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Types of Capacitors and their Construction

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Ceramic capacitor

These capacitors are used in everyday products ranging from audio to RF. Their values range from a few picofarads to around 0.1 microfarads. These act as a dielectric and have a fixed value always. It is built of two or more alternating layers of ceramic and a metal layer acting as electrodes in the capacitor. The arrangement of the ceramic material expresses the electrical behavior and application. Ceramic capacitor types are by far the most commonly used type of capacitor being cheap and reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use. In view of their constructional properties, these capacitors are widely used both in leaded and surface mount formats. Ceramic capacitors can be made to work with voltages in the range of 2kV up to 100 kV. Ceramic capacitors rated for operation at 175°C. This is unique as the defined temperature coefficient is ±15% from -55°C to +125°C the maximum operating temperature is 175°C. These capacitors are indeed suitable for PSU (power supply unit) as they are used in everyday PSU’s.

Electrolytic capacitor

Aluminum electrolytic capacitors are created from two foils and a paper spacer soaked in electrolyte. One out of the two aluminum foils are covered with an oxide layer, and the foil acts as the anode, while the uncoated one acts as a cathode. Electrolytic capacitors are capacitors that are polarized. They can offer very high capacitance values usually higher than 1µF, and are most widely used for low frequency applications – PSU’s, decoupling and audio coupling applications as they have a limited frequency if they are around 100kW. These capacitors are cost efficient and can easily provide a larger capacitance per volume than different types of capacitors. This gives a range of different uses where high currents or low frequencies are involved. Aluminum electrolytic capacitors are usually used in applications such as audio amplifiers of all types (hi-fi to mobile phones) and in PSU. These capacitors have been around for many years. Its history can be traced back to the very early days when radio was coming into use. The typical temperature range for aluminum electrolytic capacitors is –40 ?C to 85 ?C or 105 ?C. Electrolytic Capacitance temperature differs from about +5% –40% over the range with the capacitance loss all at cold temperatures. Capacitors rated –55 ?C generally only have –10% to –20% capacitance losses at –40 ?C. Ten SMD electrolytic capacitors are marked with the value and working voltage. One of the methods to calculate the working voltage is to include their value in microfarads (m F), and another is to use a code. Using the first method a marking of 33 6V would indicate a 33 mF capacitor with a working voltage of 6 volts.

Mica capacitor

Silver mica capacitors are made by sandwiching mica sheets coated with metal on each side. This assembly is then covered in epoxy to protect it from the environment. Silver mica capacitors are not very popular, but they still offer very high levels of stability, low loss, and accuracy where space is not important. Mica capacitors have a relatively small capacitance value: usually between a few pF, up to a few nF. The largest capacitance mica capacitors can reach values of 1µF, however these are not common. The two important reasons for the decline in the use of these capacitors are their size, resulting from the materials used and their construction. The cost of silver mica capacitors is also higher than many other types that can often be used these days. The high cost of these results in poor efficiency of businesses that may use these. Mica capacitors are mostly rated for voltages between 100 and 1000 volts, although there are special high-voltage mica capacitors designed for radio frequency transmitter use which are rated at up to 10 kV. The average temperature coefficient is around 50 ppm/°C but this may vary dependant on the type of mica capacitor it is. This may not be suitable for a PSU as they are only used in RF transmitters nowadays. The minimum tolerance for silver mica capacitor values can be as low as ±1%.

Plastic capacitors

These capacitors are mainly known as Film/foil capacitors or metal foil capacitors. These are made with two plastic films as the dielectric. Each layer is wrapped with a thin metal foil, usually aluminum which works as electrodes. Advantages of this construction type are easy electrical connection to the metal foil electrodes, and its ability to handle high current surges. The capacitances from these capacitors range from below 1nF to 30µF. their working voltages are as low as 50V, but can go up to above 2kV. The working temperature for a plastic capacitor is usually +70°C. This workable temperature makes this capacitor suitable for PSU.

Paper capacitors

Paper capacitor uses paper as the dielectric to stockpile electric charge. It includes aluminum sheets and paper sheets. These sheets are soaked with oil or wax for protection of the capacitor. Paper capacitors have a capacitance range of 500pF to 50µF and a high working voltage. Because of this reason they are used for high voltage equipment. The working voltage of a paper capacitor does not usually go above 600 volts. The downside of paper capacitors is that they have high leakage rates, making them unsuitable for AC coupling, and their tolerances are no better than 10% to 20%, making them unsuitable for precision timing circuits.

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