Current control device and method

Claim 2

In a welding circuit having a transformer welding electrodes connected to the secondary of the transformer and an AC voltage source connected to the primary of the transformer, an improvement for regulating current in said primary winding comprising: a synchronizing circuit means for generating a signal in fixed phase relationship with the zero crossings of the signal from said AC voltage source; means for generating a nonlinear control signal in synchronism with the signal from said synchronizing circuit, said control signal having a decelerating negative slope during one portion thereof and an accelerating negative slope during a second portion thereof; a conduction sensing circuit means for generating a conduction signal indicative of whether or not a voltage exists across said primary; a compensation circuit means responsive to said synchronizing signal and said conduction signal for temporarily clamping the initial output level of said control signal during the times between the zero crossings of the voltage from said AC voltage source and the next interruption of current through said primary; means for comparing said nonlinear control signal with a reference signal and for generating a switching signal indicative of whether or not said control signal is less than said reference signal; and first switch means responsive to said switching signal for permitting current to flow between said AC voltage source and said primary in response to said switching signal.

Claim 3

The invention as claimed in claim 1 wherein said means for generating a nonlinear control signal comprises a first voltage follower amplifier, a second voltage follower amplifier, an energy storage means between the output of said first amplifier and the positive input of said second amplifier, a resistor connected between the output of said second amplifier and the positive input of said first amplifier, a second energy storage means connected between the input of said first amplifier and a reference potential, and second switch means for de-energizing said first energy storage means responsive to the signal from said synchronizing circuit and third switch means responsive to said synchronizing circuit for energizing said second energy storage means to a predetermined initial level.

Claim 4

The combination as set forth in claim 2 wherein said first and second energy storage means comprise first and second capacitors respectively and including a resistor and diode in parallel therewith connected between the positive input of said second amplifier and a first DC voltage source, said diode connected to conduct positive current toward said first capacitor, and also including a second DC voltage source having a voltage greater than said first DC voltage source connectable through said third switch means to said second capacitor for initially charging said second capacitor to the level of said second DC voltage source.

Claim 5

The invention as set forth in claim 1 wherein said compensation circuit includes gating means having inputs thereto connected to the outputs of said synchronizing circuit, said comparing means and said conduction sensing circuit for generating a compensation signal only during the time periods between a zero crossing of the signal from said AC voltage source and the next interruption of current through said primary by said first switch means.

Claim 6

In a transformer circuit having a primary winding, a secondary winding and an AC voltage source for delivering a signal therefrom connected to the primary winding, an improvement for regulating current in said primary winding comprising: a synchronizing circuit means for generating a signal in fixed phase relationship with the zero crossings of the signal from said AC voltage source; means for generating a non-linear control signal in synchronism with the zero crossings of the signal from said AC voltage source, said control signal having a decelerating negative slope during one portion of said signal and an accelerating negative slope during a second portion of said signal and approaching a constant during the latter part of said second portion, said means for generating said nonlinear control signal comprising a first voltage follower amplifier, a second voltage follower amplifier, an energy storage means between the output of said first amplifier and the positive input of said second amplifier, a resistor connected between the output of said second amplifier and the positive input of said first amplifier, a second energy storage means connected between the input of said first amplifier and a reference potential, and second switch means for deenergizing said first energy storage means responsive to the signal from said synchronizing circuit and third switch means responsive to said synchronizing circuit for energizing said second energy storage means to a predetermined initial level; means for comparing said nonlinear control signal with a reference signal and for generating a switching signal indicative of whether or not said control signal is greater than said reference signal; and first switch means responsive to said switching signal for permitting current to flow between said AC voltage source and said primary winding in response to the switching signal from said comparing means.

Claim 7

In a transformer circuit having a primary winding, a secondary winding and an AC voltage source for delivering a signal therefrom connected to the primary winding, an improvement for regulating current in said primary winding comprising: a synchronizing circuit means for generating a signal in fixed phase relationship with the zero crossings of the signal from said AC voltage source; means for generating a non-linear control signal in synchronism with the zero crossings of the signal from said AC voltage source, said control signal having a decelerating negative slope during one portion of said signal and an accelerating negative slope during a second portion of said signal and approaching a constant during the latter part of said second portion, said means for generating said nonlinear control signal comprising a first voltage follower amplifier, a second voltage follower amplifier, an energy storage means between the output of said first amplifier and the positive input of said second amplifier, a resistor connected between the output of said second amplifier and the positive input of said first amplifier, a second energy storage means connected between the input of said first amplifier and a reference potential, and second switch means for deenergizing said first energy storage means responsive to the signal from said synchronizing circuit and third switch means responsive to said synchronizing circuit for energizing said second energy storage means to a predetermined initial level; means for comparing said nonlinear control signal with a reference signal and for generating a switching signal indicative of whether or not said control signal is greater than said reference signal; and first switch means responsive to said switching signal for permitting current to flow between said AC voltage source and said primary winding in response to the switching signal from said comparing means.

Claim 8

The invention as set forth in claim 5 including a compensation circuit means synchronized with the zero crossings of the signal from said AC voltage source for temporarily clamping the initial energy level of said second energy storage means at a constant.

Claim 9

The combination as set forth in claim 6 including conduction sensing circuit means for unclamping the energy level of said second energy storage means when the current through said primary is next interrupted in response to the opening of said first switch means.