Inverters are circuits that convert dc to ac. More precisely, inverters transfer power from a dc source to an ac load. The controlled full-wave bridge converters in Chap. 4 can function as inverters in some instances, but an ac source must pre- exist in those cases. In other applications, the objective is to create an ac voltage when only a dc voltage source is available. The focus of this chapter is on invert- ers that produce an ac output from a dc input. Inverters are used in applications such as adjustable-speed ac motor drives, uninterruptible power supplies (UPS), and running ac appliances from an automobile battery.