Figure 5.12, Isolated Switching Mode Power Supply Circuit. On the left is a line plug. The bottom, wide, prong goes to the bottom AC input of a bridge rectifier. The top prong goes through a fuse to the top AC input. C1 is connected from the positive to the negative output of the bridge. There are two N P N transistors that have their emitters connected to the negative of the bridge. The positive connects to the center tap of a primary winding on a special transformer. The ends of this winding go to the collectors of the two transistors. There is another center tapped winding on the left side of the core. Its ends are connected to the bases of the two transistors. A resistor, R2, connects from the positive bridge output to the center tap of the base winding. Another resistor, R1, connects from the center tap to the negative of the bridge. A capacitor, C2, is in parallel with R1. The loan secondary winding has no center tap. Another bridge rectifier is connected to it in the usual way. A capacitor, C3, is connected to the bridge in the usual way. The positive bridge output goes to the positive output of the power supply. The negative of the bridge goes to the negative supply output. End verbal description.