The Murata Electronics PRF family of ceramic thermistors (or Posistors) are designed for overheat protection of power FETs in point of load (POL) DC to DC converters and other power supply applications. Each part has two temperature sensing points and features characteristics curves that rise very sharply. The series is represented in sizes from 0402 to 0805, has a resistance of 470 ohms at 25°C, rising to 4.7 kohms between 65 and 145°C, rising further to 47 Kohms between 80 and 150°C (depending on the part number). The PRF series offers a quick and easy design for repeatable overheat sensing providing resettable protection in the circuit because there is no hysteresis. With the decreasing size of today's power supply assemblies, the resulting increase in thermal density means these systems have higher risk of overheating. Increasing use of the distributed power architecture means there are a greater number of points that are likely to overheat. Murata Electronics' PRF series of ceramic thermistors increase their resistance very sharply when exposed to temperatures over a certain level and are ideal for high accuracy overheat sensing. Additionally, this characteristic provides a simple and reliable overheat sensing circuit. A change in the conditions around the FET such that the device went from normal levels to overheating, would produce a more than one hundred-fold increase in the resistance of the part. Compared with IC solutions, Murata Electronics PRF series represents a smaller and simpler solution to overheat detection and can be mounted anywhere that is required on the assembly, extremely close to a FET. It is also possible to sense multiple different temperatures in multiple different areas simply by connecting PRF thermistors in series. By applying an appropriate voltage dividing resistor, a circuit with multiple thermistors in series can easily be used to drive a transistor or FET to shut down the power supply. This eliminates the necessity for A/D converters and control software. Further attributes of the PRF series are an operating temperature range of -40 to +125°C (+150°C for automotive grade version), parts can detect overheat temperatures between 65 and 145°C, maximum operating voltage is 32V DC. Besides PTC thermistors for temperature and current sensing, Murata Electronics also makes a variety of NTC thermistors for current sensing and temperature sensing applications in sizes as small as 0201.