CAPACITOR LOSSES

If a charged capacitor is kept aside then it is found that after some time its charged gets reduced or lost.
The reason behind the side effect is capacitor losses which are as fallows.

1.RESISTANCE LOSS:

There always exists some resistance in the capacitor plates, connecting leads and wires and it causes loss of electrical energy. Therefore, the loss of electrical energy caused due to resistance of the capacitor is known as resistance loss (I^2R).

2.LEAKAGE LOSS:

A minute flow of electrons from negative to positive plate of the capacitor always exists in a charged capacitor through the dielectric. The capacitor gets heated up due to this leakage.  In this way, the loss of electrical energy caused due to flow of current through the dielectric of the capacitor is known as the leakage loss.
Since, no ideal insulator is available hence the leakage loss cannot be eliminated completely. Of course, the use of a dielectric having high dielectric constant can be reduces the leakage loss, e.g. ceramic.

3.DIELECTRIC LOSS:

If a charged capacitor is short-circulated with a piece of wire, it gets discharged. But, on testing the capacitor after some time a little amount of charge is found in the capacitor. The reason behind the side effect is dielectric absorption. In this way, it becomes evident that the electron orbits distributed while charging have not restored their original arrangement even after discharging the capacitor.

The aforesaid effect increases even further if A.C. applied across the capacitor and it goes on increasing with a rise in the frequency. In this way, the absorption of electrical energy by the dielectric on high frequencies is termed as dielectric loss.

The electron orbits get continually disturbed if A.C. voltage is applied across the capacitor and the loss of electrical energy occurred is termed as dielectric hysteresis loss.              

    

Capacitor and Classification of Capacitors

In simple language, a capacitor is a component that conducts energy in an electric field between two charged "plates" for a short period of time. The electric charge is then used or dissipated at an appropriate time. The capacitor essentially works along the same lines as the battery you might find in a flashlight, but with a few
minor differences.

Though any two conductors separated by an insulator have a capacitance; but a system of two or more conductors duel separated by an insulator when given the shape of a component to present a definite amount of capacitance is called a capacitor.

A capacitor is also a very useful component of electronic circuits like inductors and resistors. It is used in amplifiers, oscillators, filter circuits and many other types of electronics circuits.

Classification of capacitors

Fixed capacitor: A capacitor having a fixed capacitance value is called a fixed capacitor. Its capacity can't be changed easily, i.e. paper, mica, electrolyte etc.

Adjustable capacitor: A capacitor whose value can easily be changed with the help of a screw driver is called an adjustable capacitor. Its capacitance can be set at
the desired value, i.e. trimmer, padder etc.

Variable capacitor: A capacitor whose value can easily be set with the help of its shaft between its minimum and maximum values is called a variable capacitor, i.e. gang capacitor.

 Fixed capacitors

1. Paper capacitors:

This type of capacitor is made by two long aluminium foils  duel separated by wax paper strips and rolled together to take a cylindrical shape. A connecting is joined to the each aluminium foil and the capacitor is with a suitable resin binder.


Paper Capacitor



Characteristics:

Value is 0.0001 µF to 2.0 µF.
Working voltage is up to 2000 volts D.C.
Only fixed capacitors are made.
Small in size and cheap in cost.
Unsuitable for high frequency circuits.

2. Mica capacitors:

This type of capacitor is made by two brass or alloy metal plates separated by a thin sheet of mica. For making a capacitor of high capacitance value, a number of two plates systems are joined together. The whole combination is covered with a suitable resin binder to take cuboids shape.

Mica Capacitor

Characteristics:

Value is 5 pF to 0.05 µF.
Working voltage is 500 to 2500 volts.
Fixed and adjustable capacitors are made.
Suitable for high frequency. Unaffected from dampness. Capacitance value remains almost stable.

3. Polystre or styroflex capacitors:

Polystre Capacitor

This type of capacitor is made by same as paper capacitor. But instead of paper dielectric a very fine polythene sheet is used as dielectric.

Characteristics:

Value is 2.5 pF to 0.05 µF.
Working voltage is up to 400 volts D.C.
 Only fixed capacitors are made.
Size is smaller than paper capacitors.
Suitable for high frequency circuits and miniature equipments.

