It is also a nonlinear device and provides very good transient voltage surge protection. The resistance material in a metal oxide varistor mainly consists of Zinc Oxide grains that are pressed as a ceramic mass.  Eventually, it proceeds into a shorted circuit condition as the energy discharges create a conductive channel through the oxides. Cumulative degradation occurs as more surges happen. 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. Application of sustained over-voltage to a MOV can cause high dissipation, potentially resulting in the MOV device catching fire. 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 â¦ They have been intensively used in high power, high voltage applications. STE produce high quality Zinc Oxide Varistor. 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. Other sustained and harmful over-voltages may be lower and therefore ignored by a MOV device. Components101 is a resource dedicated for electronics design engineers, covering product news, analysis and articles on latest electronics components. 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 lightning strikes a nearby power line, the high voltage causes the MOV to â¦ (mm) Device Model Number Brand Maximum Ratings (85°C) Specifications (25°C) Typical Capacitance @ f=1MHz (pF) Continuous Transient VNOM Varistor Peak Price Each Voltage Max. MOV a.k.a varistors is commonly used along with fuse in parallel to the circuit that is to be protected. The final and most important step of all is selecting the model that can provide the required clamping voltage. 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. Western Electric 3B varistor made in 1952 for use as click suppressor in telephone sets, Circuit of the traditional construction of varistors used as click suppressors in telephony. Crosby (, AT&T Bell Laboratories, Technical Staff, R.F. 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.. 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.. A user may have no indication when the surge suppressor has failed. When a small voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. Learn More The typical response time is always fixed as 100nS. Although the device can handle the surge current the manufacturers recommend replacing the device if there is an occurrence of surge current. Continuous Voltage Max. A metal oxide varistor (MOV) is a device used as a component in electrical equipment. 250VAC 330VDC 72 Joules. 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.  A typical surge protector power strip is built using MOVs. 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. All series are full compliance with UL, VDE, CQC certificate Our Metal Oxide Varistors are used for protecting circuits from excessive transient voltages in perfect way. Lower Voltage Varistor for Surge Protector D28 Characteristic: 1. The Specification of a MOV depends on the following. 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. 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. A wide range of Metal Oxide Varistors is bringing forth by us to the customers. Metal oxide varistor â Described above, the MOV is a nonlinear transient suppressor composed of zinc oxide (ZnO) Silicon carbide varistor â At one time this was the most common type before the MOV came into the market. Distributor of metal oxide, thermofuse and multilayer varistors. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. 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. 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. Note: Line voltage operation. Note: Cross ECG524V42. 47, no. significantly exceeds the manufacture's "Absolute Maximum Ratings"). 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. This high voltage will decrease the resistance value of the MOV to a very low value making it appear like a short. In the most common type of surge protector, a component called a metal oxide varistor, or MOV, diverts the extra voltage. Model Size Disc Dia.  It was constructed from a small copper disk, of which one side was formed a layer of cuprous oxide. 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. Varistor Voltage (@ 1mA DC) Max. This value can be determined by running all the devices within a specific controlled circuit with specific values. A varistor is an electronic component with an electrical resistance that varies with the applied voltage. If excessive current is conducted by a MOV, it may fail catastrophically, keeping the load connected, but now without any surge protection. STM32F2 Series High-Performance Microcontrollers, STM32F4 Series High-Performance Microcontrollers, STM32F7 Series Very High-Performance Microcontrollers, STM32F0 Entry-Level ARM® Cortex®-M0 Microcontrollers, STM32F1 Series Mainstream Microcontrollers, STM32F3 Series Mixed-Signal Microcontrollers, How does Quality Factor or Q-Factor Impact the Performance of an Inductor, How does Input Impedance and Output Impedance Affect the Performance of an Operational Amplifier. Grondahl and P.H. Phys., 10, 736 (1971). It is the steady-state DC voltage to which the typical leakage current will be less than the specified value. Find out the amount of energy absorbed by the varistor in case of a surge. TDK Electronics metal oxide varistors are designed for specific applications and should not be used for 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. Part No. There will not be any capacitance effect when the voltage reaches the clamping voltage as the varistor starts its normal functioning. J. Appl. Under normal utility voltage conditions, this is not a problem. 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). MOVs tend to be more suitable for higher voltages, because they can conduct the higher associated energies at less cost.. 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. 