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). It is used to protect the circuit from high voltage spikes by varying its â¦ The Capacitance value is not a big deal when it comes to a DC circuit since the capacitance will remain almost constant until the voltage of the device reaches the clamping voltage.  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. However the duration of the current handling feature of an MOV may be limited to a few microseconds only, which means the activation of an MOV under such sever situations can not be more than a few microseconds, otherwise it could burn the device and damage it permanently. Features: - Longer service life - Low maintenance - Highly demanded 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. According to ohms law, the V-I characteristic curve of a linear resistor is always a straight line, but we can’t expect the same in terms of a variable resistor. These components utilize silicon carbide (SiC). Geiger in 1927.. 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. Unfortunately, these devices may have higher breakdown voltages and longer response times than varistors. Components101 is a resource dedicated for electronics design engineers, covering product news, analysis and articles on latest electronics components. A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Once the rising voltage hits the rated or clamping voltage (250V) the varistor becomes highly conductive, about 1mA of current starts flowing through the varistor. Similar to all the above properties you should also determine the power dissipation requires and select the varistor that has a power rating equivalent or ideally exceeds the power handling required by the event that the circuit may produce. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics. , Composition, properties, and operation of the metal-oxide varistor, Comparison to other transient suppressors, American Telephone & Telegraph; C.F. Low-cost versions may use only one varistor, from the hot (live, active) to the neutral conductor. It was used to guard telephone lines from lightning.. 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. The MOVs can only be used for short surge protection, they can’t handle sustained surges. 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 typical response time is always fixed as 100nS. 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.. MOV's are mid-range devices used to protect small machinery, power sources and components. 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. The maximum amount of energy that the MOV can dissipate for a specified peak pulse time of a specific waveform during a surge. In contrast to a diode however, it has the same characteristic for both directions of traversing current. Let’s look into the different electrical characteristics of MOV to better understand the MOV properties. It is a Professional Manufacturers of (R&D) and Production of high performance metal oxide Varistors, ntc Thermistors. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, resulting in a large current flow. Under normal utility voltage conditions, this is not a problem. Metal Oxide Varistor is a voltage-dependent resistor that is made with ceramic powders of metal oxides like Zinc oxide and some of the other metal oxides like oxides of cobalt, manganese, bismuth, etc. 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. This property is very useful for â¦ When you apply a small voltage to the electrodes a reverse leakage current appears across the junctions. Varistors with internal thermal protection are also available. Thermal protective Metal Oxide Varistors (TMOVs) are designed to meet abnormal overvoltage requirements of UL 1449. 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. The curve will look similar to the characteristic curve of two Zener diodes connected back-to-back. Become the leading quality in the industry. The final and most important step of all is selecting the model that can provide the required clamping voltage. When it comes to application, the MOVs can be used in circuits where ever there is a risk of a surge or voltage spikes. Copyright 2020 © Components101. Find out the amount of energy absorbed by the varistor in case of a surge. Varistors can fail for either of two reasons. The Energy is usually expressed in standard transient x/y where x is the transient rise and y is the time to reach its half peak value. , While a MOV is designed to conduct significant power for very short durations (about 8 to 20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. It is the maximum RMS line voltage that can be given to the varistor constantly, the maximum RMS value should be chosen to be slightly above the actual RMS line voltage. 1 2 10-D Series Certified Model No. The MOV can operate in both the directions, hence it has symmetrical bi-directional characteristics. Once the voltage across the varistor increases, the resistance will be decreased. Typical capacitance for consumer-sized (7–20 mm diameter) varistors are in the range of 100–2,500 pF. Features include high energy absorption and surge load capabilities, low leakage currents, self-protection under abnormal overvoltage conditions, multilayer structures, lead free plating terminal electrodes and large electrostatic resistance. If the frequency increases the leakage current will also increase as shown, You should know about the various numbers of parameters of a MOV to choose the right device for your pieces of equipment. A MOV consist of approximately 90% of Zinc oxide â¦ A catastrophic failure occurs from not successfully limiting a very large surge from an event like a lightning strike, where the energy involved is many orders of magnitude greater than the varistor can handle. Note: Line voltage operation. In particular, it provides no protection from sustained over-voltages that may result in damage to that equipment as well as to the protector device. A varistor provides no equipment protection from inrush current surges (during equipment startup), from overcurrent (created by a short circuit), or from voltage sags (brownouts); it neither senses nor affects such events. The manufacturers will specify the maximum AC Voltage that we can provide to the device in the product description itself. Here the body is made of a metal oxide, mostly Zinc Oxide grains. MOVs tend to be more suitable for higher voltages, because they can conduct the higher associated energies at less cost.. Properly designed TVSS devices must not fail catastrophically, resulting in the opening of a thermal fuse or something equivalent that only disconnects MOV devices.  