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.