Features: - Longer service life - Low maintenance - Highly demanded Metal Oxide Varistors Littelfuse Inc. Our Metal Oxide Varistors are used for protecting circuits from excessive transient voltages in perfect way. In contrast to a diode however, it has the same characteristic for both directions of traversing current. D. Månsson, R. Thottappillil, "Comments on ‘Linear and nonlinear filters suppressing UWB pulses’", IEEE Transactions on Electromagnetic Compatibility, vol. A Metal Oxide Varistor (MOV) is an electronic device that protects an appliance’s power supply from voltage spikes and surges in the AC power line. The Metal Oxide Varistor or MOV is a voltage dependent, nonlinear device that provides excellent transient voltage suppression. This is useful for controlling how much electric current travels to certain parts of electronic devices. A Metal Oxide Varistor or MOV is the blue or orange-colored circular component that you can commonly spot on the AC Input side of any Power Supply Circuit. Cautions and warnings General 1. significantly exceeds the manufacture's "Absolute Maximum Ratings"). Crosby (, AT&T Bell Laboratories, Technical Staff, R.F. When a small voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. Thermal protective Metal Oxide Varistors (TMOVs) are designed to meet abnormal overvoltage requirements of UL 1449. The Metal Oxide Varistor is designed to protect various types of electronic devices and semiconductor elements from switching and induced lightning surges. Now that we have discussed what a MOV is and how it is used to protect your circuit from voltage spikes, let’s conclude the article with few design tips which will come in handy when you are designing your circuit. [13] Eventually, it proceeds into a shorted circuit condition as the energy discharges create a conductive channel through the oxides. So if you find a MOV damaged in any power circuit it is possibly because the circuit went through many voltage spikes. MOVs are specified according to the voltage range that they can tolerate without damage. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. This property is useful in protecting the circuits from high voltage spikes; hence they are mostly used as surge protectors in an electronic network. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered. So, an MOV is a large number of diodes connected in series. When we increase the applied voltage in the range of 200-250V, the resistance decreases and the varistor starts conducting and a few micro-amperes of current starts flowing, which doesn’t make much difference in the curve. Let’s discuss more on how MOV working in a circuit. Metal Oxide Varistor – Basics MOV is the most commonly used type of varistor. Where Xc is the capacitive reactance and f is the frequency of the AC supply. Package: 14mm disc, radial leads. Energy rating is often defined using standardized transients such as 8/20 microseconds or 10/1000 microseconds, where 8 microseconds is the transient's front time and 20 microseconds is the time to half value. Rey (ed.). These varistors were constructed by layering an even number of rectifier disks in a stack and connecting the terminal ends and the center in an anti-parallel configuration, as shown in the photo of a Western Electric Type 3B varistor of June 1952 (below). Other important parameters are the varistor's energy rating in joules, operating voltage, response time, maximum current, and breakdown (clamping) voltage. 250VAC 330VDC 72 Joules. 3, pp. A MOV inside a transient voltage surge suppressor (TVSS) does not provide complete protection for electrical equipment. Basic operation, electrical characteristics, and applications will be discussed. It is the steady-state DC voltage to which the typical leakage current will be less than the specified value. However, they can handle significantly higher fault currents and withstand multiple high-voltage hits (for example, from lightning) without significant degradation. This type is commonly known as the metal-oxide varistor (MOV). Metal Oxide 680V Film 14D-680K Piezoresistor Zinc Oxide Varistor Movs Various blue zinc oxide resistors for lightning protection Metal Oxide Varistor For Protect Semiconductor Devices of 14D MOV 14D102K Varistor for indus protection Geiger in 1927.[2]. Multi-layer varistor (MLV) devices provide electrostatic discharge protection to electronic circuits from low to medium energy transients in sensitive equipment operating at 0-120 volts dc. Metal oxide varistor is a voltage dependent resistor. Metal Oxide Varistors (MOV, 's) are epoxy encapsulated zinc oxide discs with radial or axial leads. The final and most important step of all is selecting the model that can provide the required clamping voltage. A varistor is an electronic component with an electrical resistance that varies with the applied voltage. It is also a nonlinear device and provides very good transient voltage surge protection. The ceramic powders of the metal oxides are kept intact between two metal plates called the electrodes. Metal oxide Varistors (MOV): Since SiC Varistors had some serious drawbacks, another type of Varistors the metal oxide Varistors were developed. The curve will look similar to the characteristic curve of two Zener diodes connected back-to-back. Grondahl and P.H. MOVs degrade from repeated exposure to surges[23] and generally have a higher "clamping voltage" so that leakage does not degrade the MOV. So, an