symbols used to indicate a LDR, one of the most commonly used symbol is shown in the figure below. The arrow indicates light falling on it.


Working Principle of LDR

A light dependent resistor works on the principle of photo conductivity. Photo conductivity is an optical phenomenon in which the materials conductivity is increased when light is absorbed by the material.
When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence when light having enough energy strikes on the device, more and more electrons are excited to the conduction band which results in large number of charge carriers. The result of this process is more and more current starts flowing through the device when the circuit is closed and hence it is said that the resistance of the device has been decreased. This is the most common working principle of LDR.

Characteristics of LDR

LDR’s are light-dependent devices whose resistance is decreased when light falls on them and that is increased in the dark. When a light dependent resistor is kept in dark, its resistance is very high. This resistance is called as dark resistance. It can be as high as 1012 Ω and if the device is allowed to absorb light its resistance will be decreased drastically. If a constant voltage is applied to it and the intensity of light is increased the current starts increasing.

The figure below shows the resistance vs. illumination curve for a particular LDR.



Photocells or LDR’s are nonlinear devices. Their sensitivity varies with the wavelength of light incident on them. Some photocells might not at all response to a certain range of wavelengths. Based on the material used different cells have different spectral response curves.

When light is incident on a photocell it usually takes about 8 to 12 ms for the change in resistance to take place, while it takes one or more seconds for the resistance to rise back again to its initial value after removal of light. This phenomenon is called a resistance recovery rate. This property is used in audio compressors.

Also, LDR’s are less sensitive than photodiodes and phototransistors. (A photodiode and a photocell (LDR) are not the same, a photo-diode is a pn junction semiconductor device that converts light to electricity, whereas a photocell is a passive device, there is no p-n junction in this nor it “converts” light to electricity).

Types of Light Dependent Resistors

Based on the materials used they are classified as:

1. Intrinsic photo resistors (Undoped semiconductor): These are made of pure semiconductor materials such as silicon or germanium. Electrons get excited from valance band to conduction band when photons of enough energy fall on it and the number charge carriers are increased.

2. Extrinsic photo resistors: These are semiconductor materials doped with impurities which are called dopants. Theses dopants create new energy bands above the valence band which is filled with electrons. Hence this reduces the bandgap and less energy is required in exciting them. Extrinsic photo resistors are generally used for long wavelengths.

Construction of a Photocell

The structure of a light-dependent resistor consists of a light-sensitive material which is deposited on an insulating substrate such as ceramic. The material is deposited in the zigzag pattern in order to obtain the desired resistance and power rating. This zigzag area separates the metal deposited areas into two regions. Then the ohmic contacts are made on either side of the area. The resistances of these contracts should be as less as possible to make sure that the resistance mainly changes due to the effect of light only. Materials normally used are cadmium sulfide, cadmium selenide, indium antimonide, and cadmium sulphonide. The use of lead and cadmium is avoided as they are harmful to the environment.




Applications of LDR

LDR’s have low cost and simple structure. They are often used as light sensors. They are used when there is a need to detect absences or presences of light like in a camera light meter. Used in street lamps, alarm clock, burglar alarm circuits, light intensity meters, for counting the packages moving on a conveyor belt, etc.


2. Variable Resistor (VR)

The variable resistor means its resistance value can be adjusted (similar to a potentiometer).

There are a rotating shaft and a wiping contact. Basically, there is a resistive semicircular bar or coil and by wiping the contact we change the effective length of the resistive element and hence the resistance gets changed. One example of such resistors is rheostat. The variable resistor or rheostat can also be a linear sliding-type where the sliding contact moves on the resistive element linearly for adjustment of the effective resistance of the resistor.



Definition of Variable Resistor

It is an electronic component. It is applied in an electronic circuit for adjusting circuit resistance to control voltage or current of that circuit or part of that circuit. The electrical resistance is varied by sliding a wiper contact along a resistance track. Sometimes the resistance is adjusted at preset value as required at the time of circuit building by adjusting screw attached to it and sometimes resistance can be adjusted as when required by controlling knob connected to it. The active resistance value of the variable resistor depends upon the position of the slider contact on the resistance track.

It mainly consists of a resistance track and a wiper contact. The wiper contact moves along the resistance track when the adjustable component is adjusted. There are mainly three different types of resistance track used in this resistor they are carbon track, cermet (ceramic and metal mixture) track and wire wound track. Carbon track and cermet track are used for high resistance application whereas wire wound track is used for low resistance variable resistor. The resistance tracks generally are of a circular shape – but a straight track is also used in many cases.

Variable Resistor Connection

It is used as a rheostat when one end of the resistance track and wiper terminal are connected to the circuit and other terminal of resistance track remains open. In this case the electrical resistance between connected terminal and wiper terminal depends upon the position of the wiper (slider) on the resistance track. A variable resistor can also be used as a potentiometer when both ends of the resistance track are connected to the input circuit and one of the said ends of resistance track and wiper terminal is connected to the output circuit. In this case all three terminals are in use. Sometimes in electronics circuit there may be requirement of adjustable resistance but this adjustment is required only once or very often. This is done by connecting preset resistors in the circuit. Preset resistor is one kind of variable resistor whose electrical resistance value can be adjusted by adjusting an adjustable screw attached to it.

Types of Variable Resistor

Resistance track wise there are mainly two types of resistance track available one is linear track and other is logarithmic track. In linear track the resistance value varies linearly with changing slider position on the track. That means the resistance and the position of slider, form a straight line characteristics curve. When the resistance of variable resistor, varies logarithmically with position of the slider contact on the resistance track, the track is referred as logarithmic track.
The resistance value and type of track are marked on the resistor itself. For example when a variable resistor is marked as 5K9 LIN means it has maximum 5.9 kilo Ω resistance and has a linear resistance track. Again when a resistor is marked as 2M LOG, it will have maximum 2 mega Ω resistance and it has logarithmic track. Preset resistors are linear track type.
But the variable resistors used for volume control in sound system are mainly LOG type as our ears have logarithmic response to the loudness. In GOL resistor, the resistance changes slowly at beginning and rapidly at towards end of the track.

Uses of Variable Resistors

A variable resistor can be used mainly in two different ways. When one end of resistance track and wiper terminal is connected with circuit then current through the resistor limits according to the position of the wiper contact on the resistance track. As the wiper contact slides away from the connected end of the resistance track, the resistive value of the resistor increases and current goes down through the circuit. That means the variable resistor behaves like a rheostat.

Another use is as a potentiometer. In this case the two ends of resistance track are connected with a voltage source. Hence voltage drop across the resistance track is equal to the value of voltage source. Now the output or load circuit is connected across one end of the resistance track and wiped terminal. Hence voltage across the load terminals is the fraction of source voltage and it depends upon the position of the wiper terminals on the resistance track. This is another widely used application of variable resistors. This is needless to say, potentiometers are used to control voltages whereas rheostats are used to control electric currents.

Preset Variable Resistor

This is a micro version of the variable resistor. Preset resistors are directly mounted on the circuit board and adjusted only when the circuit is built. There is an adjustable screw attached to the resistor and a small screwdriver is required to adjust this screw for desired resistance value. These resistors are quite cheaper than standard variable resistor available in the market.


3. Non-Linear Resistor or Varistor

They are also known as varistors. They are popular for having the non-linear V-I characteristics curve. That is its resistance is not uniform and it does not obey Ohms law. They are made of materials such as silicon carbides, zinc oxide.

There are three types of varistors:

Silicon carbide disc type varistor
Silicon carbide rod type varistor
Zinc oxide type varistor

4. Metal Film Resistor and Carbon Film Resistor

The resistor is constructed by means of deposition a thin film of a conductive material such as pure carbon or metal on an insulating core. The desired value of resistance of metal film resistor or carbon film resistor can easily be obtained by either trimming the layer of the thickness or by cutting helical grooves of suitable pitch along its length. Metallic contact cap is fitted at both ends of the resistor. The caps are in contact with the conductive film or helical grooves. The lead wire is welded to the end caps. Metal Film Resistor or Carbon Film Resistor can be made up to a value of 10,000 MΩ and the size of this type of resistor is much smaller than a wire wound resistor. Because of their constructional features, these resistors are fully non – inductive. The accuracy level of metal film resistors can be of order ± 1 % and they are suitable for high-grade applications. Carbon film resistors give lower tolerances and smaller values of electrical resistance than those available with a metal film.


