Metal Oxide Varistors (MOV)

an Metal Oxide Varistors (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. Under normal utility voltage conditions, this is not a problem. 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. Application of sustained over-voltage to a mov metal oxide varistor can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.

metal oxide varistor application

MOVs are specified according to the voltage range that they can tolerate without damage. Other important parameters are the metal oxide varistor application energy rating in joules, operating voltage, response time, maximum current, and breakdown (clamping) voltage. 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.
Response time
The response time of the varistors is not standardized. 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. 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. When subjected to a very fast, <1 ns rise-time transient, response times for the MOV are in the 40–60 ns range.
Capacitance

The Applications of High voltage varistor

To protect telecommunication lines, transient suppression devices such as 3 mil carbon blocks (IEEE C62.32), ultra-low capacitance varistor metal oxide , and avalanche diodes are used. For higher frequencies, such as radio communication equipment, a gas discharge tube (GDT) may be utilized.[citation needed] A typical surge protector power strip is built using xatge MOV . Low-cost versions may use only one varistor, from the hot (live, active) to the neutral conductor. A better protector contains at least three varistors; one across each of the three pairs of conductors. 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.

metal oxide varistor application

In general, the primary case of varistor breakdown is localized heating caused as an effect of thermal runaway. metal oxide varistor application is to a lack of conformity in individual grain-boundary junctions, which leads to the failure of dominant current paths under thermal stress. If the energy in a transient pulse (normally measured in joules)MOV Block is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. This (catastrophic) failure occurs when "Absolute Maximum Ratings" in manufacturer's data-sheet are significantly exceeded.

Electrical characteristics of varistor metal oxide

A varistor metal oxide 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. However, a polymer arrester may not be able to successfully limit a very large surge from an event like a lightning strike where the energy involved is many orders of magnitude greater than it can handle. Follow-through current resulting from a strike may generate excessive current that completely destroys the varistor.

Lesser surges still degrade it, however. Degradation is defined by manufacturer's life-expectancy charts that relate current, time and number of transient pulses. The main parameter affecting varistor life expectancy is its energy (Joule) rating. As the energy rating increases, its life expectancy typically increases exponentially, the number of transient pulses that it can accommodate increases and the "clamping voltage" it provides during each transient decreases. The probability of catastrophic failure can be reduced by increasing the rating, either by using a single varistor of higher rating or by connecting more devices in parallel. A varistor is typically deemed to be fully degraded when its "clamping voltage" has changed by 10%. In this condition it is not visibly damaged and it remains functional (no catastrophic failure).

Porcelain housed arrester

Metal Oxide Varistors (MOV) current-voltage characteristics for zinc oxide (ZnO) and silicon carbide (SiC) devices
The most common 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) sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction,Porcelain housed arrester allows current to flow in only one direction.

The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and a large current flows. The result of this behaviour is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.

metal oxide varistors application

Traditional Metal oxide varistors schematic symbol. It expresses the diode-like behavior in both directions of current flow.
Modern varistor schematic symbol.
A metal oxide varistors application is an electronic component with an electrical resistance that varies with the applied 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. In contrast to a diode however, it has the same characteristic for both directions of traversing current. At low voltage it has a high electrical resistance which decreases as the voltage is raised.

Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered.
The development of the varistor, in the form of a new type of rectifier (copper oxide), originated in the work by L.O. Grondahl and P.H. Geiger in 1927. The name varistor is a portmanteau of varying resistor. The term is only used for non-ohmic varying resistors. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics.

Metal Oxide Varistors (MOV)

While an Metal Oxide Varistors (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. Under normal utility voltage conditions, this is not a problem. 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. Application of sustained over-voltage to a mov metal oxide varistor can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.

A 130 volt, 150 J MOV that has undergone catastrophic failure, apparently as a result of a lightning strike, showing evidence of heat and smoke. The 3 amp fast-blow fuse immediately in front of the varistor blew during the same event.
A series connected thermal fuse is one solution to catastrophic MOV failure. Varistors with internal thermal protection are also available.
There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating MOVs under over-voltage conditions. 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. If excessive current is conducted by a MOV, it may fail catastrophically, keeping the load connected, but now without any surge protection. A user may have no indication when the surge suppressor has failed. Under the right conditions of over-voltage and line impedance, it may be possible to cause the MOV to burst into flames,[5] the root cause of many fires[6] and the main reason for NFPA’s concern resulting in UL1449 in 1986 and subsequent revisions in 1998 and 2009. Properly designed TVSS devices must not fail catastrophically, resulting in the opening of a thermal fuse or something equivalent that only disconnects MOV devices.

