Selection points of the semiconductor discharge tube:
1, the maximum instantaneous peak current IPP must be greater than the standard value of communication equipment. Such as the type of FCC IPP should be greater than 100A; Bellcore 1089 IPP should be greater than 25A (Part68A).
2, the transition voltage VBO must be less than the maximum allowable instantaneous peak voltage of the protected circuit.
3, the semiconductor arrester is in a conducting state, the power loss of P should be less than the rated power of Pcm, Pcm=KVT*IPP, K which is decided by the short circuit current waveform. For the exponential wave, Fang Bo, sine wave, triangular wave K value were 1, 1.4, 2.2, 2.8.
4, the reverse breakdown voltage VBR must be greater than the maximum operating voltage of the protected circuit. As in the POTS application, the maximum ringing voltage (150V) peak voltage (150*1.41=212.2V) and DC bias peak (56.6V) and 268.8V devices, so choose VBR more than 268.8V. Also in the ISDN application, the maximum DC voltage (150V) and the maximum signal voltage (3V) sum of 153V, so should choose VBR greater than 153V devices.
5, if the semiconductor arrester through large inrush current after reset, the current must be greater than the system can maintain the current IH devices can provide value. In addition to lightningsurge, semiconductor arrester is pressure devices used, have mounted, in-line and axial lead type three package form. In circuit protection scheme, semiconductor arrester in general parallel circuit, the device moves, the highest value, can be regarded as open, almost no impact on the circuit. When the abnormal pulse, the resistance moment decreased, the instant release of current. When the abnormal high pressure disappears, and it returns to the high resistance state, the circuit works normally.