However, the carbon film posses a mildly negative temperature coefficient of resistance which is very useful for certain electronic circuits.

Carbon composition resistors are very small in size and have less power loss. Also, the resistors can have a very high value even up to few megaohms. These are so small that we cannot even indicate the value with readable digits on it. For that, we use colour codes on the resistor body to indicate the resistance value.

Construction of Carbon Composition Resistors

The main conductive part of a carbon composition resistor is made of carbon clay and leads are made of tinned copper. It is enclosed in a plastic or ceramic case to protect it from moisture and duct. It normally has diameters less than 10 mm. For higher power dissipation the size of the resistor should be increased. The shape of the resistor is of a cylindrical type.





There are two types of color coding are used in carbon composition resistor and they are

1. General Color Coding.
2. Precision Color Coding.

The general colour coding has four colour bands and it is used in general purpose resistors that have the tolerance of ± 5% or more. Here, the first two colour bands represent the numeric part of the resistance value. The third band is the multiplier. For tolerance, the fourth band is used.



The precision colour coding has five colour bands to indicate the resistor value. The only difference from the general colour coding is that here the first three colour bands indicate the numeric value, the fourth band indicates the multiplier and the last colour band indicates the tolerance. The precision colour coding is used where tolerance is less than ± 2%.



Advantages of Carbon Resistors
They are cheap.
They have a small size.

Disadvantages of Carbon Resistors
They are noisy.
They are very sensitive to temperature changes.
The power dissipation capacity is small.

The carbon resistor is very widely used in general-purpose electronic circuits due to their small size. As electronic circuits require very small currents, carbon composition resistors are suitable and safe. Because of so many drawbacks, these resistors cannot be used in all types of electric circuits but due to their low cost and small size, they are very popular.


5. Wire Wound Resistor

In wire wound resistor a wire of manganin or constantan is wound around a cylinder of insulating material. The temperature coefficient of resistance of manganin and constantan is almost zero. So, resistance variation with temperature of these resistors is negligible. The wounded wire is covered with an insulating cover such as baked enamel. This cover of insulating heat resistible material resists the effect of ambient temperature variation. Different sizes and ratings of wire wound resistors can easily be achieved by using different lengths and diameters of the wire. These resistors are easily available for a wide range of ratings. The range of resistance values varies from 1 Ω to 1 MΩ. The typical tolerance limit of these resistors varies from 0.01 % to 1 %. They can be used for high power applications of 5 to 200 W dissipation ratings. The cost of these resistors is much higher than carbon resistors. Normally a wire wound resistor is used where a carbon composition resistor cannot meet the purpose because of its limitations.

The main disadvantage of this resistor is the inductance that arises because of its coil-like structure. At high frequency, the behavior of the circuit may be changed due to its reaction. This problem can be solved if one half of the wire is wound in one direction and another half in the opposite direction so that the inductance due to these two halves cancels each other hence the net inductive effect of the resistor becomes nil. The non-inductive wire wound resistor is ideal for the high-frequency circuit but it is costlier than an ordinary one.



Definition

Wire has certain resistance which is of finite value. This value can vary a lot – it may be small or it may be large depending on the material of the wire used. The resistance is directly proportional to the length of the wire – these are the main 2 principles used in the construction of the wire wound resistor.
Now, for metal or conductor the resistance directly proportional to the temperature, so when the temperature is increased, its resistance also increases. We do not want the resistance to be varying with the temperature and it is not possible to construct a material which has no variation with temperature. However, that can be minimized by the use of the material which has a low-temperature coefficient. For the construction of wire wound resistor, we generally use material which has high resistivity.





Need for Wire Wound Resistor

We know that the carbon resistors are cheap as well as they have small size. But why it is so that we use wire wound resistors also?? The answer to the question is very simple. The carbon resistor has very small power rating. Also, it has very sensitive to temperature variations. They are not reliable, very sensitive to noise. So in the case of a wire wound resistors, those disadvantages are minimized so we use wire wound resistors. But cost will increase as the resistor is costlier compared to carbon resistors.

Construction of Wire Wound Resistor

Wire wound resistors are constructed of the material which has high resistivity and also low temperature coefficient. Generally we use alloys to construct the resistor. Constantan or manganin wire may be used. But the other allows may be used also which satisfies the desired criteria. Insulation is provided so that it can provide safety. The terminals are made up of tinned alloy. The construction varies according to the accuracy desired, but for highly accurate system, the cost of the resistor will also increase. For the resistor to be highly accurate, special alloys are used for providing long term stability and low temperature coefficient. Tolerance as low as ± .0005 % can also be achieved.
The wire wound resistor has a resistance which varies from 1 ohm to 1 Mega Ohm and power dissipation may vary from .5 watt to 250 watt. The tolerance level may be there from 5 % to 10 %.

Application of Wire Wound Resistor

The wire wound resistor has a very wide range of application, especially when we need variable or adjustable resistor, or if we need a fixed resistor which has to dissipate larger power, this may be used. We can construct variable resistor, such as potentiometers, rheostat.

Rheostat is a three terminal device which has two fixed contacts and one sliding contact which is used to adjust the resistance value. If we connect only two fixed point then rheostat acts as a potential divider. When all three are used, then it can vary the resistance with the help of a sliding contact.

rheostat principle

In case of a potentiometer we have wires and a rotating shaft so that the resistance can be adjusted.

Advantages of Wire Wound Resistor

It can be used in higher power circuits compared to carbon resistors.

It is not that sensitive to noise compared to carbon resistor.

It is thermally stable.

Disadvantages of Wire Wound Resistor

It is costlier compared to carbon size

It has large size

It can be said that this resistance are costlier so they may be used wherever it is desired to use. These resistors cannot be used in electronic circuits also. But it is a very important type of resistor we have and mostly used in high power application whenever we cannot use carbon resistors and also they provide excellent thermal stability also.

6. Thermistor

The word thermistor means a thermal resistor. Its resistance value changes with the change in the temperature. Most thermistors have a negative temperature coefficient which means its resistance will fall down when the temperature increases. These are normally made of semiconductor materials. Resistance up to a few megaohms can be obtained from thermistors. They are used to detect the small temperature changes, when there is a temperature change, however small, there will be a large change in the value of the resistance.





7. Carbon Composition Resistor

A carbon composition resistor (also known as a carbon resistor) is a very commonly used resistor. These resistors are of low cost and easy to construct. Carbon resistors are mainly made of carbon clay composition covered with a plastic case. The lead of the resistor is made of tinned copper.

The main advantages of these resistors are that they are easily available in the local market and they are very durable too. These resistors are available in a wide range of values. It is available in as low as 1 Ω value and it is also available in as high as 22 Mega Ω value. But the main disadvantage is that they are very much temperature sensitive. The tolerance range in resistance of carbon composition resistor is of ± 5 to ± 20 %.

This type of resistor has a tendency of electric noise due to the passage of electrical current from one carbon particle to others. Where low cost is the main criterion for designing a circuit rather than its perfection of performance, these resistors are normally used. Carbon resistors are provided with a different colored band on their cylindrical bodies. These color bands are code for the resistance values of resistors along with their tolerance range.

ET Lesson No 10: Voltage

ET Lesson No 10: Voltage

In our previous sections, we have been discussed the appearance of Voltage, the relationship, the characteristics, and the simplifications. Please go through the previous sections back, if you were unable to catch up and then continue further reading.

Voltages in Series

A series circuit or series connection means when two or further electrical components are linked together in a chain-like arrangement within a circuit. In this kind of circuit, there is only a single way for the charge to pass throughout the external circuit. The potential variation in charge across two points in an electrical circuit is termed as voltage. In this article, we can discuss in detail about the voltage in the series circuits.

The battery of a circuit provides energy for the charge to pass through the battery and to create a potential difference among the ends of the external circuit. Now, if we assume a cell of 2 volts, it will create a potential difference of 2 volts across the external circuit. The electric potential value at the positive terminal is 2 volts greater than the negative terminal. So, when charge flows from the positive to the negative terminal, it causes a loss of 2 volts in electrical potential. This is termed as voltage drop. This happens when the electrical energy of the charge is converted into some other forms (mechanical, heat, light, etc) while passing through the components (resistors or load) in the circuit.

If we consider a circuit with more than one resistor connected in series and are powered with a 2V cell, the total loss of electrical potential is 2V. That is, there will be a certain voltage drop in each connected resistor. But we can see that the sum of voltage drop of all the components will be 2V which is equivalent to the voltage rating of the power source.

