Power sources are available to provide direct current (DC), alternating current (AC), or both. A
transformer or an alternator type of source is used for AC welding, and transformer/rectifier or motor
generator type for DC welding. Some power sources (single phase transformer/rectifier or alternator
rectifier type) can be used for AC and DC welding. Inverters are becoming popular due to their
portability and smooth operating characteristics. Figure 4.5 shows a typical inverter power source.