Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT. Similar to diodes, thyristors, also called silicon controlled rectifiers (SCRs), pass current in one direction from the anode to cathode, and block current flow in the other direction. However, current passage can be controlled through a "gate" terminal, which requires a small current pulse to turn on the thyristor so it can start conducting. Thyristors are four-layer devices, composed of alternating layers of n-type and p-type material, thereby forming PNPN structures with three junctions. The thyristor has three terminals; with the anode connected to the p-type material of the PNPN structure, the cathode connected to the n-type layer, and the gate connected to the p-type layer nearest the cathode. The objective of this experiment is to study a controlled thyristor-based half-wave rectifier at different conditions, and understand how different timings of the gate pulse affect the DC output voltage.