An excitation control circuit for a brushless synchronous welding generator, in which the stator-mounted excitation winding is fed from a separate voltage source via two parallel-connected power transistors with independently adjustable base circuits, one transistor controlling the excitation current in the idling mode, the other in the welding mode. A change-over switch, responding to an electromagnet in the welding current circuit, alternatingly energizes one transistor, while blocking the other.