Surge Suppressors for the Protection of Solid-State Devices

Semiconductor devices are sensitive to overvoltages and must be protected against such potential sources of damage. Typical devices used for this purpose are capacitors, selenium diode suppressors, and avalanche diodes. In many industrial applications, however, switching overvoltages contain so much energy that these devices are inadequate, not in terms of voltage limiting capability, but in terms of energy absorbing capability. Some high energy overvoltages are described and methods of calculating both their magnitude and energy content are presented. The difficulties of protecting semiconductor devices against these overvoltages are discussed, particularly for those cases where it is desirable to have the surge suppressor on the dc side of the installation for economic reasons or for protection against possible surges generated from the dc side. A surge suppressor developed specifically for high energy overvoltages is then described, and typical test results are presented.