Transformer comprising a toroidal core, wherein the transformer has a primary winding and a secondary winding which are wound on the toroidal core, wherein the secondary winding has part-windings (S1, S2), wherein the part-windings are at a distance from one another, in particular at a regular distance from one another, in the circumferential direction of the toroidal core, wherein the intermediate regions present between the part-windings in the circumferential direction comprise turns (P1, P2) of the primary winding, wherein the transformer has a flux-concentrating member which is arranged outside the spatial region around which the primary winding and the secondary winding are wound, and arranged outside the toroidal core, wherein the flux-concentrating member has a first ferrite ring which is arranged coaxially with the toroidal core, wherein the first ferrite ring is axially at a distance from the toroidal core together with the primary winding and the secondary winding, wherein the wall thickness of the first ferrite ring is smaller in the axial direction than in the radial direction, wherein the flux-concentrating member has a second ferrite ring which is arranged coaxially with the toroidal core, wherein the wall thickness of the second ferrite ring is smaller in the radial direction than in the axial direction, wherein the radial-distance region covered by the second ferrite core is at a distance from the radial-distance region covered by the toroidal core together with the primary winding and the secondary winding, wherein the axial region covered by the second ferrite core is encompassed by, or overlaps with, the axial region covered by the toroidal core together with the primary winding and the secondary winding. wherein the transformer has a primary winding and a secondary winding which are wound on the toroidal core, wherein the secondary winding has part-windings (S1, S2), wherein the part-windings are at a distance from one another, in particular at a regular distance from one another, in the circumferential direction of the toroidal core, wherein the intermediate regions present between the part-windings in the circumferential direction comprise turns (P1, P2) of the primary winding, wherein the transformer has a flux-concentrating member which is arranged outside the spatial region around which the primary winding and the secondary winding are wound, and arranged outside the toroidal core, wherein the flux-concentrating member has a first ferrite ring which is arranged coaxially with the toroidal core, wherein the first ferrite ring is axially at a distance from the toroidal core together with the primary winding and the secondary winding, wherein the wall thickness of the first ferrite ring is smaller in the axial direction than in the radial direction, wherein the flux-concentrating member has a second ferrite ring which is arranged coaxially with the toroidal core, wherein the wall thickness of the second ferrite ring is smaller in the radial direction than in the axial direction, wherein the radial-distance region covered by the second ferrite core is at a distance from the radial-distance region covered by the toroidal core together with the primary winding and the secondary winding, wherein the axial region covered by the second ferrite core is encompassed by, or overlaps with, the axial region covered by the toroidal core together with the primary winding and the secondary winding.