The invention relates to a method for regulating a welding current source with a current transformer, which has a series resonant circuit on the primary side and a parallel resonant circuit on the secondary side, the series resonant circuit being supplied with a variable alternating voltage by a bridge circuit and the parallel resonant circuit providing energy to a welding process by way of a rectifier, and a control unit controlling the bridge circuit in dependence on at least one state variable of the welding current source. In order to develop the method in such a way as to make regulation possible at low cost and with as little power loss as possible, it is proposed according to the invention that only the primary current or a state variable on the primary side corresponding to the primary current is recorded as the electrical-current state variable of the welding current source and a control signal dependent on the primary current or on the state variable corresponding thereto is fed to the control unit. A welding current source for carrying out the method is also proposed.