Littelfuse TMOV34S® Varistor Becomes Industry's Only Device Recognized to UL1449 up to 750 VAC Continuous Operating Voltage

CompanionTMOV25S Series Ideally Suited for Outdoor LED Lighting Market

CHICAGO - Littelfuse, Inc. (NASDAQ/NGS: LFUS), the worldwide leader in circuit protection, today announced the addition of the TMOV34S® Varistor Series to its Thermally-Protected MOV (TMOV®) line of products with UL1449 recognition to the demanding higher range voltage values from 115VAC to 750VAC. TMOV34S Series devices are the industry's only varistors that carry UL1449 recognition to 750VAC to protect circuits from abnormal overvoltage conditions. TMOV34S Varistor Series' higher voltage range makes it an ideal solution for solar power inverter and high voltage power supply applications.

Due to the close proximity of their integrated thermal element to the MOV body, they can offer quick thermal response in a far smaller component, an important advantage over competitive solutions that rely on mechanical designs. The TMOV34S Series joins the TMOV25S Varistor Series already available from Littelfuse, which is finding wide acceptance in outdoor LED lighting applications.

The 25mm-square-format TMOV25S® Series Varistor line is designed for applications that require meeting the abnormal overvoltage requirements of UL1449. Devices in the TMOV25S Varistor Series incorporate a patented thermally responsive element that will open in the event of overheating due to abnormal overvoltages. This series of products is based on the Littelfuse UltraMOV Series, which meets the surge suppressor component recognition requirements of UL1449 for both cord-connected and permanently connected Surge Protection Device (SPD) end products. These devices can be wave soldered without the need for special or expense assembly processes. With a standard operating voltage range of 115VAC to 750VAC to accommodate common AC line voltages, a wider operating voltage range than competitive products, they offer a high peak current rating of 20kA to help circuit designers meet SPD Type 1 requirements easily.

Unlike other products on the market that employ mechanical means of thermal protection that add bulk, the TMOV25S Series Varistor line has integrated thermal protection, allowing for a smaller package size that is more compatible with luminaire designs. The temperature-protected 25mm Varistor disc not only ensures the TMOV25S Series passes the new DOE Surge Immunity standards for Outdoor LED Lighting, but provides integrated thermal protection to guard against end-of-life MOV failures and temporary overvoltage faults.

The 25mm Varistor disc in the TMOV25S Series features a very robust design engineered to withstand multiple instances of 10,000A surge current (8x20microsecond waveform) without degradation. The fail-safe mechanism integrated into the TMOV25 Series simplifies placing the Varistor on the very front end of outdoor LED luminaire designs. Although a series fuse is typically used on the front end to protect standard Varistor discs, the TMOV25S Series device often makes this unnecessary. (Littelfuse recommends customers consult with their safety/compliance engineers to ensure safety compliant designs.) If the TMOV25S Series Varistor disc gets degraded due to multiple high surge events, the integrated thermal element will open and protect the MOV from failing and damaging the luminaire assembly.

The TMOV25S Series includes an optional third leg, designed to allow the Varistor to indicate that it has activated its self-protection function, thereby notifying the luminaire system that protection is no longer available, so the front end TMOV25 Series Varistor or the luminaire now requires replacement.

Devices in the TMOV34S Varistor Series combine a 34mm-square-format Varistor element (MOV) with high surge capability (up to 40kA) with an integrated thermally activated element. This element will open in the event of overheating due to abnormal overvoltage, limited current conditions. TMOV34S Series devices can offer quick thermal response to overvoltages in high energy circuits due to the close proximity of the integrated thermal element to the MOV body. The integrated configuration also offers lower inductance than most discrete solutions, resulting in improved clamping response to fast overvoltage transients. Some TMOV34S devices include a monitor lead, which may be connected to signaling circuitry to indicate if the MOV has been disconnected from the circuit.

TMOV34S Series devices are designed to suppress voltage transients by clamping them to a safe level; they are also engineered to disconnect themselves from high energy circuits safely in a sustained overvoltage, limited current condition as outlined in UL1449. Because they use the same pin layout as a standard 34mm Varistor, the two-leaded version of the TMOV34S Series can be used to replace standard devices without the need for a board redesign; the TMOV34S Series also offers the added functionality of thermal protection that standard Varistor devices don't provide.

Together, the TMOV34S and TMOV25S Varistor Series offer our customers a wider range of circuit protection options and exemplify our commitment to provide the industry's broadest and deepest portfolio of these solutions," said Littelfuse Product Manager Johnny Chang.

Littelfuse, the leader in Varistor technology, provides a comprehensive range of products and solutions that provide overcurrent protection for any electronic application. With 85 years of experience in building and supplying overcurrent protection products, Littelfuse is dedicated to providing application expertise and support that meets or exceeds customers' needs.


TMOV34S and TMOV25S Series Varistor samples are available now for bulk orders; sample requests through authorized Littelfuse distributors worldwide. For a listing of Littelfuse distributors, please visit

For More Information

For more information about Littelfuse and its circuit protection products, please visit the Littelfuse at or contact the Littelfuse Technical Support line at 1-800-999-9445. For circuit protection application design ideas, please visit the new Application Design Center section of the Littelfuse Web site.

About Littelfuse

Founded in 1927, Littelfuse, Inc., the worldwide leader in circuit protection, offers the industry's broadest and deepest portfolio of circuit protection products and solutions. Littelfuse devices protect products in virtually every market that uses electrical energy, from consumer electronics to automobiles to industrial equipment. In addition to its Chicago, Illinois, world headquarters, Littelfuse has more than 20 sales, distribution, manufacturing and engineering facilities in the Americas, Europe and Asia. Technologies offered by Littelfuse include Fuses; Gas Discharge Tubes (GDTs); Positive Temperature Coefficient Devices (PTCs); Protection Relays; PulseGuard® ESD Suppressors; SIDACtor® Devices; Silicon Protection Arrays(SPA(TM)); Switching Thyristors; TVS Diodes and Varistors. The company also offers a comprehensive line of highly reliable Electromechanical and Electronic Switch and Control Devices for commercial and specialty vehicles, as well as underground Power Distribution Centers for safe control and distribution of electricity in mining operations.


For more information, please visit

Littelfuse, Inc.

8755 West Higgins Road

Chicago, IL 60631


Marketing Contact:

Rhonda Stratton

Marketing Communications Manager

Littelfuse, Inc.



All Topics