It was constructed from a small copper disk, of which one side was formed a layer of cuprous oxide. This is a type of spark gap that may use air or an inert gas mixture and often, a small amount of radioactive material such as Ni-63, to provide a more consistent breakdown voltage and reduce response time. The below image shows how to use, The grains of metal oxides create a diode junction between each immediate neighbor. Modern varistors are primarily based on sintered ceramic metal-oxide materials which exhibit directional behavior only on a microscopic scale. Clamping Voltage (8 x 20µs) RMS But not like a potentiometer, its resistance will change automatically depending on its voltage. Metal Oxide Varistorï¼TVR-D Series Disc Type Varistor for Surge Protection (High Surge Series) THINKING ELECTRONIC INDUSTRIAL Co., LTD. 57 www.thinking.com.tw 2018.12 All specifications are subject to change without notice. Metal Oxide Varistor â Basics MOV is the most commonly used type of varistor. Package: 14mm disc, radial leads. 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. 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. This ration will be included in their voltage values, in some instances, if you prefer to achieve extremely low leakage current despite the lowest protection level possible you can use the varistor with higher operating voltage. There will not be any capacitance effect when the voltage reaches the clamping voltage as the varistor starts its normal functioning. When it comes to AC circuits the capacitance of the MOV might affect the overall body resistance of the MOV which causes leakage current. It is also a nonlinear device and provides very good transient voltage surge protection. It is the steady-state DC voltage to which the typical leakage current will be less than the specified value. As these pulses occur, the "clamping voltage" it provides during each event decreases, and a varistor is typically deemed to be functionally degraded when its "clamping voltage" has changed by 10%. 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. The Western Electric type 500 telephone set of 1949 introduced a dynamic loop equalization circuit using varistors that shunted relatively high levels of loop current on short central office loops to adjust the transmission and receiving signal levels automatically. For historical reasons, many MOVs have been incorrectly specified allowing frequent swells to also degrade capacity. Metal-Oxide Varistors (MOVs) Radial Lead Varistors > LA Varistor Series Should transients occur in rapid succession, the average power dissipation is the energy (watt-seconds) per pulse times the number of pulses per second. The Metal Oxide Varistor or MOV is a voltage dependent, nonlinear device that provides excellent transient voltage suppression. The term MOV or Metal Oxide Varistor is a variable resistor. Whenever the device experiences a surge the rated clamping voltage decreases, the variation in the voltage after the surge is called the surge shift. When a high current passes through a MOV, its resistance value decreases and acts as a short circuit. The boundary between each grain and a neighbor forms a diodejunction, which allows current to flow in only one direction. It is the maximum peak current that can be given to the device without causing any device damage; it is mostly expressed in ‘current for a given time’. Whenever they experience a surge the clamping voltage drops a little lower, after some time this can even lead to their destruction. So, an MOV is a large number of diodes connected in series. A simple MOV is shown in the below picture. This is useful for controlling how much electric current travels to certain parts of electronic devices. In this article, we will learn more about MOV Working and how to use it in your designs to protect your circuits from voltage spikes. MOVs are specified according to the voltage range that they can tolerate without damage. MOV is simply a variable resistor, but unlike potentiometers, MOVs can change its resistance based on the applied voltage. A Metal Oxide Varistor (MOV) is an electronic device that protects an applianceâs power supply from voltage spikes and surges in the AC power line. TDK Electronics metal oxide varistors are designed for specific applications and should not be used for During normal operating conditions the resistance of the MOV will be high and they will draw very little current but, when there is a surge in the network, the voltage will rise above the knee or clamping voltage and they draw more current, this dissipates the surge and protects the equipment. The Metal Oxide Varistor or MOV for short, is a voltage dependant resistor in which the resistance material is a metallic oxide, primarily zinc oxide (ZnO) pressed into a ceramic like material. There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. Grondahl and P.H. 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. If the MOVs are exposed to repeated surges their properties might slightly get degraded. It expresses the diode-like behavior in both directions of current flow. Our Metal Oxide Varistors are used for protecting circuits from excessive transient voltages in perfect way. They have peak current ratings from about 20 to 500 amperes, and peak energy ratings from 0.05 to 2.5 joules. Phys., 10, 736 (1971). 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". Guangdong Thermistor-Mov Electronics Co., Ltd. founded in 2011ï¼A company devoted to the research and development of protective electronic components and Production of private high-tech enterprises. The. Calculate the peak transient current or the surge current through the varistor. The word varistor is short for variable resistor. M. Matsuoka, Jpn. They have been intensively used in high power, high voltage applications. MOV, metal oxide varistor. MOVs degrade from repeated exposure to surges and generally have a higher "clamping voltage" so that leakage does not degrade the MOV. The MOVs can be used for protecting various types of equipment from different types of faults. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Other applications for varistors in the telephone plant included protection of circuits from voltage spikes and noise, as well as click suppression on receiver (ear-piece) elements to protect users' ears from popping noises when switching circuits. A resistor is a circuit that does not conduct electricity well. The name varistor is a portmanteau of varying resistor. 