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Thermal protection

USN 1206 - Temperature sensitive SMD fuse

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Electrical and electronic equipment can not always count on constant voltage, constant current or constant working temperatures. Various influences lead to fluctuations, which must be secured by suitable means.

Overcurrent, overvoltage and undervoltage

An overcurrent protection device interrupts and maintains an electrical circuit when the electrical current exceeds a defined current level for a predetermined time. An overcurrent can be caused, for example, by overload or a short circuit.

Surges can be caused by a flash, by capacitive or by inductive couplings of other electrical systems. Electrostatic discharge (ESD) can also produce overvoltage.

When the mains voltage drops, so called undervoltage switches are needed. They are used to switch off electrical equipment, machines and systems when the voltage is too low, and prevent their restarting after a voltage failure.


The ever higher power density in electronic circuits and the trend towards miniaturization often lead to dangerously elevated temperatures. An increasing number of functions are packaged in compact modules which then also have a correspondingly high power consumption. Even slightly inflated currents in power electronics with little power dissipation lead to elevated temperatures of approximately 200 °C. The possible consequences are serious: damage or detachment of surrounding components, damage to the printed circuit board structure or, in the worst case, even the triggering of a fire.

Thermal runaway

With a power semiconductor (e.g. MOSFET) the drain-source transmission resistance increases with rising temperatures, when connected, which results in an increasing loss of power in the barrier layer. If the elements are not sufficiently cooled - the high power density permits cooling - the power loss output in the form of heat can no longer be sufficiently dissipated, which also increases the transmission resistance.

This process escalates and ultimately leads to destruction of the component.

RTS Reflowable Thermal Switch

RTS is a particularly compact overtemperature protection device for power semiconductors in SMD technology. RTS stands for "Reflowable Thermal Switch". It was developed to protect highly integrated power electronics from overheating, such as those used in the automotive, medical and many other industries.

The new type of overtemperature protection shines with the smallest dimensions and highest load capacity. Operating currents up to 100 A at rated voltages of up to 60 VDC can be handled by the RTS, which is just 6.6 x 8.8 mm in size.

Customer-specific variants are available with shunt or additional overcurrent protection, which further reduces space requirements. RTS meets the requirements of AEC-Q200 and MIL-STD.


USN 1206 Temperature-sensitive SMD fuse

The USN 1206 has been developed as an SMD temperature protection for power semiconductors (e.g., MOS FETs) in automotive applications. At the same time, it also provides protection against overcurrent. The USN 1206 from SCHURTER has high I2t values (slow characteristic) and a rated current of 12 A at 32 VDC. The fuse has a current-time characteristic which shifts as a function of the ambient temperature. As a result, a specific triggering at a certain threshold value can be achieved with increasing temperature.

The USN 1206 from SCHURTER is not a pure thermal fuse. It needs a current flow to trigger. The temperature-sensitive SMD fuse is therefore reflow solderable.


New technologies always place new demands on device protection, which often can only be met with tailor-made solutions.

Tony Flury, Sales Manager Customized Projects Europe, SCHURTER AG

Safety is our business

Innovation and engineering

SCHURTER is a leading innovator and manufacturer of fuses, connectors, circuit breakers, input systems, and EMC products as well as a PCB assembly service provider for the electronics industry worldwide. Success for and together with our customers is our permanent incentive. We are accustomed to being innovative to meet challenges in diverse markets. We boldly realize new ideas, and we support and drive forward our R&D teams, each day anew.

Quality across the entire line

Products and services from SCHURTER meet the highest demands on quality – because SCHURTER uses quality-, environmental- and safety management systems such as ISO 9001, ISO 14001, ISO 45001, the Six Sigma method, and the EFQM Excellence Model. All products carry country-specific testing labels such as VDE, ENEC, UL, and CCC. Further, customers profit from excellent service and short delivery times thanks to a well-organized international network of Group companies and distributors.

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