CA1310707C - Arc welding system - Google Patents

Abstract

"IMPROVED ARC WELDING SYSTEM"

Abstract of the Disclosure An improved electronic welding station is disclosed.
The welding station provides for an improved arc striking capability by providing a higher arc striking voltage and a large arc striking current and, once the arc is struck, automatically switches over to preselected parameters for conducting the welding operation. Also disclosed are a method for preventing transistor failure due to loads which tend to cause a very large instantaneous current flow and an apparatus for protecting the driver circuit and the remaining output transistors in the event that one of the output transistors should suffer a collector-to-base short. The welding station also describes a method of operating the cooling fan at a speed commensurate with the cooling requirements and periodically reversing the voltage to the cooling fan so as to extend the operating lifetime of the fan brushes. The welding station also has several shutdown circuits which protect the components of the welding station in the event of cooling fan failure or excessive heating of the weld station. The welding station also provides for a shutdown period for cooling off in the event that the maximum allowable instantaneous current is exceeded.

Description

1 3 1 ~07 "IMPROVED ARC WELDING SYSTEM"

Techaical Field This iS related to Canadian patent Application Serial No. 521,140 , filed October 22, 1986, by Malcolm T. Gilliland, and entitled "DISTRIBUTED STATION
WELDING SYSTEM". The present ;nvent;on relates to improvements in an arc welding station.

Background of the Invention The present invention describes improvements to the weld selector stations described in ~e above patent application.
The improvements also are applicable to other elechonic welders which use a plurality of paralleled transistors to provide the desired output current and/or which use different striking and welding voltages.

2 s In welding and other power systems which provide a high current capability, a number of transistors are generally operated in parallel, with emitter resistors for current balancing, to prov;de the required output current. However, catastrophic failures, involving some or all of the output transistors, sometimes occur. This type of catastrophic failure usually results from an unusually large current surge which des~roys first one transistor and then, by a chain reaction, causes the destruction of some or all of the remaining transistors. Ln the past, it was generally believed that the failure was caused by the large current destroying the emitter-base or the base-collector junction of the ~Irst transistor.

However, it has been found that the failure of the ~Irst transistor is not always due primarily to the failure of the j-unctions but can be attributed to ~ailure of the bonding wire be~veen the emitter and the external cormection to the power transistor. During large S current surges, the transistor junctions are, to some degree, protected from failure by over heating because of the relatively large thermal mass of the junction and the high thermal conductivity between the junction, subs~rate, and heat sink.
However, the emitter bonding wire ha~ very little thermal mass o and the thermal conductivity between the emitter bonding wire and the heat sink is very low. Therefore, the large current surge o~rerhea~s the emitter bonding wire and causes a failure by causing the emitter bonding wire to melt through, detach from the emitter bonding pad, or detach from the emitter contactO The net result is that the emitter is suddenly opened, the VcBo rating of the transistor is exceeded and then the collector-base junction of the transistor breaks down. The failure of the collector-base junction of the ~lrst transistor applies the full collector voltage to the bases of the remaining transistors. This, in turn, prevents the remaining - 2 transistors from being turned off. These remaining transistors, in turn, draw large currents, overheat, and fail. Therefore, there is a need ~or a method of preventing current surges of such magnitude as to melt or detach the emitter bonding wire. ~ ermore, there is a need for an apparatus to protect the other parallel transistors in 2s the event that the collector-to-base junction of a first transistor fails.
Also, the voltage and current produced by the collector-base junction failure *equently overloads the driver circuit, thereby causing the driver circuit to be destroyed. There is therefore a need for a method of preventing destruction of the driver circuit in the event of a failure of one or more of the output transistors.
The weld selector station described in CDN Patent Application Serial No. 521,140 describes a peak current detector 3 5 which, if the instantaneous current exceeds a predeterrnined value, 1 3 1 ~707 interrup~s the drive to ~he power transistors until the reason for the e~cessive current is corrected. However, in some situations, where the reason for the excessive current is correctable but persis~ent, the repeated penodic SUFge~S of the e~cessive current CaII cause overheating of,the power tlansis~ors. There~re, ~ere is a need for an apparatus to protect ~e power transistors from ove~eating caused by repeated, excessive current flows.
Electronic welders, and many non-electronic welders, have a cooling fan to pr~vent the components of the welder from overhea~ing in normal use. These fans generally have a DC motor since only D~ wer is a~aila~le. These fan motors are generally conventio~al DC motors in ~at they have a pair of brushes, one for ~e positive terminal and one fo~ the negative terminal. As these bmshes wear, they must be periodically replaced or the fan will fail and ~e components of the welder will overheat. Generally, ~e brush connected to the positive terminal wears faster and, when it is replaced, there is frequently a substantial amount of brush left connected to the negative terminal. ~Iowever, ~ese brushes are generally replaced 2 as a pair. It has been found t~t ~e tLme between replacement of the pairs of brushes can be e~ended if, periodically, ~e, positive and negative ~erminals to ~e fan are reversed so ~at, alternately, a particular bNsh is connected to ~ positive voltage supply and then to the negative voltage supply. Therefore, there is a need ~or 2 s an apparatus for periodically reversing ~e polanty of ~e voltage applied to ~e fan motor.
The speed at which the fan operates also affects ~he lifetime of the brushes; high fan speeds mean shorter life and vice versa. Typically, the cooling ~an has only one speed. However, the components of ~e welder generally require full cooling only when welding is actually being per~ormed and can operate with reduced cooling between welding operations. Therefore, running the fan at hi8h speed when welding operations are actually in progress and running the fan at a lower speed at other times will increase ~e lifetime of ~e brushes. Therefore, there is a need for l3ln707 an apparatus which will operate ~e cooling fan at ~igh speed when welding operations are in progress and at a lower s~ed at o~er times.
A coolirlg farl,failure will often go ~oticed by ~e welder because of ~e ~nbierlt noise level. However, when ~e cooling fan fails, ~e heat ge~erated by welding operations and~ in some cases, by a xtandby mode, can cause the comp~nents of th~
welding station to overheat and fail. Therefore, the~e is a need for an apparatus which automatica~ly shuts down the welding station in t~e event ~at ~e cooling ~an fails.
Even if the cooling fan is fillly operational, ;f ~e air flow into ~e welding station is bloc~ed or restricted, ~e amb;ent temperature is excessively high~ and/or the particular welding operation causes an excessive amount of heat to ~e generated by ~e components of the welding station, ~e in~eInal components of the welding station will overheat and fail. Therefore, ~ere is a need for an apparatus which monitors ~e teInperature inside the welding sta~ion and disables the welding station in the event that the internal temperature becomes excessively high.
2 0 During norrnal usage, ~e tip of ~e welding rod may become dirty or deformed, such as with a ball of metal on ~e end as opposed to a sharply ~runcated tip. In such cases~ ~e striking and arc characteristies will be irregular until such time as the dirt or deformity is removed. It has been found ~at this dirt or 2 s deformity can be removed by applying a large current surge to the welding rod at the time the arc is first struck. This large curreIlt destroys ~e dir~ or deformity at the end of the welding rod.
Therefore, ~ere ;s a need for an apparatus ~or applying a large current surge to the welding rod at ~e time of st~iking ~e arc so as to remove any dirt or deformity at ~e end of the welding rod.
- Summary of the Inve~tion The present invention describes methods and apparatus for constructing an improved weld selector station which meets the needs described above. Genera~ly stated, the 1 3 1 0 ~

present invention describes improvements which prolong the lifetimes of the components of the welding station and provide for improved striking and operating characteristics.
More particularly described, the present invention descrlbes a method of operating the power transistors to prevent emitter bonding wire failure and an apparatus to prevent chain reaction failures of the paralleled power transistors.
Also more particularly described, the presen-t invention describes an apparatus for periodically reversing the operating voltage of the cooling fan and automatically adjusting the speed of the cooling fan in response to operating conditions so as to prolong the life of the brushes on the cooling fan.
Also more particularly described, the present invention describes an apparatus for shutting down the weld selector station in the event that the cooling fan fails or the internal temperature of the weld selector station becomes excessive.
Also more particularly described, the present invention describes an apparatus for optimizing the output of the welding station for both striking and welding conditions.
~lthough several aspects and features of the invention will become apparent herein from the detailed description of a preferred embodiment, the invention to which the claims herein are directed are more particularly set forth herein.
The invention in one broad aspect as claimed herein provides an improved arc welding station, comprising control means for selecting desired parameters for a welding operation, drive means responsive to the control means for providing drive power and output means responsive to the drive power for providing an output current to a welding operation. The drive power is sufficient to cause the output means to operate near a saturated state when the output current is less than a predetermined output current and the drive power iB limited to a predetermined drive power so that a condition tending to increase the output current in excess of the predetermined output current ..1~,,`.~

