Engine driven arc welder

Claim 1

An engine driven arc welder comprising: an engine; a generator for welding driven by said engine to produce an a.c. output; a rectifying circuit for converting the a.c. output of said generator into a d.c. output; a switching circuit for allowing the d.c. output of said rectifying circuit to undergo switching control by varying an ON/OFF period in dependence upon a current control signal to thereby form a switching controlled output current that is output to welding terminals; a current detecting circuit for detecting the output current delivered to the welding terminals to form a detected signal; a voltage detecting circuit for detecting a voltage across said welding terminals; a variable reference voltage circuit for producing a reference voltage in response to the voltage detected by said voltage detecting circuit; a reference signal formation circuit including a voltage responsive circuit which has a reference voltage source and a resistor voltage dividing circuit connected to the reference voltage source for outputting a divided voltage; a voltage responsive circuit having a conduction control element for varying the divided voltage of said resistor voltage dividing circuit to control the resistance of said resistor voltage dividing circuit by making said conduction control element conductive so as to branch the current flowing through said resistor voltage dividing circuit when a reference voltage of said variable reference voltage circuit is high, and for providing a reference signal having a voltage-current characteristic with a first reference value when the reference voltage of said variable reference voltage circuit is higher than a first predetermined value, and having a second reference value which is higher than the first reference value when the reference voltage of said variable reference voltage circuit is lower than a second predetermined value, and having a third reference value of drooping characteristic linearly connecting the first reference value to the second reference value when the reference voltage of said variable reference voltage circuit is between the first and second predetermined values; and a current control circuit for comparing the detected output current of said current detecting circuit with the reference signal of said reference signal formation circuit to deliver a compared result to said switching circuit as the current control signal to adjust the switching-controlled output current to a set current.