Patent ID: 6849828

Claim:
Method of controlling a welding current source ( 1 ) having a resonant circuit ( 27 ), provided in the form of a serial/parallel converter, whereby a bridge circuit ( 28 ), comprising individual switching elements ( 32 - 35 ), is controlled by a control system ( 4 ) and a consumer, in particular a welding process, is supplied with energy, in particular with voltage and current pulses from a power source ( 29 ), controls the bridge circuit ( 28 ), whereby the control system ( 4 ) controls the bridge circuit ( 28 ) during normal operation in such a way that the bridge circuit ( 28 ) is switched by the control system ( 4 ) consecutively on the basis of the control states (S 1 -S 4 ) stored in the control system ( 4 ) so that the bias point ( 57 ) on a character curve of the resonant circuit ( 27 ) lies outside a resonance frequency and whenever a change in resistance occurs at the consumer, the control system ( 4 ) operates with the bridge circuit ( 28 ) is operated at the natural frequency of the resonant circuit ( 27 ) on the basis of the control states and sequence stored for the special operating mode, characterised in the control states (S 1 -S 4 ) fixed for normal operation of the bridge circuit ( 28 ) provided as a full bridge are a positive drive phase—control state (S 1 )-, a positive freewheeling phase—control state (S 2 ) —, a negative drive phase—control state (S 3 )—and a negative freewheeling phase—control state (S 4 )—and, in the special operating mode, the bridge circuit ( 28 ) is switched from a drive phase—control state (S 1 or S 3 )—preferably consecutively, into one of several alternative control states (S 5 or S 6 ) in which the switching elements ( 34 ; 35 ) of one bridge branch are deactivated and the switching elements ( 33 ; 32 ) of the other bridge branch remain activated and the control system ( 4 ) monitors how often a switch is made from one special mode (S 5 ; S 6 ) to the other special mode (S 6 ; S 5 ).