1 3 ~ 7 causes the output means to operate less near the saturated state and more toward an active state.
Another aspect of the claimed invention pertains to a welding power supply having a control means for selecting desired welding parameters, a drive means responsive to -the control means for providing drive power and an output means responsive to the drive power for providing an output current to a welding operation. There is provided an improved method for operating the welding power supply, comprising the steps of selecting a desired maximum output current, the desired maximum output current being less than a current required to detach or damage a conductor in the output means and limiting the drive power to a value which causes the output means to operate slightly out of a saturated mode when the output means is providing the desired maximum output current.
Another aspect of the claimed invention pertains to a welding power supply having a control means for selecting desired welding parameters, a drive means responsive to the control means for providing drive power and an output means responsive to the drive power for providing an output current to a welding operation. An improved method is provided for operating the welding power supply, comprising the steps of selecting a desired maximum output current, the desired maximum output current being less than a current required to detach or damage a conductor in ~5 the output means, limiting the drive power to a value which prevents the output means from providing an output current greater than the desired maximum output current, monitoring the output current, removing the drive power from the output means if a peak value of the output current exceeds a first predetermined value and removing the drive power from the output means if an average value of the output current exceeds a second predetermined value.
Still further, the invention as claimed provides an improved arc welding station, comprising control means for selecting desired parameters for a welding operation, drive means responsive to the control means for providing drive power, the 1 31 ~707 drive power not exceeding a first predetermined value and output means responsive to the drive power for providing an output current to the welding operation, the output means comprising a transistor. The transistor has a drive input terrninal connected S to the drive means, a power supply input terminal connected to a power source, an output point and a conductor connecting the output point to an output terminal, the ou-tput terminal being connected to the welding operation. First curren-t de-tection means is responsive to a peak value of the output current exceeding a first predetermined value for causing the drive power to be removed from the output means and second current detection means is responsive to an average value of the output current exceeding a second predetermined value for causing the drive power to be removed from the output means wherein the first predetermined value is adjusted so that the output means cannot conduct an output current greater than a second predetermined value, the second predetermined value being less than an amount necessary to cause damage to or detachment of the conductor.
Further still the invention pertains to a welding station comprising an output stage and a driver stage for providing drive power to the output stage, the output stage comprising at least one transistor, the transistor having a drive input terminal, a power supply input terminal, an output point and a bonding wire connecting the output point to an output terminal. There is provided a method of reducing the probability of the bonding wire detaching or burning through due to an instantaneous current flow through the transistor, comprising the steps of (a) connecting a load to the output terminal, (b) adjusting the load to cause a predetermined output current to flow through the output stage, (c) adjusting the drive power to cause a predetermined voltage to be present between the power supply input terminal and the output terminal and (d) repeating steps (b) and (c) as necessary to sirnultaneously obtain the predetermined output current and the predetermined voltage, wherein the transistor operates slightly in an active mode at the predetermined output current so that, for loads tending to cause .
``'' 1 ~ 1 0707 the output current to exceed the predetermined output current, the drive power is insufficient to support the output current and the bonding wire is protected.
That the present invention accomplishes these and other aspects will be apparent from the detailed description of the preferred embodiment.
Brieî Description of the Drawings Figure 1 is a block diagram of the improved weld selector station of the preferred embodiment.
Figure 2 is a schema~ic diagram of the power and trigger circuit of ~e pre~erred embodiment.
Figure 3 is a schematic diagrarn of ~e switching and shutdown driver of the preferred embodiment.
Figure 4 is a schematic diagram of ~he current detection circuits of the preferred ~mbodiment.
Figure S is a schematic diagram of the transistor protection circui~ of ~e preferred embodiment.
Figure 6 is a schematic diagrun of the low f~equency pulsewiddl modulator of ~e preferred embodiment.
~ igure 7 is a schematic diagram of ~e high freqllency pulsewidth modulator of ~e prefe~ed embodiment.
Figure 8 is a schematic diagram of the high/low 20 feeder voltage switchover control circuit of the preferred embodiment.
Figure 9 is a schematic diagram of ~e power supply circuits of the preferred em~odiment.
Figure 10 is a schematic diagram of dle STICK &
2 s TIG control circuit of the preferred embodiment.
Detailed Description Turning now to the drawin~, in which lilce numerals represent like components ~roughout the several ~igures, the 30 preferred embodiment of the present invention will be described.
Deta;ls of construction and operation of weld selector station 16 and its components are provided in CDN Patent Application Serial No. 521,140, filed October 22, 1986~ by Malco~n T. Gi~iland, entitled "Distributed Station Welding System", which may be referred to for further details~ Whenever possible, the component name and number used in ~he figures are the sarne as that used in Patent Application Serial No. 521, laQ
Figure 1 is a block diagram of the preferred embodiment of the present invention. An external DC power S supply (not shown) is comlected to apply a positive voltage to the V~ terminal and a negative voltage to the GROUND rN termirlal.
The output of weld selector station 16 is taken from ou~put terminal 717 and GROUND OUT telminal 19. Weld selector station 16 has the following major components: power and trigger circui~ 702, shunt circuits 50a-SOd, arc sustainin~ resistor 4S, a plurality of power transistor circults 55a-SSf, transistor protection circuit 707, highJlow voltage switchover circuit 86, short circuit detector 72, over curr~nt detector 73, peak current detec~or 80, STICK & TIG control 30, low frequency pulse modulator 32, high frequency pulse modulator 34, switching, shutdown and driver circuit 37, and circuit power supplies 38.
Wi~ the exception of power and trigger 702a and transistor protection circuit 707, the operation of the other primary components is essentially the same as described in Patent 2 0 Application Serial No. 521; 140 .
The VIN terminal is coDnected by conductor 14 and onloff switch 700 to the anode of reverse protection diode 20. The anode of diode 20 is connected to conductor 21 which is the plus 80 volt supply for most of the components. ~s will be e~plained in more detail later, power and trigger circuit 702 provides operating power to the transistor circuits 55a-SSf and also shuts down weld selector station 16 in the event of fan failure or overheating. Shunt circuits 50a-SOd protect transistors 56a-56f from transient voltages when transistors 56a-56f are switching 3 0 from the on condition to d~e off condition. In a typical welding operation, transistors 56a-56f will be rapidly switched on and of~
so as to maintain the desired arc and deposition rate chara~teristics. Arc sustaining resistor 45 provides a limited current flow when transistors 56a-56f are off so that the arc will be sustained and not quenched. The output of arc sustaining ~31~7~7 resistor 45, shunt circuits 50a-SOd, and transistor circuits 55a-55f are connected to output terminal 717 ~rough a ~lrst inductor 62, a first resistor 64, and, selectively, through a second, variable resistor 66 and a second, vanable inductor 70. Swi~ch 715 allows S the welder to select whe~er resistor 66 and inductor 70 are placed in series with the output on terminal 717. Typically, resistor 66 and inductor 70 will be used when additioIlal current limiting features are required, such as when low frequency pulse modula~or 32 is set to a low fre~uency. Resistor 46 and inductor 70 are made variable so that, for si~ations whe~in the combination of inductor 62 al}d resistor 64 proYid~s ~suffilcient current limiting but the combination of inductors 62 and 70 and resistnrs 64 and 66 provide too much eurrent limiting, resistor 6S
and inductor 70 may be adjusted to provid~ a desi~d degree of current limiting. This allows ~e welder to adjust resistor 66 and inductor 70 and position switch 715 to obtain the arc characteristics most desirable for the type of welding being conducted.
Flywheel diode 61 protects ~ransistors 56a-56f from 2 0 reverse voltages caused by inductor 62 and/or inductor 70 and, by conducting and blowing fuse 24, protect the weld selector station 16 from the inadvertent application of ~e negative power supply lead to output terminal 717. A 2.5 ohm resistor 711 and a 0.22 microfarad capacitor 712, connected in series, are placed in parallel widl flywheel diode 61. Resistor 711 and capacitor 712 perform two functions: acting as a snubber circuit to protect flywheel diode 61; and, when weld selector station 16 is ~lrst hlrned on, conducting a suffilcient amount of current ~rough arc sustaining resistor 45 to trigger peak culTent detector 80. When peak current detector 80 is triggered, it shuts down some of the circuits of station 16 for three minutes. The components of weld selector station 16 are ~erefore allowed a three minute time to stabilize. Also, in the event of a peak current in excess of the preset value, weld selector station 16 is shut down for a three 3s minute period ~o allow transistors 56a-56f and other circuits to cool down to nolmal operating temperature.
A 1,000 ohm resistor 701 is placed in parallel widl capacitor 22. Resistor 701 provides discharge path for capaci~or 22 in the even~ that po,wer is turned of~ via swi~ch 700, or interrupted via ~e blowing of fuse 24. Resistor 701 is added as a sa~ety feature and does not otherwise af~ect ~e operation of weld selector station 16.
Connected between output terminal 717 and ground in conductor 15 is a stliking assist circuit composed of two series circuits. The ~lrs~ series circuit is ~c combination of rwerse biased diode 721 in parallel with 10 ohm resistor 720. The second series circuit is 30,000 micrQ~arad capacitor 722 in parallel with 1,000 o~m bleeder resistor 723. The striking assis~ circuit insuIes a good initial strike and arc, even when ~e tip of the welding rod is di~y or deformed, by providing a large current surge at the instant the arc is struck. Prior to ~e arc being struck, capacitor 722 charges through resistor 720 to the voltage on output terminal 717, nominally 80 volts. ~en the arc is struck, capacitor 722 2 0 discharges through diode 721 and dle arc. Because of ~e size of capacitor 722, dle initial current surge, when the ar is ~lrst st~uck, is sufficiently large to disin~egrate. aIly dirt or deforrnities on the welding rod and also prevents the arc from starting and them immediately quenching due to irregularities on the work 2 s surface. The striking assist circuit, other ~an assisting in striking ~e arc, does not otherwise affect the operation of station 16.
Bleeder resistor 723 provides, ~or safety purposes, an alternate discharge path for capacitor 722.
Optional diode 725, shown.in phantom, is not necessary for the operation of selector station 16 but provides an additional feature to protect against the misapplication of the supply voltage to the weld selector station 16. If, ~or example, the negative supply lead is inadvertently connected to the GRVTJND
OUT terminal 19 and the positive supply lead connected to the VIN tenninal, the GROUND IN term~nal or output terrninal 717, 1 3 1 07")7 diode 72~ will be reversed biased and prevent this incorrect application of the supply voltage from adversely affecting the welding power supply or weld selector station 16.
Turn now to Figure 2, which is a schematic diagram of power and trigger circuit 702. Eighty volt conduc~or 21 is connected to conductor 731 via 5 amp fuse 730. In ~e event of a short in circuit 702, fuse 730 will blow thereby interrupting power to circuit 702 and shutting down weld selector station 16.
Conductor 731 is connected by the parallel combination of 25 kilohm resistor 736 and the coil of latching relay 735 to the anode of diode 737. The cathode of diode 737 is connected by the parallel combination of 40 microfarad capacitor 740 and 5 kilohm resistor 741 to conductor 743. Conductor 743 is selectably connected to 80 volt return conductor 23 ~rough switch 794.
Conductor 743 is also connected to conductor 751 through 751 through fuse 744. Conductor 751 is selectably connected to conductor 752 via trigger switch 745, which is bypassed by capa.~itor 746. Conductor 752 is connected to the anode of diode 747. The cathode of diode 747 is selectably connected to 80 volt return conductor 23 via switch 795, which is bypassed by capacitor 750.
In the preferred embodiment, latching relay 735, such as the Potter & Brum~leldl~KUR-llDll 24VDC impulse relay, has two sets of single-pole, double-throw contac~s. The 2 s no~nally closed contact of ~e first set and the normally open contact of the second set are connected to bmsh 733b of ~an 733.
The normally open contact of the ~lrst set and the norrnally closed contact of the second set are connected to brush 733a of fan 733.
The center contact of ~e second set is connected to 80 volt re~urn 3 0 conductor 23 ~rough fan failure relay 742. Fan failure relay 742 is connected to Figure 4 as shown by dashed line 793. The center contact of ~e first set is connected to 80 volt conductor 731 via a 135 ohm resistor 732.
First consider the polarity reversing effects of latching relay 735. Each time switch 794 or the combination of * Trademark 11 1 3 1 07~7 switches 745 and 795 is operated to connect conductor 743 with 80 volt return conductor 23, capacitor 740 wi:ll provide a momentary current path for relay 735, which will cause relay 735 to advance to its alternate latching position. Then, when switches 794, 745 S and 795 are positioned s~ ~at conductor 743 is isolated from conductor 23, resistor 741 will discharge capaci~or 740 so ~at ~e next time ~e switehes are closed capacitor 740 will provide ano~er current pulse to advance relay 735 to its ne~t latching position. From an inspection of ~e winng connec~ion to the contacts of relay 735 it will be appreciated that, upon each operation of relay 735, the voltage applied to fan 733 is reversed in polarity so dlat, ideally, brushes 733a and 733b each spend a similar amount of time connected to the positive supply voltage and the wear on brushes 733a and 733b is more uniform. Diode 737 prevents negative ~ansients on conductor 731 ~om activating relay 735. Resistor 736 provides a shunt pa~ for the coil of relay 735 to discharge when conductor 743 is isolated from 80 volt return conductor 23.
In order ~o further extend ~e li~etirne o~ brushes 733aand 733b,~an 733isselec~bly operated ata ~gh oralow cooling speed. ~ ~e low cooling speed, resistor 732 is comlected in series wi~ fan733 thereby reducing the operating ~e voltage to fan 733, reduc~g its speed, and reducing ~e wear on brushes 733a and 733b. However, when full cooling is required, resistor 732is 2 s bypassed so that fan 733a receives full voltage and operates at maximum speed. Two options, 753 and 754, are shown which selectably bypass resistor 732 and provide fullvoltagetofan733.
In the ~lrst option 753, resistor 732is connec~ed in parallel with the series combLnation of a normally open set of 3 0 contacts of relay 420 and a normally open set of contacts of relay 774. When both relay 420 and relay 774 are activated, resistor 732 is bypassed and fan 733 receives full operating vo~tage. l~e operation of relay 420 is described in conjunction with Figure 8.
Relay 420 is energized only when welding is actually in progress and is de-energized during the arc striking period and when 12 1 31 07~)7 welding is not ~n progress. As will be shown below, relay 774 is energized during arc striking and actual welding operations and is de-energized only when switches 794, 745 and 795 a~e positioned such that conduc~or 743 is isola~ed from 80 volt retum co~ductor s ~3.
In ~e second option 75a" resistor 732 is selectably bypassed by transistors 756 and 757 and diode 755 or by switch 796 and a set o~ contacts of relay 774. I~ ~is option, conductor 734 is connected to ~e emiKer of transistor 756. Transistors 756 and 757 are connected in a Darlington configuration. The collectors of transistor 756 and 757 are connected to dle cathode of diode 755. The anode of diode 755 is connected to conductor 731.
The base of transistor 757 is connected to the cathod~ of diode 755 through resistor 760 and a parallel switching circllit formed by ~e noImally open contac~s of relays 763 and 765. I~ any olle of relays 763 or 765 is activated then ~ransistors 756 ~d 757 will be turned on and resistor 732 will be bypassed, thereby applying full operating vol~age to ~an 733. The parallel combination of the contacts ~or relays 763 and 765 is bypassed, to reduce noise 2 0 impulses on the base of trarlsistor 757, by a s~unt circuit consisting of resistor 761 in series with capaci~or 762. Diode 755 preveIl~s negative transients on conductor 731 from adversely affecting ~ansistors 756 and 757.
Conductor 63 is connected to one end of ~e coil of 2 s relay 763 through resistor 764. The o~er end of the coil of relay 763 is connected to conductor 65. Conductor 6S is also conrlected one of coil 765 through resistor 76~. The other end of the coil of relay 765 is connected to conductor 67. ~ the preferred embodiment, relay 763 and 765 are reed relays. Relays 763 and 765 are responsive to ~e voltage drop across, and therefore the current through, resistors 64 and 66, respectively, of Figure 1.
Ther~fore9 when a welding operation begins and current flows through resistors 64 and/or 66, relays 763 and/or 76S will close, thereby activating transistors 756 and 757, shunting resistor 732, 3 5 and providing full operating voltage to farl 733. Resistors 764 and 766 are used to prevent excessive current flow in relays 763 and 765. Also, resistor 732 is bypassed and fan 733 operates a~ full speed when relay 774 is activated if switch 796 is closed. In the preferred embodiment switch 796 is closed if MIG operations are being performed.
Of course, for proper cooling, fan 733 must run in dle sarne direction, such as clockwise, regardless of Lhe polarity of the applied voltage. Therefore, if polarity reversal is used, a permanent magn~t fan is inappropriate and, in the preferred embodiment, a DAYT0~2M277 AC motor is used for fan 733.
Relay 774 selectively provides opera~ing power to kansistors 56a-S6f of Figure 1. Relay 774 has several sets of con~acts. Conductor 42 is connected to the center contact of a first set of contacts on relay 774. The nolmally open contact of this set iS connected to conduc~or 44. When relay 774 is activated operating power is then provided to ~e power output transistors 56a-56f of Figure 1. Conductor 731 is connected to ~e a~ode of ~everse vol~age blocking diode 775. The anode of diode 775 is connec~ed to one end of the coil of relay 774. ~ ~e preferred embodiment, relay 774 has two windings: one winding is used for iI~itially pulling in ~e contacts, and bo~ windings are used to hold ~he contacts in. Coil 774a has a resistance of appro~mately 3,000 o~ns and coil 774b has a resistance of approximately 75 ohms.
When relay 774 is not energized, coil 774a is bypassed so ~at a 2s large current flows through coil 774b and rapidly pulls in the contacts. However, once ~e contacts are pulled in coil 774a is no longer bypassed and the total resistance of coil 774 is appro~imately 3,000 QhIIlS. Therefore, relay 774 has a high pull in current and a low hold ~ cu~ent.
Conductor 731 is connected to ~e anode of reverse voltage blocking diode 775. The ca~ode of diode 775 is connected to one end of coil 774b. The other end of coil 774b is connected to one end of coil 774a, one end of potentiometer 772, one end of resistor 773, and the center contact of a single pole single throw nolmally closed set of contacts on relay 774. The other end of coil *Trademark , 774a is connected to ~he no~nally closed contac~ of ~e above set of contacts and ~o one end of capacitor 771. ~he other end of capacitor 771 is connected to ~e o~er end of potentiome~er 772.
l'he wiper contact of potentiome~er 772 is connected to the other end of resistor 773. Conductc~r 778 is connected one end of a ~ermostatically controlled circuit breaker 770. The other end of circuit breaker 770 is connected to conductor 743.
Consider now the opera~ion of relay 774. Assume first that switches 794, 795 and 745 are positioned such ~at 0 conductor 743 is not connec~ed ~o 80 volt return conductor 23.
Relay 774 will be de~nergized, and ~e contacts will be positioned such that coil 774a is bypassed. Assume now ~at one or more of the swi~ches is closed so as to connect conduc~ors 743 and 23. 'rhe full 80 volt potential on conductor 731 will be applied across coil 774b thereby providing a large amount of eurrent to cause rapid pull in. As soon as relay 774 pulls in the first set of contac~s will open and coil 774a will no longer be bypassed ~ereby raising ~e resistance of the coil of relay 774 from 75 ohms to approximately 3,000 ohms and reducing ~e current ~rou~ the coil of relay 774 20 to a much smaller value. However, ~is value is still more than suf~leient to keep relay 774 pulled in. Also, once ~elay 774 pulls in, capacitor 771 will begin charging ~rough potentiometer 772 and resistor 773.
Assume now that switches 794, 795 and 745 are 2s operated so that conductor 743 is isolated from conductor 23.
Capacitor 771 will then begin discharging ~rough potentiometer 772, resistor 773 and coil 774a. Capac;tor 771 therefore provides a delay period before coil 774 drops out. This delay period can be adjusted by potentiometer 772. Therefore, relay 774, in conjunction with capacitor 771, potentiometer 772 and resistor 773 provides a ~ast pull in, slow drop out relay system for providing operating power to transistors 56a-56f.
It will be recalled tl~at another set of contacts of relay 774 are present in ~e two options, 753 and 754, for adjusting the speed of cooling fan 733. Therefore, when relay 774 is energized 1S 1 ~ 1 07~7 so as to provide operating power ~o power transistors 56a-56f, ~an 733 reseives the full operating voltage and operates at its maximum cooling capacity.
Thermostatically controlled circuit breaker 770 is preferably mounted on the support post for arc sustaining resistor 45 of Figure 1. In the event ~at the temperature of resistor 45 becomes excessive, such as might happen if switch 794 is closed and the welding head is placed in contact with a ground, the temperature of resistor 45 would increase, thereby causing circuit breaker 770 to open, de-energizing coil 774, and removing operating voltage from resistor 45 and transistors 56a-56f until ~e temperature of resistor 45 had retumed to an acceptable level.
Conductor 731 is connec~ed to ~e anode of a reverse voltage blocking diode 783 and to one end of ~e coil of motor control relay 784. ~e ca~ode of diode 783 is connected t~ough resistor 782 to the parallel combination of capacitor 780 and ~e coil of relay 781. The other end of capacitor 780 and coil of relay 781 is connected to conductor 751. The other end of the coil of 2 o motor relay 784 is connected to the nonnally open contact of relay 781. The center contact of relay 781 is also connected to conductor 751. Motor relay 784 controls ~e operation of ~e feed motor in ~e welding head. Dashed line 792 indicates the connection between motor relay 784 and the contacts for relay 784 2 5 in Figu~e 8. If switches 794, 795 andJor 745 operate at such that conductor 743, and therefore conductor 751, are connected to conductor 23, then relay 781 and therefore relay 784 will be activated. Likewise, if ~e switches are opera~ed such as to isolate conductor 751 from conductor 23 then relays 781 and 784 will be de-energized. Resistor 782 is a voltage step down resistor so as to allow 24 volt relay 781 to operate from the 80 supply. Capacitor 780 provides a delay drop out time for relays 7~1 and 784 so dlat the feeder motor will continue operating for a short period after ~e switches are open.
Conductor 731 is also connected to the anode of 3s reverse voltage blocking diode 790 and, through switch 797, to 16 ~51~7 one termi~al of gas valve 791. The cathode of diode 790 is connected to one end of capacitor 785 and one end of resistor 787.
The other end of resistor 787 is connected to one of the coil of relay 786. The o~er end of capacitor 785 and dle other end of the coil of relay 786 are e~ected to conduc~or 751. The other tenninal of gas valve 791 is cormected to the normally open contact of relay 786. ~he center contact of relay 786 is connected to conductor 752. Resistor 787 is a voltage step down resistor which allows relay 786 to operate from the 8~ volt supply.
Capacitor 78$ provides a discharge pa~ and a con~olled drop out ~ime ~r relay 786. Note ~at, in order to activate gas valve 791, switches 745 and 797 and eidler switch 794 or switch 795 must be closed. It will be recalled ~at switch 745 is ~e trigger switch on ~e welding head. ~ s~,vitch 745 is open then relay 7g6 will be de-energized and gas valve 791 will be closed. However, If switch 745 and ei~er switch 794 or swi~ch 795 are closed, then relay 786 will be activa~ed and gas valve 791 will be energized. Switch 797 is closed when shielding gas is desired, such as for MIG and TIG
operations, and opened when shielding gas is not desired, such as 2 0 for STICK operations.
From the above, it will be appreciated ~hat power and trigger cireuit 701 provides numerous ~eatures which protect ~he equipment from abuse or e~ccessive temperature conditions and provide controlled drop out times which assist in assuring dlat dle 2 5 termination point of the weld being made is a good weld and is not irregular in any manner.
Turn now to Figure 3 which is a schematic diagram of switching, shutdown and driver circuit 37. The construction and operation of switching, shu~down and driver circuit 37 is the same as described in Patent Application Serial No.521, 14o, with two exceptions. The ~lrst exception is that conductor Xl is directly connected to pin 1 of optoisolator 112 instead of, as in ~e former circuit, being coMec~ed through a resistor. The resistor has not been eliminated entirely, but has been moved to Figure 4 for 3 5 clarity.

