A circuit component (L1) with controllable impedance, includes a body (1) of a magnetizable material, a main winding (A1) wound round the body (1) about a first axis and a control winding (A2) wound round the body (1) about a second axis, at right angles to the first axis, where the main winding (A1) is arranged for connection to a working circuit in which the circuit component (L1) is to be employed and the control winding (A2) is arranged for connection to a control unit for controlling the impedance in the working circuit. The circuit component or a similar transformer device can be included in various current and voltage regulating devices.