Mathematically, we can express it as

By using Ohm’s law the individual voltage drops can be calculated as

Now, we can assume a series circuit comprises of 3 resistors and powered by a 9V energy source. Here, we are going to find out the potential difference at different location during the passage of current throughout the series circuit. The locations are marked in red color in the circuit below. We know that current passes in the direction from positive terminal towards the negative terminal of the source. The negative sign of the voltage or potential difference represents the loss in potential due to the resistor. The electrical potential difference of different points in the circuit can be represented with the help of a diagram called electric potential diagram that is shown below.

In this example, the electrical potential at A = 9V since it is the higher potential terminal. The electrical potential at H = 0V since it is the negative terminal. When the current passes through the 9V power source, the charge gains 9V of electrical potential, which is from H to A. While the current passes throughout the external circuit, the charge loses this 9V completely. Here, this happens in three steps. There will be drop in voltage when the current passes through the resistors but no voltage drop occurs when the passage is through the mere wire. So, we can see that between the points AB, CD, EF and GH; there is no voltage drop. But between the points B and C, the voltage drop is 2V. That is the source voltage 9V becomes 7V. Next, between the points D and E, the voltage drop is 4V. At this point, the voltage 7V becomes 3V. At last, between the points F and G, the voltage drop is 3V. At this point, the voltage 3V becomes 0V. The portion of the circuit between the points G and H, there is no energy for the charge. So, it desires an energy boost for the passage through the external circuit again. This is provided by the power source as the charge passes from H to A.The several voltage sources in series can be replaced by a single voltage source by taking the sum total of all the voltage sources. But we have to consider the polarity as shown below.

AC Voltage Sources in Series

This is something important and should be clearly taken into mind. In the case of AC voltage sources in series, the voltage sources can be added or combined together to form a single source provided that the angular frequency (ω) of the connected sources are identical. If the AC voltage sources connected in series are of different angular frequencies, it can be added together provided the current through the connected sources is the same.

Application of Voltage in Series Circuits

1. Voltage divider.
2. Fire alarm battery.
3. Batteries in remote, toys etc.
4. Lighting purposes in train, Christmas tree etc.

Voltage Regulators

In electrical circuits, we sometimes need a stable voltage across a particular load. The voltage across the load should not vary due to changes in the input voltage or due to the load itself. For such applications, we need a voltage regulator. Today we are going into the nitty-gritty of voltage regulators and we are going to study the different types of voltage regulators.

When a reliable source of voltage is required, we use a voltage regulator. It has a very simple feed-forward design and uses negative feedback loops. Refer to the diagram below to understand more:

Unregulated voltage enters the controller. A part of the output is fed to the sampling circuit, which in turn feeds it back to the comparator circuit. The voltage level is compared with the reference voltage. Appropriate corrections are made and send back to the controller. In this manner, the voltage is regulated.

Different types of Voltage Regulators

There are mainly two types of voltage regulators:

1. Linear voltage regulators
2. Switching voltage regulators

Linear Voltage Regulators

Linear voltage regulators operate like a voltage divider. It uses the FET in the ohmic region. The resistance of the linear voltage regulator changes with the load and gives a constant voltage output. Below is a picture of LM7805, one of the popular linear voltage regulator. They are based suited for low cost low power applications.

There are two types of linear voltage regulators:

1. Series Voltage Regulator
2. Shunt Voltage Regulator

Series Voltage Regulator

A simple series voltage regulator has a variable element like a transistor whose resistance varies on a variable input voltage, thereby keeping the output voltage constant and steady.

Shunt Voltage Regulator

This works similar to the series voltage regulator but is connected in the circuit in parallel or in shunt connection. All the excess voltage is sent to the ground. Shunt voltage regulators are mainly used for precision current limiters, voltage monitoring, error amplifiers etc.

To summarise, here are the advantages and disadvantages of linear voltage regulators

Advantages of Linear Voltage Regulators

• Cheap
• Lower electromagnetic interference and noise than switching voltage regulators.
• Provides constant output voltage for low power applications

Disadvantages of Linear Voltage Regulators

• Very inefficient
• Needs additional heat sink due to the amount of heat generated
• Can’t get an output higher than the input.

Switching Voltage Regulators

Switching voltage regulators uses a controlled switch to regulate the voltage hence the name. They are used where there is a large difference between the input and output voltage. They are more efficient but introduce greater complexity in the circuitry.

Switching regulators switches on and off rapidly to change the output according to the requirement. They use transistors which turns on and off depending on the desired voltage level.

There are different ways in which switching regulators can be used :

Boosting (step-up)

This is used to produce a higher regulated output voltage by boosting the input voltage.

In the image above, an 8-40V is being stepped down to 5V output.

Boosting/Bucking (Inverter)

In this configuration, both stepping up and stepping down the regulated output voltage is possible. This is used if there is a requirement for increasing or decreasing the output voltage from time to time. Inverting the output voltage is also possible.

Switching regulators are often used where power efficiency is a big concern and when the higher or lower output voltage is needed.

Advantages of Switching Voltage Regulators

It has higher power conversion efficiency than linear voltage regulators

Do not require heat sinks

Can be used when there is a huge difference between input and output voltage.

Disadvantages of Switching Voltage Regulators

Produces more electromagnetic interferrance and noise.

It is more complex.

More costly.

Regulated Power Supply

What is a Regulated Power Supply?

A regulated power supply converts unregulated AC (Alternating Current) to a constant DC (Direct Current). A regulated power supply is used to ensure that the output remains constant even if the input changes. A regulated DC power supply is also known as a linear power supply, it is an embedded circuit and consists of various blocks. The regulated power supply will accept an AC input and give a constant DC output. The figure below shows the block diagram of a typical regulated DC power supply.

The basic building blocks of a regulated DC power supply are as follows:

1. A step-down transformer
2. A rectifier
3. A DC filter
4. A regulator

Operation of Regulated Power Supply

Step Down Transformer

A step down transformer will step down the voltage from the ac mains to the required voltage level. The turn’s ratio of the transformer is so adjusted such as to obtain the required voltage value. The output of the transformer is given as an input to the rectifier circuit.

Rectification

Rectifier is an electronic circuit consisting of diodes which carries out the rectification process. Rectification is the process of converting an alternating voltage or current into corresponding direct (DC) quantity. The input to a rectifier is AC whereas its output is unidirectional pulsating DC.

Although a half wave rectifier could technically be used, its power losses are significant compared to a full wave rectifier. As such, a full wave rectifier or a bridge rectifier is used to rectify both the half cycles of the ac supply (full wave rectification). The figure below shows a full wave bridge rectifier.

A bridge rectifier consists of four p-n junction diodes connected in the manner shown above. In the positive half cycle of the supply, the voltage induced across the secondary of the electrical transformer i.e. VMN is positive. Therefore point E is positive with respect to F. Hence, diodes D3 and D2 are reversed biased and diodes D1 and D4 are forward biased. The diode D3 and D2 will act as open switches (practically there is some voltage drop) and diodes D1 andD4 will act as closed switches and will start conducting. Hence a rectified waveform appears at the output of the rectifier as shown in the first figure. When voltage induced in secondary i.e. VMN is negative than D3 and D2 are forward biased with the other two reversed biased and a positive voltage appears at the input of the filter.

DC Filtration

The rectified voltage from the rectifier is a pulsating DC voltage having very high ripple content. But this is not we want, we want a pure ripple free DC waveform. Hence a filter is used. Different types of filters are used such as capacitor filter, LC filter, Choke input filter, π type filter. The figure below shows a capacitor filter connected along the output of the rectifier and the resultant output waveform.

As the instantaneous voltage starts increasing the capacitor charges, it charges until the waveform reaches its peak value. When the instantaneous value starts reducing the capacitor starts discharging exponentially and slowly through the load (input of the regulator in this case). Hence, an almost constant DC value having very less ripple content is obtained.

Regulation

This is the last block in a regulated DC power supply. The output voltage or current will change or fluctuate when there is a change in the input from ac mains or due to change in load current at the output of the regulated power supply or due to other factors like temperature changes. This problem can be eliminated by using a regulator. A regulator will maintain the output constant even when changes at the input or any other changes occur. Transistor series regulator, Fixed and variable IC regulators or a zener diode operated in the zener region can be used depending on their applications. IC’s like 78XX and 79XX (such as the IC 7805) are used to obtained fixed values of voltages at the output.