the Specifications of metal oxide varistor application

Voltage rating
MOVs are specified according to the voltage range that they can tolerate without damage. Other important parameters are the metal oxide varistor application energy rating in joules, operating voltage, response time, maximum current, and breakdown (clamping) voltage. 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.
Response time
The response time of the varistors is not standardized. 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. 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. When subjected to a very fast, <1 ns rise-time transient, response times for the MOV are in the 40–60 ns range.
Capacitance

Typical capacitance for consumer-sized (7–20 mm diameter) varistors are in the range of 100–1,000 pF. Smaller, lower-capacitance varistors are available with capacitance of ~1 pF for microelectronic protection, such as in cellular phones. These low-capacitance varistors are, however, unable to withstand large surge currents simply due to their compact PCB-mount size.

the introduction of metal oxide varistors application

Traditional Metal oxide varistors schematic symbol. It expresses the diode-like behavior in both directions of current flow.
Modern varistor schematic symbol.
A metal oxide varistors application is an electronic component with an electrical resistance that varies with the applied 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. In contrast to a diode however, it has the same characteristic for both directions of traversing current. At low voltage it has a high electrical resistance which decreases as the voltage is raised.

Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered.
The development of the varistor, in the form of a new type of rectifier (copper oxide), originated in the work by L.O. Grondahl and P.H. Geiger in 1927. The name varistor is a portmanteau of varying resistor. The term is only used for non-ohmic varying resistors. Variable resistors, such as the potentiometer and the rheostat, have ohmic characteristics.

Mov metal oxide varistor

The structural characteristics of the varistor varistor metal oxide different from ordinary resistor, which is based on nonlinear characteristics of semiconductor material made of
Ohm's law to comply with ordinary resistor, and varistor voltage and current is nonlinear relationship was special. When applied across the varistor voltage is lower than the nominal rated voltage, resistance value varistors approaches infinity, almost no current flows through the interior. When the voltage across the TGE Metal Oxide Varistors(MOV) slightly higher than the nominal rated voltage, the varistor will quickly breakdown conduction by a High Performance Varistor state to a low resistance state, current also increases dramatically.

metal oxide varister

Innovative elements: Zinc Oxide blocks for high performance requirements, system studies functional powder type, size, density, surface condition, surface treatment, surface area and powder activity of the influence of the resistance properties, the successful development of sensitive resistance high-performance composite particles. The product is uniformly mixed with zinc oxide, after pressing and sintering can effectively improve the performance of varistors, reached the advanced level of developed countries today.
Benefit Analysis: Zinc Oxide discs and surge arresters have important applications in the field of transmission and distribution engineering and construction of power grids, subway rail transportation, military and civilian communications facilities, the development of high performance metal oxide varister and surge arresters is significant .

High Performance Varistor

High Performance Varistor and surge arrester varistor high performance requirements, system studies functional powder type, size, density, surface condition, surface treatment, surface area and powder activity of the influence of the resistance performance, success develop efficient varistor composite particles.
Second, the specific description:
1. Application: metal oxide varistors and surge arresters manufacturing enterprises.
2, the technical indicators: application to high-performance anti-corona resistance, surge voltage insulation coating material, its performance over similar foreign products; applied to large current insulating coating material, such as zinc oxide insulating layer side valve D3 with ordinary Composite arrester valve side insulation coating compared to the 4 / 10μs standard indicators of the impact of high current 65 ~ 70kA, more than GB11032-2000 standard (45kA), and reached the international IEC-60099-4 standard (65kA).

添加图片说明

Varistor is a voltage

Varistor is a voltage limiting protection devices. Nonlinear characteristic use varistors, when an overvoltage occurs between two poles varistor varistor voltage can be clamped to a relatively fixed voltage value, metal oxide arrester in order to achieve protection of the post-stage circuit. The main parameters of mov metal oxide varistor are: varistor voltage, current capacity, junction capacitance and response time.

mov metal oxide varistor

TGE Mov varistor is a non-linear voltage characteristics of the resistance of the device is mainly used in the voltage clamp circuit withstand over-voltage, absorbing excess current to protect sensitive devices. English name called "Voltage Dependent Resistor" abbreviated as "VDR", or called  mov varistor. Varistor resistive material is a semiconductor, so it is a variety of semiconductor resistor. "Zinc oxide" Now a lot of use of (ZnO) varistor metal oxide, its main material divalent element zinc (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, the zinc oxide  High voltage varistor is a "Ⅱ-Ⅵ family-oxide semiconductor." In China Taiwan, varistors called "surge absorber", sometimes also referred to as "electric shocks (surge) suppressor (absorber)."