The second difference is the setting of potentiometer lSl. Previously, potentiometer lSl was set so as to allow transistors 56a-56f to remain in saturation for a given emitter current. However7 as described in the background, transistors 56a-56f were subject to occasiorlal failure due to burn ~rough or detachment of the emitter bonding wire on these transistors. In ~e preferred embodiment, potentiometer lSl is adjusted so that transistor 56a-56f operate slightly out of ~e saturated region and into the active operating region. Of course, in this mode of opera~ion the power dissipation of transistors 56a-56f is slightly greater but well within their ratings. The protection mechanism is as follows. Previously, potentiometer lSl was set to assure that the transistors remained in salturation. Therefore, if the load increases, the current through the transistors increased and ~e emitter bonding wire, being thermally isolated, overheated and burned through or detached. However, in the preferred embodiment, the power transistors are now operated slightly in the active region. Therefore, if ~e load resistance decreases such 2 0 that the transistor current would tend to increase, the base drive to the transistors is insuf~lcient to allow the emitter current to increase and, instead, ~e collector-emitter voltage across the power transistors increases as ~e power transistors come further out of saturation. Therefore, the current through the power ~ansistors is limited and ~ere is a substantially reduced number of 2 5 ~ailures due to emitter wire bum through or detachment.
In the preferred embodiment, a load is placed upon output terminal 717 of Figure 1 so as to cause approximately 50 amps to flow through each power transistor 56a-56f.
Potentiometer lSl is then adjusted to giYe approximately lS to 18 volts for the collector-to-emitter voltage for the group of transistors. If higher power transistors are used such ~at each transistor is rated at 100 amps con~inuous current theIl, with ~e load adjusted so that each lTansistor provides approximately 100 amps, potentiometer lSl is adjusted to provide a 20 volt collector-3 5 to-emitter voltage. Since the base drive current is limited by ~e 18 ~ 3 1 0707 setting of potentiometer 151, the emitter current of transistors 56a-5Sf is limited, thereby preventing destruction of the emitter bonding wire on transistors 56a-56f.
Turn now to Figure 4 which is a schematic diagrarn of peak current detector ~0, short circuit detector 72, and over current detector 73. The construction and operation of short circuit detector 72 and over current detector 73 are the same as described in Patent Application Serial No. 521,140. The one minor difference being that ~e anode of diode 191 of short circuit detec~or 72 is conneeted to output terminal 717 instead of conductor 71. Briefly s~ated, relay 197 is energized whenever the output voltage on terminal 717 exceeds a predeterrnined value, approximately 15 to 20 volts, and is de-energized when the voltage on terminal 717 is below this value, such as when ~e welding tip is shorted to ground. Short circuit detector 72 disables weld selector station 16 when such a short occurs. Over current detector 73 measures the voltage across resistor 64 of Figure 1 and disables weld selector station 16 whenever the average output current, 2 0 which passes through resistor 64, exceeds a predete~nined value.
The improvements to peak current detector 80 will now be discussed. Peak current detector 80 disables the output of weld selector station 16 when the peak current output exceeds a predetermined value and, when this shutdown occurs9 keeps the weld selector station 16 disabled ~or a nominal period, three minutes, so as to allow time for the components of weld selector station 16, especially transistors S6a-56f, to return to normal operating temperature.
The plus 15 volt supply conductor 440 is connected to one end of a thermostatically controlled circuit breaker 800. The other end of circuit breaker 800 is connected to ~e center contact of fan failure relay 742 (Figure 2). l*le normally open contact of relay 742 is connected to conductor 801 which applies plus 15 volt power to components 802 and 830. Circuit breaker 800 is mounted Oll resistor 93 of Figure 1 and shuts down weld selector 3s station 16 in the event that resistor 93 becomes excessively hot 19 ~ 3 ~ 0707 - from an excessive ambient temperature or from prolonged heavy duty usage of weld selector station 16. In the event that ~an 733 of Figure 2 fails, fan failure relay 742 will be de-energized thereby opening the contacts, removing operating voltage from peak current detector 80, and s~utting down weld selector station 16.
Comporlent 802 is a Silicon General SG3524 regula~ing pulsewid~h modulator, used as a 22 pulse per minute (pprn) oscillator. Component ~02 also has an internal S volt regulator, the output of which is on pin 16, which provides operating power to component 176. Component 176 is a Silicon General SG1549 current sense latch, used as a peak curren~
detector. Details of operation of components 176 and 802 have been published by and are available from the manufacturer upon request, and have also been described in Patemt Application Senal No. 521,140. Component 830 is a 555 one shot, con~lgured to operate as a three minute timer. Details of construction and operation of 555-type circuits have been published by numerous manufacturers.
Peak current detector 80 operates in one of two modes depending on the position of switch 838. When switch 838 is in the open position, a peak current which is in excess of the allowable peak current, will cause peak current detector 176 and 22 ppm oscillator 802 to interrupt the welding arc at a 22 ppm rate. When switch 838 is in the closed position, a peak current 2 5 which is in excess of the allowable peak current, will cause peak culTent detector 176 and three minute timer 830 to shut down welding selector station 16 for a ~ree minute period. For normal operation switch 838 would be in the closed position. However, if desired, switch 838 may be placed in ~he open position. However, less protection will be afforded. Switch 838 should always be closed for pulse operation, especially low frequency pulse operation, where the reactance of inductors 62 and 70 is insufficient to limit the output current to a safe level.
It will be noted that component 802 is being utilized to provide two functions: a 5 volt regulator to provide power for component 176; and a 22 ppm oscillator to periodically reset peak current detector 176. In order to achieve these ~wo functions component 802 is connected as follows: conductor 801 is connected to pin 1~; 15 vvlt retuIn conductor 441 is connected to S pins 4, 5, 8, and 10; ~e c,ompensating input on pin 9 is connected to conductor 441 via ~e parallel com~ination of a one micro~arad capacitor 811 and 2200 ohm resistor 812; a 301 kilohm tin~ing resistor 813 is connected between pin 6 and conductor 441; and ~e series combination of a 22 microfarad timing eapacitor 814 and a 100 ohm current limiting resistor 815 ~e c~nnec~ed be~ween pin 7 and conductor 441. Resistor 815 is used to limit the discharge current from capacitor 814 and protect the diseharge circuit in component 802. A 0.1 microfarad noise bypass capacitor 803 is connected between pins 4 and 15 of component 802. The plus 5 volt output of component 802 on pin 16 is connected by conductor 810 to pins 12 and 13, one end of a 22 microfarad filter capacitor 805, one end of a 0.1 microfarad noise bypass capacitor ~04, the power supply iIlpUt (pin 8) of component 176, and one end of a 50 percent voltage divider formed by 5.1 kilohm resistors 806 and 807. The o~er end of resistor 807 is connected to conductor 441.
The junction of resistors 806 and 807 is connected pins of 1 and 2 of component 802. The reset inputloscillator output (pin 33 of component 802 is connected by conductor 816 to pin 7 of cornponent 176 through a 100 kilo}~n resistor 817, and to pin 6 of 2 s component 176 through a 1 microfarad capacitor 820.
Resistor 813 and capacitor 814 cause component 802 to oscillate at a ~requency of approximately 22 ppm. Pin 7 of eomponent 176 is the reset input and pin 6 of component 176 is ~e peak current detector output.
In normal operation, oscillator 802 will provide reset pulses to peak current detector 176 at ~e 22 ppm rate. However, if peak current detector 176 has not ~ripped dlese reset pulses will have no effect.
If peak current detector 176 is triggered by an 3 5 excessive current, then pin 6 will go high and reset oscillator 802.

