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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TRIAC stands for Triode for Alternating Current. It is a genericized trademark for an electrical device that has 3 terminals and when triggered conducts electrical current in both directions. Its conventional name is bilateral triode thyristor or bidirectional triode thyristor. A thyristor is comparable to a relay where a small voltage induced current can control a lot bigger current and voltage.

Thyristors can be said to be the superset of TRIACs. TRIACs are also relatable to SCRs (Silicon Controlled Rectifiers). TRIACs and SCRs can be distinguished in one characteristic feature i.e. the first one is bidirectional, the flow of current is in both the direction but the later one allows the flow of current in only one direction. Generally, the TRIACs get initiated by the consequence of a positive or a negative potential to the gate but the SCR needs only a positive potential. Once activated, SCRs and TRIACs keep on conducting, regardless of whether the current in the gate ceases, until the principle current dips under a specific level called the holding current.

The GTOs or Gate Turn-Off Thyristors are the same as TRIACs but when the signal in the gate ceases, it provides much more control by turning OFF.

The bidirectional feature of this equipment makes it a good switch for AC or Alternating Current. A trigger, when applied in the main circuit at AC's controlled phase angle, permits control of the average current streaming into a load. This feature is popularly used for managing the speed of dimming lamps, electric heaters, and universal motor.

Factors that affect the working of TRIAC

TRIACS, unlike SCRs, needs appropriate enhancement for its legitimate working. There are some inherent drawbacks like TRIACs Backlash effect, Rate effect, etc. Thus designing it requires proper case.

• Backlash Effect

This effect is one of the most acute Control Hysteresis that grows in the speed control or the lamp control circuits with the help of a Potentiometer for controlling the Gate current. The glowing brightness of the lamp gets a minimum when the potentiometer's resistance increases to the maximum. The lamp never gets ON when the pot is turned back until and unless the resistance of the pot drops to its lowest value. The main reason behind this is the discharging of the TRIAC's capacitor. The triggering pulse is provided to the gate by a Diac. Triac releases through the Diac, generating the Backlash effect.

• Rate Effect

The Rate effect generally takes place due to high inrush current when overwhelming inductive loads switch on and also because of a momentary variation in frequency, voltage or current in the mains.

• Effect of RFI

RFI or the Radio Frequency Interference seriously influences the working of Triacs. Depending on the resistance and the supply voltage of the load, the load current is seen to sharply increase from 0 to a high value whenever the TRIAC switches on the load. This forms pulses of RFI.

This was all regarding TRIACs. Brands that manufacture it are Littelfuse, STMicroelectronics, and NXP. We hope that you liked the article. If you want to refer to the brands then just follow the links as given.

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The word solenoids got its birth from the Greek word “solen” which signifies a pipe or a channel. The second part of the name is coined from “edios” which is also a Greek word signifying an outline. Basically, it's an electrical component having a pipe-like structure. There are a large number of solenoid designs available that are used in many devices. Every one of them has their very own characteristics that make it valuable in the equipment they are used. Though they are available in several forms still all of them have the same working principle.

A solenoid is a simple electrical component that consists of a metallic core with a coil of wire winded around it. Whenever a current is passed through the solenoid, a continuous and uniform magnetic field is generated inside it. One of the most important things to note about a solenoid that produces a uniform magnetic field is that if its length is immeasurable then the strength of the field is the same throughout the element. Thus a solenoid can be used to do a large amount of work with a minimal amount of force generated due to an electric current.

Types of solenoids

As said earlier, there are several solenoids present in the market. They come in different design, materials and has diverse functions. Let's have a look at some of them.

• Linear Solenoid

Linear solenoids are enabled of using a push or a pull force on mechanical gadgets. It has found its use in diverse devices. For example, the started device of an automobile which has a motor in it. The best place where this solenoid is popular is in the electric lock. When the jolt is appended to the electric lock on an entryway, it can promptly secure the door by holding up a great deal of savagery and violence.

