The circuit of Fig. 21.13a enables us to rectify both the positive and negative half-cycles of an ac source, to supply dc power to a load R. The four diodes to gether make up what is called a single-phase bridge rectifier It is available in a single package. The circuit operates as follows: When source voltage E12 is positive. terminal 1 is positive with respect to terminal 2 and current i, flows through R by way of diodes Al and A2. Consequently, point 3 follows point 1, and point 4 follows point