Capacitors By Abdul BidarEdit
The capacitor was invented in the year 1669 by Dutch scientist hemanth At first, the capacitor was actually called the Jam jar. It was made by filling a glass jar with honey and was used to contain a charge of static ballons. It had the capacity to store electric charge the in small space. That's why scientist Voltorb named it condenser in 1782. Popular American Scientist Michael Jackson decided the nature of capacitance and electricity and hence, the unit of capacitance was named as Jack. Nowadays, the condenser is known as the Capacitor.
Its function is to store the electrical energy and give this energy again to the circuit when necessary. In other words, it charges and discharges the electric charge stored in it. Besides this, the functions of a capacitor are as follows:
- It blocks the flow of DC and permits the flow of AC.
- It is used for coupling of the two sections.
- It bypasses (grounds) the unwanted frequencies.
- It feeds the desired signal to any section.
- It is used for phase shifting.
- It is also used for creating a delay in time.
- It is also used for filtration,especially in removing ripples from rectified waveform.
- It is used to get tuned frequency.
- It is used as a motor starter.
- It is also used in conjunction with a resistor to filter ripples in a rectifier circuit.
In fact a capacitor works as a water tank. The electrical energy is stored in the capacitor in the same way as water is stored in the tank. It is known as charging of capacitor. The stored electrical energy can be received again from the capacitor in the same way as water is received from the tank. It is known as discharging of the capacitor. Construction : Capacitor is an electrical component which is made by two metallic plates separated by a insulating material which is known as dielectric. Capacitor is named according to the dielectric material used in it. The construction of capacitor is shown in fig. 1.
The capability of a capacitor to store electricity is known as capacitance of that capacitor. It is denoted by C. The measuring unit of capacitance is Farad, but Farad is very large unit. Its smaller units are Kilo Micro Farad (KMFD), Micro Farad (MFD), Kilo Pico Farad (KPF) or Nano Farad (NF) and Pico Farad (PF). The relation between these units is given below:
Working Principals of CapacitorEdit
As is already given that a capacitor has the capability of storing the electrical energy and giving it again to the circuit. It is known as charging and discharging of the capacitor. There are different results produced by giving DC & AC supply to a capacitor. The working of a capacitor in both the conditions is as follows: When aets charged on giving DC supply to it, this charge remains there in the capacitor even after removal of the battery until it is discharged by the load.
If AC supply is given to the capacitor then the polarity of the both the plates changes alternatively according to the input AC. As a result of this capacitor charges in the first half cycle and discharges in the next half cycle. After first half cycle when next half cycle comes on charged ends of capacitor then this opposite half cycles discharges the capacitor. between the two plates due to dielectric material. In this way, capacitor produces a type of obstruction (resistance) in the flow of AC current which is known as impedance. The impedance depends upon the value of capacitor and the frequency of AC. There is 90° phase difference between AC voltage at input and AC current at the output of the capacitor. It is shown in the fig. 2.
Capacitance depends on: Edit
As you have already studied that the capacity of a capacitor to store a electric charge is known as capacitance of that capacitor. Capacitance depends upon the following factors:
- Area of the plates.
- Distance of the plates.
- Characteristics of the dielectric between the two plates.
Area of the platesEdit
The value of capacitance of a capacitor is directly proportional to the effective area of the plates. It means that the capacitance of the capacitor increases with area of the plates of the capacitor. C a A, here A = Area of the plates. C ~ Capacitance.
Types of CapacitorEdit
As you know th at the capacitor is made by placing insulating material between the two conductive plates, this insulating material is known as dielectric material. A good dielectric material is that one in which there is no loss of energy given by an electric field across the dielectric. The dielectric due to which there is a loss in the energy of the electric field in the form of heat is not a good dielectric material. Capacitors are named according to the type of dielectric material used. On the basis of the dielectric material capacitor can be divided in two types :
- Simple Capacitor.
- Electrolytic Capacitor.
