A method and device for controlling a power source of a welding, cutting or plasma coating system is provided. The power source comprises a measuring part and a controllable clocked power part. A value correlating with a characteristic variable of the power part to be controlled is continuously measured by means of the measuring part, to obtain an electrical measured variable. The electrical measured variable is at least approximately integrated starting from a prescribed initial value over a prescribed integration time, the duration of which corresponds to one or more clock periods of the clocked power part. A measure value is continuously determined from the integration value and used to control the power part.