The fundamental power-processing properties of switching converter circuits are modeled using generalized power-conservative (POPI) networks. Depending on the application, it may be most appropriate to model the first-order converter properties as those of an ideal transformer, gyrator, loss-free resistor, or other POPI network. These basic functions can be obtained either through selection of a topology that naturally possesses the desired characteristics or by addition of a suitable control network. Some well-known converter topologies are shown to behave naturally as gyrators, loss-free resistors, and constant power networks. The application of the gyrator to network two voltage sources and the use of the loss-free resistor as a unity power factor rectifier are described.