Thermal protection — The final authority in the safety chain

Thursday, 01 October, 2020

Overcurrents aren’t the only threat to modern electronics. Excessively high temperatures are increasingly becoming the number one enemy due to high power density. But how can such a danger be avoided? It makes sense to use thermal fuses. Or even better: thermal fuses with that certain extra.

A characteristic of modern electronics is their enormously high power density. More and more components and functions have to fit in the smallest possible space. This leads to particularly powerful products with small dimensions, with minimal risk potential. We are talking about thermal runaway. Thermal runaway refers to the overheating of a technical apparatus due to a self-reinforcing, heat-producing process. This damage usually causes the destruction of the equipment and often leads to fire or explosion.

Current measuring sensor

The temperature dependence of the electrical resistance of components must always be taken into account when designing assemblies and circuits. This property for measuring the current can also be used specifically.

Since overtemperature protection is usually triggered solely by thermal conditions and largely ignores the current flow, it often makes sense to combine such overtemperature protection with a current measuring sensor in the form of a shunt.

This means that a rapidly occurring fault (overcurrent) can be detected and interrupted by means of a shunt. A creeping temperature increase can be detected and interrupted by the thermal protection device.

The shunt — a low-impedance resistor with the lowest possible temperature dependence — allows precise measurements of the current flowing through the component, regardless of the ambient temperature. In the standard version of the RTS with shunt, the resistance of the measuring sensor is 500 μΩ. The small voltage dropping at this resistance is measured. Electronic circuits can also process lower voltages at the shunt. The lower the voltage, the less the measuring device influences the circuit. A controller processes the measured values received and can react with a separation of the circuit if the current is too high.

With shunt, the impedance of the RTS shows a significantly lower temperature dependence. For a clearer image, click here.

To learn how SCHURTER can help you with thermal protection, click here.

  1. Application Note: Protection against thermal runaway
  2. Application Note: Thermal fuses for Automotive

Top image credit: ©

Originally published here.

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