Abstract: A method for operating a single-phase, mid-frequency welding transformer formed with a transformer core having a primary coil and a secondary coil connected into a secondary circuit has several steps. The several steps include regulating a magnetic flux density (B) in the transformer core between an upper flux density threshold value (Bm) and a lower flux density threshold value (?Bm), by applying, in alteration, a first voltage (UDC) and a second voltage (?UDC) to the primary coil of the transformer, and regulating a load current (ibr) in the secondary circuit between an upper load current threshold value (ibr-zg) and a lower load current threshold value (ibr-sp), by applying, in alternation, a third voltage (0V)to the primary coil of the transformer.

Abstract: The invention relates to a method for operating a transformer (130), in particular a (single-phase) mid-frequency welding transformer, with a transformer core (131) with a primary winding (132) and a secondary winding (133), which is connected into a secondary circuit (120), comprising the regulation of a magnetic flux density (B) in the transformer core (131) between an upper flux density threshold value (Bm) and a lower flux density threshold value (?Bm) and the regulation of a load current (ibr) in the secondary circuit (120) between an upper load current threshold value (ibr-zg) and a lower load current threshold value (ibr-sp). The invention likewise relates to a corresponding apparatus (200). The invention reduces in particular voltage peaks and saturation effects, which otherwise occur during operation of a mid-frequency transformer.