Littelfuse Releases New Thermally-Protected MOV Varistor

Littelfuse, Inc. introduced the two-leaded version of the TMOV34S series, an addition to the TMOV® series which is a thermally protected varistor that represents a new development in circuit protection. It consists of a 34mm square-format varistor element (MOV) with an integrated thermally active element. The thermal element is designed to open and safely disconnect the device in the event of overheating due to certain conditions.

The company claims that this patented design is superior to the use of the discrete thermal cutout (TCO) and MOV combination because it offers a faster disconnection time, more reliable operation, reduces part count and can be wave soldered.

Unlike varistors that do not have thermal protection, the TMOV34S series varistor is designed specifically to help customers meet the abnormal overvoltage conditions specified in Section 37 of UL 1449. This new device will enable compliance with the 3rd edition of UL 1449 when it comes into force.

The company states that designers can use this technology to improve product safety and reliability, and to make their own designs compliant with UL 1449. Suggested applications include TVSS products, ac power protection modules, ac power meters, uninterruptible power supplies and power supplies for cell phone base stations.

The TMOV34S is also already available in the three-lead version; the third lead is an indicator option that may be used to signal that the device has disconnected itself from the circuit.

Steady-state ac voltage ratings range from 115 to 750V. Single pulse energy ratings for the 8/20 s current wave per UL 1449 are up to 40kA, and single pulse energy ratings for a 2ms current wave range from 235 to 1050J. Operating ambient temperature is -55 to +85°C.

The TMOV34S series are available in quantities of 180 pieces now.