The high signal on pin 6 will also attempt to reset peak current detector 176 via pin 7. However, in some cases this signal will be insufficient to provide a proper reset for peak current detector 176. Therefore, oscillator 802 will provide a reset pulse to pin 7 S approximately three seconds later. This assures that peak current detector 176 is properly reset within appro~imately ~hree seconds of being triggered. Peak current detector 176 will also trigger three minute delay timer 830 and allow time for the internal components to return to normal operating temperature.
Peak current detector 176 and short circuit detector 72 also operate to prevent starting an arc when there is a large ball on the end of the welding rod. It will be appreciated that striking an arc with a large ball on the end of ~e welding rod is undesirable since the ball contains oxides which rnake for an irnproper, porous weld. A large ball, with oxidation, would also have a poor contact conductivity. Therefore, in order to strike the arc, the ball must often be placed in contact with the welding surface. This causes a low voltage to appear on conductor 717 and relay 197 drops out thereby shutting down weld selector station 16. The welder must 2 then remove the welding rod and cut off the ba~l. The welder can then resume the welding operation. Also, if an arc is struck with the ball on the end, a large current will be required to melt the ball and this large current will trigger peak current detector 176, thereby shutting down the operation of weld selector station 16 2 5 until the ball has been removed from the welding rod. Therefore, peak current detector 176 and short circuit detector 72 operate to insure that the welder ~egins the operation with a properly cut welding rod rather than with a welding rod having a large ball on the tip.
3 0 As explained in Patent Application Serial No.
52l,l4a, peak current detector 176 responds to the current flowing through power transistors 56a-56f of Figure 1 by measuring the voltage developed across the two tap points on resistor 25 of Figure 1. These two tap points are brought out as conductors 76 and 77. Circuitry between conductors 76 and 77 22 1 3 ~1 0 ~

and pins 3 and 4 of detector 176 is slightly different from that in the above patent application. The operation of the present circuitry is similar to the original circuitry but provides for a more convenient board layout and slightly improYed resistance to noise ~ansients. Conductor 77 is connected to the ca~hode of diode 821. The anode of diode 821 is connected by a 15 vol~ returr conductor 441 to the negative te~ninal of 220 microfarad capacitor 823, one end of 470 ohm resistor 824, one end of 0.22 microfarad capacltor 827, and pin 4 of detector 176. C:onduc~or 76 is connected to one end of 470 ohm ~esistor &22. The o~er eI~d of resistor 822 is connected to the positive te~ 1 of cap~citor 823, the o~her end of resistor 824, and one end of ~he series combination of 5,000 ohm potentiometer 82$ and 11,000 ohm resistor 826. 'rhe other end of this series combination is connected ~o the other end of capacitor 827 and to pin 3 of detector 17~.
A1~ough precise values have been given for these components, these are nominal values and may be varied substantially depending upon the peak culTent response characteristics desired.
2 o In practice, the circuit has functioned satisfactorily with resistor 822 ranges of 50 to 2500 ohms, capacitor 823 values between 0 and 1,000 micro~arads, and resistor 826 values between 6 and 11,000 ohms. Using maximum values for resistor 822 and capacitor 823 the time constant of the input circuit is approximately 0.4 seconds, where if using the nominal value 2s shown, ~he time constant is approximately 52 milliseconds.
Potentiometer 825, resistor 826 and capacitor 827 have a negligible ef~ect upon the time constant and primarily serve to reduce high frequency noise transients which may not be absorbed by electrolytic capacitor 823. The resistance between pins 3 and 4 of component 176 is approximately 500 ohms, as listed by the manufacturer. Therefore, potentiometer 825 and/or resistor 826 are used to set ~e actual peak current threshold value at which detector 176 trips. The high comrnon mode inputs of detector 176 are not used and therefore pins 1 and 2 are connected together by 35 conductor 177.