4. Ceramic capacitors:



Ceramic Capacitor


This type of capacitor is made in tubular, disc or pin –up shape. It employs a ceramic dielectric which is a compound of titanium, barium, magnesium and strontium. This compound has a dielectric constant of up to 6000. Aluminium, tin or silver is used for making conductor plates in these capacitors.

Characteristics:

Value is 2.5pF to 0.22µF.
Working voltage is 50 to 1500 volts D.C.
 Only fixed capacitors are made.
It can be made very small in size.
Suitable for high frequency. It can be designed to have a positive, zero or negative temperature coefficient. It has a long working life.

5. Electrolytic capacitors:

Electrolytic Capacitor

This type of capacitor consists of an electrolyte between two sets of plates called positive and negative that is why it is known as electrolytic capacitor. Like a secondary cell when an electrolytic capacitor is connected across D.C., a chemical action takes place and an insulating layer is formed on the positive plates. The layer so formed acts as a dielectric. There are two types of electrolytic capacitors which are as follows:

Wet type:

This type of capacitor consists of a cylindrical aluminium pot which is filled with a solution of boric acid and sodium borate. (Solution of ammonium borate, sodium phosphate, aluminium borate etc also may be used). A group of plates is placed in the solution which may be of many diversified shapes. When the plate group and the pot is connected to D.C. positive and negative respectively, the electrolysis action is started. As a result of said action, a very thin layer of aluminium oxide is formed on the positive plates which act as dielectric.

The above explain action is called ‘forming’ and it is performed in factories during manufacturing.

Dry type:

In a dry type electrolytic capacitor the solution is replaced by a paste. Its construction process is similar to that used for paper capacitor. Long and thin aluminium foil separated by paper sheets embedded in the electrolytic paste is rolled to take a cylindrical shape and roll is fitted in aluminium.  There is no possibility of
leakage in a dry electrolytic capacitor; hence these capacitors are used commonly in electronic circuits.

Characteristics:

Value is 1µF to 2000µF.
Working voltage is up to 450 volts D.C.
Only fixed capacitors are made.
Small size in consideration to their high capacity (it is due to very thin layer of dielectric).Suitable for filter circuits.

6. Oil dielectric capacitors:

Oil Dielectric Capacitor

This type of capacitors consists of brass or iron conductor plates separated by oil dielectric. A mineral oil or hydrogenated caster oil is suitable for the purpose. These capacitors are made in cuboid shape.

Characteristics:
Value is 0.001µF to 0.1µF.
Working voltage is up to 25000 volts D.C.
Only fixed capacitors are made.
These capacitors have a long life. Suitable for transmitters.

7. Air dielectric capacitors:

Air Dielectric Capacitor

In this type of capacitors, air is used as dielectric between conductor’s plates. Usually, these capacitors are made in variable type.

Characteristics:

Value is 5 pF to 600 pF.
Working voltage is up to 500 volts D.C.
Usually variable type capacitors are made.
These capacitors are made in small and large both sizes.
Suitable for tuning circuits.

 Adjustable capacitors:

1. Trimmer:

Trimmer

 Its capacitance value is kept between 3 to 30 pF or 4 to 70pF. Its types are as follows:

Parallel plate type:

Parallel Plate Capacitor

It consists of two alloy metal plates placed parallel to each other. One plate is fitted on Bakelite or a porcelain base and the other one is a tension plate which is fitted in such a way that the distance between the two plates can be adjusted by a screw. The variation in distance between the two plate varies the capacitance value of the trimmer. A mica sheet works as dielectric between the two plates.

Cup type:

It consists of two aluminium cups having different diameters. One cup is kept stable while the other one inverted over the first can be adjusted to desired position with the help of a screw. The variation of distance between the two cups varies the capacitance value of the trimmer. Air works as dielectric between the two cup.

Wire type:

It consists of a thick enameled copper wire erected on the chassis by soldering its one end and a thin enameled copper wire wound over the thick one. The stray capacitance which exists between any two turns of the thin wire is utilized in it. The value of its capacitance can be varied by changing the distance between the turns of thin wire with the help of an insulated strip.

Disc type:

It consists of two semi-circular discs of brass. One disc is kept fixed and the other one can be rotated with the help of a screw over the first one. A mica sheet or polythene a sheet may be used as dielectric between the two discs. The value of its capacitance can be varied by changing the effective area between the two discs.