添加图片说明

Varistor in parallel:

When a TGE mov varistor for counter nominal discharge current can not meet the requirements, it should be used in parallel with multiple varistors. Sometimes in order to reduce the limit voltage, even if the nominal discharge current to meet the requirements adopted
A plurality of mov metal oxide varistor in parallel. Pay particular attention to that when the TGE metal oxide varistor theory in parallel, must be consistent with carefully selected parameters (for example: ΔU1mA≤3V, Δα≤3) paired to
To ensure uniform distribution of current

The nominal discharge current calculation:

TGE mov varistor nominal discharge current should be greater than required to withstand inrush current or potential annual maximum surge current. The nominal discharge current should be fixed TGE MOV surge life count curve
More than 10 times the value of impact is calculated about 30% maximum impact through traffic (ie 0.3 IP) around

Varistor resistive material is a semiconductor

TGE metal oxide varistor symbol resistive material is a semiconductor, so it is a variety of semiconductor resistor. "Zinc oxide" Now a lot of use of (ZnO) varistor, it has two main material
Price element (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, the zinc oxide metal oxide varistor basics is a "Ⅱ-Ⅵ family-oxide semiconductor."
Varistor protection, the vast majority of applications, it can repeatedly effect, but sometimes also to make it into the current fuse as a "one-off" protection device. For example, and then
On some of the short-circuit current transformer load contacts varistors. The most important feature of the TGE varistor metal oxide is added on top of it when voltage drops below its threshold "UN" when the current flowing through it is extremely small, phase
When in a shut valve, when the voltage exceeds the UN, the surge current flowing through it, is equivalent to the valve open. Using this feature, you can suppress the circuit often appear abnormal over-voltage protection
Protect circuitry from overvoltage damage.

Expressions varistors deteriorate

TGE metal oxide varistor identification is a zinc oxide as the main body, add a polycrystalline semiconductor ceramic element more metal oxides, classic electronic ceramics made. Because of its unique grain boundary junction
Structure, at a certain electric field, the grain boundary by a heat conductive conduction electron-emitting instantly converted to electron tunneling conduction, as the voltage increases abruptly decreases its resistance value, having excellent non-linear volt Ante
Sex. So, when there is over-voltage, grain boundaries electron tunneling suppression overvoltage peak growth, absorbing part of the over-voltage energy, and thus play a protective role on the line or equipment.
However, regardless of varistors used in power lines or electrical lines, if the various types of overvoltage occurs frequently, then the varistors will be frequent movement to suppress the release of over-voltage amplitude and to absorb
Surge energy, protection of electrical equipment and components, which will inevitably lead to degradation in performance varistors and even failure.
Varistor failure mode there are three kinds: (1) deterioration of the performance of the leakage current increases, the breakdown voltage decreased significantly until zero; (2) burst, surge energy if overvoltage caused by too much, more than
The chosen varistor metal oxide limit the capacity, the will of ceramic varistor overvoltage occurs when suppressing burst phenomenon; (3) the perforation, especially if the over-voltage spikes high, causing varistors
Ceramic instantaneous electrical breakdown, showing perforation.
Wherein, under the premise of making grade lightning protection, varistor failure mode most of the performance degradation and perforations (ie short circuit), so when you use varistors, must with
Series with a suitable circuit breaker or fuse, to avoid a short circuit caused the accident.
Currently, the popular over-voltage protection is to TGE metal oxide varistor sizing with current limiting, over-current and deterioration warning means organically together internationally, in addition to its over-voltage protection function, but also with
To prevent deterioration of its own, resulting in a short circuit function.

What varistor is it?

Refers to the resistance value of the TGE metal oxide varistor symbol voltage-sensitive resistor, that is, within a certain range of the resistance value of current and voltage with the voltage change.
Varistor resistive material is a semiconductor, so it is a variety of semiconductor resistor. "Zinc oxide" Now a lot of use of (ZnO) high voltage varistor, it has two main material
Price element (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, the zinc oxide varistor is a "Ⅱ-Ⅵ family-oxide semiconductor."
Varistors useful? "Safety valve" effect TGE varistor metal oxide circuit, its greatest feature is added on top of it when the voltage is below its threshold "UN" when the current flowing through it is extremely small, the equivalent of
A shut the valve, when the voltage exceeds UN, surge current flowing through it, is equivalent to the valve open. According to the features, it can suppress the circuit often appear abnormal over-voltage protection
Protect circuitry from overvoltage damage.

