An electric transformer circuit for connecting electrical equipment, such as a renewable energy-based generator or an energy storage system, to an electric grid. The circuit includes a first voltage converter connected to the equipment; a transformer connected to the first converter and a second voltage converter connected to the transformer and the electric grid. The transformer is a weakly coupled transformer, the magnetic coupling between the first coil and the second coil being less than 0.7. The transformer includes a first and second capacitor respectively associated with a first and second coil so as to form, with the corresponding coil, a circuit resonating at frequency f0. The electric transformer circuit can be included in an electric installation.