Ceramic PTC thermistor operates as resettable fuse

September 29, 2016 // By Christoph Hammerschmidt
The PRG series of ceramic PTC thermistors from Murata is specifically for providing a resettable fuse function within a broad range of automotive and industrial automation equipment. In cases of excessive current, the thermistor element heats up and the resistance increases sharply. Once the temperature has fallen back to its normal temperature, current flow is restored. This effect can be utilized by using the PRG as a resettable fuse.

In comparison to polymer based PTC devices, Murata’s PRG series offers better stability and can operate over a higher current and voltage range. For example, a polymer PTC thermistor’s resistance characteristic changes when it is soldered in place and every time it operates. However, the ceramic-based PRG does not exhibit such changes in resistance making it a more reliable and predictable protection device.

The PRG series can be used for a variety of LED lighting and sensor/control protection for automotive applications. In the case of providing thermal protection for LED lighting it has the additional benefit that no additional LED driver is required to provide this function. By matching the PTC characteristic of the PRG device to the thermal derating curve of the LED it can operate in-line to the LED, saving component cost and board space. Short circuit protection of parking sensors, infotainment units and ADAS systems can also be provided by the PRG.

For factory automation equipment the PRG series can be used to protect the I/O lines of motor drive circuitry, programmable logic controllers (PLC), and for positional sensors and actuators. In order to match the factory automation standard 24 VDC line, the PRG series has a maximum voltage 32 VDC.

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