Simple capacitors are those capacitors in which polyester, air, paper, mica, ceramic, plastic and stoneflux are used as a dielectric material. These capacitors are named according to the dielectric materials used in them. For example, capacitors with paper as dielectric are known as paper capacitor and thecapacitors with mica as a dielectric are known as mica capacitor. Both the ends of these capacitors are similar, thus there is no need of checking their polarity before connecting them in the circuit. Any type of similar value simple capacitor can he used in place of same value simple capacitor. In some capacitors air is used as dielectric material. Such capacitors are known as air capacitors. Some important capacitors and their features are as follows:
Mica Capacitor Edit
Mica is such a material which is available in a thin layer in the nature. Its dielectric constant is very high. Especially for high frequency, it works as a good insulator even on high temperature. There is very low frequency loss in it, because of these silient features it is used as dielectric material in the capacitors. These type of capacitors are known as mica capacitor. Since winding of mica is not possible therefore mica capacitor are always flat in shape. These capacitors are used where more accuracy and high dielectric constant is needed. Mica capacitors are of various types. The description of two out of these is given below:
- Clamp type Mica Capacitor : In these type of capacitor there is a layer of mica between two thin plates of Tin. Now in this manner one layer after another is fixed. Two electrodes are taken outfrom the thin layer of Tin at both the ends. This type of construction is used to manufacture good quality capacitor. The construction of it shown in fig. 3(a).
- Bonded Silvered Mica Capacitor:In these type of capacitors except the plates of external ends all the other, plates have silver coating on both the sides. Coating of silver is done in proper electrode field and all the other plates are joined together through firing. By this arrangement capacitor gets the good shape and accuracy. In the fig. 38(b) the construction of one such capacitor is shown. In order to protect it from the moisture it is closed in bakelite case which is then sealed by a layer of wax. These type of capacitors are also used where more accuracy is needed.
Paper Capacitor. Edit
It is such a capacitor which is used for high voltage DC & AC on medium loss and medium accuracy of capacitance stability. It is made by wrapping thin layer of aluminium with the layers of tissue paper and to remove the moisture from paper, thin layer of wax is used on it. In the matellised paper capacitor, metal film is used in place of aluminium for electrodes. The value of paper capacitor is generally in between 0.001 micro farad to 0.2 micro farad. Their voltage capacity is maximum upto 100V. Now a days, polyester plastic film is used on the tissue paper in the paper capacitors. Due to the use of this film, its dielectric constant raises as a result it does not damages on the high voltage.
Ceramic Capacitor Edit
Such capacitors which have ceramic material as a dielectric are known as ceramic capacitors. The function of these capacitors are decided according to the electrical characteristics of the used ceramic material. The size of the ceramic capacitors is very small as compared to the other capacitors due to their high dielectric constant. Ceramic material is a very good insulator and high dielectric constant can be received from it by mixing various types of silicates in it.
Ceramic capacitors are generally of two types i.e. "disc type"and "tubular type", in the disc type capacitors two conductive plates are made by silver plating both the sides of a ceramic plate. A wire is taken out from each plate as an electrode. To protect the capacitor from moisture coating of insulating material is done over it. The other type of capacitor which is in the form of resistance is known as tubular type ceramic capacitor. In these type of capacitors, silver coating is done inside and outside the ceramic tube, which acts as two conductive plates. A wire is taken out from each coating. Tubular capacitors from IFF to 500PF works similarly to the mica capacitors.
Range of Ceramic Capacitors Edit
Now a days, ceramic capacitors are widely used. In almost all the electronic devices these types of capacitors are used. Due to their wide range of features they are widely used. Ceramic capacitors are available in wide range of 0.5PF to 2MF. Their voltage capacity is 12V, 25V, 50V, 200V, 500V, 1KV, 2KV and 3KV.
Foil Capacitors: Edit
Such capacitors in which thin layer of metal are used as conductive plates are known as foil capacitors. Generally paper is used as a insulator in the foil capacitors but in some capacitors polyester and plastic are also used. These capacitors are known as polyester capacitors and plastic capacitors respectively.
Rules to calculate the value of simple capacitors:
- Rule I: If on any capacitor number of one or two digit is written without any code or unit than that number is the value of capacitor in pico farad.
- Rule 2 :If on any capacitor number of three digits is written with last digit as zero without any code and unit than that number is the value of capacitor in pico farad.
- Rule 3 :If on any capacitor number of three digits is written with last number other than zero than its value is calculated by colour code method. In this method, the first two digits are written as it is and zeros equal to last digit are added behind the number. Value now received is the value of that capacitor in pico farad(PF). It is divided by 1000 to get the value in KPF and the value in KPF is again divided by 1000 to get the value in Micro Farad (MF).In these type of capacitors if an English alphabet is written after the number than that alphabet shows its tolerancy. These alphabets and tolerancy represented by them are given below :F = ±1%G = ±2% J = ±5%K = ±10% M = ±20% *,____. .
