A 3 V thermostat circuit

An integrated thermostat circuit is described in this paper. It contains a bandgap reference, a temperature sensor and two hysteresis comparators. Two temperature trip points are generated by dividing down the bandgap voltage reference using three external resistors or an internal resistive network. The temperature sensor circuit generates a voltage proportional to temperature. Two comparators are designed for a 3 degree C internal hysteresis, and their outputs support CMOS/TTL logic levels. The circuit works with a supply voltage of 2.7 V to 10 V. It shows a trip point accuracy better than 2 degree C at room temperature and 3 degree C over the temperature ranging from -40 degree C to 125 degree C. The temperature sensor output voltage slope is 6.25 mV per degree C. The thermostat is fabricated using a standard bipolar process, and packaged in an 8-pin SOT package.