Electrical essays: A nonlinear problem

The ordinary rectifier circuit is used in many applications. Single-phase excitation is the most common for low power requirements. In order to increase the ripple frequency and thus simplify the filter design, it is necessary to introduce some phase inverter device, usually a transformer with a center tapped secondary, and full-wave rectification is obtained. Under such condition of operation the average currents through each half of the secondary are equal and their directions are such as to produce a net zero average magnetomotive force on the core of the transformer. As the magnetomotive force due to the primary current must oppose that due to the secondary currents, and as the net secondary magnetomotive force has zero average, the primary current will have zero average.