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Talk about the application scope and selection method of semiconductor discharge tube
Semiconductor discharge tube is a kind of overvoltage protection device, which is made of thyristor principle. It relies on the breakdown current of PN junction to trigger the conduction of discharge, and can flow a large surge current or pulse current. The range of its breakdown voltage constitutes the range of overvoltage protection.
Semiconductor discharge tubes have a wide range of applications and can be used in modems, fax machines, PBX systems, telephones, POS systems, analog and digital cards, etc. The following points should be noted when selecting a semiconductor discharge tube: the maximum instantaneous peak current IPP must be greater than the specified value of the communication equipment standard. For example, IPP of FCC Part68A type should be greater than 100A; IPP of Bellcore 1089 should be greater than 25A.
The breakover voltage VBO must be less than the maximum instantaneous peak voltage allowed by the protected circuit. When the semiconductor discharge tube is in the on state (conduction), the lost power P should be less than its rated power Pcm,Pcm = KVT * IPP, where K is determined by the waveform of the short-circuit current. For exponential wave, square wave, sine wave, triangle wave K values are 1.00,1.4,2.2,2.8.
The reverse breakdown voltage VBR must be greater than the maximum operating voltage of the protected circuit. For example, in POTS applications, the sum of the maximum ringing voltage (150V) peak voltage (150*1.41=212.2V) and the DC bias peak value (56.6V) is 268.8V, so devices with VBR greater than 268.8V should be selected. For example, in ISDN applications, the sum of the maximum DC voltage (150V) and the maximum signal voltage (3V) is 153V, so devices with VBR greater than 153V should be selected.
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