Fronius International Gmbh

Franz Peter Musil

Peter Lattner

Christian Magerl

Friedrich Steinmaurer

Robert Eberl

Andreas Prinz

The invention relates to a method for contactless ignition an arc (L) between an electrode () and a workpiece () which is to be welded, for carrying out a welding process, wherein a welding current (I) and a welding voltage (U) are provided at an output () of a welding current source (), wherein the welding current source () contains a resonance converter () for generating a periodically varying, preferably substantially sawtooth-shaped, open circuit welding voltage (U) with voltage maxima (U) which recur periodically with a repetition rate (f) and a welding current source () for carrying out the igniting process. In order to achieve reliable contactless ignition of the arc (L) without complicated circuitry, the resonance converter () is formed by a series-parallel resonant converter, and temporally synchronous high-frequency pulses (U) are superimposed on the open circuit welding voltage (U) in the region of at least some of the periodically recurring voltage maxima (U) of the open circuit welding voltage (U).

Method for contactlessly striking an arc and welding current source for carrying out a striking process

To enable in a circuit arrangement () with a transformer with center tap the voltage measurement on the secondary side simply and safely, it is provided that at least two series-connected resistors (R, R) are connected between the two outer connections (A, A) of the secondary side of the transformer (T) to form a measurement point (P) between the two resistors (R, R), and a voltage measurement unit (V) is provided to measure the voltage (U) between the measurement point (P) and the second output pole (), which corresponds to the output voltage (U).

Circuit assembly having a transformer with centre tapping and measuring of the output voltage

In order to set the output voltage of a resonant converter to a desired value by means of a simple additional circuit while the resonant converter is in open circuit operation, it is intended that at least one capacitor each (C, C) is connected in parallel to the electrical switching elements (S, S) of the secondary side of the resonant converter ().

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Steinerkirchen a. d. Traun, Austria

Franz Peter Musil