The MDC501-18io2 from Littelfuse is a Silicon Controlled Rectifier with Breakover Voltage 1800 V, Breakover Current 503 A, Gate Trigger Voltage 0.85 V, Gate Trigger Current 1195 A, Temperature Operating Range -40 to 125 Degree C. Tags: Surface Mount. More details for MDC501-18io2 can be seen below.