With IC’s like LM 317 and 723, we can adjust the output voltage to a required constant value. The figure below shows the LM317 voltage regulator. The output voltage can be adjusted by adjusting the values of resistances R1 and R2. Usually, coupling capacitors of values about 0.01µF to 10µF need to be connected at the output and input to address input noise and output transients. Ideally, the output voltage is given by

The figure above shows the complete circuit of a regulated +5V DC power supply.

Linear, Shunt, and Zener Diode  

What is Voltage Regulation

A voltage regulator is an electronic or electrical device which can sustain the voltage of power supply within suitable limits. The electrical equipment connected to the voltage source should bear the value of the voltage. So, the source voltage should be in a certain range which is acceptable for the connected pieces of equipment. This purpose is fulfilled by implementing a voltage regulator. It regulates the voltage regardless of the alteration in the input voltage or connected load. It works as a shield for protective devices from damage. It can regulate AC and DC voltages depending on the design.  

Types of Voltage Regulators

There are two main types of voltage regulators available: 

Linear Voltage Regulators Switching Voltage Regulators   

These can be further classified into more specific voltage regulators, as discussed below. Linear Voltage Regulator

This type of voltage regulator performs as a voltage divider. It employs FET in Ohmic region. The steady output is sustained by varying the resistance of voltage regulator with respect to the load. Generally, these types of voltage regulator are of two types:

1. Series voltage regulator
2. Shunt voltage regulator

Series Voltage Regulator

It implements a variable element positioned in series with the connected load. The steady output is sustained by varying the resistance of this element with respect to the load. They are of two types that are briefed below. Discrete Transistor Series Voltage Regulator

Here from the block diagram, we can see an unregulated input is first fed into a controller. It actually controls the input voltage magnitude and given to the output. This output is given to the feedback circuit. It is sampled by the sampling circuit and given to the comparator. There it is compared by the reference voltage and given back to the output.

Here, the comparator circuit will give a control signal to the controller whenever there is an increase or decrease in the output voltage. Thus, the controller will reduce or increase the voltage to the acceptable range so that a sustained voltage will get as the output. Zener Diode as Voltage Regulator

When a zener diode is used as a voltage regulator, it is known as a zener controlled transistor series voltage regulator or an emitter follower voltage regulator. Here, the transistor used is emitter follower (see figure below). The emitter and the collector terminals of the series pass transistor used here are in series with respect to load. The variable element is a transistor and the zener diode will supply the reference voltage.

Shunt Voltage Regulator

Shunt voltage regulator provides a way from the supply voltage reaching to ground with the help of a variable resistance. From the load, the current is shunted away from the load to the ground. We can simply say that this regulator can absorb current and it is less efficient compared to series voltage regulator. The applications include error amplifiers, voltage monitoring, precision current limiters etc. They are of two types that are briefed below. Discrete Transistor Shunt Voltage Regulator

Here, the current is shunted away from the load. The controller will shunt a portion of the total current that is developed by the unregulated input which is given to the load. The voltage regulation takes place across the load. Here, the comparator circuit will give a control signal to the controller whenever there is an increase or decrease in the output voltage because of the variation in load. Thus, the controller will shunt the extra current from the load so as to get a sustained voltage as the output.  

Zener Controlled Transistor Shunt Voltage Regulator

Here, the unregulated voltage is directly proportional to the voltage drop occurs in the series resistance. This voltage drop is related to the current given to the load. The output voltage is related to the transistor base emitter voltage (VBE) and the zener diode.

Advantages of Linear Voltage Regulator	Disadvantages of Linear Voltage Regulator
Design is very simple	Low efficiency
Less output ripple	Space requirement is large
Response time is fast	Voltage cannot be increased
Less noise	Heat sink is sometimes required

Switching Voltage Regulator

This regulator quickly switches a device in series to on and off. Like the linear regulators, a feedback mechanism is incorporated here to control the quantity of charge carried to the load. This quantity is set as the duty cycle of the switch. The output voltage can be greater or the polarity of output can be opposite that of the input by using this voltage regulator. This is highly efficient voltage regulator. Three different types are step up voltage regulator, buck voltage regulator and boost/buck voltage regulator. The most simplified circuit diagram of switching voltage regulator is shown below.

Advantages of Switching Voltage Regulator	Disadvantages of Switching Voltage Regulator
Efficiency is very high.	Complex design
Size and weight are very low.	Expensive
Boost or buck or inverting or buck/boost is possible.	Noise is high
Less noise	Transient recovery time is time-consuming

Application of Voltage Regulators

The applications for voltage regulators include:

• Power distribution system
• Automobile alternator
• Power station generator plant
• Computer power supplies

Voltage Follower & Multiplier

Voltage follower is an Op-amp circuit whose output voltage straight away follows the input voltage. That is output voltage is equivalent to the input voltage. Op-amp circuit does not provide any amplification. Thus, voltage gain is equal to 1. They are similar to discrete emitter follower. The other names of voltage follower are Isolation Amplifier, Buffer Amplifier, and Unity-Gain Amplifier. The voltage follower provides no attenuation or no amplification but only buffering. This circuit has an advantageous characteristic of very high input impedance.

This high input impedance of voltage follower is the reason of it being used in several circuits. The voltage follower gives an efficient isolation of output from the input signal. The circuit of voltage follower is shown below.

Now, let us go through the most fundamental law; that is Ohm’s law.

So, we can say that when resistance increases, the current drawn from the power source decreases. Thus, we conclude that the power is unaffected if the current is feeding a load of high impedance.

For understanding this concept and the use of voltage follower, we can go through the following examples.

First, we can consider a circuit of low impedance load and a power source is feeding it shown below. Here, a large amount of current is drawn by the load due to the low resistance load as explained by Ohm’s law. Thus, the circuit takes a large amount of power from the power source, resulting in high disturbances in the source.

Next, we can consider that we are giving the same power to the voltage follower. Because of its very high input impedance, a minimal amount of current is taken by this circuit. The output of the circuit will be same as that of the input due to the lack of feedback resistors.



Voltage Follower in Voltage Divider Circuits

In every circuit, voltage is shared or distributed to the impedance or resistance of the connected components. When Op-amp is connected, the major part of voltage will drop across it due to high impedance. So, if we use voltage follower in voltage divider circuits, it will let adequate voltage to be supplied across the load.

Let us go through a voltage divider circuit with voltage follower as shown in the figure below.

Here, the voltage divider is in the middle of two 10 KΩ resistors and the Op-amp. This Op-amp will offer input resistance of some hundreds of megaohm. Now, we can assume it to be 100 MΩ. So the equivalent parallel resistance will be 10 KΩ || 100 KΩ.

So, we get 10KΩ || 10KΩ. We know that the voltage divider which comprises of two similar resistances will offer exactly the half of the voltage in the power source. We can prove it using voltage divider formula as follows:

Thus, this 5V will drop across the 10KΩ resistance in the top and 5V drop across the resistance 10KΩ in the bottom and the load resistance 100Ω (since 10 KΩ||100 Ω, same voltage will drop in resistors which are in parallel).

From this, we have seen how the Op-amp works as a buffer for getting the desired voltage to the connected load. In the same circuit with the absence of voltage follower, it will not work due to the lack of supply of sufficient voltage across the load.

Mainly, voltage follower is implemented in circuits for two reasons. One is isolating purpose, and the other is for buffering the output voltage from an electrical or electronic circuit to get the desired voltage to the connected load.

Advantages of Voltage Follower

Provides power gain and current gain.
Low output impedance to the circuit which uses the output of the voltage follower.
The Op-amp takes zero current from the input.
Loading effects can be avoided.

Applications of Voltage Follower

Buffers for logic circuits.
In Sample and hold circuits.
In Active filters.
In Bridge circuits via transducer.

It is in actuality a modified capacitor filter circuit (rectifier circuit) which makes a DC output voltage that is two or more than two times the AC peak input. In this section, we can look into full-wave voltage doubler, half-wave voltage doubler, voltage tripler and finally quadrupler.

Half Wave Voltage Doubler

The input wave form, circuit diagram and output waveform is shown in figure 1. Here, all through the positive half cycle, the forward biased D1 diode conducts and diode D2 will be in off condition. In this time, the capacitor (C1) charges to VSmax (peak 2o voltage). All through the negative half cycle, the forward biased D2 diode conducts and D1 diode will be in off condition. In this time C2 will start charging.