The QUtpUt of component 176 on pin 5 is an open collector output which is low when detector 176 has been tripped and an open circuit otherwise. Pin S is connected to conductor 833 via the series combination of diode 831 and a 24.9 ol~n resistor 832. Conductor 833 is connected to the normally open contac~ of relay 190, the normalIy closed con:act of relay 197, and one end of a 60.4 ohm resistor ~34. The other end of resistor 834 is connected to the negative telminal of a 150 micro~arad capacitor 835 and to conductor 75. Conduc~or 81 is connected to the' o~er end of capacitor 835 and to plus 15 volt conductor 801. ~he center contacts of relays 190 and 197 are connec$ed to 15 vo:lt return conductor 441. Conducto.~. 81 and 75 are connected to the inputs of optocoupler 112 and SWitChiIlg9 sh~t down and ~iver circuit 37 of Figure 3. As explained in Patent Application S~rial No.
521, l4Q,if optocoupler 112 is tuIIled on circuit 37 removes base drive from power transistors 56a-56f ~ereby shutting down weld selector station 16. Therefore, if the peak current exceeds the allowable peak current ~en detector 176 will connect pin 5 to pin 4, thereby tu~ning on optoisolator 112. Likewise, if ~e average cu~rent is in excess of ~he allowable average current, ~en relay 190 will be activated, connectirlg conductor 441 to conductor 833, and optoisolator 112 will ~ turned o~, thereby shut~ing down weld selector station 16. Finally, if ~e voltage on output terminal 717 is less than the minimum arc welding voltage, approximately 20 volts, relay 197 will be de-energized, thereby connecting conductor 441 to conductor 833 which, in turn, turns on optoisolator 112 and shuts down weld selector station 16.
Therefore, circuits 72, 73 and 80 shut down and protect weld selector station 16 in the event of a shorted output tem~inal, 3 excessive average current, or e~cessive peak current, respectively, by removing base drive from power transistors 56a-56f.
Output pin S of detector 176 is connected to ~he negated trigger input (pin 2) of timer 830 ~rough a 2.2 kilohm resistor 836. Therefore, whenever current detector 176 is tnggered, tirner 830 is also triggered. However, blocking diode 24 1 3~ 0707 831 preYents the operation of relays 190 and 197 ~rom activa~ing three minute timer 830. Pin 2 of tirner 830 is corLnected to 15 volt conductor 801 ~rough the parallel combination of a 6.8 kilo~n resistor 840 and a 4.7 mierofarad capacitor 387. The ~lltering action provided by reslstors 836 and 840 and capacitor 837 prevents noise transients ~rom triggenng timer 830. Fifteen volt conductor ~01 is also connected to ~e negated rese~ input (pin 4) and the Vcc input (pin 8) of timer 830. Conductor 801 is also connected to one end of 10 megohm timing resistor 841. The o~er end of resistor 841 is comlected to threshold (pin 6) and discharge (pin 7) te~minals of timer 830 and to one end of 15 microfarad timing capacitor 842. The o~her end of capacitor 842 is connected to 15 volt retum conductor 441. Resistor 841 and capacitor 842 cause timer 830 to have a time constant of approximately three minutes. l~e three minute time period is no~
critical and longer or shorter shut down periods may be desirable for different welding applications. The purpose o~ the timeout period is to assure that any components overheated by the excessive peak current have had time to cool down to normal operating temperature. Therefore, for cooler ambient temperatures or where ~ere is a higher forced air flow shorter times may be used, such as 10 seconds. Also, the timeout period alerts ~e person performing the welding operation that an excessive current has occurred and that the various controls should 2 5 be checked for proper setting for the type of welding operation being conducted.
The ground terminal (pin 1) of tirner 830 is connected to conductor 441. The control terminal (pin S) is connected to conductor 441 via a 0.01 microfarad capacitor 843.
The output of timer 830 is connected to the anode of diode 844 hrough switch 838. The cathode of diode 844 is connected to ~e cadlode of diode 845 and one end of time delay relay reed 846.
The anode of diode 845 and the other end of relay 846 are connected to conductor 441. Use of shunting diode 845 in parallel 35 widl the coil of relay 46 is well known. The use of additional I ~0~07 - blocking diode 844 to provide further protection for timer 830 is the same as the use of diode 410 of Figure 8, the operation of which was described in Patent Application Serial No.s21,140 The normally closed contact of relay 846 is connected to lS volt conductor 801. The center contact of relay 846 is connected to one end of the coil of power shut down relay 847. The other end of the coil of relay 847 is cormected to 15 volt return conductor 441.
Two relays, 846 and 847, are used because of the limited drive capability of timer 830.
When tirner 83û is triggered by peak current detector 176, the output of timer 830 on pin 3 will be approxima~ely 15 volts, thereby activating relay 846, which in turn de-energizes relay 847. Relay 847 is connected to Figure 9 as shown by dashed line 848. Relay 847, as shown more completely in Figure 9, interrupts the 80 volt supply to STICK & TIG control circuit 30, and pulsewidth modulators 32 and 34. This assures that base drive is removed ~rom power transistors 56a-56f for the three timeout period whenever the peak current threshold is exceeded. Of 2 o course, if switch 838 is open, then tirner 830 will be disconnected from relays 846 and 847 and the three minute timeout will not occur. However, component 176 will still briefly interrupt the welding operation each tirne an excessive peak current occurs.
Tum now to Figure 5 which is a schematic diagram of transistor protection circuit 707. Conductor 40 is the drive output from switching, shutdown and driver circuit 37 Conductor 41 is the base drive return conductor. Conduc~ors 710a-710f are connected to the bases of transistors 56a-56f, respectively, of Figure 1. Conductor 40 is connected to one end of crowbar circuit 862a and one end of 10 ampere fuse 860. The other end of fuse 860 is connected by conductor 861 to one input of crowbar circuits 862b-862g and one end of 1.5 ampere fuses 863a-863f. The other end of fuses ~63a-863f are connected to output conductor 71 Oa-710f, respectively. Conductor 41 is connected to the other input of crowbar circuits 862a-862g. In the 3s preferred embodiment, a crowbar circuit and a fuse are mounted 1 31 ~7G7 - on the same board as the associated transistor. For example, crowbar 862b and fuse 863a a~e mounted on the same board as transistor 56a. This provides for a faster response :~rom the crowbar circuit and the fuse. Protection circuit 707 pro~ects switching~ shutdown and driver circuit 37 and the remaining output transistors 56 in the event ~at one of the output ~ansistors 56 suffers a ~ailure which shorts dle base and collector terminals of ~at transistor and places ~e filll collec~or voltage upon the base drive lines 710.
Assume, for e~ample, that transis~or 56a suf~ers such a failure. The filll collector voltage will then appear on conductor 710a and, through fuse 863a, on conductor 861 and, through fuse 860, on conductor 40 which goes back to driver circuit 37. The collec~or voltage on conductor 710a wi11 cause the remaining transistors 56b-56f to be turned on without any means of turning ~hem off, possibly cause destruction of driver circuit 37, and, because transistors 56b-56f are maintained in the OIl condition, eventually causing the destruction of transistors 56b-56f.
However, crowbar circuits 862a-862g and fuses 860 and 863a-863f preve~t the failure of transistor ~6a from causing ~he destruction or failure of circuit 37 or transistors 56b-56f. When the full collector voltage is placed on conductor 710a crowbar circuit 862b will be triggered thereby blowing fuse 863a and isolating the base of transistor S6a. Therefore, the shorted base-2s collector junction of transistor 56a can no longer cause the collector voltage to be applied to the bases of transistors 56b-56f or to the output of circuit 37. Also, the collector voltage on conductor 710a will trigger crowbar circuit 862a which blows fuse 860 thereby removing output drive from transistors 56a-56f.
The result is ~at ~e failed transistor is isolated by ~use 863a and weld selector station 16 is shut down by the blowing of fuse 860.
If weld selector station 16 were allowed to continue to operate with one power transistor isolated then the remaining power transistors would have to earry the current normally 3s carried by the failed transistor. This would eventually cause the 27 ~ 31~i~/O~

- remaining transistors to overheat and be destroyed. However, the blowing of fuse 860 removes dAve power from these transistors and shuts down weld selector station 16 until the defective transistor, its associated fuse, and fuse 860 are all replaced.
Therefore, the failure of a single transistor does not lead to the failure of all the transistors and of driver circuit 37.
Crowbar circuits 862a-862g are identical and are constructed as follows. The positive input is connected to one end of a 470 ohm resistor 864 and to the anode of a silicon con~olled recti~ler (S(: R) 866. The o~er end of resistor 864 is connected to the cat~ode of a 9.1 volt zener diode 865. The anode of diode 865 is connected to the gate of SCR 866 and to the anode of diode 867.
lhe ca~ode of diode 867 is connected to ~he anode of diode B70.
The anode of diode 870 is connected to the cathode of SCR 866 and to one end of a 0.05 ohm resistor 871. The other end of resistor 871 is connected to the anode of blocking diode 872. The cathode of diode 872 is connected to the negative input terrninal of crowbar circuit 862a. The operation of crowbar circuit 862a is conventional: when an excessive voltage is present, such as when ~he collector voltage is applied to conductor 710a, zener diode 865 will conduct, thereby tuming on SCR 866, which will remain on until the current flow through SCR 866 is reduced below the threshold value, such as by the blowing of fuses 860 and 863a.
Diodes 867, 870 and 872 prevent crowbar circuit 862a from being 2s activated by voltages which would be applied to conductor 40 during normal operation of circuit 37. In normal operation, a crowbar circuit 862 will trigger when approximately 15 to 17 volts is applied. A single crowbar, such as 862b, may be used in place of crowbars 862b-~62g, but the response time will be slowed due to the inherent inductance and capacitance of the conductors, and a lesser degree of protection will be obtained.
Turn now to Figure 6 which is a schematic diagram of low frequency pulsewidth modulator 32. As explained in Patene Application Serial No. 52].,140, pulse modulator 32 is a low 3s frequency, input voltage compensated, selectively adjustable 2 8 .~ 7 0 ~

