These low-voltage dual bidirectional thyristor protectors are designed to protect ISDN applications against transients caused by lightning strikes and a.c. power lines. Offered in two voltage variants to meet battery and protection requirements, they are guaranteed to suppress and withstand the listed international lightning surges in both polarities. Transients are initially clipped by breakdown clamping until the voltage rises to the breakover level, which causes the device to crowbar. The high crowbar holding current prevents d.c. latchup as the current subsides. These monolithic protection devices are fabricated in ion-implanted planar structures to ensure precise and matched breakover control and are virtually transparent to the system in normal operation.