Polymer film capacitors, or film dielectric capacitors or plastic film capacitors or film capacitors are generally known as power film capacitors and "film caps". These are those electrical capacitors having an insulating plastic film (dielectric).

Depending on the needed dielectric strength, the dielectric films are drawn into a much thinner thickness and are then offered with electrodes. The electrodes used in these capacitors might be metalized zinc or aluminum applied legitimately to the plastic film’s surface, or a different metallic foil. 2 of the conductive layers are winded in a cylindrical shape, generally flattened to decrease the requirement of mounting space on a printed circuit board. They may be also stacked as multiple layers to form the body of a capacitor. Along with electrolytic capacitors and ceramic capacitors, film capacitors are the most popular and common capacitors type for utilizing electrical equipment. They are utilized in several DC and AC electronics and microelectronics circuits.

Though the constructions and materials utilized for larger power film capacitors are very much the same as that of ordinary film capacitors, capacitors coming with a very high rating of power for power system applications and electrical installations are often categorized separately due to some historical reasons. Today several modern electronic equipment have got the ability to manage the level of high powers that was earlier one of the biggest constraints of components related to "electrical power". The difference between "electrical" and "electronic" rating of power has become less distinct. In the earlier time, the line of boundary between these two families was approximately 200 Volt-Ampere but the modern ones are well made to manage high power levels.

Example manufacturing process

The example discussed below describes a common assembling process stream for wound metalized plastic film capacitors.

• Metallization and Film stretching – To uplift the value of capacitance of the capacitor, the plastic film is drawn utilizing an exceptional expulsion procedure of bi-pivotal extending in transverse and longitudinal direction.
• Film slitting - The mother folds are cut into little portions of plastic film in the necessary width.
• Winding – 2 films are then made to roll together into a cylindrical winding.
• Flattening – The winding is then generally flattened into the shape of an oval by utilizing mechanical pressure.
• Application of Metallic Contact layer – A liquefied contact metal like zinc or tin is used to cover up the projecting end electrodes.
• Healing – Healing is done by applying an absolutely adjusted voltage over the electrodes of the winding with the goal that any current deformities will be "consumed with extreme heat".
• Impregnation – For protection from moisture, the winding is made to impregnate using silicone oil (insulating fluid).
• Attachment of terminals – The capacitor’s terminals are welded on the end metal contact layers.
• Coating – Succeeding the attachment, the body of the capacitors is dunked into a protective coating.
• Electrical final test – Before the use of every capacitor it is important to test it for the desired parameters, like, Impedance, Capacitance or dissipation factor.

Brands that manufacture film capacitors are Kemet, Panasonic, and EPCOS. Make sure to follow them using the links as provided.

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A varistor is an electrical device having an electrical resistance that differs with the potential applied to it. A varistor is popularly known as Voltage Dependent Resistor (VDR). It possesses a non-ohmic and non-linear Current-Voltage characteristic which is equivalent to a diode. Unlike the diode, it has a similar characteristic for the flow of both directions of current. Customarily, varistors were made by joining 2 rectifiers i.e. either the germanium-oxide or the copper-oxide rectifier in a configuration that is anti-parallel. The electrical resistance of the varistor is high at low voltage but as the voltage increases the resistance decreases. The varistors that are used presently are fundamentally dependent on sintered ceramic metal-oxide materials. On a microscopic scale, it shows directional behavior. This category is popularly known as MOV or Metal Oxide Varistor.

Varistor serves as a compensation and a control element in the electrical circuit either to defend against excess voltage or to offer optimal operating conditions. When utilized as defending devices, they shunt the current established by the exorbitant voltage away from touchy segments when activated.

Composition

As said earlier, the newest form of varistor that is used is the Metal Oxide Varistor. This kind of varistor is constituted by a ceramic mass of zinc oxide grains with metal oxides (like a small quantity of cobalt, bismuth, manganese oxides) placed in the middle of 2 metal plates, which comprise the device’s electrodes. A diode junction is formed between each grain and its neighbor.