- pulsewid~ modulator. 'rhe improvements to pulse modulator 32 are as follows: during striking, and before the arc has been struclc, the duty cycle of ~e output is increased so as to provide a higher output voltage which makes striking the arc easier and, once the arc is stIuck, reverting t~ the preselected pulsewidth desired for the actual welding operation; during the striking operation, amd before the arc is struck, the frequency of the output of modulator 32 is substantially increased so ~at, when the arc is struck, inductors 62 and 70 of Fig~re 1 wi~l ha~ a higher reactance and prevent the previously mentioned higher stri~ing voltage frnm causing arl initial e~cessive current flow and, once the arc is struclc, dle frequency of the output of modulator 32 retu~ns to the vallle preselected ~or ~e welding operation; half frequency or ifiull ~requency outputs, which affects ~e average ou~Lpu~ voltage, can be selected ~o tailor the output characteristics to the immediate welding job; and a very low frequency mode is available, which is useful for certain types of welding.
I~ will be recalled that the vol~age on pin 9 of 2 0 component 261 dete~nines ~e duty cycle of the output pulse. This voltage on pin 9 is deterrnined by the voltage d~vider action of resistors 302 and 313, and potent;ometers 303, 305 and 306.
During the striking operation, resistor 302 is partially or co m pletely bSlpassed by optically coupled switch g88a a~d potendometers 891 and 892, ~ereby increasing dle voltage on pin 9 and increasing the duty cycle of the output pulse. In the preferred embodiment, potentiometer g91 is rnounted for access by thg welder and potentiometer 892, which is not accessible by ~e welder, is adjusted to provide ~e maximum duty cycle which can be selected by the welder using potentiometer 891. One end of 3 potentiometer 892, the wiper of potentiometer 892, and one end of potentiometer 891 are connected to the junction of resistor 302 and potentiometer 303. The other end potentiometer 892 is connected to the wiper contact of potentiometer 891. The other end of potentiometer 891 is connected to the anode of diode 890, the emitter of transistor 882b of optocoupler 882, and one end of 2~

one megohm resistor 887. ~he other end of resistor 887 is connected to the base of transistor 882b. The collector of transistor 882b is connected to ~e cathode of diode 890 and to switch to plus 80 volt supply line 951. ~Yhen transistor 882b is turned Oll, potentiometers'891 and 892 shunt resistor 302, thereby providing a higher voltage on pin 9 of component 261. However, when transistor 882b is turned off, then potentiometers 891 and 892 have no e~fec~ on ~e duty cycle. Conductor 705 is connected to the anode of blocking diode 880. The ca~ode of diode 880 is connected ~o the positive te~al of 220 microfarad capaci~or 881 and to the anode of emitting diode 882a of optocoupler 882. The cathode of diod~ 882a is connected to the ne~ative terminal of capaci~or 881 through a 4.7 kilohm resistor 883. The negative terminal of capacitor 881 is also connected to one end of a 47 ohm resistor 886, and the wiper contact and one end of 25 kilohm potentiometer 884. The other end of resistor 886 is connected to the positive terminal of a 22 microfaMd capacitor 885. The other end of capacitor 885 and the other end potentiometer 884 are 2 o connected to 80 volt return conductor 23.
Dunng the striking operation, and before the arc is struck, conductor 705, as shown in Figure 8, is connected to plus 80 volts thereby turning on optocoupler 882 and increasing the duty cycle of dle outpu~ pulses. After d~e arc is struck, conductor 705 is isolated from the 80 volt supply, optocoupler 882 turns off, 2 5 and ~e duty cyçle returns to the duty cycle selected for welding operations. Resistor 883 limits the current ~rough diode 882a.
Capacitor 881 provides a filtering action to prevent noise transients from adversely effecting the operation of optocoupler 882. Capacitor 885 provides ~or a fast tum on for diode 882 and potentiometer 884 provides the discharge pa~ for capacitor 885 and allows selection of the turn on delay time of optocoupler 882.
Diode 880 and schottky diode 890 preven~ negative transients from hanning optocoupler 882.
(: omponent 261 may be either a National 3s Semiconductor LM3524 or a Silicon General SG3524 regulating 30 1 3 1 07~7 pulsewidth modulator. The timing resistor input (pin 6) of component 261 is connected to one end of the series string of 2210 ohm resistor 297 and 5 kilohm potentiometer 905. The other end of the series combination is connected to one of potentiometer 903, one end of potentiome~er 904, and the collector of transistor 897b of optoisolator 897. The base of transistor 897b is connected to a 1 megohm resistor 901, to the emitter of transistor 897b and to 66.7 volt conductor 430. The wiper contact and the o~er end of potentiometer 904 are connected to the wiper contact of potentiometer 903. The other end of potentiometer 903 is connected to 66.7 volt conductor 430 through-22 kilohm potentiometer 902. Conductor 704 is connected to the anode of reverse voltage blocking diode 896. The ca~ode of diode 896 is connected to dle anode of emitting diode 897a of op~ocoupler 897.
The eathode of diode 897a is conrlected to 80 volt return conductor 23 through a 4.7 kilohm resistor 900.
As will be shown in the discussion of Figure 8, conductor 704 is connected to dle plus 80 volt supply during ~e striking opera~ion~ and is disconnected after the arc has been struck. Therefore, during the striking operation, alld be~re the arc has been struck, optocoupler 897 will be turned on and potentiometers 903, 904 and~2 will be bypassed, ~ereby leaving only resistor 297 and potentiometer 905 connected to pin 6 of component 261. Potentiometer 905 is adjusted to provide an 2 5 oscillation frequency of 3 kiloher~z for component 261.
Therefore, during the striking operation, component 261 oscillates at a higher ~requency which, as mentioned above, provides better current l~mlting action at the instant the arc is struck. Once the arc is struck optocoupler 897 is tumed off, potentiometers 902, 903 and 904 now have an e~fect upon the resistance seen by pin 6 of component 261, and the ~requency of oscillatiorl of component 261 for use during welding is set to the desired frequency by potentiometer 903. Potentiometer 902 is adjusted to provide for a maximum oscillation frequency during 35 welding operations and potentiometer 904 is set to provide the 3' 1 3 1 0707 - minimum frequency which can ~e used during welding operations. Potentiometer 903 is generally available to the welder whereas potentiometers 902 and 904 are not accessible by the welder.
The timing capacitor input (pin 7~ of component 261 is connected to one end of 0.1 n~icroiFarad capacitor 300 and one end of 100 ohm current limiting resistor 893. The odler end of resistor 893 is cormected through switch 894 to the positive terminal of 22 microfarad capacitor 89S. The other end of capacitors 895 and 300 are connected to 66.7 volt conductor 430.
When switch 894 is open capacitor 895 is disconnected from ~e timing circuit and ~erefore capacitor 300, in co~junction with ~e resistors connected to pin 6, determine the ~equençy of oscillation of component 261. When switch 894 is open, component 261 typically provides an oscillation ~equency range of 500 to lS00 Hertz and, when optocoupler 897 is turned on9 an oscillatior frequency of 3000 Hertz. However, when switch 894 is closed, capacitor g95 substantially lowers the oscillation frequency of component 261 and provides a frequency range of 0.2 Hertz to 6.82 Hertz. Also, when switch 894 is closed, the frequency of oscillation of component 261 during the striking operation, before the arc is s~uck, is appro~imately 13.6 Hertz.
The emitter A output (pin 11) of component 261 is connected to one end of switch 906. The emitter B (pin 14) output of conductor 261 is connected to ~e center contact of switch 907a.
2 5 One contact of switch 9~7a is connected to dle o~er end of switch 907 and to one contact of switch 380a. I~e other contact of switch 907a is cormected to ~e other contact of switch 380a. l~e center contact of switch 380a is connected to conductor 33. Switches 380a and 907a are connected by dash lines 911 and 912, respectively, through ~e remaining portions of switches 380 and 907, respectively, in Figure 7.
The position shown for switch 907a is typically used for aluminum welding whereas the other switch position is typically used for steel welding. When switch 907 is in the 3s aluminum welding position, switch 906 may be closed to provide - an output pulse frequency which is equal to the oscillation frequency of component 261 or, if switch gO6 is open~ an output pulse fre~quency which is one half the oscillation frequency of component 261. This arises because of the structure of component 261. I~e oscillator of co~ponent 2~1 is used to toggle a flip-flop the {2 and negated Q OlltpUtS of which are used to drive ~e two output transistors (A and B) into alternate states (on and o~f3.
Therefore, if only the output of transistor B (pin 14) is used the output pulse frequency will be one half of ~e oscillation ~equency but, when swi~ch 906 is elosed so that the outputs ~pin 11 and pin 14) of bQ~ transistors are coImeçted in parallel the output ~lse frequency is the same as ~he oscillation frequency of componen~
261. It should be noted that the position of switch 906 does not affect the pulsewidth of ~e two outputs, but detennines whether one output, or both, are used. Therefore, in a given time period, there will be one or ~vo pulses, each having the same pulsewid~, and the duty cycle for that ~ime period will be affected accordingly. When switch 906 is closed, since there are now two 2 o pulses during dle same period that ~ere would have been only one pulse if switch 906 were open, ~en the average ouq?ut vol~age of weld selector station 16 will increase and, ~ecause ~e frequency of ~he pulses has doubled, inductor 62 and 70 will provide an improved cuITent limiting action.
Switch 380a provides a choice of two different types 2 $ of modulation. When switch 380a is in the position shown, high frequency pulsewidth modulator 34 (Figure 7) will provide ou :put pulses only when the output of low frequency pulsewidth modulator 32 is a logic 1. When switch 380a is in the other position the outputs of low frequency pulsewid~h modulator 32 30 and high frequency modulator 34 are connected in parallel so ~at the output pulses provided by low frequency modulator 32 are interspersed by the output pulses provided by high frequency modulator 34. It will be noted that switch 906 only has an affect when switch 30a is in ~e position shown.

33 l 31 ~70~

- Turn now to Figure 7 which is a schematic diagram of high frequency pulsewidth modulator 34. The basic principles of construction and operation of high fiequency pulsewidth modulator 34 are the s~ne as described in Patent Application Serial No. 521,140. However, like low frequency pulsewidth modulator 32, high frequency pulsewidth modulator 3d, has an optically coupled switch 888b which, when conductor 705 is connected to the plus 80 volt supply, ~urns on and allows o potentiometers 920 and 921 to shunt resistor 362, thereby increasing the du~ cycle of dle ou~tput of component 321. ~ing the strilcing operation, switch 888b and potentiometers 920 and 921 increase the duty cycle of the output puls s and there~ore irlcrease ~e average output voltage which allows for an improved striking operation. A 1210 ohm resistor 922 has been inseIted between conductor 323 and ~e top end of dead band adjustment potentiometer 3g4. It will be recalled that dead band adjustment potentiome~er 384 sets the maximum possible duty cycle of the output pulses of component 321. Resistor 922 has bePn added in order to limit the range of adjustrnent provided by potentiometer 3~4.
Dashed line 911 indica~es the connection from switch 380a of Figure 6 to switch 380b. In ~is embodiment, the value of resistor 381 has been changed to 100 ohms to provide for improved performance characteristics when low frequency pulsewidth modulator 32 is used to turn pulsewid~ modulator 34 on and of~. Also, a 200 ohm resistor 924 has been added between the anode of diode 383 and 66.7 volt conductor 430. This resistor was not i~ the original high frequency pulsewidth modulator 34 circuit and it has been found that the frequency range available for pulsewidth modulator 34 was somewhat dependent upon the particular component 321 used. The addition of resistor 924 corrects this problem so that the fuU frequency range is available and is not dependent upon the characteristics of a particular component 321.
3s 34 ~ 3 1 ~71~7 - Switch 907b has also been added between conduc~or 330 and the anode of diode 383. When switch 907b is in the position shown, which is used primarily for welding aluminum~
component 321 is responsive to the setting of dead band adjus~nent potentiometer 3g4 and, when switch 380b is in the position shown, is also responsive to the output of low frequency pulsewidth modulator 32. When switch 907b is in the other position~ the output of component 321 is dependent only upon the output of STICK & TIG con~rol 30. This other position for switch 907b is generally used for welding steel.
Turn no~ to Figure ~, which is a schematic diagram of the high-low voltage switchover circuit. The basic construction and principles of operation of switchover circuit 86 are as previously described in patent application 521,140. More precisely, when conductor 17 has no voltage (as in a short) or a low voltage (an arc is being sustained) then relay 411 will not be activated, but when a voltage higher ~an an arc sustair~ing voltage (such as the striking voltage) is present on conductor 71 then operational amplifier 397 will energize relay 411. The improvements to switchover circuit 86 are described below.
The normally open contact of relay 411 is now connected to conductor 705 which, it will be recalled, goes to Figure 6 (low frequency pulsewidth modulator) and Figure 7 (high frequency pulsewidth modulator). When a high voltage is present on conductor 71, such as during the arc striking operation, but be~ore the arc is struck, relay 411 will be energized thereby connecting conductor 705 to plus 80 volt connector 21, turning on optocouplers 888a and 888b (Figures 6 and 7, respectively). This causes pulsewidth modulators 32 and 34 to operate at the higher duty cycles and frequencies, previously described, which assist in the arc striking operation.
Once the arc is struck relay 411 is de-energized thereby disconnecting conductor 705 and then connecting conductor 412 to 80 volt conductor 21. Conductor 412, as in the 3s original circuit, is still connected to transfer relay 420. When a 1 ~ /ù~

