In the figure we show how to use one of the four comparators in the LM336 in a temperature alarm. As the temperature rises, the voltage at the transistor collector decreases and with that, when the switching point, determined by R4 and R5, is reached, the comparator output goes to high level, triggering the relay. The critical components of this circuit that must be selected to obtain the trip at the desired temperature are R4 and R5 whose relation determines the trip point, and R1 and R2 which determines the sensitivity. The sensor is a general-purpose silicon NPN transistor, which can be installed away from the device. We do not give the pinout of the integrated, as any of the four comparators in the LM339 can be used independently.
