Evaluation of a novel PTC thermistor for telecom overcurrent protection

This paper presents a novel PTC thermistor for telecom overcurrent protection. The proposed thermistor is composed of Mn(NO3)2-doped(Ba0.7368Ca0.1Sr0.16Sb0.0032)Ti1.01O3 (abbreviated BCST) and a small amount of SiO2 and is fabricated using traditional ceramic processes. By integrating compositional modification, dopant addition and double annealing techniques, good static material properties are obtained, including a room resistance (R25 °C) of 14.3 Ω, a resistivity jump (ρmax/ρmin) of 3.2 × 106, a temperature coefficient of resistance (TCR) of +20.4%/°C, and a maximum operating voltage (Vo) of 357.5 Vrms. In order to evaluate the dynamic characteristics of the device when working in rated and trip conditions, two simulation circuits are designed in accordance with ITU-T recommendation K.30. In the simulation circuit for the rated test, the thermistor is required to pass 110 mA for 1 h with a 50 V dc supply. The results indicate that a stable operation cannot be maintained when the thermistor operates at ambient temperatures exceeding 45 °C. In the simulated trip test, the circuit assumes a 220 V ac power contact with a transition current of 1 Arms and the response time of the thermistor is measured under a range of ambient temperatures. It is found that the response time of the device is always less than 4 s over the temperature range of −10 to 80 °C. The present static and dynamic evaluation results demonstrate that the developed BCST thermistor satisfies the requirements of telecom overcurrent protection.