The main parameters and damaged varistor form

ZnO varistor is a zinc oxide as the main component of the metal oxide semiconductor non-linear resistance element; resistance to voltage sensitive, when the voltage reaches a certain value, the resistance quickly turned. Since the varistor has a good non-linear characteristics, through traffic, low residual voltage levels, fast action and free wheeling characteristics. It is widely used in electronic equipment, lightning protection.
The main parameters:
1, residual voltage: the highest peak occurring in the varistor voltage high current waveform by specifying its ends.
2, flow capacity: After a predetermined time interval and applying a predetermined frequency waveform current in the varistor, the maximum current amplitude variation was still varistor reference voltage within the specified range can pass through.
3, the leakage current: the role of the reference voltage, the current flowing in the varistor.
4, rated working voltage: allow long-term continuous work across the varistor frequency RMS voltage is applied. The TGE mov metal oxide varistor transient overvoltage energy absorption after their own temperature, at this voltage normal cooling, no heat damage.
Lack of varistors: (1) a large parasitic capacitance varistor having a large parasitic capacitance, typically a few hundred to several thousand pF range. In the high-frequency signal system can cause high-frequency signal transmission distortion, causing the system to normal operation. (2) the presence of the varistor leakage current leakage current index is not only related to the normal operation of the protection of electronic systems, but also related to the varistor aging and life itself.
Varistor damage in the form of: (1) When the varistor suppression of transient over-voltage energy greater than its rated capacity, the TGE Varistor for counter will damage due to overheating, mainly for shorts, opens.

How to pick a good varistor?

In practice, it should be the right choice resistor. This article describes the common resistor fixed resistors, fuse resistors, thermistors, Metal oxide varistors, varistor, humidity resistance and other selection methods. ʱ??
Varistor selection
Varistors are mainly used in a variety of electronic products, over-voltage protection circuit, it has a variety of models and specifications. The main parameters of the selected varistor (including nominal voltage, maximum continuous operating voltage, maximum limit voltage, current capacity, etc.) must comply with the requirements of the application, in particular, the nominal voltage must be accurate. The nominal voltage is too high, would not achieve the over-voltage TGE metal oxide varistor basics protection, nominal voltage is too low, the varistor easily malfunction or breakdown.

How to judge the quality of varistor?

Varistor it with the voltage applied on top of it increasing, its resistance value can be changed from MΩ (megohms) level to mΩ (milliohms) level. When low voltage TGE metal oxide varistor application works in leakage current region, showing great resistance, leakage current is very small; when the voltage rises into the non-linear zone, when the current is within a large range, voltage changes little , showed good pressure limiting characteristic; voltage rises again, the varistor into the saturated zone, showing a small linear resistance, due to the current large, over time it will make varistor overheating or even burst.
Set the multimeter measurement 10k file, table pen connected to both ends of the resistor, the varistor should exhibit marked resistance multimeter, if you exceed this value is large, then the TGE metal oxide varistor sizing has been damaged.

Zinc oxide varistors application principle

Varistor is a voltage limiting protection devices. Nonlinear characteristic use varistors, when an overvoltage occurs between two poles varistor varistor voltage can be clamped to a relatively fixed voltage value, in order to achieve protection of the post-stage circuit. The main parameters of TGE Glass Coating varistors are: varistor voltage, current capacity, junction capacitance and response time.
Response time is ns grade varistor, faster than the air discharge, TVS tube slightly slower than under normal circumstances for an electronic circuit overvoltage protection to meet the requirements of its response speed. When the junction capacitance varistors are generally on the order of hundreds to thousands of pF range, in many cases should not be directly applied in the protection of high-frequency signal lines, the application of the AC circuit protection, since it greatly increases the drain junction capacitance current protection circuit is designed to take full account. Varistor flow capacity is large, but smaller than the gas discharge tube.
Varistors being protected electrical equipment or components used in parallel. When the circuit appears lightning over voltage or over-voltage transient operating Vs, TGE Metal Oxide Varistors(MOV) and the protection of equipment and components withstand Vs, due to the fast response of the varistor, it nanosecond time quickly render Nonlinear excellent electrical properties (see Figure 3 in the breakdown zone), then the voltage drop across the varistor rapidly, far less than the Vs, on such equipment and components to be protected actual withstand voltage is much lower than had voltage Vs, so that the equipment and components from over-voltage shocks.

