CPTC Thermistor Application Note Temperature Sensor 1. Brief of product The resistance prevails on high resistance or lower resistance by the change of ambient temperature, opening the return circuit by clear change of resistance. It can avoid damage and protect the element. The characteristics are various of control temperature and satisfied with different demand. 2. Main parameter a、Temperature of sensor (TS) b、Resistor of temperature at TS+5℃ (RTS+5℃,Min.) c、Resistor of temperature at TS-5℃ (RTS-5℃,Max.) d、Resistor of temperature at 25℃ (R25) e、Maximum operating voltage (Vmax) 3. Principle of temperature sensor The PTC thermistor is connected into the bridge arm of a comparator circuit (see Fig. 27). At normal temperature, PTC thermistor resistance (Rp ) is lower than Rs, so the comparator's output voltage will be low. When over temperature occurs, the PTC thermistor will quickly heat up to its switch temperature, its resistance will be higher than Rs , causing Vo to increase to a level sufficient to activate a trip (see Fig.28). Fig.1 Typical comparator circuit THINKING ELECTRONIC INDUSTRIAL Co., LTD. Fig.2 Typical switch characteristic 1 www.thinking.com.tw 2008.07 CPTC Thermistor Application Note 4. Circuit for application typical Fig.3 Temperature protection of electric motors Fig.4 Liquid-level indication Fig.6 Alarm installation Fig.5 Temperature compensation of transistor circuits THINKING ELECTRONIC INDUSTRIAL Co., LTD. 2 www.thinking.com.tw 2008.07