MOV is a large number of, Let’s look into the different electrical characteristics of MOV to better understand the, The MOV can operate in both the directions, hence it has symmetrical bi-directional characteristics. Lower Voltage Varistor for Surge Protector D28 Characteristic: 1. Manufacturer's life-expectancy charts relate current, severity, and number of transients to make failure predictions based on the total energy dissipated over the life of the part. If excessive current is conducted by a MOV, it may fail catastrophically, keeping the load connected, but now without any surge protection. Metal Oxide Varistor (MOV) Data Sheet Features Wide operating voltage (V 1mA) range from 18V to 1800V Fast responding to transient over-voltage Large absorbing transient energy capability Low clamping ratio and no follow-on current Meets MSL level 1, … MOV a.k.a varistors is commonly used along with fuse in parallel to the circuit that is to be protected. But not like a potentiometer, its resistance will change automatically depending on its voltage. The sub-nanosecond MOV response claim is based on the material's intrinsic response time, but will be slowed down by other factors such as the inductance of component leads and the mounting method. This thermal runaway is due to a lack of conformity in individual grain-boundary junctions, which leads to the failure of dominant current paths under thermal stress when the energy in a transient pulse (normally measured in joules) is too high (i.e. Guangdong Thermistor-Mov Electronics Co., Ltd. founded in 2011,A company devoted to the research and development of protective electronic components and Production of private high-tech enterprises. The accumulation of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs.[10]. 671-672, Aug. 2005. http://www.littelfuse.com/~/media/electronics_technical/application_notes/varistors/littelfuse_the_abcs_of_movs_application_note.pdf, https://www.nist.gov/pml/div684/upload/Lower_not_better.pdf, http://www.research.usf.edu/dpl/content/data/PDF/05B127.pdf, "Metal Oxide Varistor (MOV) – Electronic Circuits and Diagram-Electronics Projects and Design", https://www.gegridsolutions.com/app/DownloadFile.aspx?prod=surge_arresters&type=1&file=7, "Detailed Comparison of Surge Suppression Devices", "UL1449 3rd Edition Overview - Surge Protection - Littelfuse", https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/Electrical/RFDataAssessmentforElectricalSurgeProtectionDevices.ashx?la=en, "Metal Oxide Varistors | Circuit Breakers Blog – Expert Safety and Usage Information", http://www.esdjournal.com/techpapr/Pharr/INVESTIGATING%20SURGE%20SUPPRESSOR%20FIRES.doc, https://en.wikipedia.org/w/index.php?title=Varistor&oldid=996689580, Articles with unsourced statements from September 2015, Articles with unsourced statements from December 2020, Articles with unsourced statements from September 2014, Creative Commons Attribution-ShareAlike License, This page was last edited on 28 December 2020, at 02:51. Multilayer Varistors They have peak current ratings from about 20 to 500 amperes, and peak energy ratings from 0.05 to 2.5 joules. The radial leaded disc type is the most common version. The MOVs can be used for protecting various types of equipment from different types of faults. Calculate the peak transient current or the surge current through the varistor. There will not be any capacitance effect when the voltage reaches the clamping voltage as the varistor starts its normal functioning. LITTELFUSE METAL OXIDE VARISTORS For quantities greater than listed, call for quote. Let’s look into the different electrical characteristics of MOV to better understand the MOV properties. This value can be determined by running all the devices within a specific controlled circuit with specific values. [14] Other applications, such as power transmission, use VDRs of different construction in multiple configurations engineered for long life span.[15]. It is the amount of current drawn by the varistor when it is operating below the clamping voltage that is when there is no surge in the network. Since the varistor is connected parallel with the device to be protected the varistor leakage resistance drops rapidly when the frequency increases. MOVs are also used in some cases like microwave mixers for modulation, detection and also frequency conversion which aren’t the most known applications of MOV. There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. [1] Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non-ohmic current–voltage characteristic that is similar to that of a diode. The term MOV or Metal Oxide Varistor is a variable resistor. