Compact Overvoltage Protection with an Integrated Fuse

TDK Corporation is exhibiting its new EPCOS ThermoFuse™ NT14 and NT20 series protected varistors at this week's electronica trade fair in Munich, Germany. The new ThermoFuse components feature a footprint that fits into existing circuit board layouts.

The NT14 series (disk diameter 14mm) is designed to absorb maximum surge currents with an 8/20-μs pulse of 6kA at rated voltages of between 130Vrms and 680Vrms, while the NT20 series (disk diameter 20mm) has a surge current capability with an 8/20-μs pulse of 10kA at rated voltages of between 130Vrms and 750Vrms.

The NT14 and NT20 series offer a maximum energy absorption of up to 220J and 480J for 2ms, respectively. Both series are available in 2-leaded and 3-leaded types, with the third lead used to monitor whether the fuse has been activated.

ThermoFuse varistors are uniquely designed disk varistors that are connected in series with a thermally coupled fuse and are therefore intrinsically safe. If the varistor overheats, the patented thermal fuse trips and isolates the varistor from the grid with unrivalled dependability.

This prevents any potential damage on the PCB or to components located near the varistor and increases the reliability of the equipment to be protected. Thanks to their thermal resistance and flame-retardant design of the epoxy coating, the ThermoFuse NT series meet UL 94 V-0 requirements, and are also listed as Type 4CA in UL 1449, 4th edition.

With their compact dimensions and excellent surge current capability over a broad range of voltages, the NT types are suitable for use in a wide range of applications, such as ballasts for lighting, home appliances, power supplies, inverters for solar installations, frequency converters for drives, and smart meters. They can also be used for the general protection of electrical wiring and installations.

Main applications

• Ballasts for lighting, home appliances, power supplies, inverters for solar installations, frequency converters for drives, smart meters
• General protection of electrical wiring and installations

Main features and benefits

• Compact size
• Wide range of voltages from 130Vrms to 750Vrms
• High surge current capability of up to 10kA
• UL 1449 listed