Silicon controlled rectifier (SCR) forward-breakover voltage
Thyristors 12 Silicon controlled rectifier (SCR) Turning SCR off When the gate returns to 0 V after the trigger pulse is removed, the SCR cannot turn off; it stays in the forward- conduction region. The series switch in part (a) simply reduces the anode current to zero and causes the SCR to turn off. The parallel switch in part (b) routes part of the total current away from the SCR, thereby reducing the anode current to a value less than I H .
Thyristors 13 • Holding current, I H . Value of anode current below which the SCR switches from the forward conduction region to the forward blocking region. I H increases with decreasing values of I G , and is maximum for I G = 0. Silicon controlled rectifier (SCR) SCR Specifications
Thyristors 14 • Circuit fusing (I 2 t) rating Indicates the maximum forward surge current capability of the device. If this rating is exceeded, the device will be destroyed due to excessive power. I S surge current , and t max max imum duration of surge current . I 2 t ( rating ) t max I S 2 where One SCR application is as a surge protection device, and the circuit fusing rating is critical. Silicon controlled rectifier (SCR) SCR Specifications