The S4040RQ2TP from Littelfuse is a Silicon Controlled Rectifier with Breakover Voltage 400 V, Breakover Current 40 A, Gate Trigger Voltage 1.8 V, Gate Trigger Current 0.045 A, Temperature Operating Range -40 to 125 Degree C. Tags: Through Hole. More details for S4040RQ2TP can be seen below.