Coupling arrangement for a welding apparatus

Claim 1

In a power supply coupling arrangement for a welding apparatus of a type suitable for MIG-welding, and which operates under conditions whereby at certain times a short-circuit occurs at the load and at other times an open-circuit occurs at the load, which arrangement includes a controllable electrical power source capable of supplying the current taken by the load over a given load voltage range, a first electrical circuit means that detects the current taken by the load and establishes an electrical signal corresponding to such load current, and a second electrical circuit means that detects the voltage applied to the load and establishes an electrical signal corresponding to such load voltage, the improvement which comprises in combination a third electrical circuit means coupled to said first and second electrical circuit means to receive therefrom said load current signal and said load voltage signal, and coupled to said electrical power source to control the current and voltage delivered to the load thereby in accordance with said load current and load voltage signals and predetermined response characteristics established by circuit elements of said third electrical circuit means, said response characteristics being such as to provide a given incremental step in the current delivered to the load and a prescribed rate of increase of said current in response to the occurence of a short-circuit at the load, said third electrical circuit means including a transistor connected in series with the load to regulate the current flow thereto, and a pulse-width modulator responsive to said load voltage and current signals and responsive to a command input signal to establish a pulse sequence output signal in which the pulse-width is determined by the instantaneous values of said load voltage and current signals and by said command input signal, said pulse sequence output signal being utilized to control the effective conductivity through said transistor.