Throughout the next positive half cycle, D2 is at reversed biased condition (open circuited). In this time C2 capacitor gets discharged through the load and thus voltage across this capacitor gets dropped.

But when there is no load across this capacitor, then both the capacitors will be at charged condition. That is C1 is charged to VSmax and C2 is charged to 2VSmax. Throughout the negative half cycle the C2 gets charged yet again (2VSmax). In the next half cycle, a half wave which is filtered by means of capacitor filter is obtained across the capacitor C2. Here, ripple frequency is same as the signal frequency. The DC output voltage of the order of 3kV can be obtained from this circuit.

Full Wave Voltage Doubler

The input waveform of full-wave voltage doubler is shown below.

The circuit diagram and output waveform is shown in figure 3. Here; all through the positive cycle of input voltage, the diode D1 will be in forward biased condition and capacitor C1 will gets charged to VSmax(peak voltage). At this time, D2 will be in reverse biased condition. All through the negative cycle of input voltage, the D2diode will be in forward biased condition and the capacitor C2 gets charged. If the load is not connected across the output terminals, the total voltages of both the capacitorsare obtained as the output voltage. If some load is connected across the output terminals, then output voltage

We can see that, both the half-wave and full-wave voltage doubler will give 2VS MAX as output. It does not require any centre-tapped transformer. The peak inverse voltage rating of diodes will be equal to 2VS MAX. When compared to half wave voltage doubler, the full-wave voltage doubler can simply filter high frequency ripples and output ripple frequency will be equal to twice the supply frequency. But the problem in full-wave voltage doubler is that; in between the input and output, the common ground is absent.

Voltage Tripler and Quadrupler

Using the method of extension of half-wave voltage doubler circuit, any voltage multipliers (Tripler, Quadrupler etc) can be created. When both the capacitor leakage and load are small, we can achieve tremendously high DC voltages by means of these circuits that include several sections to step-up (increase) the DC voltage.

Here; all through the first positive and negative half cycle is same as that of half-wave voltage doubler. Throughout the next positive half cycle, D1 and D3 conducts and C3 charges to 2VSmax. Throughout the next negative half cycle, D2 and D4 conducts and C4 charges to 2VSmax. When more diodes and capacitors are added, every capacitor will get charged to 2VSmax. At the output; odd multiples of VSmax can be attained, if measured from the top of transformer 2o winding and even multiples of VSmax can be attained, if measured from bottom of 2owinding of transformer.

Application of Voltage Multiplier

• Cathode ray tubes.
• Cathode ray tubes in oscilloscope, Television receivers, Computer display.
• X-Ray systems
• Lasers
• Ion pumps
• Copy machines
• Electrostatic systems
• Photomultiplier tubes
• Travelling wave tubes (TWT)

And several other devices which involves low current and high voltage applications.

Voltage Sources & Voltage to Current Converter

As an introduction, we can go through the Electrical source. It is nothing but a device which can deliver electric power to a connected circuit. They can be a current source or a Voltage source. Here, we can discuss about the voltage source which is most commonly used. Voltage source is in fact a passive element which can create a continuous force for the movement of electrons through the wire in which it is connected. It is usually a two terminal device.

Types of Voltage Source

Independent Voltage Source: 

They are of two types – Direct Voltage Source and Alternating Voltage Source.

Dependent Voltage Source: 

They are of two types – Voltage Controlled Voltage Source and Current Controlled Voltage Source.

Independent Voltage Source

The voltage source which can deliver steady voltage (fixed or variable with time) to the circuit and it does not depend on any other elements or quantity in the circuit.

Direct Voltage Source or Time Invariant Voltage Source The voltage source which can produce or deliver constant voltage as output is termed as Direct Voltage Source. The flow of electrons will be in one direction that is polarity will be always same. The movement of electrons or current will be in one direction always. The value of voltage will not alter with time. Example: DC generator, battery, Cells etc.

Alternating Voltage Source

The voltage source which can produce or deliver alternating voltage as output is termed as Alternating Voltage Source. Here, the polarity gets reversed at regular intervals. This voltage causes the current to flow in a direction for a time and after that in a different direction for another time. That means it is time varying. Example: DC to AC converter, Alternator etc.

Dependent or Controlled Voltage Source

The voltage source which delivers an output voltage which is not steady or fixed and it always depends on other quantities such as voltage or current in any other part of the circuit is termed as dependent voltage source. They have four terminals. When the voltage source depends on voltage in any other part of the circuit, then it is called Voltage Controlled Voltage Source (VCVS). When the voltage source depends on current in any other part of the circuit, then it is called Current Controlled Voltage Source (CCVS) (shown in figure below).

Ideal Voltage Source

The voltage source which can deliver constant voltage to the circuit and it is also referred as independent voltage source as it is independent of the current that the circuit draws. The value of internal resistance is zero here. That is, no power is wasted owing to internal resistance. In spite of the load resistance or current in the circuit, this voltage source will give steady voltage. It performs as a 100% efficient voltage source. All of its voltage of the ideal voltage source can drop perfectly to the load in the circuit.

For understanding the ideal voltage source, we can take an example of a circuit shown above. The battery shown here is an ideal voltage source which delivers 1.7V. The internal resistance RIN = 0Ω. The resistance load in the circuit RLOAD = 7Ω. Here, we can see the load will receives all of the 1.7V of the battery.

Real or Practical Voltage Source

Next, we can consider a circuit with practical voltage source having an internal resistance of 1Ω in the similar circuit which is explained above. Due to the internal resistance, there will be small amount of voltage drop in the RIN. So, the output voltage will be reduced to 1.49V from 1.7V. So in practical cases there will be reduction in source voltage due to the internal resistance.

We can now conclude that the ideal voltage source is kept as models and the real voltage source is made with minimum internal resistance to get the voltage source close to the ideal one with minimum power loss.

The circuits in instrumentation for analog representation of certain physical quantities (weight, pressure, motion etc), DC current is preferred. This is because DC current signals will be constant throughout the circuit in series from the source to the load. The current sensing instruments also have the advantage of less noise. So, sometimes it is essential to create current which is corresponding or proportional to a definite voltage. For this purpose Voltage to Current Converters are used. It can simply change the carrier of electrical data from voltage to current.

Simple Voltage to Current Converter

When we confer about the connection between voltage and current, it is obvious to mention the Ohm’s law.

.

We all know that when we supply a voltage as input to a circuit which comprises of a resistor, the proportional current will commence to flow through it. So, it is clear that the resistor decides the current flow in a voltage source circuit or it performs as a simple voltage to current converter for a linear circuit.

The circuit diagram of a resistor which performs as a simple voltage to current converter is represented below. In this diagram, the electrical quantities such as voltage and current are represented through bars and loop respectively.

But practically, the output current of this converter depends directly on the voltage drop across the connected load in addition to the input voltage. Since, VR becomes . This is the reason why this circuit is said to be an imperfect one or bad or passive version.

Voltage to Current Converter Using Op-Amp

Op-amp is implemented to simply convert the voltage signal to corresponding current signal. The Op-amp used for this purpose is IC LM741. This Op-amp is designed to hold the precise amount of current by applying the voltage which is essential to sustain that current through out the circuit. They are of two types that are explained in detail below.

Floating Load Voltage to Current Converter

As the name indicates, the load resistor is floating in this converter circuit. That is, the resistor RL is not linked to ground. The voltage, VIN which is the input voltage is given to the non-inverting input terminal. The inverting input terminal is driven by the feedback voltage which is across the RL resistor. This feedback voltage is determined by the load current and it is in series with the VD, which is the input difference voltage. So this circuit is also known as current series negative feedback amplifier.

For the input loop, the voltage equation is

Since A is very large,

So,

Since, the input to the Op-amp,

From the above equation, it is clear that the load current depends on the input voltage and the input resistance. That is, the load current, , which is the input voltage. The load current is controlled by the resistor, R. Here, the proportionality constant is 1/R. So, this converter circuit is also known as Trans-Conductance Amplifier. Other name of this circuit is Voltage Controlled Current Source.

The type of load may be resistive, capacitive or non-linear load. The type of load has no role in the above equation. When the load connected is capacitor then it will get charge or discharge at a steady rate. Due to this reason, the converter circuit is used for the production of saw tooth and triangular wave forms.