When the electrodes are given a small potential difference then only a small amount of current flows through the diode junction which is a result of reverse leakage. On the other hand when a large voltage is applied on the electrodes a large amount of current flows, as the diode junction separates itself because of the combination of electron tunneling and thermionic emission. The consequence of the above-said behavior is a non-linear Current-Voltage characteristic where the MOV possesses a low resistance at high voltage and high resistance at low voltage.

Voltage Rating

MOVs are categorized by the range of voltage that they can endure without damage. The other parameter is the varistor’s breakdown voltage, maximum current, energy rating in joules, response time and operating voltage.

The rating of energy is regularly characterized utilizing institutionalized transients like 10/1000 microseconds or 8/20 microseconds. Here 10 microseconds are the front time of the transient and 1000 microseconds is the time of half value.

Capacitance

The range of capacitance for varistors which are consumer-sized i.e. 7 to 20mm in diameter is from 100pF to 2,500pF. Varistors that are used in micro electric protection have low capacitance like around 1pF. You can get this kind in cellular phone. These varistors having low capacitance cannot withstand the flow of a large amount of current as the PCB mount size is compact.

Response time

The response time of the MOV isn't institutionalized.

Hope you liked the article on Varistors. Brands that make them are Littelfuse, EPCOS, Panasonic. You can refer to them using the links as provided. Thank you for reading.

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A Gas Discharge Tube or a Gas Plasma Arrestor is an arrangement of gas in an electrode inside a temperature-resistant and an insulating envelope. Gas Discharge Tubes results in the phenomena linked with the electric release in gases and gets initiated by converting the gas into ions with an applied voltage adequate to cause electrical conduction by the basic principle of the Townsend discharge. A gas discharge lamp is an electric light that takes the help of Gas Discharge Tubes; these consist of neon lights, metal-halide lamps, fluorescent lamps, and sodium-vapor lamps. Some specific gas discharge tubes like thyratrons, ignitrons and krytrons support as switching devices.

The required voltage for initiating and sustaining the discharge completely depends on the pressure, the amount of gas-filled in the tube as well as its geometry. Though the envelope is made up of glass, military tubes use glass-lined metal most often while power tubes use ceramics frequently.

As said earlier, the principle mechanism is the Townsend discharge. It is defined as the sustained increase of electron stream by ion impact when a critical estimation of the strength of the electric field for the thickness of the gas achieved. With the increase in the electric field, various discharge phases are encountered. The gas utilized significantly impacts the parameters of the cylinder. The breakdown potential difference relies on the distance between the electrodes and the composition of gas inside the tube.

Gas Used

• Hydrogen – It is used in tubes that require fast switching.
• Deuterium – It is used in neutron generator as well as UV lamps for UltraViolet spectroscopy.
• Noble Gases – It is used for several purposes, from switching to lightning.
• Elemental Vapors – Mercy vapors is used in ignitors, mercury-arc valves etc; Sodium vapors in sodium-vapor lamps; Sulfur vapor in sulfur lamps.

Gas Pressure

The gas pressure is kept between 0.001 and 1,000 Torr. But generally, it is kept between 1 to 10 torr. Factors that affect the gas pressure are as follows:

• Sputtering of cathode – With an increase in pressure, it gets reduced.
• Ignition Voltage or the Breakdown Voltage
• Backfire Voltage
• Operating Voltage
• Current Density
• Lifetime of the tube – Tubes having lower pressure have a short duration of life because of the gas consumption.

Gas Purity

To maintain the desired properties it is important that the gas present inside the tube needs to be kept pure; even a small quantity of impurities can significantly change the values of the tube; the presence of gases that are non-inert results in the increment of burning as well as the breakdown voltage. One can get to know the presence of impurities inside the tube by experiencing the change in the color of the gas glowing. Leakage of air inside the tube results in the introduction of oxygen, which is exceptionally electronegative and represses the generation of electron avalanches. This leads the discharge to look milky, reddish or pale. Traces of mercury vapors gleam pale blue, darkening the original gas shading. To forestall outgassing of the components of the tube during the process, a bake-out is required before loading up the tube with gas and fixing it.

This was a brief idea about the Gas Discharge Tube. We hope that you liked it. Brands that make Gas Discharge Tubes are Bourns, Littelfuse, and EPCOS. Make sure to check them out.

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