- low or no vol~ge is present on conductor 71, relay 420 is activated ~ereby providing the voltage tap selected by switch 425 to feeder conerol circuit 99. This causes motor 940 to operate a~ ~e desi~d speed for welding operations. However, when a higher voltage is present on conductor 71, ~uch as before dle arc is st~uck, relay 411 will be energized, relay 420 will be de-energized, and coIlductor 97 will be connected to conductor 91 thereby providing the correct vol~age to motor 940 for ~e speed desired during the p~eliminary set up and arc s~iking operation. One change has also been made with respect to the connections for switch 425.
Previously, in the position shown, switch 425 was cor~ected to conductor 71. However, switch 425 is now connected to plus 80 volt conductor 21. This provides a higher operating voltage ~or feeder control ~9 in cases where dle arc voltage is too low to provide for reliable operation of motor 940.
Relay 420 now also has one additional set of contacts ~shown as the lower set of con~cts). The center contac~ of this set of contacts is connected ~o plus 80 volt conductor 21. The 2 o normally closed contact set of contacts is connected to conductor 704 which is connected ~rough diode 896 to optocoupler 897 of Figure 6 (low frequency pulsewidth modulator 32). When conductor 71 has a high voltage present, such as during the striking operation, relay 420 will be de-energized and conductor 704 will be connected to plus 80 volt conductor 21. This tums on optocoupler 807 of Figure 6 thereby causing low ~requency pulsewid~ modulator 32 to provide the higher pulse ~requency desired for the striking operation. Once an arc is stluck, the voltage on conductor 71 will drop below the ~reshold voltage, thereby causing relay 4'20 to be energized and disconnecting conductor 704 from conductor 21. Ihis causes low frequency pulsewidth modulator 32 to switch to the frequency set ~or the welding operation. Referring briefly to Figure 2, if the first option 753 is used, conductor 704 may be connected to the normally open contact shown. It will be recalled that the first 3s option 753 is one of two options provided to increase the speed of 36 1~707 cooling fan mo~or 733 when welding op~erations are actually in progress.
The motor speed control circuit of switchover control circuit 86 has al,so been modified. Conductor 412 is connected to ~e anode of reverse voltage blocking diode 931. The cathode of diode 931 is connected to the anode of emitting diode 932a of optocoupler 932. The ca~ode of 932a is connected ~rough a 4.7 kilohm resistor 937 to conductor 751. The base of transistor 932b of optocoupler 932 is connect~ed by 1 megohm resis$or 933 to the emitter of transistor 932b. The emitter of tr,ansistor 932b is connected to the anode of reverse voltage protection schottlcy diode 934 and to the wiper contact of speed control potentiometer 84. The collector of tr,ansistor 932b is connected to the ca~hode of 934, to one end of potentiometer 84, ,and, via conductor 96, to one of the speed control inputs on i~eeder control circuit 99. Another end OI potentiometer 84 is connected by the parallel combination of 2.2 kilohm resistor 93''"and speed vernier switch 936 to the other speed control input of feeder 2 o control 99. When switch 936 is closed, resistor 935 is bypassed so that speed control potentiometer 84 operates over its noIma range. However, when switch 936 is open, resistor 935 limits the range of control of potentiometer 84 thereby causing potentiomster 84 to cause a more fime (vernier) adjustment of the speed of motor 940.
2 s When a high voltage is present on conductor 71, such as during ~e striking process, relay 411 will be energized thereby causing optocoupler 932 to be tu~ed o~f, and placing the full resistance of potentiometer 84 across the speed control inputs of feeder control 99. The speed of motor 940 is inversely 3~ propor~ional to dle resistance connected across dle speed control inputs of control circuit 99. There~ore, during the striking operation, motor 940 operates at a reduced speed which is desirable for set up and striking operations. However, once the arc is struck, relay 412 will be de-energized, thereby tuming on 3 5 optocoupler 932 and shorting out the portion of potentiometer 84 be~ween its eenter contact and conductor 85. This provides for a higher speed for feeder con~rol motor 940, as adjusted by the position of the wiper on potentiometer 84, during the actual welding operation. The con~rol of the speed of motor 940 is therefore essentially idéntical to that described in Patent Application Serial No. 521,140, but has been implemented via optocoupler 932 instead of via an additional relay.
Feeder control ci~uit 99 has two output termina~ for providing drive power to ~eeder motor 940. The negative output terminal (A-) is connected to one brush of motor 940 and to ~e normally closed contact of a se~ of contacts of relay 784. The other brush of motor 940 is cormected to one end of one microfarad surge absorbing capacitor 941 and to the center contac~ of this set of eontacts of relay 784. The positive terminal (A+~ is connected to the other terminal of capacitor 941 and to the nolmally open contact of this set of contacts of relay 784. The connection and operation of relay 784 is as descri~ed in Figure 2.
When wire feeding is not desired, relay 784 is in the de~nergized 2 o position shown, which depIives motor 940 of operating power and fi~er uses mntor 940 as a brake in ~e event ~at motor 940 was previously operating. When wire feed~g operation is desired, relay 784 is energized and operating power is applied to motor 940.
Turn now to FigNre 9 which is a schematic diagram 2 5 of ~e circuit power supplies 38. The description and operation of circuit power supplies 38 is essentially as dlat described in Patent Application Serial No. 5 21, 14 0. The improvement~ to the power supplies 38 consist of ~e addition of fuse 950, to protect voltage regulator 501, and a set of contacts of relay 847~ which switch operating power to STICK ~c TIG control 30, low frequency pulse modulator 32, and high frequency pulse modulator 34. Plus 80 volt conductor 21 is connected ~rough fuse 950 to conductor 952.
Conductor 952 is selectably connected by a set of contacts of relay 847 to switched plus 80 volt conductor 951. Fuse 950 protects 3s voltage regulator 501 in ~e event that circuits 30, 32, or 34 draw 38 l 3 1 0707 - ~oo much current. The set of contacts shown for relay 847 intelmpt operating power to circuits 30, 32, and 34 if the three minute time delay cooling off period has been selected and a peak current in excess of the allowable peak current occurs. The operation of relay 847 is described more fillly in conjunction with Figuse 4.
Turn now to Figure 10 which is a schematic diagram of STICK & TIG circuit 30. The construction and principl s of operation of circuit 30 are the same as described in Patent Application Serial No. 521,140. Circuit 30 monitors ~e current output and provides a cwrent feedback signal which controls the pulsewidth of the ou~put of high frequency modulator 34.
However, circuit 30 now receives operating power via switched 80 volt conductor 951 instead of via 80 volt conductor 21. This provides for the shut down of circuit ~0 in the event that the three rminute tirne delay cool down period is selected and a peak current in excess of the allowable peak culTent has occurred.
The table below lists several different modes of welding operations and the nominal switch settings for these operations. It must be emphasized that these switch settings are merely nominal and that other switch settings may be desirable depending upon the particular type of welding being performed, the type of material being welded, the thich~ess of the material being welded, the diameter of the welding rod etc. Also, 2s depending upon the range of welding operations that may be performed, it is often desirable to make some of the switches interlocking so that certain features cannot be activated at the same time other features are activated. For example, switches 310 and 254 may be interlocking so that STICK & TIG con~ol 30 and low 3 frequency pulse modulator 32 cannot be activated at the sarne time.
Also, switches 370 and 3%0 may be interlocking so that high frequency pulse modulator 34 cannot be activated when low frequency pulse modulator 32 is activated and switch 380 is in the ALT2 position. The decision ~o make switches interlocking or non-interlocking and, if interlocking, which switches should be 3g 1310707 - mterlocking, will depend upon the number of di~eren~ options which are to be made available to the welder p¢r~olming the welding operation.
NOMINAL SWlTCH SETTINGS

_ , . ...... __ _ Switch 794, No. 254 310 370 380 715 795 1 0 e--_ _ _ . _ , SllCK LF HF ALTl/ ou~PU'r ~ & TIG PWM PWM AL12 SE~L. ..
MODE ~ CONTROL
__ , . . . ___ MIG OFF OFF ON X PULSE OP~SNLD
TIG OFF OFF ON X STICK & CLOSLD
STICK ON OFF OFF X STICK & CLOSED1 ~Ode 1) TIG OPEN
STICK ON OF~ ON X SIICK & OPEN/
(MOde 2) TIG CLOSED
2 O CH~PPED OFF ON ON ALTl PULSE CLOSED
UN- OFF ON OFF ALr2 MIG ~ OPEN/
CH~PPED PIJLSE CLOSED
PUT SE
~ . . _ ._ From the detailed description above, it will be 3 0 appreciated that the present invention describes an improved weld selector station having improved self protection features, improved arc striking and swi~chover characteristics, great versatility and a longer operating time between maintenance periods.
Also, based upon the foregoing detailed descr~ption, numerous variations and modi~lcations to the present invention 1 ~ ~ (3~07 - will be appareIlt to those skilled in the ar~. Therefore, the scope of the present invention is to be limited only by ~he cla~ms below.

Claims (63)

1. In a welding station comprising an output stage and a driver stage for providing drive power to said output stage, said output stage comprising at least one transistor, said transistor having a drive input terminal, a power supply input terminal, an output point, and a bonding wire connecting said output point to an output terminal, a method of reducing the probability of said bonding wire detaching or burning through due to an instantaneous current flow through said transistor, comprising the steps of:
(a) connecting a load to said output terminal;
(b) adjusting said load to cause a predetermined output current to flow through said output stage;
(c) adjusting said drive power to cause a predetermined voltage to be present between said power supply input terminal and said output terminal; and (d) repeating steps (b) and (C) as necessary to simultaneously obtain said predetermined output current and said predetermined voltage;
wherein said transistor operates slightly in an active mode at said predetermined output current so that, for loads tending to cause said output current to exceed said predetermined output current, said drive power is insufficient to support said output current and said bonding wire is protected.

