Resistance welding apparatus (2; 3; 3A, 4) for the resistance welding of at least one component (6, 7), comprising a welding tool comprising at least one welding electrode (11, 12) which is to be contacted with the at least one component (6, 7) for the purpose of welding, at least one welding transformer for feeding an electric current to the welding tool during the welding of the at least one component (6, 7), a series circuit comprising two transistors (41, 42; 43, 44), which are connected between the welding tool and an output on the secondary side of the welding transformer, characterized in that the welding transformer has a polarity switching module and the resistance welding apparatus has a control device, for controlling the polarity of the at least one welding transformer by transmitting polarity information (25A, 25B; 26A, 27A; 28A, 29A), which is linked with a power terminal (U 1) on the primary side of the at least one welding transformer, to the polarity switching module, wherein the polarity information (25A, 25B; 26A, 27A; 28A, 29A) is information about how the polarity of the at least one welding transformer is to be switched, wherein the polarity switching module is configured to evaluate the polarity information (25A, 25B; 26A, 27A; 28A, 29A) for the purpose of switching the polarity of the at least one welding transformer, and wherein the polarity switching module is configured, in each case depending on the polarity information (25A, 25B; 26A, 27A; 28A, 29A) and a polarity preselection preset in the polarity switching module, to switch one transistor (41; 43) of the series circuit in a positively conducting fashion depending on the evaluation result and to switch the other transistor (42; 44) of the series circuit in a negatively conducting fashion during synchronous operation with electric current to the welding tool, as a result of which the polarity of said one transistor (42; 44) of the series circuit is rotated relative to the polarity of the other transistor (41; 43) of the series circuit, and such that the polarity of the at least one welding transformer is switchable in order to realize a polarity-switchable welding voltage (U21, U22) and a polarity-switchable welding current at the welding transformer. a welding tool comprising at least one welding electrode (11, 12) which is to be contacted with the at least one component (6, 7) for the purpose of welding, at least one welding transformer for feeding an electric current to the welding tool during the welding of the at least one component (6, 7), a series circuit comprising two transistors (41, 42; 43, 44), which are connected between the welding tool and an output on the secondary side of the welding transformer, characterized in that the welding transformer has a polarity switching module and the resistance welding apparatus has a control device, for controlling the polarity of the at least one welding transformer by transmitting polarity information (25A, 25B; 26A, 27A; 28A, 29A), which is linked with a power terminal (U 1) on the primary side of the at least one welding transformer, to the polarity switching module, wherein the polarity information (25A, 25B; 26A, 27A; 28A, 29A) is information about how the polarity of the at least one welding transformer is to be switched, wherein the polarity switching module is configured to evaluate the polarity information (25A, 25B; 26A, 27A; 28A, 29A) for the purpose of switching the polarity of the at least one welding transformer, and wherein the polarity switching module is configured, in each case depending on the polarity information (25A, 25B; 26A, 27A; 28A, 29A) and a polarity preselection preset in the polarity switching module, to switch one transistor (41; 43) of the series circuit in a positively conducting fashion depending on the evaluation result and to switch the other transistor (42; 44) of the series circuit in a negatively conducting fashion during synchronous operation with electric current to the welding tool, as a result of which the polarity of said one transistor (42; 44) of the series circuit is rotated relative to the polarity of the other transistor (41; 43) of the series circuit, and such that the polarity of the at least one welding transformer is switchable in order to realize a polarity-switchable welding voltage (U21, U22) and a polarity-switchable welding current at the welding transformer.