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A thermal switch (sometimes thermal reset or thermal cutout (TCO)) is a device which normally opens at a high temperature (often with a faint "plink" sound) and re-closes when the temperature drops. The thermal switch may be a bimetallic strip, often encased in a tubular glass bulb to protect it from dust or short circuit. Another common design ...
Over large changes in temperature, calibration is necessary. Over small changes in temperature, if the right semiconductor is used, the resistance of the material is linearly proportional to the temperature. There are many different semiconducting thermistors with a range from about 0.01 kelvin to 2,000 kelvins (−273.14 °C to 1,700 °C). [15]
Circuit-breakers can be placed at portions of a circuit in series to the path of current it will affect. If more current than expected goes through the circuit-breaker, the circuit breaker "opens" the circuit and stops all current. A fuse is a common type of circuit breaker that involves direct effect of Joule-overheating.
The diagram shows an equivalent thermal circuit for a semiconductor device with a heat sink: Q ˙ {\displaystyle {\dot {Q}}} is the power dissipated by the device. T J {\displaystyle T_{\rm {J}}} is the junction temperature in the device.
A resettable fuse or polymeric positive temperature coefficient device (PPTC) is a passive electronic component used to protect against overcurrent faults in electronic circuits. The device is also known as a multifuse or polyfuse or polyswitch .
An inrush current limiter is a device or devices combination used to limit inrush current. Passive resistive components such as resistors (with power dissipation drawback), or negative temperature coefficient (NTC) thermistors are simple options while the positive one (PTC) is used to limit max current afterward as the circuit has been operating (with cool-down time drawback on both).
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Another style of protection is to measure the temperature of the outside of the transistor, as an estimate of junction temperature, and reduce drive to the device or switch it off if the temperature is too high. If multiple transistors are used in parallel, only a few need to be monitored for case temperature to protect all parallel devices.