Ground Load Voltage to Current Converter
This converter is also known as Howland Current Converter. Here, one end of the load is always grounded. For the circuit analysis, we have to first determine the voltage, VIN and then the relationship or the connection between the input voltage and load current can be achieved.

For that, we apply Kirchhoff’s current law at the node V1

For a non-inverting amplifier, gain is   
 
Here, the resistor, .

Hence,
 
Therefore the voltage in the output will be

Thus, we can conclude from the above equation that the current IL is related to the voltage, VIN and the resistor, R.

Application of Voltage to Current Converter

• Zener diode tester
• Low AC and DC Voltmeters
• Testing LED
• Testing Diodes

Voltage Regulator 7805

All voltage sources cannot able to give fixed output due to fluctuations in the circuit. For getting constant and steady output, the voltage regulators are implemented. The integrated circuits which are used for the regulation of voltage are termed as voltage regulator ICs. Here, we can discuss the IC 7805.

The voltage regulator IC 7805 is actually a member of the 78xx series of voltage regulator ICs. It is a fixed linear voltage regulator. The xx present in 78xx represents the value of the fixed output voltage that the particular IC provides. For 7805 IC, it is +5V DC regulated power supply. This regulator IC also adds a provision for a heat sink. The input voltage to this voltage regulator can be up to 35V, and this IC can give a constant 5V for any value of input less than or equal to 35V which is the threshold limit.

PIN 1-INPUT - The function of this pin is to give the input voltage. It should be in the range of 7V to 35V. We apply an unregulated voltage to this pin for regulation. For 7.2V input, the PIN achieves its maximum efficiency.

PIN 2-GROUND - We connect the ground to this pin. For output and input, this pin is equally neutral (0V). PIN 3-OUTPUT - This pin is used to take the regulated output. It will be

Heat Dissipation in IC 7805

In IC 7805 voltage regulator, lots of energy is exhausted in the form of heat. The difference in the value of input voltage and output voltage comes as heat. So, if the difference between input voltage and the output voltage is high, there will be more heat generation. Without a heat sink, this too much heat will cause malfunction.

We call, the bare minimum tolerable difference between the input and output voltage to keep the output voltage at the proper level as dropout voltage. It is better to keep the input voltage 2 to 3V greater than the output voltage, or a suitable heat sink should be placed to dissipate excess heat. We have to calculate the heat sink size properly. The following formula will give an idea of this calculation.

Now, we can analyze the relation of generated heat and the input voltage value in this regulator with the following two examples.

Assume a system with input voltage 16V and required output current be 0.5A.

So, heat generated

Thus, 5.5W heat energy is wasted and the actual energy used

That is almost double energy is wasted as heat.

Next, we can consider the case when input is lower, say 9V.

In this case, heat generated

From this, we can conclude that for high input voltage, this regulator IC will become highly inefficient. 

Internal Block Diagram of 7805 Voltage Regulator
The internal block diagram of IC 7805 is represented in the figure below:

The block diagram comprises of an error amplifier, series pass element, current generator, reference voltage, current generator, starting circuit, SOA protection and thermal protection. Here the operating amplifier performs as an error amplifier. The Zener diode is used for giving the reference voltage. It is shown below.

The transistor is the series pass element here. It is used for dissipating additional energy in the form of heat. It controls the output voltage by controlling the current among the input and output. SOA is the Safe Operating Area. It is in fact the conditions of voltage and current in which the equipment is expected to work without any self-damage. Here for the SOA protection, bipolar transistor is implemented with a series resistor and an auxiliary transistor. Heat sink is implemented for thermal protection when there is high supply voltage.

Regulated Power Supply Circuit

The voltage regulator 7805 and the other components are arranged in the circuit as shown in figure.

The purposes of coupling the components to the IC7805 are explained below.

C1– It is the bypass capacitor, used to bypass very small extent spikes to the earth.

C2 and C3– They are the filter capacitors. C2 is used to make the slow changes in the input voltage given to the circuit to the steady form. C3 is used to make the slow changes in the output voltage from the regulator in the circuit to the steady form. When the value of these capacitors increases, stabilization is enlarged. But these capacitors single-handedly are unable to filter the very minute changes in the input and output voltages.

C4– like C1, it is also a bypass capacitor, used to bypass very small extent spikes to the ground or earth. This is done without influencing other components.

Applications of Voltage Regulator 7805 IC

Current regulator

Regulated dual supply

Building circuits for Phone charger, UPS power supply circuits, portable CD player etc

Fixed output regulator

Adjustable output regulator etc.

Voltage Doubler

Voltage doubler, as the name indicates it can deliver the output voltage which is double as that of the input voltage. It is a voltage multiplier with the voltage multiplication factor equal to 2. The circuit is formed by an oscillating AC input voltage, two capacitors and two diodes. The input is AC voltage and the output will be DC voltage with twice the peak value of the input AC. Heavy and expensive step-up transformers can be replaced in some applications by this voltage doubler.

Types of Voltage Doubler

Next, we are going to discuss about the two types of voltage doubler- Half-wave voltage Doubler and Full-wave voltage Doubler.

Half Wave Voltage Doubler

The figure below, shows, a simple DC voltage doubler circuit. Here, it is clear that both the capacitors and the diodes operate together to create the double voltage output.

Now, we can go through the working of the half wave DC voltage doubler. All over the positive half cycle of the AC sine wave, the first diode (D1) is conducting. That is forward biased state and it will charge the connected capacitor (C1) equal to the peak value of AC secondary voltage of transformer (VSMAX). This capacitor is unable to get discharged due to the unavailability of a path. So, it will remain in the fully charged condition. Next, all over the negative half cycle, the second diode (D2) is conducting or forward biased state, and the first diode (D1) is non-conducting or in reversed biased state. The reversed biased diode (D1) will block the discharging of the connected capacitor (C1) and the forward biased diode (D2) will charge the connected capacitor (C2).

Here we can apply the Kirchhoff’s voltage law to the outer loop which starts from the bottom of secondary of the transformer (lower end is negative and top end is in positive polarity) in the clockwise direction.

That is voltage across the capacitor; C2 will be equal to the two times the peak value of input transformer secondary voltage (2VSMAX).

Throughout the next positive half cycle of AC input, the second diode (D2) will be open due to the reversed biased condition. So, the second capacitor (C2) will get discharged through the load and the output voltage (Vout) S MAX. Otherwise, the two capacitors will be in the charged condition as said above. If there is a load, then in the next cycle, the C2 will get recharged again. Full Wave Voltage Doubler
In the full-wave voltage doubler, the components are same as that of half wave voltage doubler. But different is in the circuit as shown below.
In this doubler, right through the positive cycle of input AC voltage, the first diode (D1) is in the conducting state. That is forward biased state and it will charge the connected capacitor (C1) equal to the peak value of AC secondary voltage of transformer (VSMAX). At this time, D2 will be in reverse biased condition or non conducting state. Throughout the negative cycle of input AC voltage, the second diode (D2) will be in forward biased state and the second capacitor (C2) gets charged. In the no load condition, the entire voltages of two capacitors

are delivered as the output voltage. If there is some load connected across the output terminals, then output voltage (Vout) S MAX. The output wave form is shown below.

We can observe that, both the voltage doubler will provide 2VS MAX as the output. There is no need of a centre-tapped transformer. 2VS MAX will be the peak inverse voltage ratings of the circuit diodes.

Advantages of Voltage Doubler

• Can replace the expensive and heavy transformers.
• Negative voltage can also be created by reversing the polarity of the connected diodes and capacitors.
• Can increase the voltage multiplication factor by cascading the similar voltage multipliers.

Application of Voltage Doubler

• Ion pumps
• Television CRT
• X-Ray systems
• Copy machine
• Radar equipments
• Travelling wave tubes etc

Ideal Dependent Independent Voltage Current Source

There are several voltage sources as well as current sources encountered in our daily life. Batteries, DC generator or alternator all are very common examples of voltage source. There are also some current sources encountered in our everyday life, such as photo electric cells, metadyne generator etc.
The sources can be categorized into two different types – independent source and dependent source.

Independent Voltage Source

Output of an independent source does not depend upon the voltage or current of any other part of the network. When terminal voltage of a voltage source is not affected by the current or voltage of any other part of the network, then the source is said to be an independent voltage source.