Zinc oxide varistors

"Varistor" is a non-linear voltage characteristics of the resistance of the device is mainly used in the voltage clamp circuit when subjected to excessive pressure, absorb excess current to protect sensitive devices. English name called "Voltage Dependent Resistor" abbreviated as "VDR", or called "Varistor". Varistor resistive material is a semiconductor, so it is a variety of semiconductor resistor. "Zinc oxide" Now a lot of use of (ZnO) varistor, its main material divalent element zinc (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, the zinc oxide varistor is a "Ⅱ-Ⅵ family-oxide semiconductor." In China Taiwan, varistors called "surge absorber", sometimes also referred to as "electric shocks (surge) suppressor (absorber)."

The role of high performance and High Performance Varistor

mov varistor what's the use? The most important feature High Performance Varistor is added on top of it when a voltage lower than its threshold "UN" when little current flowing through it, the equivalent of a shut valve when the voltage exceeds the UN, its resistance becomes smaller, so that makes it the current flowing through the surge change on other circuits is unlikely to reduce applied voltage sensitive circuitry on the follow-up. Using this feature, you can suppress the circuit often appear abnormal over-voltage, over-voltage protection circuit from damage.
For example: Our household power circuit TV on the use of zinc oxide varistors efficient, high breakdown Varistor for counter used here is 470V, the maximum surge voltage when the transient (non-RMS) when more than 470V High Performance Varistor is a manifestation of his clamping characteristics, the high voltage is pulled down, so that the subsequent circuit work within a safe

Selection and precautions High Performance Varistor

Selection of High Performance Varistor before, you should know the following relevant technical parameters: Nominal voltage is at a predetermined temperature and direct current flow, voltage across the varistor efficient. Leakage current is at 25 ℃, when the application of the maximum continuous DC voltage, high varistor flowing current. Voltage rating refers Glass Coating varistors ating current pulses through 8/20 presented at both ends voltage peaks. Through traffic is applying a predetermined peak current pulse current (8 / 20μs) waveform when. Surge environmental parameters include a maximum inrush current Ipm (or the maximum surge voltage and surge Vpm source impedance Zo), surge pulse width Tt, two adjacent surge minimum interval Tm and the High Performance Varistor predetermined operating lifetime, the total number of surge pulses N and the like.

Generally, metal oxide varistor function often with the protection device or devices in parallel, under normal circumstances, High Performance Varistors across the DC or AC voltage should be lower than the nominal voltage, even when the power fluctuations at worst should not be selected higher than the rated maximum continuous operating voltage, the maximum continuous operating voltage value corresponding to a nominal voltage value is the choice of values. Overvoltage protection areas for the application, the varistor voltage value should be greater than the voltage value of the actual circuit, the general should be selected using the following formula: VmA = av / bc where:

a circuit for the voltage fluctuation coefficient; v DC operating voltage for the circuit (when ac rms); b for the varistor voltage error; c to component aging coefficients,; VmA actual value thus calculated is 1.5 times the operating voltage of the DC In exchange the state should also consider the peak, and therefore the results should be expanded to 1.414 times.

High Performance Varistor works

Response time and high voltage varistoris ns level, faster than gas discharge tube, slightly slower than the TVS tube, generally used in electronic circuit overvoltage protection to meet the requirements of its response speed. When High Performance Varistor junction capacitance range is generally on the order of hundreds to thousands of Pf, in many cases should not be directly applied in the protection of high-frequency signal line, the application in the protection of the AC circuit, as it greatly increases junction capacitance leakage current protection circuits designed to take full account. High Performance Varistor flow capacity is large, but smaller than the gas discharge tube. High Performance Varistor referred VDR, is a non-linear voltage-sensitive semiconductor element overvoltage protection.
l When applied to the Varistor for counter voltage is below its threshold, the current flowing through it is extremely small, it is equivalent to a resistance infinite resistance. That is, when a voltage is applied on top of it is below its threshold, which is equivalent to an OFF state of the switch.
l When applied to the High Performance Varistor voltage exceeds its threshold, the surge current flowing through it, which is equivalent to the resistance infinitely small resistance. That is, when added on top of it higher than its threshold voltage, which is equivalent to a closed switch.

