The gate-triggered SCR turn-on transient

Summary

Soon after the application of the forward bias to the p gate of an SCR in the off-state, the cathode starts emitting electrons in an area in the vicinity of the gate contact. These electrons are collected by the center junction, are swept into the n base, and slightly forward bias the p emitter (the anode junction). Holes begin to flow in the direction of the collecting center junction; when they reach the p base they increase further the electron injection. This process continues until eventually the holding current density J _h of the device is exceeded and the device is latched in. The time necessary to reach 10 percent of the final anode current—counted from the beginning of the gate current pulse—is designated as the delay time. The time interval between the 10 and 90 percent of I _A is called the rise time t _r. Beyond the 0.9 I _A point, the current increases usually with much smaller rate: the current spreads laterally from a comparatively small area until the whole cathode area conducts. The full current is reached after some time t _s. These three time intervals are evaluated on the basis of the thyristor charge-control model.