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 Metal Oxide Varistor or MOV is a voltage dependent, nonlinear device that provides excellent transient voltage suppression. 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's are mid-range devices used to protect small machinery, power sources and components. Both types are available over a wide range of voltages. If the MOVs are exposed to repeated surges their properties might slightly get degraded. In consumer electronics, particularly surge protectors, the MOV varistor size employed is small enough that eventually failure is expected. The curve will look similar to the characteristic curve of two Zener diodes connected back-to-back. 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 boundary between each grain and a neighbor forms a diodejunction, which allows current to flow in only one direction. 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 radial leaded disc type is the most common version. 420VAC / 560VDC 160 Joules 100mW. 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. The probability of catastrophic failure can be reduced by increasing the rating, or using specially selected MOVs in parallel.. It provides very good voltage transient protection and is now quite popular. For higher frequencies, such as radio communication equipment, a gas discharge tube (GDT) may be utilized. Another method for suppressing voltage spikes is the transient-voltage-suppression diode (TVS). 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. A MOV consist of approximately 90% of Zinc oxide and a small amount of other metal oxides. 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). So if you find a MOV damaged in any power circuit it is possibly because the circuit went through many voltage spikes. Become the leading quality in the industry. When the voltage is within the rated limits the resistance of the MOV will be very high and hence all the current flows through the circuit and no current flows through the MOV. 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. Multilayer Varistors The term MOV or Metal Oxide Varistor is a variable resistor. 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. New. In contrast to a diode however, it has the same characteristic for both directions of traversing current. 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. Traditional varistor schematic symbol, used today for the diac. 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¦ Another type of transient suppressor is the gas-tube suppressor. At low voltage the varistor has a high electrical resistance which decreases as the voltage is raised. 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. 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. Metal Oxide Varistors (MOV, 's) are epoxy encapsulated zinc oxide discs with radial or axial leads. 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. It was used to guard telephone lines from lightning.. The ceramic powders of the metal oxides are kept intact between two metal plates called the electrodes. 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 response time of the MOV is not standardized. The accumulation of randomly oriented grains is electrically equivalent to a network â¦ 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. LITTELFUSE METAL OXIDE VARISTORS For quantities greater than listed, call for quote.  In this condition the varistor is not visibly damaged and outwardly appears functional (no catastrophic failure), but it no longer offers protection. A series connected thermal fuse is one solution to catastrophic MOV failure. Modern varistors are primarily based on sintered ceramic metal-oxide materials which exhibit directional behavior only on a microscopic scale. The most common modern type of varistor is the metal-oxide varistor (MOV). 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. 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. The manufacturers will specify the maximum AC Voltage that we can provide to the device in the product description itself. Metal oxide Varistors (MOV): Since SiC Varistors had some serious drawbacks, another type of Varistors the metal oxide Varistors were developed. This property is very useful for â¦ There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. 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. 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. Let’s discuss more on how MOV working in a circuit. Package: 14mm disc, radial leads. Copyright 2020 © Components101. This can be determined by using all the absolute maximum load of the varistor during a surge within the environment and the specifications provided in the datasheet. 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. Every semiconductor varistors will have capacitance value depending on the area which also inversely depends on its thickness. The maximum amount of energy that the MOV can dissipate for a specified peak pulse time of a specific waveform during a surge. Normally, the MOV has very high electrical resistance. MOV is simply a variable resistor, but unlike potentiometers, MOVs can change its resistance based on the applied voltage. Smaller, lower-capacitance varistors are available with capacitance of ~1 pF for microelectronic protection, such as in cellular phones. 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. But when a voltage spike occurs in the main voltage, it appears directly across the MOV since it is placed in parallel to AC mains. Advertisement. The boundary between each grain and a neighbor forms a diode junction, which allows current to flow in only one direction. The most common modern type of varistor is the metal-oxide varistor (MOV). 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. 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. Transient voltage surge suppressor. 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%. 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