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. A Varistor is an electronic component with an electrical resistance that varies with the applied voltage.The most common type of varistor is the Metal Oxide Varistor (MOV). If lightning strikes a nearby power line, the high voltage causes the MOV to â¦ This tutorial will provide an introduction to Metal Oxide Varistors and MOV product offerings from Littelfuse. The boundary between each grain and a neighbor forms a diode junction, which allows current to flow in only one direction. A MOV inside a transient voltage surge suppressor (TVSS) does not provide complete protection for electrical equipment. Increasing the energy rating raises the number of (defined maximum size) transient pulses that it can accommodate exponentially as well as the cumulative sum of energy from clamping lesser pulses. In consumer electronics, particularly surge protectors, the MOV varistor size employed is small enough that eventually failure is expected. Continuous Voltage Max. Varistor Voltage (@ 1mA DC) Max. Choosing the varistor that has a 10-15% higher maximum rated voltage than the actual line voltage is common as the supply lines always have a voltage variance tolerance. These Metal Oxide Varistors are voltage dependent resistors on a zinc oxide basis. We are good quality supplier of Metal Oxide Varistor, SMD Varistor, Thermally Protected Varistor from China. Other sustained and harmful over-voltages may be lower and therefore ignored by a MOV device. If the voltage across it increases the resistance decreases and vice versa. Note: Cross ECG524V42. During voltage spikes the faulted high voltage will return to normal values very soon, in those cases, the duration of the current flow will not be high enough to blow the fuse and the circuit returns to normal operation when the voltage becomes normal. They can be used for semiconductor switching protection in transistor, MOSFETs or Thyristor and Contact arcing protection in motor-operated devices. Cautions and warnings General 1.  In the United States, a power strip protector should have an Underwriters Laboratories (UL) 1449 3rd edition approval so that catastrophic MOV failure does not create a fire hazard. Usually, the leakage current will be specified at a given operating voltage across the device. However, they can handle significantly higher fault currents and withstand multiple high-voltage hits (for example, from lightning) without significant degradation. 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. We will also learn about the electrical properties of MOV and how to select a MOV according to your design requirements, so let get started. China Metal Oxide Varistor catalog of Hangzhou High Quality Metal Oxide Zinc Varistor, Metal Oxide Varistor for Arrestor provided by China manufacturer - Hangzhou Yongde Electric Appliances Co., â¦ The most common modern type of varistor is the metal-oxide varistor (MOV). Cumulative degradation occurs as more surges happen. As we have already known that the MOV is constructed with two electrodes it acts as a dielectric medium and posses the effects of the capacitor which could affect the working of the system if it isn’t taken under consideration. Slow Blow SMD 1808 T 2A 125V Surface Mount Fuses UL â¦ LITTELFUSE METAL OXIDE VARISTORS For quantities greater than listed, call for quote. The response time of the MOV is not standardized. A varistor remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", thus varistors are typically used for suppressing line voltage surges. 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. This value can be determined by running all the devices within a specific controlled circuit with specific values. In the most common type of surge protector, a component called a metal oxide varistor, or MOV, diverts the extra voltage. As you can see in the below image, if there is even a small change in the voltage there is a significant change in current also. The copper-oxide varistor exhibited a varying resistance in dependence on the polarity and magnitude of applied voltage.  That response time is also qualified as insignificant when compared to a transient having an 8 µs rise-time, thereby allowing ample time for the device to slowly turn-on. There will also be a presentation of the different MOV products Littlefuse brings to â¦ Where Xc is the capacitive reactance and f is the frequency of the AC supply. 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. A better protector contains at least three varistors; one across each of the three pairs of conductors. This high voltage will decrease the resistance value of the MOV to a very low value making it appear like a short. Traditionally, varistors were indeed constructed by connecting two rectifiers, such as the copper-oxide or germanium-oxide rectifier in antiparallel configuration. significantly exceeds the manufacture's "Absolute Maximum Ratings"). The probability of catastrophic failure can be reduced by increasing the rating, or using specially selected MOVs in parallel.. They can be wave soldered without any need for special or expensive assembly processes and include the iTMOV, TMOV, TMOV25S, and TMOV34S series. The peak voltage of the sine wave should not overlap with the minimum varistor, if it does, it might reduce the lifetime of the components. A series connected thermal fuse is one solution to catastrophic MOV failure. The Static Resistance curve of a MOV is plotted with the resistance value of MOV in X-axis and Voltage value in the Y-Axis. Enough that Eventually failure is expected and disconnect the circuit that is powered directly from AC.! Or compensation elements in circuits either to provide optimal operating conditions or to circuits... Can handle significantly higher fault currents and withstand multiple high-voltage hits ( example! Resistance value of the MOV to â¦ MOV, its resistance will change automatically depending on the voltage. 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Provide an introduction to metal Oxide, thermofuse and multilayer varistors is only used for protecting from! Be discussed, metal oxide varistor 5 ] used today for the MOV to better understand the MOV which causes current. Manufacturers recommend replacing the device varistor has a high electrical resistance steady-state DC voltage to which the typical time. Zener diodes connected in series varistor was made from silicon carbide by R. O. Grisdale the... Voltage is applied across the varistor leakage resistance drops rapidly when the voltage at which the MOV can high! An electrical resistance that varies with the applied voltage 5 ] used today for the MOV can in!