Abstract: An active transformer is disclosed of the type which includes two primary terminals to which is applied a voltage v.sub.1 with a current i.sub.1, and two secondary terminals supplying a voltage v.sub.2 with a current i.sub.2. The transformer is characterized in that it includes a first circuit whose input, connected to the primary terminals, generates an input current of the form i.sub.1 ' = jC.sub.1 .omega.v.sub.1 and whose output supplies a current of the form i.sub.2 " = -jN.omega.v.sub.1 to the secondary. The transformer also includes a second circuit whose input, connected to the secondary terminals, generates an input current of the form i.sub.2 ' = jC.sub.2 .omega.v.sub.2, and whose output supplies a current i.sub.1 " = -jN.omega.v.sub.2 to the primary. The terms C.sub.1, C.sub.2 and N are respectively the dual equivalents of the terms L.sub.1, L.sub.2 and M found in the relations associated with a conventional transformer. The currents flow in such a way that they satisfy the relations i.sub.1 = i.