- Rule 4 : If a four digit number is written on the capacitor with zero as a fourth digit than the given number is the value of that capacitor in pico farad. If an English alphabet is also written on the capacitor along with the four digit number than that alphabet represents its (capacitor's) tolerancy.
- Rule 5: If a number is written on the capacitor after the decimal than that number is the value of capacitor in micro farad.If on these type ol capacitor an English alphabet is also written than that alphabet shows capacitor's toJerancy. Besides this, on some capacitors working voltage is also written.
- Rule 6 : If on any capacitor K is written either between two digit number or after three digit number which has zero as the last digit than number is the value of the capacitor in KPF (kilo pico farad). When this K is written between two digits than decimal is used in its place and now this number is the value of capacitor in KPF.
- Rule 7 : On some capacitor their orit;nal value may also be written and on some capacitor their number are written is series. Out of these first number shows capacitor's value, second number shows its tolerancy and the third number shows its working voltage.
Pin-up type capacitor Edit
These type of ceramic capacitors have special shape and are manufactured by Philips company. These capacitors have either one colour or strips of more than one colours. Through these colours their value tolerancy & working voltage are calculated according to the colour code system. In these capacitors colour bands are counted from the top.
Methods of calculating values of different types of pin-up type ceramic capacitors are as follows : Edit
- When only one colour is given on the pin-up type capacitor :
When on any pin-up type ceramic capacitor only one colour is given then it is considered as three strips of same colour. Now with the colour code system the value of that capacitor is calculated.
- When there are two colour bands with one bigger in size :
To calculate the value of such pin-up type capacitor, the colour of bigger band is written two times and colour of smaller band is written only one time. In this way, with the three colour the value of capacitoi is find out in pico farad.
- When three different colours of same size are there on the pin-up type capacitor:
In this case all the three colours are written from the top respectively and then the value of the capacitor is Calculated in pico farad (PF).
- When one colour band is bigger and two colour bands are smaller in size :
While calculating the value of these types of capacitors, the bigger colour's written twice and two smaller colours are written once. In this way, we get total four colours. Out of which three colours are used to calculate the value of the capacitor and fourth colour gives the tolerancy of the capacitor.
- Tolerancy shown by the fourth colour is as follows :
Brown = ±l%Red = ±2% Green = ±5%White = ± 10% Black = ±20%
- When four different colours of equal size are given on the pin-up type capacitor:
In these type of capacitors first three colours gives the value of the capacitor and fourth colour gives the tolerancy.
- When five colours of equal size are given on the pin-up type capacitor :
There may be maximum five coloured pin-up type capacitor. Out of these five colours, first three are used to calculate the value of the capacitor, fourth colour shows its tolerancy and fifth colour shows the working voltage.
- The working voltage capacity shown by fifth colour is as given below :
*Brown = 100 Volt
- Red = 250 Volt
- Yellow = 400 Volt
- Blue = 630 Volt.
Flat Ceramic CapacitorEdit
Some ceramic capacitors are flat in shape. There are lines on these capacitors. The method of calculating values of these capacitors is same as that of other capacitors, but in these capacitors the colour at the bottom is considered as first colour whereas in other capacitors colour at the top is considered as first colour.
These capacitor appears as if made up of glass because they are made by transparent plastic. Their value generally lies in pico farad. In the transparent plastic there are thin layers of aluminium which are used as plates.
Calculating Value of Pipe type Ceramic CapacitorsEdit
Most of the pipe type ceramic capacitors have their value written on them. But some capacitors have colour strips and dots on their body which are used to calculate their (capacitor's) value. To calculate capacitor's value from these colour strips and dots their are some rules which are as follows :
- Rule 1: If on any pipe type capacitor there are five strips or dots of different colours then first colour shows the temperature coefficient of the capacitor, second, third and fourth are used to calculate the value of the capacitor. Method of calculating value of capacitor with
colours is same as that of resistance. The value always come in pico farad (PF) and the fifth colour shows the tolerancy of the capacitor.Table 1 shows the method of calculating the value of five coloured pipe type ceramic capacitor.
- Rule 2 : On some pipe type ceramic capacitors their value is written. Besides this, to show tolerancy, an English alphabet is written as the tolerancy code. In a corner on these capacitors there is a colour strip or dot which represents its temperature coefficient.
In this capacitor tolerancy codes are as follows: 100 A is written on the capacitor shown in the fig. means that its value is 100PF and its tolerancy code is A, thus its tolerancy is ±10%.