Low-power temperature detector and rate of temperature change detector

A temperature detection switch and a “rate of temperature change” detection switch are designed by using the dependence of the inverse saturation current of the p-n junction on temperature. This current is compared to the constant reference current in the case of the temperature detector or, for the detector of the rate of temperature change, to the inverse saturation current of another p-n junction, having different thermal time constant and different junction area. Relying upon the shape of the static characteristic of the constant reference current source, realized in a usual manner, and the inversely polarized p-n junction, the low-power current comparator is realized by a simple series connection of the current sources, with the supply voltage applied at the end points and the detector output voltage derived from the midpoint. Besides describing the operating principle, the paper contains the analysis of the thermal model of the switches and the accuracy investigations. The design criteria are experimentally confirmed. Due to their accuracy (0.1°C), simplicity, and extremely low power consumption (supply current is less than 10 μA), present detectors are especially suitable for applications in fire alarms.