High Performance Varistor

mov varistor is a non-linear voltage characteristics of the resistance of the device is mainly used in the voltage clamp circuit when subjected to excessive pressure, absorb excess current to protect sensitive devices. English name called "Voltage Dependent Resistor" abbreviated as "VDR", or called "Varistor". High Performance Varistor resistive material is a semiconductor, so it is a variety of semiconductor resistor. Now extensive use of "zinc oxide" (ZnO) varistors efficient, its main material divalent element zinc (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, zinc oxide varistor is an efficient "Ⅱ-Ⅵ Group oxide semiconductor." In China Taiwan, Glass Coating varistors called "surge absorber", sometimes also referred to as "electric shocks (surge) suppressor (absorber)."
High Performance Varistor is a voltage limiting protection devices. Efficient use of

the nonlinear characteristics of the varistor, when an overvoltage occurs between the two poles of the varistor efficient, high varistor voltage can be clamped to a relatively fixed voltage value, in order to achieve protection of the post-stage circuit. The main parameters and High Performance Varistors are: varistor voltage, current capacity, junction capacitance and response time.

The basic characteristics of high performance and High Performance Varistor

(1) protection feature, when the impact of the strong impact of the source (or inrush current Isp = Usp / Zs) does not exceed a predetermined value, High Performance Varistor limit voltage must not exceed the protected object can withstand impact resistance voltage (Urp ). Varistor for counter product
High Performance Varistor product

(2) impact resistance, namely High Performance Varistor itself should be able to withstand the impact of current, the impact energy, and several attacks have appeared when the average power.

(3) Life has two properties, one continuous working voltage of life, namely High Performance Glass Coating varistors (hours) at a predetermined ambient temperature and system voltage conditions should be able to work reliably stipulated time. Second, the impact of life, that can reliably withstand the impact of the number of times specified.

(4) High Performance Varistor after intervention system, in addition to protect a "safety valve", it will also bring some additional impact, which is the so-called "secondary effects", it should not reduce the normal performance of the system. Then there are factors to consider three, one High Performance Varistor itself capacitance (tens to tens of thousands PF), the second is in the system voltage leakage current, three are non-linear current through High Performance Varistor coupled source impedance effects on other circuits.

Junction capacitance varistors typically hundreds to thousands of magnitude range Pf

Mov varistor grade ns response time, faster than the gas discharge tube, slightly slower than the TVS tube, under normal circumstances electronic circuit for overvoltage protection to meet the requirements of its response speed. High voltage varistor junction capacitance range is generally on the order of hundreds to thousands of Pf, in many cases should not be applied directly the protection of high-frequency signal lines, and the application of the AC circuit protection, since it will increase the junction capacitance greater leakage current protection circuits designed to take full account. Metal oxide varistors  through-flow capacity is larger, but smaller than the gas discharge tube. Varistors referred VDR, it is a non-linear voltage-sensitive semiconductor element overvoltage protection.

When applied to the varistor voltage is below its threshold, the current flowing through it is extremely small, it is equivalent to a resistance infinite resistance. That is, when a voltage is applied on top of it is below its threshold, which is equivalent to an OFF state of the switch.
When applied to the varistor voltage exceeds its threshold, the surge current flowing through it, which is equivalent to the resistance infinitely small resistance. That is, when added on top of it higher than its threshold voltage, which is equivalent to a closed switch.

Varistor resistive material is a semiconductor

"Mov varistor" is a kind of non-linear voltage characteristics of resistance devices, mainly used for in-circuit withstand overvoltage voltage clamp, absorb excess current to protect sensitive devices. English name called "Voltage Dependent Resistor" abbreviated as "VDR", or called "Varistor". Varistor resistive material is a semiconductor, so high voltage varistor is a variety of semiconductor resistor. "Zinc oxide" Now a lot of use of (ZnO) varistor, its main material divalent element zinc (Zn) and hexavalent elemental oxygen (O) of the composition. So from the point of view of materials, the zinc oxide varistor is a "Ⅱ-Ⅵ family-oxide semiconductor." In China Taiwan, metal oxide varistors  called "surge absorber", sometimes also referred to as "electric shocks (surge) suppressor (absorber) . "

Varistor is a voltage limiting protection devices. The use of nonlinear characteristics of the varistor, when an overvoltage occurs in between the two poles of the varistor, the varistor voltage can be clamped to a relatively fixed voltage value, in order to achieve protection of the post-stage circuit. The main parameters of varistors are: varistor voltage, current capacity, junction capacitance and response time.