2. An improved arc welding station, comprising:
control means for selecting desired parameters for a welding operation;
drive means responsive to said control means for providing drive power, said drive power not exceeding a first predetermined value;
output means responsive to said drive power for providing an output current to said welding operation, said output means comprising a transistor, said transistor having a drive input terminal connected to said drive means, a power supply input terminal connected to a power source, an output point, and a conductor connecting said output point to an output terminal, said output terminal being connected to said welding operation;
first current detection means responsive to a peak value of said output current exceeding a first predetermined value for causing said drive power to be removed from said output means; and second current detection means responsive to an average value of said output current exceeding a second predetermined value for causing said drive power to be removed from said output means;
wherein said first predetermined value is adjusted so that said output means cannot conduct an output current greater than a second predetermined value, said second predetermined value being less than an amount necessary to cause damage to or detachment of said conductor.

3. The improved arc welding station of Claim 2 wherein said output means comprises a plurality of said transistor connected in parallel.

4. The improved arc welding station of Claim 3 wherein said first predetermined value causes a specified voltage to appear between said power supply input terminal and said output terminal when a specified current is flowing through said output means.

5. The improved arc welding station of Claim 2 wherein said first predetermined value causes a specified voltage to appear between said power supply input terminal and said output terminal when a specified current is flowing through said output means.

6. The improved arc welding station of Claim z wherein said conductor comprises a bonding wire.

7. The improved arc welding station of Claim 2 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

8. The improved arc welding station of Claim 2 and further comprising:
timing means responsive to said first current detection means detecting said peak value of said output current exceeding said first predetermined value for causing said drive power to be removed from said output means for a predetermined period.

9. The improved arc welding station of claim 2 and further comprising:
means for providing a reset signal to said first current detection means.

10. An improved arc welding station, comprising:
control means for selecting desired parameters for a welding operation;
drive means responsive to said control means for providing drive power, said drive power being limited to a predetermined value;
output means responsive to said drive power for providing an output current to said welding operation, said output means comprising a transistor having a drive input terminal connected to said drive means, a power supply input terminal connected to a power source, an output point, an output terminal for providing said output current to said welding operation, and a conductor connecting said output point to said output terminal;
first current detection means responsive to a peak value of said output current exceeding a first predetermined value for causing said drive power to be removed from said output means; and second current detection means responsive to an average value of said output current exceeding a second predetermined value for causing said drive power to be removed from said output means;
wherein said predetermined value of said drive power prevents said output current from reaching a value which causes detachment of or damage to said conductor.

11. The improved arc welding station of Claim 10 wherein said output means comprises a plurality of said transistor connected in parallel.

12 . The improved arc welding station of Claim 11 wherein said predetermined value causes a specified voltage drop between said power supply input terminal and said output terminal when a specified current is flowing through said output means.

13 . The improved arc welding station of Claim 10 wherein said predetermined value causes a specified voltage drop between said power supply input terminal and said output terminal when a specified current is flowing through said output means.

14. The improved arc welding station of Claim lo wherein said conductor comprises a bonding wire.

15 . The improved arc welding station of Claim 10 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

16. The improved arc welding station of Claim 10 and further comprising:
timing means responsive to said first current detection means detecting said peak value of said output current exceeding said first predetermined value for causing said drive power to be removed from said output means for a predetermined period.

17. The improved arc welding station of Claim 10 and further comprising:
means for providing a reset signal to said first current detection means.

18. An improved arc welding station, comprising:
control means for selecting desired parameters for a welding operation;
drive means responsive to said control means for providing drive power;
output means responsive to said drive power for providing an output current to a welding operation;
said drive power being sufficient to cause said output means to operate near a saturated state when said output current is less than a predetermined output current; and said drive power being limited to a predetermined drive power so that a condition tending to increase said output current in excess of said predetermined output current causes said output means to operate less near said saturated state and more toward an active state.

19. The improved arc welding station of Claim 18 wherein said output means comprises a plurality of transistors.

20. The improved arc welding station of Claim 19 wherein said predetermined output current is insufficient to cause damage to or detachment of a conductor in any transistor of said plurality of transistors.

21. The improved arc welding station of Claim 20 wherein said conductor comprises a bonding wire.

22 . The improved arc welding station of Claim 18 wherein said predetermined output current is insufficient to cause damage to or detachment of a conductor in said output means.

23. The improved arc welding station of Claim 22 wherein said conductor comprises a bonding wire.

24. The improved arc welding station of Claim 18 and further comprising:
current detection means responsive to a peak value of said output current exceeding a predetermined value for causing said drive power to be removed from said output means.

25. The improved arc welding station of Claim 2 4 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

26. The improved arc welding station of Claim 2 4 and further comprising:
timing means responsive to said current detection means detecting said peak value of said output current exceeding said predetermined value for causing said drive power to be removed from said output means for a predetermined period.

27. The improved arc welding station of Claim24 and further comprising:
means for providing a reset signal to said current detection means.

28. The improved arc welding station of Claim18 and further comprising:
current detection means responsive to an average value of said output current exceeding a predetermined value for causing said drive power to be removed from said output means.

29. The improved arc welding station of Claim18 and further comprising:
first current detection means responsive to a peak value of said output current exceeding a first predetermined value for causing said drive power to be removed from said output means; and second current detection means responsive to an average value of said output current exceeding a second predetermined value for causing said drive power to be removed from said output means.

30. The improved arc welding station of Claim 29 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

31. The improved arc welding station of Claim 29 and further comprising:
timing means responsive to said first current detection means detecting said peak value of said output current exceeding said first predetermined value for causing said drive power to be removed from said output means for a predetermined period.

32. The improved arc welding station of Claim 29 and further comprising:
means for providing a reset signal to said first current detection means.

33. The improved arc welding station of Claim 18 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

34. An improved arc welding station, comprising:
control means for selecting desired welding parameters;
drive means responsive to said control means for providing drive power;
limiting means connected to said drive means for limiting said drive power to a predetermined maximum drive power, output means responsive to said drive power for providing a desired maximum output current to a welding operation;
wherein said predetermined maximum drive power is sufficient to allow said output means to provide said desired maximum output current to said welding operation but insufficient to allow said output means to provide an output current larger than said desired maximum output current; and wherein said predetermined maximum drive power causes said output means to operate slightly out of a saturated operating region when said output means is providing said desired maximum output current.

35. The improved arc welding station of Claim 34 wherein said limiting means comprises a resistor.

36. The improved arc welding station of Claim 34 wherein said output means comprises a transistor.

37. The improved arc welding station of Claim 36 wherein said predetermined maximum drive power limits said output current to a value which does not cause damage to or detachment of a conductor in said transistor.

38. The improved arc welding station of Claim 37 wherein said conductor comprises a bonding wire.

39. The improved arc welding station of Claim 34 and further comprising:
current detection means responsive to a peak value of said output current exceeding a predetermined value for causing said drive power to be removed from said output means.

40. The improved arc welding station of Claim 39 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

41. The improved arc welding station of Claim 3 9 and further comprising:
timing means responsive to said current detection means detecting said peak value of said output current exceeding said predetermined value for causing said drive power to be removed from said output means for a predetermined period.

42. The improved arc welding station of Claim 39 and further comprising:
means for providing a reset signal to said current detection means.

43. The improved arc welding station of Claim 34 and further comprising:
current detection means responsive to an average value of said output current exceeding a predetermined value for causing said drive power to be removed from said output means.

44. The improved arc welding station of Claim 3 4 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

45. In a welding power supply having a control means for selecting desired welding parameters, a drive means responsive to s a id control means for providing drive power, and an output means responsive to said drive power for providing an output current to a welding operation, an improved method for operating said welding power supply, comprising the steps of:
selecting a desired maximum output current, said desired maximum output current being less than a current required to detach or damage a conductor in said output means;
limiting said drive power to a value which prevents said output means from providing an output current greater than said desired maximum output current;
monitoring said output current;
removing said drive power from said output means if a peak value of said output current exceeds a first predetermined value; and removing said drive power from said output means if an average value of said output current exceeds a second predetermined value.

46. The improved method of Claim 45 wherein said conductor is a bonding wire.

47. The method of Claim 45 and further comprising the steps of:
monitoring an output voltage provided to said welding operation; and removing said drive power from said output means if said output voltage is less than a predetermined voltage.

48. The method of Claim 45 wherein said drive power is removed from said output means for a predetermined period if said peak value of said output current exceeds said first predetermined value.

49. The method of Claim 45 and further comprising the steps of:
monitoring an output voltage provided to said welding operation; and removing said drive power from said output means if said output voltage is less than a predetermined voltage.

50. In a welding power supply having a control means for selecting desired welding parameters, a drive means responsive to said control means for providing drive power, and an output means responsive to said drive power for providing an output current to a welding operation, an improved method for operating said welding power supply, comprising the steps of:
selecting a desired maximum output current, said desired maximum output current being less than a current required to detach or damage a conductor in said output means;
and limiting said drive power to a value which causes said output means to operate slightly out of a saturated mode when said output means is providing said desired maximum output current.

51. The improved method of Claim 50 wherein said conductor is a bonding wire.

52. The method of Claim 50 and further comprising the steps of:
monitoring said output current; and removing said drive power from said output means if a peak value of said output current exceeds a predetermined value.

53. The method of Claim 52 and further comprising the steps of:
monitoring an output voltage provided to said welding operation; and removing said drive power from said output means if said output voltage is less than a predetermined voltage.

54. The method of Claim 52 wherein said drive power is removed from said output means for a predetermined period if said peak value of said output current exceeds said predetermined value.

55. The method of Claim 50 and further comprising the steps of:
monitoring said output current; and removing said drive power from said output means if an average value of said output current exceeds a predetermined value.

56. The method of Claim 50 and further comprising the steps of:
monitoring said output current;
removing said drive power from said output means if a peak value of said output current exceeds a first predetermined value; and removing said drive power from said output means if an average value of said output current exceeds a second predetermined value.

57. The method of Claim 56 and further comprising the steps of:
monitoring an output voltage provided to said welding operation; and removing said drive power from said output means if said output voltage is less than a predetermined voltage.

58. The method of Claim 56 wherein said drive power is removed from said output means for a predetermined period if said peak value of said output current exceeds said first predetermined value.

59. The method of Claim 50 and further comprising the steps of:
monitoring an output voltage provided to said welding operation; and removing said drive power from said output means if said output voltage is less than a predetermined voltage.

60. An improved arc welding station, comprising:
control means for selecting desired welding parameters;
drive means responsive to said control means for providing drive power;
limiting means connected to said drive means for limiting said drive power to a predetermined maximum drive power, output means responsive to said drive power for providing a desired maximum output current to a welding operation;
first current detection means responsive to a peak value of said output current exceeding a first predetermined value for causing said drive power to be removed from said output means; and second current detection means responsive to an average value of said output current exceeding a second predetermined value for causing said drive power to be removed from said output means;

wherein said predetermined maximum drive power is sufficient to allow said output means to provide said desired maximum output current to said welding operation but insufficient to allow said output means to provide an output current larger than said desired maximum output current.

61. The improved arc welding station of Claim 60 and further comprising:
short circuit detection means responsive to a low output voltage being provided by said arc welding station for causing said drive power to be removed from said output means.

62. The improved arc welding station of Claim 60 and further comprising:
timing means responsive to said first current detection means detecting said peak value of said output current exceeding said first predetermined value for causing said drive power to be removed from said output means for a predetermined period.

63. The improved arc welding station of Claim 6 0 and further comprising:
means for providing a reset signal to said first current detection means.