These dual unidirectional thyristor devices protect SLICs and ISDN power feeds in central office, access and customer premises equipment against overvoltages on the telecom line. Each protector section consists of a voltage-triggered unidirectional thyristor with an anti-parallel diode. In the negative polarity, the thyristor allows signal voltages, without clipping, up to the maximum off-state voltage value, VDRM, see Figure 1. Voltages exceeding VDRM are limited and will not exceed the breakover voltage, V(BO), level. If sufficient current flows due to the overvoltage, the thyristor switches into a low-voltage on-state condition, which diverts the current from the overvoltage through the thyristor. When the diverted current falls below the holding current, IH, level the thyristor switches off and restores normal system operation. Positive overvoltages are limited by the conduction of the anti-parallel diode. The TISP1xxxH3BJ is available in four voltages and has a 100 A 10/1000 current rating. These protectors have been designed particularly for use in equipment that must meet the following standards and recommendations: GR-1089-CORE, TIA-968-A (replaces FCC Part 68), ITU-T K.20, K.21 and K.45. Housed in a SMB03 package (3-pin modified SMB/DO-214AA), these parts are space efficient to replace protection designs of 100 A 10/1000 or less which use multiple SMBs or a 6-pin SMT package.