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Metal oxide varistors consist of approximately 90% zinc oxide as a ceramic base material plus other filler materials for the formation of junctions between the zinc oxide grains. Wire Core SMD Design 2410 Surface Mount Fuses 6125 Metric F1A250V For Overcurrent Protection Get Best Price. Metal Oxide Varistor – Basics Definition: The most commonly used form of a varistor is the Metal Oxide Varistor, which is also a voltage dependant and non-linear resistor connected to the electrical and electronic circuits to protect against the switch, lightning surges, and to achieve high suppression of transient voltage. Once the voltage across the varistor increases, the resistance will be decreased. Model Size Disc Dia. The copper-oxide varistor exhibited a varying resistance in dependence on the polarity and magnitude of applied voltage. New. Depending on the level of conducted current, dissipated heat may be insufficient to cause failure, but may degrade the MOV device and reduce its life expectancy. The word varistor is short for variable resistor. When you apply a small voltage to the electrodes a reverse leakage current appears across the junctions. They are voltage dependent, nonlinear devices that provide transient... Metal oxide varistors, also known as MOVs are one of the most common types of varistors. This tutorial will provide an introduction to Metal Oxide Varistors and MOV product offerings from Littelfuse. If the frequency increases the leakage current will also increase as shown in the non-conducting leakage region of the V-I characteristics curve discussed above. MOUSER STOCK NO. For higher frequencies, such as radio communication equipment, a gas discharge tube (GDT) may be utilized. The MOVs are mostly used in surge-protected adaptors and strips, Power supplies that are connected to the mains, Telephone and other communication lines, Industrial high energy AC line protection, data systems or power systems, protection of general electronic equipments such as cell phones, digital cameras, personal digital assistants, MP3 players and notebook computers. [6], Another type of varistor was made from silicon carbide by R. O. Grisdale in the early 1930s. Although diodes do not have as much capacity to conduct large surges as MOVs, diodes are not degraded by smaller surges and can be implemented with a lower "clamping voltage". The MOVs should always be connected in parallel for increased energy handling capability and if you want to get higher voltage rating you should connect it in series. [3] It was constructed from a small copper disk, of which one side was formed a layer of cuprous oxide. Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. It is the time at which the varistor starts conducting after the occurrence of the surge, in many instances, there isn’t an exact response time. The maximum amount of energy that the MOV can dissipate for a specified peak pulse time of a specific waveform during a surge. Although the device can handle the surge current the manufacturers recommend replacing the device if there is an occurrence of surge current. This curve can be used to understand how much resistance will be across your MOV at different voltage levels. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics. The randomness of orientation of ZnO grains in the bulk of this material provided the same voltage-current characteristics for both directions of current flow. Myers, L.S. Metal-oxide varistors (MOVs) are available in a variety of form factors and sizes for a broad range of applications. Normally, the MOV has very high electrical resistance. The manufacturers will specify the maximum AC Voltage that we can provide to the device in the product description itself. All rights reserved, Metal Oxide Varistor (MOV) – Working, Application, Design Tips and Selection Guide, A Metal Oxide Varistor or MOV is the blue or orange-colored circular component that you can commonly spot on the AC Input side of any, MOV is simply a variable resistor, but unlike, If the voltage across it increases the resistance decreases and vice versa. In the early 1970s, Japanese researchers recognized the semiconducting electronic properties of zinc oxide (ZnO) as being useful as a new varistor type in a ceramic sintering process, which exhibited a voltage-current function similar to that of a pair of back-to-back Zener diodes. This arrangement provides low resistance to current flowing from the semiconducting oxide to the copper side, but a high resistance to current in the opposite direction, with the instantaneous resistance varying continuously with the voltage applied. All series are full compliance with UL, VDE, CQC certificate The boundary between each grain and a neighbor forms a diodejunction, which allows current to flow in only one direction. They have been intensively used in high power, high voltage applications. When the transient voltage across the varistor is equal to or higher than the clamping voltage the resistance of the varistor becomes small which turns it into a conductor due to the avalanche effect of the semiconductor material. Continuous Voltage Max. [citation needed], Composition, properties, and operation of the metal-oxide varistor, Comparison to other transient suppressors, American Telephone & Telegraph; C.F. The above curve is the voltage and the resistance curve of a MOV, at the normal voltage the resistance is at its peak, but as the voltage increases the resistance of the varistor decreases. Metal Oxide Varistor B72230M ***M401 Thermal Protective Varistor MT30*** PPD VAR PD 2020-01-10 Please read Cautions and warnings and Page 7 of 10 Important notes at the end of this document. The Metal Oxide Varistor can be considered as another type of variable resistor that can vary its resistance based on the applied voltage across it. This type contains a ceramic mass of zinc Varistors can fail for either of two reasons. Low-cost versions may use only one varistor, from the hot (live, active) to the neutral conductor. It provides very good voltage transient protection and is now quite popular. It was used to guard telephone lines from lightning.[7]. 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