2. Padder:

Padder

It is also an adjustable capacitor whose capacitance value can be adjusted between 400 to 600 pF with the help of a screw. It consists of two or more plate couples. The value of its capacitance can be varied by changing the distance between the plates. Mica sheets are used as dielectric between the plates.
 Trimmers and padders are used for frequency setting purpose in radio receivers.

 Variable capacitors:

Variable Capacitor

A radio receiver consists of more than one tuning circuits which require more than one variable capacitors controlled by a single shaft.  These capacitors are called ‘gang capacitors’. A gang capacitor consists of two sets of plates –one is known as stator and the other as rotor. The rotor plates group can be rotated through an angle of 180º. The value of its capacitance can be varied by changing the effective area between the two plate groups. Its capacitance value is kept between 30pF to 600pF. For a valve type radio receiver 135pF to 500pF and for a transistorized radio receiver 90pF to 210pF capacitors are used. Air works as dielectric between the two plate groups.

Types of resistors

When a wire or a piece of a material is used as a component for producing resistance in a circuit, it is called a resistor. Resistors used in electronic equipments are classified as under on the basis of their construction: carbon, wire wound, ballast, PTC, NTC, varistor, LDR, etc.  

Carbon resistors:

Carbon Film Resistor

Carbon is a non metallic and ideal material for making resistor. Resistors made of carbon or graphic are called carbon resistors. They are of following two main types:
1.    carbon composition resistors :
Resistors made by compressing carbon powder while using a suitable resin binder are called composition resistors. They are of following two types:
(a)    Pallet or slug type :

Pallet Resistor

For making this type of resistors, carbon black or graphite powder is moulded into small cylindrical piece while using an appropriate resin binder. During moulding, two leads of tinned copper wire are also attached, one on each side. A defensive coating is made over moulded pieces. After heat treatment the resistor becomes ready for use.

(b)    Filament type carbon composition resistor:
For making this type of resistors, carbon powder is deposited over porcelain or glasses both the ends, one on each side. Finally, the resistor is enclosed with a phenolic (water proof) layer.
Carbon composition resistors are made in the range of 2 ohms to 10 mega ohms with 1/8, 1/4, 1/2, 1 and 2 watts power ratings.

2.    Film carbon resistors:

Carbon Film Resistor

These types of resistors are made by depositing hydrocarbon vapors on a ceramic capillary pipe at 900-1100°c temperature. Resistor s of small values are made by depositing metal oxide (of palladium, nickel, chromium metals) on a ceramic capillary pipe. Resistors of first type are also known as pyrolytic resistors and of second type as metal oxide film resistors. Tinned copper or silver wires are used as leads for these resistors.

This type of resistors is made in range of 1 ohm to20 mega ohms with ½ watts power rating.

Properties of carbon resistors:

(A)    Merits :
(1)    Size is quite small up to 6mm ×1mm.
(2)     Mass is quite less up to 1 gram.
(3)    High value resistors (1 mega ohm and above) can be made easily.
(4)    They can carry high frequency   circuits.
(5)    Their temperature coefficient lies within 0.02 to 0.1.

(B)    Demerits:
(1)    Temperature   and humidity affects their values.
(2)    Their current carrying capacity is restricted, since their wattage is limited up to 2 watts.
(3)    It is complicated to make a carbon resistor of a value below 2 ohms.
(4)    Their stability and reliability are poor.


Wire wound resistors:

Wire Wound Resistor

These types of resistors are made by winding a wire on an insulated former. Generally, porcelain pipe pieces are used as former and Eureka wire (an alloy of 60% nickel and 40% copper) is used as resistance wire. This type of resistor is made in the range of 0.01 to 1 mega ohms with 5 to 50 watts power rating.

They are also able to handle much higher electrical currents than other resistors of the same ohmic value with power ratings in excess of 300 Watts. These high power resistors are moulded or pressed into an aluminum heat sink body with fins attached to increase their overall surface area to promote heat loss and cooling.

   Wire wound resistors are classified as follows on the basis of their resistance control:
(1)    Fixed value resistor:

Fixed Value Resistor

A resistor having a fixed value of resistance is called a fixed value resistor. It has no arrangement for changing its resistance value.

(2)    Tapped resistor :

Tapped Resistor

A resistor having two, three or more values made in a single unit is called a tapped resistor.

