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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.
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 ...
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 .
When overheating, the temperature of the part rises above the operating temperature. Overheating can take place: if heat is produced in more than expected amount (such as in cases of short-circuits, or applying more voltage than rated), or; if heat dissipation is poor, so that normally produced waste heat does not drain away properly.
Electromechanical protective relays operate by either magnetic attraction, or magnetic induction. [9]: 14 Unlike switching type electromechanical relays with fixed and usually ill-defined operating voltage thresholds and operating times, protective relays have well-established, selectable, and adjustable time and current (or other operating parameter) operating characteristics.
The most popular application is the inrush protection of the AC current in switching power supplies (SPS). The primary reason for having surge current suppression in a SPS is to protect the diode bridge rectifier as the input or charging capacitor is initially charged. This capacitor draws significant current during the first half AC cycle and ...
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The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit.