What Is TMOV
TMOV stands for thermally protected metal oxide varistor. It is a type of metal oxide varistor that includes built-in thermal protection to prevent catastrophic failure due to sustained overvoltage conditions. TMOVs are commonly used in surge protection devices and electronic equipment to safeguard against transient voltage surges and provide reliable overvoltage protection. Littelfuse TMOV Thermally Protected Varistors are radially leaded metal oxide varistors (MOVs) with a thermally activated element designed to open during overheating. The integrated thermal element and the enclosure design work together to facilitate surge-protection module compliance to UL1449.
Advantages of TMOV
Safety
TMOVs offer an additional layer of safety with built-in thermal protection that disconnects the varistor from the circuit in case of overheating, reducing the risk of catastrophic failure.
Compatible
TMOVs can be easily integrated into existing surge protection systems or electronic circuits, providing seamless protection without requiring complex installation procedures.
Reliability
TMOVs provide reliable overvoltage protection for sensitive electronic equipment by absorbing and dissipating transient voltage surges, ensuring the longevity and performance of connected devices.
Versatility
TMOVs are suitable for a wide range of applications, including surge protection devices, power supplies, industrial equipment, and telecommunications systems, making them versatile components for various industries.
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Why Choose Us
Our factory
We have built a modern standard workshop with an area of 9000 square meters, hired more than 100 skillful employees, and set up three modern production lines with annual output of 15 million 34S’s standard MOVs and 3 million onboard SPDs.
Our certificate
Our products have been approved by UL and TUV safety certifications. Moreover, our company has obtained ISO 9001:2018 quality management system certification.
Advanced equipment
We also own a complete list of testing equipment, including 120kA 8/20μs and 15kA 10/350μs lightning tester, 2 ms rectangular surge tester, power frequency temporary overvoltage (TOV) tester, high temperature aging test chamber, constant temperature and humidity chamber, which effectively guarantees the safety and reliability of our product performance.
Our products
We have deliberately focused on metal oxide varistor (MOV), surge protected devices (SPD), and related technology services for more than 20 years.Our main product is MOV that be used in SPD and SPD.
Introduction to the Basic Knowledge of TMOV
Thermally protected varistors are a combination of varistors (TMOV) and temperature protection components (thermal fuses). With aging and Increasing exposure to overvoltages degrades varistors and the leakage current increases. In addition, leakage currents mean losses and they corrode grounding systems. If the varistor is in the range of the Threshold voltage in operation it becomes very hot. This presents a fire hazard. For maximum protection, a thermal fuse is inserted, which in the event of overtemperature triggers. This separates the varistor from the rest of the circuit or even the whole application disconnected from the power supply.
The series of products is a two- or three-lead metal oxide varistor. One of the leads is connected to a thermal link which is designed to open when is under sustained abnormal over-voltage conditions. Traditional Metal Oxide Varistors were originally designed to protect equipment from surges at the specified rated voltage, but Metal Oxide Varistors may fail to a short-circuit condition or fail to open when subjected to sustained steady-state over-voltage above its rated specifications. TVZ has a thermal link integrated with an TMOV disk that responds to the TMOV temperature and disconnects the TMOV from the line, should the temperature or voltage exceed a certain level. Three-leaded device is designed to be connected, via the monitor lead, to an indicator (such as an LED) to provide diagnostic features indicating if the TMOV is disconnected from the circuit in the event the thermal link element opens. As a result of the integration of the thermal link attached to the TMOV disc, Thermally Protected Varistors provide an instant response to unexpected over-voltage situations. Thermally Protected Varistors offer protection to sensitive downstream electric components. Additionally, varistors are wave solderable which simplifies end product assembly by reducing the expense and rework associated with hand soldering operations.