(3)    Adjustable resistor:

Adjustable Resistor

A resistor having arrangement for changing its value within a definite range is called an adjustable resistor. It may also have an arrangement for two three values an in a tapped resistor. This type of resistor is used in mains operated value receiver and it is known as ‘mains resistor’, e.g., 1500 ohms/0.1A, 1000 ohms/0.3A.

(4)    Rheostat:

Rheostat Resistor

The resistance value of a rheostat can be varied quite easily. It is used in laboratories.

Properties of wire wound resistors:
(A) Merits:
(1)  They have a lowest tolerance value –up to 5%
(2) They have a high power rating.
(3) It is easy to construct a low valued resistor –as low as 0.01 ohms.
(4) They have a good stability and reliability.

(B)    Demerits :

(1)    Their size is quite big which is unsuitable for small sized equipments.
(2)    It is difficult to construct a high valued resistor.
(3)    It is difficult to construct variable wire wound resistor and working of such resistors is not satisfactory.
(4)    They are unsuitable for high frequency circuits because their effective resistance is increased due to presence of inductive reactance in them.


Potentiometer:

Potentiometer Resistor

 A resistor whose resistance value can be varied easily is called a potentiometer. The resistor used as volume control and tone control in a radio receiver is a potentiometer.
It consists of circular strip which is equal to 3/4th of a ring.  A carbon film is deposited on it. A moving arm which is connected t o a shaft is mounted in such a way that by rotating the shaft any resistance value between zero and maximum can be obtained.

Generally, the potentiometers are also made for special purpose in the range of 1 to 100 ohms (e.g., for controlling the e.m.f. acting in multimeter).
Carbon potentiometers are of following two types:

(1)    Linear potentiometer:

Linear Potentiometer

In this type of potentiometer, the variation in resistance value is proportional to the angle rotated by the moving arm.

(2)    Logarithmic potentiometers:

Logarithmic Potentiometer

 

In a radio receiver or an radio amplifier the A.F. signal strength has to be increased ten, hundred or thousand times for increasing the output one , two or three times respectively. Because of this reason only, the unit for the measurement of sound intensity had been selected a logarithmic unit called decibel. 

      Hence, potentiometer used in radio receivers or an audio amplifiers are of logarithmic type. In this type of potentiometer, the variation in resistance value is not proportional to the angle rotated by the moving arm. For equal angle rotation, the order of variation in the value of resistance is 1, 10, 100, 1000 ohms etc.

   Pre-set: it is a potentiometer of a very small size. It is generally mounted on the PCB of equipment. Its ohmic valve can be adjusted by means of a small screw driver during alignment of the equipment sometimes, a pre –set is referred as a ‘POT’ also. These are made in ‘linear’ as well as in ‘logarithmic’ types ranging from 100 ohms to 1 mega ohms. These are extensively erased in T.V. receivers etc. 


Special types of resistors:
 
Besides carbon and wire wound resistors some special types of resistors are also made for specific uses. They are as follows:

(1)    Ballast resistor:

Ballast Resistor

 

It is made by a substance which has a positive temperature coefficient such as nickel iron alloy. It has a property of variation in its resistance value for a change in its temperature. Hence, an increase in the magnitude of current flowing through it causes a corresponding increase in its temperature and which in turn results in an increase in its resistance value. The increase in its resistance value decreases the magnitude of current flowing through it.

In this way, a ballast resistor stabilizes the circuit current within a definite range. These resistors are used for current stabilization in various types of electronic equipments.

(2)    PTC (positive temperature coefficient )resistor :

PTC Resistor

A resistor made of a substance which has a positive temperature coefficient is called a PTC. The resistance value of PTC is directly proportional to its temperature. Hence, an increase in the magnitude of voltage applied or the external temperature causes an increase in its resistance which in turn reduces the magnitude of current flowing through it. A PTC is used for bias stabilization in transistorised circuits. There, it is connected in the emitter circuit. If due to any reason the magnitude of emitter current rises above a definite value it causes an increase in its resistance value.

 In turn, it results in a decrease in the emitter current. Therefore, the effect of increase in the magnitude of current is controlled by it. It is made by a mixture of nickel oxide, manganese oxide and cobalt oxide. It is known as thermistor also.

(3)    NTC (negative temperature coefficient )resistor :

NTC Resistor

A resistor made of a substance which has a negative temperature coefficient is called a NTC. In the beginning (after switching on the circuit), it has a very high resistance and thus the circuit current is quite small. Slowly and slowly its temperature starts to rise which results in an increase in the magnitude of current flowing through it. An increase in the magnitude of current results in an increase in its temperature which again results in an increase in the circuit current.

