What is a Capacitor ?
A capacitor is one of the most commonly used passive components found in an electric circuit. In a circuit, a capacitor can perform a variety of roles, one of which is the ability to hold charges. In a single second, a capacitor can be charged and discharged as many times as possible. A capacitor, unlike a battery, can endure a short circuit without being damaged. As a result, a capacitor is appropriate for circuits that demand rapid high current flow. It’s also great for sorting a combination of DC and AC signals (electrical voltages or currents that convey relevant information) in a circuit.
How a battery different from a capacitor ?
Even though batteries have the advantage of high capacity of storage, Voltage that is constant and may be turned on and off, better leakage current and power density, It has disadvantages like limited life cycle, long charging times, more responsiveness to temperature, voltage & current limitations, etc. Here comes the importance of capacitors that offer Long cycle life, high-temperature stability, quick charging time, and high load currents.
Capacitor unit and its equation
The capacitance is the measurement unit for the amount of charge that a capacitor can store. The capacitance can be calculated by dividing the charges on a capacitor plate by the voltage applied across the capacitor’s leads. The capacitance unit is measured in Farad, F.
C = Q/V
Where
C = Capacitance in Farad
Q = Charges on capacitor plate (coulomb)
V = Applied voltage
A basic capacitor can be made by placing two parallel metal plates close together and separating them with an electrical insulator (dielectric) placed between them. When one of the capacitor’s metal plates stores positive charges, the other stores’ negative charges at the same time. Although the dielectric can support the flow of an electric field, it cannot conduct electricity.
A capacitor’s capacitance is determined by several elements, including the area of the metal plates (A), the distance between the plates (d), and the dielectric material employed in the capacitor. The capacitance of a parallel plate capacitor can be expressed in the following terms.
Types of capacitors
Capacitors are usually named after the kind of material used as their dielectric. There are several types of capacitors such as ceramic, electrolytic, mica, polyester, porcelain, polypropylene, oil, teflon, tantalum, vaccum capacitor etc.
Ceramic Capacitor
- Ceramic capacitors are small, popular and in-expenive capacitors.
- Ceramic capacitors have a capacitance range of 10pF to 1 Microfarad
- Voltage range supported – 50 – 30000V
- Poor accuracy
- Poor temperature stability
- Moderate leakage
Electrolytic Capacitor
- Electrolytic capacitors are commonly used in power supply filters, are polarized and have short life.
- They have a capacitance range of .1 Microfarad to 1.6 Farad
- Voltage range supported – 3 – 600V
- Very Poor accuracy
- Very Poor temperature stability
- Excessive leakage problem
Mica Capacitor
- Mica capacitors are very stable and very accurate
- Exhibits low loss
- Widely used in RF circuits
- They have a capacitance range of 1 pF to 0.01 Microfarad
- Voltage range supported – 100-600V
- Better leakage current
Polyester Capacitor
- Polyester capacitors also known as Mylar capacitor
- It is one of the widely used inexpensive capacitors
- They have capacitance range of 0.001 Microfarad to 50 Microfarad
- Volatge range supported is 50 – 600V
- Good accuracy and better leakage current
- Poor temperature stability
Polypropylene Capacitor
- High quality and lowest dielectric absorption capacitor
- They have capacitance range of 100pF to 50 Microfarad
- Voltage range supported is 100-800V
- High accuracy
- Exacellent temperature stability
- Better leakage current
Porcelain Capacitor
- Efficient and have long term stability
- They have capacitance range of 100 pF to 0.1 Microfarad
- Volatage range supported is 50-400V
- Good accuracy and temperature stability
- Better leakage current
Oil Capacitor
- Oil capacitors are generally used for high voltage and high current applications
- They have capacitance range of 0.1 microfarad to 20 Microfarad
- Volatge range supported is 200- 10000V
- Size is bulky
- Long life
- Better leakage current
Teflon Capacitor
- one of the high quality and lowest dielectric absorption capacitor
- They have capacitance range of 1000pF to 2 Microfarad
- Voltage range supported is 50-200V
- High accuracy
- Exacellent temperature stability
- Better leakage current
Tantalum Capacitor
- Tantalum capacitors have high capacitance per volume.
- They are small in size and have low inductance
- the have capacitance range of 0.1 Microfarad to 500 Microfarad
- Volatge range supported is 5-100 V
- Poor accuracy
- Poor temperature stability
- Widely used in aerospace, defense and communication industries
Vaccum Capacitor
- It uses high vaccum as dielectric
- It is normally used in high voltage applications such as broadcast transmitters, RF tuners and RF amplifers
- They have capacitance range of 1pF to 5000pF
- Voltage range supported is 2000 to 35000V
- Better leakage current
Capacitor selection factors
The following are some of the most important aspects to consider while selecting a capacitor:
DC Working Voltage (DCWV): This is the maximum DC voltage that a capacitor can withstand. If a larger voltage is given to the capacitor, the dielectric will break down and the capacitor will be damaged.
Polarity Markings on Capacitors: Some capacitors have polarity markings on them to show how they should be connected in a circuit. To avoid damaging the capacitor, care must be taken to ensure that the given polarity is followed.
Tolerance refers to the range of possible capacitor values. The tolerance will be indicated in addition to the nominal capacitance stated on the body.
Temperature Coefficient: This is the change in capacitance caused by temperature changes in the capacitor. It usually lowers the capacitor’s efficiency.