November 9, 2010

Varistors: Integrated self-protection against fire hazards (TDK-EPC Corporation)

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TDK-EPC, a group company of the TDK Corporation, presents a new series of EPCOS ThermoFuse varistors (ETFV) that are protected from overload and thus prevent fires. The ETFV series consists of a disk varistor of the AdvanceD series connected in series with a thermally coupled fuse and integrated in a package. The thermo-fuse encapsulated in a special plastic disconnects an overheated varistor from the power circuit and thus prevents the flames and smoke from developing. This increases the reliability of the equipment to be protected. Thanks to their thermal resistance and flame-retarding design, ThermoFuse varistors satisfy the specifications of UL 94 V-0. They are also qualified to UL 1449 3rd Edition, UL 60691 and IEC 6 0950-1 Annex Q.

In addition to the two terminal wires for the varistor, the EPCOS ETFV series has a third terminal that may be used to send warning signals – for example, to an LED to indicate that the fuse has been activated.

The product range comprises disks with diameters of 14, 20 or 25 mm including the package. TDK-EPC is one of the few manufacturers worldwide to offer a ThermoFuse varistor with a 25-mm disk. The ETFV variants are designed to absorb maximum surge currents with an 8/20 µs pulse of between 6 and 20 kA at rated voltages of between 130 and 420 VRMS. They have a surge current capability of 20,000 A and a maximum energy absorption capacity of 700 J for 2 ms.

Applications for ETFV include household appliances, power supplies, inverters for solar installations, and drives. They are also used for the general protection of electrical wiring and installations.


  • Varistor: voltage-dependent resistor (VDR) have a high resistance in their normal state. Only when a specific voltage is attained or exceeded do they suddenly become conductive. Thanks to this characteristic, they are well suited for overvoltage protection applications.

Main applications

  • Overvoltage protection of household appliances, power supplies, inverters for solar installations, and drives, as well as the general protection of electrical wiring and installations.

Main features and benefits

  • Integrated fuse for protection against fire and smoke formation
  • Specified to UL 94 V-0, UL 1449 3rd Edition, UL 60691 and IEC 6 0950-1 Annex Q
  • High surge current capability of between 6 and 20 kA (8/20 µs)

About TDK-EPC Corporation

TDK-EPC Corporation (TDK-EPC), a TDK group company, is a leading manufacturer of electronic components, modules and systems headquartered in Tokyo, Japan. TDK-EPC has emerged from the combination of the electronic components business of TDK and the EPCOS Group and markets its products under the product brands, TDK and EPCOS.

The product portfolio includes ceramic, aluminum electrolytic and film capacitors, ferrites and inductors, high-frequency components such as surface acoustic wave (SAW) filter products and modules, piezo and protection components, and sensors. With this product spectrum TDK-EPC offers a broad range of products and solutions of outstanding value from a single source and focuses on demanding markets in the areas of information and communication technology and automotive, industrial and consumer electronics. The company has design and manufacturing locations and sales offices in Asia, Europe, and in North and South America.

Further information on the products can be found under

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