Abstract: AC/DC transformer for tapping power from an electric current loop (1) for current supply to a functional unit (2), whereby the current loop (1) conducts an alternating current preferrably having a constant frequency and amplitude for the current supply. The converter has an inductive coupling (4) to the current loop (1) and the latter constitutes a primary winding in the inductive coupling (4). At the secondary side there are provided rectifier means (LR) for DC supply to the functional unit (2), a voltage regulator (SR) for controlling an electronic switch (S), a power coil (L1) and at least one capacitor. The power coil (L1) is located at the AC side of the rectifier means (LR) and a capacitor (C1) is provided in series with the power coil (L1) and together with the latter is adapted to have resonance at a frequency coinciding substantially with the frequency of the current supply.