A transformer may include a first and a second continuous single piece multi-turn helical winding, one concentrically received by the other. The turns of the windings are electrically insulated from one another and spaced sufficiently close together to permit inductive coupling therebetween. The turns may be formed of a conductor having a rectangular cross-section, which may, or may not, include an electrically insulative sheath. The single piece multi-turn helical windings may have a continuous or smooth radius of curvature, with no discontinuities or singularities between first and second end terminals. The transformer may be formed by wrapping electrical conductor about a winding form. The transformer may be used in various electrical circuits, for example converter circuits.