TDK Corporation presents two new series of ThermoFuse varistors, which are equipped with monitor outputs and integrated thermal protective components for overvoltage protection.

The MT25 series (B72225M*) currently covers a voltage range from 150 V_RMS to 385 V_RMS, and its maximum surge current capability is 20 kA at a pulse form of 8/20 µs, according to IEC 61643-11. With dimensions of 25 x 28 x 14 mm, the completely encapsulated protective components feature a particularly compact design. Their monitor outputs are optionally available with or without electrical isolation. The MT30 series (B72230M*) includes types, which are designed for voltages from 150 V_RMS to 750 V_RMS. Its maximum surge current capability is 25 kA at a pulse form of 8/20 µs according to IEC 61643-11, with dimensions of 34 x 28 x 14 mm. The monitor outputs of these varistors are designed without electrical isolation.

The new ThermoFuse varistors are specially developed quadratic disk varistors, which are connected in series with a patented thermal protective component design. In the case of a persistent overvoltage and therefore heating of the varistor, the fuse is activated and separates the varistor from the circuit with a high level of reliability, preventing potential damage to the PCB or the components installed in the varistor’s vicinity. What’s more, disconnection from the mains protects against a thermal runaway.

Thanks to their high thermal resistance and use of flame retardant materials for the housing, the ThermoFuse MT25, and MT30 series varistors meet the requirements of flammability rating UL 94 V-0. They are listed in the UL 1449 standard 4th Edition.

These varistors’ main applications include photovoltaic inverters, powerful industrial power supplies, and inverters, as well as power supplies for lighting systems and telecommunications systems.