 In this way, after a few seconds its temperature rises to a sufficiently high value and the magnitude of current reaches at its maximum value. Under such conditions the resistance value of NTC is minimum. The device is used in timer circuits, valve filament circuits etc. if a valve filament is allowed to be heated up at a slow rate or in other words the magnitude of its heating current is controlled in such a manner that it rises slowly then the working life of a valve filament can be increased up to a great extent. It is made by graphite.

(4)    Varistor:

Varistor Resistor

It is also a special type of resistor and it has following two types:
(A)    Symmetrical varistor :

Symmetrical Varistor

It is made of carbide granules and a ceramic binder material. It has a property that its resistance value is controlled by the magnitude of current flowing through it. At high magnitude of current, the resistance is low and vice versa. Since the magnitude of current in a circuit is proportional to supply voltage, therefore, a varistor can be used for controlling voltage fluctuation within a limit of few volts. It is also known as VDR (voltage dependent resistor) and it is used for controlling voltage fluctuations.

(B)    Unsymmetrical varistor :

Unsymmetrical Resistor

It is made of a semi –conductor material. It has a property of controlling the magnitude of current of a circuit by the direction of flow of current. It is also called a varistor diode. It is used as a rectifier also in certain types of circuits.

(5)      LDR(light dependent resistor ):

LDR

It is made of selenium. It has a property that its resistance value decreases on the incidence of light rays on it and thus the magnitude of current flowing through it is increased. In other words it is a photo sensitive resistor. It is used in light operated control circuits.

 You can make a counter for counting the persons passing through a narrow path, a garage door opener which can open the door automatically on the incidence of light rays from a torch or car headlight, an automatic street light control which can switch on street lights in the night and switch off them in the day light automatically.

Types of current

Alternating current:
There are two types of current one is called alternating current, or "AC". AC current is an exact type of electric current in which the direction of the current's run is inverted, or alternated, on a regular basis.

This is the electricity that we use in our house and that you use to power most of your electrical devices. Alternating current is not easy to explain like direct current. The electricity is not afford as a single, constant voltage, but rather as a sine wave (sinusoidal) that over time starts at zero, increases to a maximum value, and then decreases to a minimum value, and it goes on again and again.

But in simple direct current circuits are usually described only by their voltage, alternating current circuits need more detail. First of all, if the voltage goes from a positive value to a negative value and reverse again, what do we say is the voltage? Is it zero, because it averages out to zero? That would look like to mean that there is no power there at all.

But visualize if you will, a wave of water flowing across the surface of the sea. The peaks and troughs of the wave seem to "cancel each other out", but the wave clearly exists and has power. Alternating current is also like this.

Waves of DC and AC current

Direct Current:

The second and simpler type of current is called direct current, abbreviated "DC". Direct current is no different electrically from alternating current excluding for the fact that it flows in the same direction at all times.

This is the type of current that is produced by batteries, static, and lightning. A voltage is produced, and possibly stored, until a circuit is completed. When we use a mobile, flashlight, portable radio, transportable CD player or almost any other type of portable or battery-powered device, you are using direct current. Most DC circuits are relatively low in voltage.

In DC circuits, the current is always the same polarity, which means that in a two-wire circuit, one "wire", or side of the circuit, is always negative, and the negative side is always the one that sends the current. There is no pulsating because there is no periodic change in current flow.

DC current is more effective for long-distance, high-voltage conduction because it results in less energy lost in conduction, but the cost of converting DC current to AC is somewhat high, so DC is usually cost-effective only for long-distance conduction.

Ohm's Law

Georg Simon Ohm was a German physicist born in Erlangen, Bavaria, on March 16, 1787. Using the results of his experiments, Georg Simon Ohm was able to describe the basic relationship between voltage, current, and resistance. These basic relationships are of such great significance, that they stand for the true beginning of electrical circuit analysis. And it is very big invention in electronics field.

Using apparatus of his own construction, Ohm determined that the current that flows through a wire is proportional to its cross sectional area and inversely proportional to its length or Ohm’s law.

In other words ohm’s law can be state as below:

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points, and inversely proportional to the resistance between them.
The mathematical equation that describes this relationship is:


                                       I = V/R

Where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.