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(Ba0.7368Ca0.1 Sr0.16Sb0.0032)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 (R-25 degrees C) of 14.3 Omega, a resistivity jump (rho max/rho min) of 3.2 x 10(6), a temperature coefficient of resistance (TCR) of +20.4%/degrees C, and a maximum operating voltage (V-o) of 357.5 V-rms. 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 110mA 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 degrees C. In the simulated trip test, the circuit assumes a 220 V ac power contact with a transition current of I A,,,,, 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 degrees C. The present static and dynamic evaluation results demonstrate that the developed BCST thermistor satisfies the requirements of telecom overcurrent protection. (c) 2005 Elsevier B.V. All rights reserved.