Parameters of TMOV
TMOV voltage
Breakdown voltage or threshold voltage, refers to the voltage value at a specified current. In most cases, the voltage values measured by 1mA DC current when passing through the TMOV can range from 10 to 9000V. It can be selected correctly according to the specific needs. The TMOV has an inflection point in the pre-breakdown area of its V ≤ I characteristic curve, which corresponds to a specific inflection point voltage and a specific inflection point voltage. When the applied voltage is higher than this inflection point voltage, the TMOV enters the "on" state (the resistance value becomes smaller); When the applied voltage is lower than this inflection point voltage, the TMOV enters the "cut-off" state (the resistance value becomes large).
Maximum continuous operating voltage(MCOV)
Because the TMOV has positive and negative symmetry volt-ampere characteristics, it can be applied to both DC circuit and AC circuit. MCOV refers to the maximum DC voltage (UDC )or the maximum AC voltage effective value (URMS) that the TMOV can withstand for a long time. TMOVs have a very special characteristic: long-term static power is very small, and instantaneous dynamic power is very large. Because the static power of TMOV is very small, the long-term working voltage applied to both ends of TMOV is absolutely smaller than its TMOV voltage UN, otherwise the TMOV will burn out due to overburden.
Maximum peal current
It is the maximum pulse current value when the TMOV voltage does not exceed ±10% for the specified impulse current waveform and the specified impulse current number at the ambient temperature of 25 ℃. In order to extend the service life of the device, the amplitude of the surge current absorbed by the ZnO TMOVs shall be less than the maximum flow rate of the product given in the manual. However, from the point of view of protection effect, the selected flow rate is required to be larger.
Residual Voltage(UR)
Residual voltage UR refers to the peak voltage at both ends of a particular waveform when the surge (surge) current flows into the TMOV. In general, the peak value of surge current flowing into TMOVs is above 1mA. For general TMOVs and protective TMOVs, the specific waveform refers to the 8 / 20 μ s standard lightning current waveform specified in IEC 60060 ≤ 2 ≤ 1973 standard, which is shown in the figure.
Residual Voltage ratio(Kp)
When the current flowing through the TMOV is a certain value, the voltage generated at both ends of the TMOV is called the residual voltage of this current value. The ratio of residual voltage to nominal voltage is the ratio of residual voltage to nominal voltage: KR=UR/UN. The residual voltage ratio reaction TMOV limits the energy of overvoltage, which has been widely used in the research of TMOV materials. It has become the standard electrical performance parameter in lightning protection TMOV, arrester valve plate and high energy TMOV valve plate.
Maximum limit voltage(Up)
Limiting voltage Up is a special form of residual voltage UR, and it is also a characteristic index to evaluate the ability of TMOVs of specific specifications to suppress transient overvoltage. A basic equivalent assessment current IP shall be specified for the TMOV of different chip diameters, and the limiting voltage Up of the TMOV of each chip diameter shall correspond to the specified good assessment current.
Ratio-voltage
The voltage ratio is the ratio of the voltage generated when the TMOV current is 1 mA to the voltage generated when the TMOV current is 0.1 mA.
Ceiling capacity(Em)
The maximum energy, Em, is the maximum energy of a surge current or a pulse current that can be dissipated by the TMOV. The meaning of bearing is that the TMOV voltage UN aftershock is less than ±10% compared with that before shock, and visual and visible mechanical damage can occur at the same time.
Electrical Characteristics of TMOV
A TMOV remains non-conductive as a shunt-mode device during normal operation when the voltage across it remains well below its "clamping voltage", thus TMOVs are typically used for suppressing line voltage surges. 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 TMOV can handle. Follow-through current resulting from a strike may melt, burn, or even vaporize the TMOV. 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. significantly exceeds the manufacture's "Absolute Maximum Ratings"). The probability of catastrophic failure can be reduced by increasing the rating, or using specially selected TMOVs in parallel.
Cumulative degradation occurs as more surges happen. For historical reasons, many TMOVs have been incorrectly specified allowing frequent swells to also degrade capacity. In this condition the TMOV is not visibly damaged and outwardly appears functional (no catastrophic failure), but it no longer offers protection. Eventually, it proceeds into a shorted circuit condition as the energy discharges create a conductive channel through the oxides.
