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Capacitors

There are many kind of capacitors, they all do same thing: store electric charge. Simplest capacitor is two conductors separated by an insulating material called the dielectric. The dielectric can be paper, plastic, film, mica, glass, ceramic, air or vacuum.

When a voltage is applied across the two plates of a capacitor, a concentrated field flux is created between them, allowing a significant difference of free electrons (a charge) to develop between the two plates.

When the voltage across a capacitor is increased, it draws current from the rest of the circuit, acting as a power load. Conversely, when the voltage across a capacitor is decreased, the capacitor supplies current to the rest of the circuit, acting as a power source.

The ability of a capacitor to store energy in the form of an electric field (and consequently is called capacitance. It is measured in the unit of the Farad (F).

1 Farad=1 F
1 Microfarad=1 uF
1 Nanofarad=1 n
i Picofarad=1 pF

Types of Capacitors

Following are some of the important types of capacitors used commonly in practical circuits.
  1. Ceramic Capacitor
  2. This is one of the most commonly and widely used capacitor in electronic components. A ceramic capacitor is a capacitor constructed of alternating layers of metal and ceramic, with the ceramic material acting as the dielectric. They are well suited for use in high frequency applications ranging up to couple of thousands of MHz. These capacitors are available from fraction of a pF to 1uF (1000000 pF)

  3. Electrolytic Capacitor
  4. Aluminum electrodes are used and they are separated by using a thin oxidation membrane. This is a most common type, polarized capacitor. Cheap, readily available, good for storage of charge. Not very accurate, leakage, drifting, not suitable for use in HF (High Frequency) circuits, available in very small to very large values in uF. The most important characteristic of electrolytic capacitors is that they have polarity. They have a positive and a negative electrode. This means that it is very important that the terminals are connected to the right poles.

  5. Tantalum Capacitors
  6. These capacitors are made of Tantalum Pentoxide. Superior to electrolytic capacitors, excellent temperature and frequency characteristics. Like electrolytic, tantalum capacitors are polarized so watch the '+' and '-' indicators. Tantalum capacitors are a little bit more expensive than aluminum electrolytic capacitors. These capacitors are very stable with temperature and frequency changes. Therefore, tantalum capacitors are used for circuits which demand high stability in the capacitance values, e.g. analog signal systems, and because the current-spike noise that occurs with aluminum electrolytic capacitors does not occur here.

  7. Metalized Polyester Film
  8. No polarity, dielectric made of Polyester.Good quality, low drift, temperature stable. Because the electrodes are thin they can be made really small. Typically used in audio and communication equipments.

  9. Trimmer Capacitors
  10. These use mostly plastic as a dielectric. The capacitance of this type of capacitors can be adjusted using a screw driver. These capacitors are adjusted at the time of manufacture of the electronic equipment.

  11. Variable Capacitors
  12. Variable capacitors are typically air-cored or sometimes uses plastic as a dielectric. Typically connected to knobs to let the user tune the capacitance, so most of them are designed to connect to a rotating knob. These capacitors are typically used in radios.

  13. Polyester Film Capacitors
  14. This capacitor uses a thin polyester film as a dielectric. Not as high a tolerance as polypropylene, but cheap and handy, temperature stable, widely used.

  15. Polypropylene Capacitors
  16. Mainly used when a higher tolerance is needed than polyester caps can offer. In these capacitors polypropylene film is the dielectric.

  17. Polystyrene Capacitors
  18. In this Polystyrene is used as a dielectric. Constructed like a coil inside so not suitable for high frequency applications. Well used in filter circuits or timing applications using a couple hundred KHz or less.

  19. Multilayer Ceramic Capacitors
  20. Dielectric is made up of many layers. Small in size, very good temperature stability, excellent frequency stable characteristics. Used in applications to filter or bypass the high frequency to ground.

  21. Silver-Mica Capacitors
  22. Mica is used as a dielectric. Used in resonance circuits, frequency filters, and military RF applications. Highly stable, good temperature coefficient, excellent for endurance because of their frequency characteristics, no large values, high voltage types available, are relatively expensive.

  23. Supercapacitor
  24. An Electric double-layer capacitor, also known as supercapacitor, supercondenser, pseudocapacitor, electrochemical double layer capacitor (EDLC), or ultracapacitor, is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors, typically on the order of thousands of times greater than a high capacity electrolytic capacitor. Whereas a regular capacitor consists of conductive foils and a dry separator, the supercapacitor crosses into battery technology by using special electrodes and some electrolyte. There are three types of electrode materials suitable for the supercapacitor. They are: high surface area activated carbons, metal oxide and conducting polymers. The high surface electrode material, also called Double Layer Capacitor (DLC), is least costly to manufacture and is the most common. It stores the energy in the double layer formed near the carbon electrode surface. To know more about supercapacitor and ultracapacitor visit below links.

    Supercapacitor overview
    Details on supercapacitor and how it works
    Manufacturer of supercapacitor

Suggested links

Types of capacitors and interesting animation of capaitor
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