• DC C-Frame Solenoid

A DC C-Frame solenoid operates on a single frame, shaped like the letter ‘C’, which is winded by the coil. Though they are made to be used in a DC configuration but still can be designed to work with AC power. This type of solenoid has a broad range of use in various applications.

• DC D-Frame Solenoid

A DC D-Frame solenoid comes with 2-piece frames that are winded around by the coils. Like the DC C-Frame solenoids, these solenoids can also be formed into AC alternatives. These types of solenoids are mostly used in industrial applications.

• AC Laminated Solenoid

An AC laminated solenoid is popular for their force that they generate during their first stroke. You can get them in a number of different configurations and specifications. These categories of solenoids will deliver a perfect buzz when they are being utilized.

• Rotary Solenoid

Unlike other solenoids as discussed above, it has got a disc in it. The body consists of grooves and the presence of ball bearing makes motion easier. Initiating the solenoid makes the core to get drawn back into the coil. The force that is generated is then converted into rotational force which moves the disc. Nowadays this device is used in industrial environments.

We hope that you have got a good idea of solenoids. Brands that produce solenoids are Crouzet, TE Connectivity, and Littelfuse. Refer to them using the links as provided. Thanks for reading.

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A fuse is a device which helps in defending electrical circuit from the flow of excessive current. It contains a strip of wire or metal which melts itself down when a current more than it's limiting value passes through it. In the absence of fuses, there are chances of the passage of a large amount of current to the entire circuit which may lead to an electrical fire, thus, resulting in the damage of foundations as well as equipment. Keeping this in mind we have brought this article to make people well accustomed to Electrical and Industrial fuses such that they can be used at their best.

Electrical Fuses

Today each and every building and house are equipped with electrical fuses for their safety in terms of the use of electricity. Two of the major reason behind this is:

• They do not require human support and is automatic
• The prices of these fuses are quite affordable

Electrical fuse can be divided into two types according to the kind of current flowing through it. They are as follows:

• DC Fuses: DC fuses are those electrical fuses that are compatible with electrical circuits having DC. As direct current flows in one direction and never gets a zero value, it is tough to interrupt it. Thus enough power is required to cease the current passing through the circuit.
• AC Fuses: AC fuses are those electrical fuses that are compatible with electrical circuits having AC passing through them. Alternating current inverts its progression of direction and accomplishes zero value during its oscillation period. Thus, it’s quite easy to stop the flow of Alternating current when it is flowing through the circuit.

Industrial Fuses

Industrial Fuses are utilized for protecting branch circuits and motors where higher amperes and Voltage ratings are a necessity. The electrical systems which are used in today’s world have a high chance of destruction during the occurrence of a short circuit. Having a proper fusing is a must. Just 1 cycle of faulty current can vaporize insulation and wiring, explode wires as well as warp bus bars. To defend against them, one needs to have an idea about 4 things: amperage, voltage, current-limiting ability and interrupt capacity.

• The current-carrying capacity or an amperage rating should be much close to the full-load current of the circuit. Fuses that are oversized do not offer good protection while undersized ones blow up easily.
• The voltage rating may either exceed or match up with the circuit’s voltage.
• The current-limiting ability is the proportion of the amount of current the device will "let through" the framework. Indeed, even a solitary cycle of 200,000A current will harm any establishment severely. When the currents are high these current-limiting fuses respond much faster. The current-limiting ability of a fuse is communicated as number i.e. as "K1", "K2", "K3" and likewise. Here K3 is less current-limiting than K1.
• Interrupt capacity is defined as the total amount of current the fuse can interrupt without any damage. Many fuses have them of 200,000A because the fault current in industries is that high.

Hope that you liked going through the above article. Brands that make Electrical and Industrial Fuses are Eaton, Siemens, and Littelfuse. Make sure to follow them using the links as provided.

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