The main parameter affecting TMOV life expectancy is its energy (Joule) rating. 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. As these pulses occur, the "clamping voltage" it provides during each event decreases, and a TMOV is typically deemed to be functionally degraded when its "clamping voltage" has changed by 10%. 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. In consumer electronics, particularly surge protectors, the TMOV TMOV size employed is small enough that eventually failure is expected. Other applications, such as power transmission, use VDRs of different construction in multiple configurations engineered for long life span.
Both theTMOV and TMOV(TM) varistors offer the same functionality as a high performance MOV (such as a Littelfuse UltraMOV(TM) Varistor) but have the added safety of an integrated thermally activated element. This element is designed to open when the MOV experiences the elevated temperatures normally associated with the abnormal sustained over-voltage limited current conditions outlined , thus reducing the potential threat of a thermal runaway condition. In addition to the integrated thermal element, theTMOV varistor includes the addition of a dedicated lead for purposes of indicating when the thermal element has opened. Thus, the iTMOV name represents "indicating" TMOV(TM).TheTMOV and TMOV(TM) varistors are intended, with appropriate enclosure design, to help facilitate TVSS module compliance sustained abnormal over-voltage, limited current requirements. Designed for TVSS modules, these innovative products can also be used in a variety of devices requiring power conditioning and protection, such as Uninterruptible Power Supplies, Power Supplies, Lighting Products and Communication Products.
In addition, when compared to a discrete thermal protection solution, the iTMOV/TMOV varistor provides better thermal response performance because the integrated thermal element is in direct contact with the MOV body. Likewise, the iTMOV/TMOV solution offers better clamping performance due to the reduced lead inductance versus a discrete design. In addition to reducing part count and increasing reliability, the iTMOV/TMOV products can be auto-inserted and wave soldered, eliminating manual component placement, and resulting in increased manufacturing throughput. These innovative products are currently available in standard 20mm packages with operating voltages ranging from 115Vac to 420Vac.
Constructed with a proprietary thermally protected varistor technology (TMOV) developed, this new varistor incorporates both a built-in thermal disconnect function and an electric arc shield. This combination provides an additional robust protection to prevent catastrophic failure and fire hazard even under the extreme circumstances of abnormal overvoltage conditions or varistor end-of-life. By incorporating the LST in your latest design, you not only will benefit from its wide operating voltage range, high surge current rating, and compliment of options for microswitch, your SPD will also be more robust to meet the protection demands of your customer’ s applications.
The flexibility of using imax rated devices with the same footprint on PCB. More options for designing remote indication/monitoring of SPD product or system via mechanically triggered AC and DC rated microswitch (Normally Open/Normally Closed, pin length, 2 pin/3 pin/without pin). Clear LST working status indication via a visual tab option that notifies service technicians and maintenance engineers to replace LST at end-of-life (EOL) to continue optimal surge protection for the end-product. Wide Operating Voltage Range: Up to 690 Vac for 50 kA version, up to 550 Vac for 75 kA version.
Our factory
GuiYang High-Tech YiGe Electronic Co., Ltd has been founded in October 2010 by four natural persons. We have deliberately focused on metal oxide varistor (MOV), surge protected devices (SPD), and related technology services for more than 20 years. As a national high-tech enterprise, we have a strong research and development (R&D) ability and competitive technological strength. We also have a long-term close cooperation with Guizhou University and obtained patents for many extraordinary inventions. Mr. Zihao Fei is our company’s legal person. He is a well-known Chinese expert in varistor technology and served in the International Electrotechnical Commission (IEC) SC37B for 5 years and Chinese Institute of Electronics (CIE) for 15 years. He participated in drawing up the international standard: IEC61643-331.2017: Components for Low-Voltage Surge Protective Devices Part 331: Performance Requirements and Test Methods for Metal Oxide Varistors (MOV). He is also the main drafter of the national standard: GB18802.331.2020: Components for low-voltage surge protective devices Part 331: Performance requirements and test methods for metal oxide varistors (MOV).
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