The HS4040NAQ2 from Littelfuse is a Silicon Controlled Rectifier with Breakover Voltage 400 V, Breakover Current 40 A, Gate Trigger Voltage 1.6 V, Gate Trigger Current 0.045 A, Temperature Operating Range -40 to 150 Degree C. Tags: Through Hole. More details for HS4040NAQ2 can be seen below.