Ceramic PTC thermistor resets fuse in automotive and industrial applications
Designed specifically to provide a resettable fuse in a range of automotive and industrial automation equipment, the PRG series of ceramic PTC thermistors have a normally low and flat resistance curve while current flows through it.
Excessive current causes the thermistor element to heat up, the value changing logarithmically once a certain temperature point has been reached, resulting in a significant reduction in current flow, explains Murata, to act as a resettable fuse, restoring current flow once the device’s temperature has reduced.
The ceramic-based thermistors offer stability and can operate over a higher current and voltage range than polymer PTC devices, says the company. For example, they do not have resistance changes when soldered in place and every time it operates.
The thermistors can be used for a variety of LED lighting and sensor/control protection for automotive applications. Providing thermal protection for LED lighting, no additional LED driver is required. 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, says the company. They can also be used for short circuit protection of parking sensors, infotainment units and ADAS.
For factory automation equipment, the series can be used to protect the I/O lines of motor drive circuitry, PLCs, and for positional sensors and actuators. To match the factory automation standard 24V DC line, the thermistors have a maximum voltage 32V DC. For this application, for example, the PRG21BC4R7MM1RK has a maximum operating voltage of 32VvDC, normal current setting of 155mA and a trip current of 330mA (both measured at 25 degree C.)