Fig. BR-1 shows the schematic of a six-pulse, controlled bridge rectifier connected to an ideal three-phase source with commutating inductances included in each phase. We'll start by first considering the operation of an uncontrolled rectifier without commutating inductances; i.e., the same circuit as shown except the thyristors are replaced by diodes and the inductors are removed. Without commutation, only two diodes will conduct at any time, one on the top half of the bridge and one on the bottom half of the bridge. Also, in order to have a voltage across the load, the two conducting diodes must be in different legs of the bridge; e.g., diodes 1 and 4 cannot be on at the same time. Thus the voltage applied to the DC load consists of a portion of a line to line voltage from the three phase source.