They can be used for single-phase line to line protection and single-phase line to line & line to ground protection in AC/DC electrical circuits. Whenever the device experiences a surge the rated clamping voltage decreases, the variation in the voltage after the surge is called the surge shift. If the MOVs are exposed to repeated surges their properties might slightly get degraded. A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Advertisement. It is called so as the component is made from a mixture of zinc oxide and other metal oxides like cobalt, manganese and so on and is kept intact between two electrodes which are basically metal plates. MOV a.k.a varistors is commonly used along with fuse in parallel to the circuit that is to be protected. 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. Thermal protective Metal Oxide Varistors (TMOVs) are designed to meet abnormal overvoltage requirements of UL 1449. Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. 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. 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 provides very good voltage transient protection and is now quite popular. Therefore it is advised to use a fuse in series with the mains line in conjunction with the attached MOV for ensuring safety to both the electronic circuit and … Subscribe to stay updated with industry's latest Electronics components and news, STM32F2 MCUs use advanced 90 nm NVM process technology with an adaptive real-time memory accelerator, STM32F4 MCUs leverage NVM technology to reach the highest benchmark scores for Cortex®-M-based MCUs, STM32F7 devices deliver the maximum theoretical performance of the ARM® Cortex®-M7 Core, STM32 development boards implement the full range of device peripherals and features of STM32 MCUs, STM32F0 MCUs offer real-time performance and low-power operation for cost-sensitive applications, STM32F1 MCUs are ideal for an array of applications in the industrial, medical, and consumer markets, STM32F3 MCUs combine a 32-bit ARM® Cortex®-M4 core with a high number of integrated peripherals, The STM32Cube with graphical software configuration tool reduces development efforts, time, and cost. This forces a large current to flow through the MOV which would blow the fuse and disconnect the circuit from the mains voltage. The typical response time is always fixed as 100nS. For higher frequencies, such as radio communication equipment, a gas discharge tube (GDT) may be utilized. To avoid these kinds of risks MOVs are mostly connected in series with a thermal switch/fuse that could activate if high current is drawn. When the MOV is not conducting it has a high resistance up to certain voltage say 0-200Volts the Curve has a linear relationship, where the current flowing through the varistor is almost zero. You should make sure that your circuit will be able to withstand this voltage, this will be the highest voltage that your circuit down line will experience. The boundary between each grain and a neighbor forms a diodejunction, which allows current to flow in only one direction. Metal oxide varistor is a voltage dependent resistor. Slow Blow SMD 1808 T 2A 125V Surface Mount Fuses UL … M. Matsuoka, Jpn. 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. This is useful for controlling how much electric current travels to certain parts of electronic devices. 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. The below image shows how to use, The grains of metal oxides create a diode junction between each immediate neighbor. Smaller, lower-capacitance varistors are available with capacitance of ~1 pF for microelectronic protection, such as in cellular phones. Susceptibility of electronic equipment to these other electric power disturbances is defined by other aspects of the system design, either inside the equipment itself or externally by means such as a UPS, a voltage regulator or a surge protector with built-in overvoltage protection (which typically consists of a voltage-sensing circuit and a relay for disconnecting the AC input when the voltage reaches a danger threshold). Varistor Voltage (@ 1mA DC) Max. The MOVs can only be used for short surge protection, they can’t handle sustained surges. 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. Since the varistor is connected parallel with the device to be protected the varistor leakage resistance drops rapidly when the frequency increases. This type is commonly known as the metal-oxide varistor (MOV). 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. 3, pp. 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. varistor voltage cover from 18V to 1.2KV, including 6KV/3KA series and high-energy series. Rey (ed.). Application of sustained over-voltage to a MOV can cause high dissipation, potentially resulting in the MOV device catching fire. For historical reasons, many MOVs have been incorrectly specified allowing frequent swells to also degrade capacity. In the 1930s, small multiple-varistor assemblies of a maximum dimension of less than one inch and apparently indefinite useful lifetime found application in replacing bulky electron tube circuits as modulators and demodulators in carrier current systems for telephonic transmission.[3]. The curve will look similar to the characteristic curve of two Zener diodes connected back-to-back. [8][9] This type of device became the preferred method for protecting circuits from power surges and other destructive electric disturbances, and became known generally as the metal-oxide varistor (MOV). Basic operation, electrical characteristics, and applications will be discussed. 420VAC / 560VDC 160 Joules 100mW. You should know about the various numbers of parameters of a MOV to choose the right device for your pieces of equipment. Usually, the leakage current will be specified at a given operating voltage across the device. Hence MOVs are normally used in parallel with a fuse, to protect circuits from high voltage spikes. 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. The power, surge current and energy rating are always selected in a way that is greater than the event anticipated, If you are uncertain about the factors of the event, the wise thing to do is to pick the device with a higher power, surge current and energy ratings. Clamping Voltage (8 x 20µs) RMS The MOVs can be used for protecting various types of equipment from different types of faults. So if you find a MOV damaged in any power circuit it is possibly because the circuit went through many voltage spikes. A user may have no indication when the surge suppressor has failed. 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. The first step of choosing a MOV is determining the continuous working voltage that will be provided across the varistor, you have to choose the varistor with maximum AC or DC voltage that matches or slightly higher than the applied voltage. Varistors can fail for either of two reasons. [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 internal structure of a MOV is shown in the below picture. This type contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides, such as small amounts of bismuth, cobalt, manganese oxides, sandwiched between two metal plates, which constitute the electrodes of the device. 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. Advertisement. Let’s look into the different electrical characteristics of MOV to better understand the MOV properties. 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. MOV, metal oxide varistor. 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. The. But, every time a spike is detected the MOV disconnects the circuit momentarily by shorting itself and damaging itself with high current each time. Features: - Longer service life - Low maintenance - Highly demanded The word varistor is short for variable resistor. 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. MOV, metal oxide varistor. 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]. Cautions and warnings General 1. Metal Oxide Varistor:TVR-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. 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. 47, no. It is the voltage at which the MOV starts to conduct and dissipate the surge current. The MOV varistor starts conducting when a specific voltage is applied across the connecting leads and stops conducting when the voltage falls below the threshold voltage. However, they can handle significantly higher fault currents and withstand multiple high-voltage hits (for example, from lightning) without significant degradation. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. [citation needed] 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. [6], Another type of varistor was made from silicon carbide by R. O. Grisdale in the early 1930s. If excessive current is conducted by a MOV, it may fail catastrophically, keeping the load connected, but now without any surge protection. They have been intensively used in high power, high voltage applications. Myers, L.S. 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. MOVs are specified according to the voltage range that they can tolerate without damage. A wide range of Metal Oxide Varistors is bringing forth by us to the customers. 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. Under normal utility voltage conditions, this is not a problem. We are good quality supplier of Metal Oxide Varistor, SMD Varistor, Thermally Protected Varistor from China. When you apply a small voltage to the electrodes a reverse leakage current appears across the junctions. 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