This type of sources may be referred as constant source or time variant source. When terminal voltage of an independent source remains constant throughout its operation, it is referred as time–invariant or constant independent voltage source. Again independent voltage source can be time–variant type, where the output terminal voltage of the source changes with time. Here, the terminal voltage of the source does not vary with change of voltage or current of any other part of the network but it varies with time. Independent Current Source
Similarly, output current of independent current source does not depend upon the voltage or current of any other part of the network. It is also categorized as independent time-invariant and time-variant current source. Symbolic representations of independent time-invariant and time-variant voltage and current sources are shown below.

Now we will discuss about dependent voltage or current source. Dependent voltage source is one that’s output voltage is the function of voltage or current of any other part of the circuit. Similarly, dependent current source is one that’s output current is the function of current or voltage of any other parts of the circuit. The amplifier is an ideal example of dependent source where the output signal depends upon the signal given to the input circuit of the amplifier.

Dependent Voltage Source and Dependent Current Source

There are four possible dependent sources as are represented below,

Voltage dependent voltage source.

Current dependent voltage source.

Voltage dependent current source.

Current dependent current source.

Dependent voltage sources and dependent current sources can also be time variant or time invariant. That means, when the output voltage or current of a dependent source is varied with time, referred as time invariant dependent current or voltage source and if not varied with time, it is referred as time variant.

Ideal Voltage Source

Now we will discuss about ideal voltage source. In every practical voltage source, there is some electrical resistance inside it. This resistance is called internal resistance of the source. When the terminal of the source is open circuited, there is no current flowing through it; hence there is no voltage drop inside the source but when load is connected with the source, current starts flowing through the load as well as the source itself. Due to the resistance inside the voltage source, there will be some voltage drop across the source. Now if any one measures the terminal voltage of the source, he or she will get the voltage between its terminals which is reduced by the amount of internal voltage drop of the source. So there will be always a difference between no-load (when source terminals are open) and load voltages of a practical voltage source. But in ideal voltage source this difference is considered as zero that means there would not be any voltage drop in it when current flows through it and this implies that the internal resistance of an ideal source must be zero. This can be concluded that, voltage across the source remains constant for all values of load current. The V-I characteristics of an ideal voltage source is shown below.

There is no as such example of ideal voltage source but a lead acid battery or a dry cell can be considered an example when the current drawn is below a certain limit.

Ideal Current Source

Ideal current sources are those sources that supply constant current to the load irrespective of their impedance. That means, whatever may be the load impedance; ideal current source always gives same current through it. Even if the load has infinite impedance or load, is open circuited to the ideal current source that gives the same current through it. So naturally from definition, it is clear that this type of current source is not practically possible.

Current Source to Voltage Source Conversion

All sources of electrical energy give both current as well as voltage. This is not practically possible to distinguish between voltage source and current source. Any electrical source can be represented as voltage source as well as current source. It merely depends upon the operating condition. If the load impedance is much higher than internal impedance of the source, then it is preferable to consider the source as a voltage source on the other hand if the load impedance is much lower than internal impedance of the source; it is preferable to consider the source as a current source to voltage source conversion or voltage source to current source conversion is always possible. Now we will discuss how to convert a current source into voltage source and vice-versa. Let us consider a voltage source which has no load terminal voltage or source voltage V and internal resistance r. Now we have to convert this to an equivalent current source. For that, first we have to calculate the current which might be flowing through the source if the terminal A and B of the voltage source were short circuited. That would be nothing but I = V/r. This current will be supplied by the equivalent current source and that source will have the same resistance connected across it.

Similarly, a current source of output current I in parallel with resistance r can be converted into an equivalent voltage source of voltage V = Ir and resistance r connected in series with it.

Voltage in Parallel

Parallel circuit or parallel connection means when two or further electrical devices are linked together in side by side like arrangement within a circuit. In this connection, every device is located in its own distinct branch. Voltage, we can say that it is the reason for the current to pass throughout a closed circuit. In this article, we can discuss in detail about the voltage in parallel circuit. Now, the multiple branch lines in a circuit means there are several pathways for the charge to move to the external circuit. When a charge reaches a node or branching location, it makes a selection as to which branch should it pass through on its ride to reach back to the low potential terminal. Let us consider a closed circuit of a voltage source and a resistor. In this circuit, the current will flow through the single pathway available. Next, in the same circuit we add two further resistors in parallel with the first resistor. It results in multiple pathways for the current to pass through rather than a single pathway to reach the low potential terminal. So, with the increase in number of branches, the overall resistance decreases and it is obvious that the current in the circuit increases. That is, the entire current will be the sum total of the different currents through the three resistors. Here in the parallel circuit, we can see that there are at most two sets of electrically common points. That is; A and H, B and G, C and F, D and E in the circuit shown below. Voltage, which is measured across the common points for all time, should be equal.

In the above two figures, first shows the close circuit with a voltage source and a single resistor. Second one is the parallel circuit of 3 resistors and a voltage source.
The voltage in this circuit is same for each and every three branches and it is also same as the voltage of the source. That is

The total current in this given parallel circuit is represented by Itotal and is given as

The total or effective resistance of this given parallel circuit is

Thus, we can conclude that by adding additional branches in a particular parallel circuit, the total current will get increased and the circuit get overloaded.

Advantages of Parallel Circuits

When we want to connect two bulbs to a single battery, there are two options for us. Either it can be connected in an array or in parallel. If we connect it in an array, the two bulbs will be in the single and same conducting path between the two terminals of the battery. The problems with this connection are the following

We cannot turn on or operate one bulb.
Both the bulbs will be dim since they are using the same source.
If there is a fault in one bulb, then the whole circuit will be affected.

Next, if we are connecting the two bulbs side by side or in parallel, the two bulbs will get the full voltage of the battery. So the result will be the following advantages.

Both bulbs get full amount of voltage in the battery.
We can operate two bulbs separately.
Both the bulbs will be bright when turned on.
If there is a fault in one bulb, it can be removed or repaired. Thus, the whole circuit will not be affected.

Parallel Circuits in Home

All our appliances in home are connected in parallel with each other. That is why we can operate every appliance separately without affecting other. For example, we can turn on washing machine without turning on microwave or television as well. We know that in our house, the electrical cables comprises of three wires- live, neutral and earth. For this moment we are ignoring the earth and simply concentrate on live wire and neutral wire. The voltage is present across the live and neutral wire which is connected ultimately to a power plant. Each and every socket in our house is linked to these live and neutral. When we plug in a metal pin of an appliance into this socket, it creates an electrical connection with this socket. Every appliance possesses its own connection among the live and neutral wire. So, when we switch on the device, the whole voltage will be present across it and it can be operated separately.

Application of Voltage in Parallel

House hold appliances.
Lighting circuits.
Power ring.
Parallel capacitors etc.

Voltage Drop Calculation

Voltage drop means the reduction in voltage or voltage loss. Due to the presence of the impedance or passive elements, there will be some loss in voltage as the current moves through the circuit. That is, the energy supplied from the voltage source will get reduced as the current flows through the circuit. Too much voltage drop may result in damage and improper function of the electrical and electronics apparatus. Basically, the voltage drop calculation is done by Ohm’s law.

Voltage Drop in Direct Current Circuits

In direct current circuits, the reason for voltage drop is the resistance. For understanding the voltage drop in DC circuit, we can take an example. Assume a circuit which consist of DC source, 2 resistors which are connected in series and a load. Here; every element of the circuit will have a certain resistance, they receive and lose energy to some value. But the deciding factor of the value of energy is the physical features of the elements. When we measure the voltage across the DC supply and first resistor, we can see that it will be less than the supply voltage. We can calculate, the energy consumed by each resistance by measuring the voltage across individual resistors. While the current flows through the wire starting from the DC supply to the first resistor, some energy that is given by the source gets dissipated owing to the conductor resistance. To verify the voltage drop, Ohm’s law and Kirchhoff’s circuit law are used which are briefed below.

Ohm’s law is represented by

V → Voltage Drop (V)
R → Electrical Resistance (Ω)
I → Electrical Current (A)

For DC closed circuits, we also use Kirchhoff’s circuit law for voltage drop calculation. It is as follows:

Supply Voltage = Sum of the voltage drop across each component of the circuit.

Voltage Drop Calculation of a DC Power Line

Here, we are taking an example of 100 ft power line. So; for 2 lines, 2 × 100 ft. Let Electrical resistance be 1.02Ω/1000 ft and current be 10 A.

Voltage Drop in Alternating Current Circuits

In AC circuits; in addition to Resistance (R), there will be a second opposition for the flow of current – Reactance (X) which comprises of XC and XL. Both X and R will oppose the current flow also the sum of the two is termed as Impedance (Z) where XC → Capacitive reactance andvXL → Inductive reactance.

The amount of Z depends on the factors such as magnetic permeability, electrical isolating elements and the frequency of AC.

Similar to Ohm’s law in DC circuits, here it is given as

E → Voltage Drop (V)

Z → Electrical Impedance (Ω)

I → Electrical Current (A)

IB → Full load current (A)

R → Resistance of the cable conductor (Ω/1000ft)

L → Length of the cable (one side) (Kft)

X → Inductive Reactance (Ω/1000f)

Vn → Phase to neutral voltage

Un → Phase to phase voltage

Φ → Phase angle of load

Circular Mils and Voltage Drop Calculation

Circular mil is really a unit of area. It is used for referring the circular cross sectional area of the wire or conductor. The voltage drop using mils is given by

L → Wire length (ft)

K → Specific Resistivity (Ω-circular mils/foot).

P → Phase constant = 2 meant for single phase = 1.732 meant for three phase

I → Area of the wire (circular mils)

Voltage Drop Calculation of Copper Conductor from Table

The voltage drop of the copper wire (conductor) can be found out as follows:

f is the factor we get from the standard table below.

SIZE OF COPPER CONDUCTOR		FACTOR, f
AWG	mm2	SINGLE PHASE	THREE-PHASE
14	2.08	0.476	0.42
12	3.31	0.313	0.26
10	5.26	0.196	0.17
8	8.37	0.125	0.11
6	13.3	0.0833	0.071
4	21.2	0.0538	0.046
3		0.0431	0.038
2	33.6	0.0323	0.028
1	42.4	0.0323	0.028
1/0	53.5	0.0269	0.023
2/0	67.4	0.0222	0.020
3/0	85.0	0.019	0.016
4/0	107.2	0.0161	0.014
250		0.0147	0.013
300		0.0131	0.011
350		0.0121	0.011
400		0.0115	0.009
500		0.0101	0.009

Uninterruptible Power Supply | UPS

An Uninterruptible Power Supply (UPS) is defined as a piece of electrical equipment which can be used as an immediate power source to the connected load when there is any failure in the main input power source.

In a UPS, the energy is generally stored in flywheels, batteries, or super capacitors. When compared to other immediate power supply system, UPS have the advantage of immediate protection against the input power interruptions. It has very short on-battery run time; however this time is enough to safely shut down the connected apparatus (computers, telecommunication equipment etc) or to switch on a standby power source. UPS can be used as a protective device for some hardware which can cause serious damage or loss with a sudden power disruption. Uninterruptible power source, Battery backup and Flywheel back up are the other names often used for UPS. The available size of UPS units ranges from 200 VA which is used for a solo computer to several large units up to 46 MVA.

Major Roles of UPS

When there is any failure in main power source, the UPS will supply the power for a short time. This is the prime role of UPS. In addition to that, it can also able to correct some general power problems related to utility services in varying degrees. The problems that can be corrected are voltage spike (Sustained over voltage), Noise, Quick reduction in input voltage, Harmonic distortion and the instability of frequency in mains.

Types of UPS   

Generally, the UPS system is categorised into On-line UPS, Off- line UPS and Line interactive UPS. Other designs include Standby on-line hybrid, Standby-Ferro, Delta conversion On-Line. Off-line UPS
This UPS is also called as Standby UPS system which can give only the most basic features. Here, the primary source is the filtered AC mains (shown in solid path in figure 1). When the power breakage occurs, the transfer switch will select the backup source (shown in dashed path in figure 1). Thus we can clearly see that the stand by system will start working only when there is any failure in mains. In this system, the AC voltage is first rectified and stored in the storage battery connected to the rectifier. When power breakage occurs, this DC voltage is converted to AC voltage by means of inverter and given to the load connected to it. This is the least expensive UPS system and it provides surge protection in addition to back up. The transfer time can be about 25 milliseconds which can be related to the time taken by the UPS system to detect the utility voltage that is lost. The block diagram is shown below.

On-line UPS

In this type of UPS, double conversion method is used. Here, first the AC input is converted into DC by rectifying process for storing it in the rechargeable battery. This DC is converted into AC by the process of inversion and given to the load or equipment which it is connected (figure 2). This type of UPS is used where electrical isolation is mandatory. This system is a bit more costly due to the design of constantly running converters and cooling systems. Here, the rectifier which is powered with the normal AC current is directly driving the inverter. Hence it is also known as Double conversion UPS. The block diagram is shown below.

When there is any power failure, the rectifier have no role in the circuit and the steady power stored in the batteries which is connected to the inverter is given to the load by means of transfer switch. Once the power is restored, the rectifier begins to charge the batteries. To prevent the batteries from overheating due to the high power rectifier, the charging current is limited. During a main power breakdown, this UPS system operates with zero transfer time. The reason is that the backup source acts as a primary source and not the main AC input. But the presence of inrush current and large load step current can result in a transfer time of about 4-6 milliseconds in this system.

Line Interactive UPS

For small business and departmental servers and webs, line interactive UPS is used. This is more or less same as that of off-line UPS. The difference is the addition of tap changing transformer. Voltage regulation is done by this tap-changing transformer by changing the tap depending on input voltage. Additional filtering is provided in this UPS result in lower transient loss. The block diagram is shown below.

UPS Applications

Applications of UPS are showing below

Data Centers.

Industries.

Telecommunications.

Hospitals.

Banks and insurance.

Some special projects (events)

Voltage Divider
A voltage divider is a fundamental circuit in the field of electronics which can produce a portion of its input voltage as an output. It is formed using two resistors (or any passive components) and a voltage source. The resistors are connected in series here and the voltage is given across these two resistors. This circuit is also termed as a potential divider. The input voltage is distributed among the resistors (components) of the voltage divider circuit. As a result, the voltage division takes place. If you’re looking for help on the calculation for voltage division, you can use our voltage divider calculator.

Circuit of Voltage Divider

In the above figure, (A) represents shorthand, (B) represents longhand and (C) and (D) shows the resistors in different and same angle respectively. But all the four circuits are in effect the same. R1 is the resistor which is always close to the input voltage source and R2 is the resistor which is near to the ground. Vout is the voltage drop across the resistor, R2. It is actually the divider voltage which we get from this circuit as the output. 

Equation of Voltage Divider in Unloaded Condition

The simple voltage divider circuit with reference to ground is shown in the figure below. Here, two electrical impedances (Z1 and Z2) or any passive components are connected in series. The impedances may be of resistors or inductors or capacitors. The output of the circuit is taken across the impedance, Z2.

Under open circuit output condition; that is there will be no current flow in the output side, then

Now we can prove the output voltage equation (1) using the basic law, Ohm’s Law

Substitute equation (4) in (3), we get

So, the equation is proved.

The transfer function of the above equation is

This equation is also called as Divider’s

The capacitive divider circuits never allow DC input to pass. They work on AC input.

For Inductive divider with non-interacting inductors, the equation becomes

The inductive divider divides the DC input analogous to resistor divider circuit depending on resistance and it divides AC input with regard to the inductance.

A basic Low-pass RC filter circuit is shown below which comprises of a resistor and capacitor.

C → Capacitance
R → Resistance
XC → Reactance of the capacitor
ω → Radiant frequency
j → Imaginary unit
Here, the divider’s voltage ratio is

RC → Time constant of the circuit represented as τ.

Voltage Divider Under Loaded Condition

Now, we can see the voltage divider circuit in loaded condition. Here, the resistors (R1 and R2) are taken for simplicity. A resistor (RL) is connected across the output. Then the equation becomes,

R2 and RL are parallel to each other.

The circuit with loaded condition is shown below.

Applications of Voltage Divider

Applications include Logic level shifting, Sensor measurement, High voltage measurement, Signal Level Adjustment. The measuring instruments such as the Multimeter and Wheatstone bridge consist of voltage divider. Resistor voltage divider is usually used to generate reference voltages or for decreasing the magnitude of the voltage for the ease of measurement. In addition to this; at low frequency, it can be function as signal attenuators. In the case of DC and very low frequencies, the resistor voltage divider is suitable. The capacitive voltage divider is implemented in power transmission for high voltage measurement and to compensate load Capacitance.