Abstract:
Apparatus, devices, and methods for providing a voltage reduction capability in a welding power source for safety purposes. The resistive load and the output voltage of the welding power source output are monitored and compared to predefined or preselected threshold values to generate a load condition signal and an output voltage condition signal (e.g., logic signals). The load condition signal and the output voltage condition signal serve as inputs to a voltage reduction device control logic which generates control signals to enable and disable the input and output of the welding power source according to the defined control logic. As a result, an extra measure of safety in preventing electrical shock is provided to users of the welding power source during hazardous operating conditions.

Description:
[0001]    The description of the preferred embodiment section and the drawings of U.S. Pat. No. 7,238,917 issued on Jul. 3, 2007 are incorporated by reference herein in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Certain embodiments relate to welding power sources. More particularly, certain embodiments relate to devices and methods for providing a voltage reduction capability in welding power sources for safety purposes. 
       BACKGROUND 
       [0003]    Several techniques have been used to reduce the open circuit voltage of an arc welding power source before the welder is to be used for a welding process. One of the most common designs is a control circuit that reduces the conduction period of the output switching devices, so the open circuit voltage is retained at a desired lower value. In an inverter type power source, the switching devices are usually in the form of field effect transistors (FETs) or insulated gate bi-polar transistors (IGBTs). Since the switching frequency is usually greater than 20 kHz, the conduction period of these switching devices is very short and depends upon the operating frequency of the inverter. In order to reduce the open circuit voltage to a low level, the minimum conduction period of the switching devices requires a complicated and electrically demanding control circuit. Power sources employing such open circuit voltage (OCV) control devices also include a circuit to release the control of the power source to allow the welding power to be obtained during welding. Such detection devices with releasing circuits are usually prone to noise and sensitivity problems. 
         [0004]    Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such approaches with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings. 
       BRIEF SUMMARY 
       [0005]    Embodiments of the present invention comprise devices and methods for providing voltage reduction capability in welding power sources for safety purposes. The resistive load and the output voltage of the welding power source output are monitored and compared to predefined or preselected threshold values to generate a load/no-load condition signal and a high/low output voltage condition signal (e.g., logic signals). The load/no-load condition signal and the high/low output voltage condition signal serve as inputs to a voltage reduction device control logic which generates control signals to enable and disable the input and output of the welding power source according to the defined control logic. As a result, an extra measure of safety in preventing electrical shock is provided to users of the welding power source in hazardous operating conditions. 
         [0006]    These and other features of the claimed invention, as well as details of illustrated embodiments thereof, will be more fully understood from the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  illustrates a schematic block diagram of an example embodiment of an electric arc welding system which may incorporate a voltage reduction capability for safety purposes, in accordance with various embodiments of the present invention; 
           [0008]      FIG. 2  is provided to illustrate a schematic block diagram of an example embodiment of a prior voltage reduction capability implemented in the prior electric arc welder embodiment (as described in the preferred embodiment section and drawings of U.S. Pat. No. 7,238,917 which are incorporated herein by reference) which may also be implemented in the electric arc welding system  900  of  FIG. 1 ; 
           [0009]      FIG. 3  illustrates a schematic block diagram of an example embodiment of an improved voltage reduction device implemented in a first embodiment of a welding power source that may be implemented in the electric arc welding system of  FIG. 1 ; 
           [0010]      FIG. 4  illustrates a schematic block diagram of an example embodiment of an improved voltage reduction device implemented in a second embodiment of a power source of the electric arc welding system of  FIG. 1 ; 
           [0011]      FIG. 5  illustrates a schematic block diagram of an example embodiment of an improved voltage reduction device implemented in a generic embodiment of a power source of the electric arc welding system of  FIG. 1 ; 
           [0012]      FIG. 6  illustrates a schematic diagram of an example embodiment of a voltage reduction device (VRD) control logic and associated logic truth table implemented in the voltage reduction devices of  FIGS. 3-5 ; and 
           [0013]      FIG. 7  is a flowchart of an example embodiment of a method for providing voltage reduction capability in the electric arc welder of  FIG. 1  using the voltage reduction devices of  FIGS. 3-5  and the voltage reduction control logic of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates a schematic block diagram of an example embodiment of an electric arc welding system  900  which may incorporate a voltage reduction capability for safety purposes in accordance with various embodiments of the present invention. The system  900  includes a power converter  910  providing welding output power between a welding electrode E and a workpiece W. The power converter  910  may be of an inverter type that includes an input power side and an output power side, for example, as delineated by the primary and secondary sides, respectively, of a welding transformer. Other types of power converters are possible as well. A wire feeder  920  feeds the wire welding electrode E toward the workpiece W. Alternatively, the electrode E may be a stick electrode and, therefore, the wire feeder  920  is not used. 
         [0015]    The system  900  further includes a waveform generator  930  and a welding controller  940 . The waveform generator  930  generates welding waveforms at the command of the welding controller  940 . The waveform generated by the waveform generator  930  modulates the output of the power converter  910  to produce the welding output power between the electrode E and the workpiece W. 
         [0016]    The system  900  may further include a voltage feedback circuit  950  and a current feedback circuit  960  to monitor the welding output voltage and current between the electrode E and the workpiece W and provide the monitored voltage and current back to the welding controller  940 . The feedback voltage and current may be used by the welding controller  940  to make decisions with respect to modifying the welding waveform generated by the waveform generator  930  and/or to make other decisions that affect safe operation of the system  900 , for example. 
         [0017]    U.S. Pat. No. 7,238,917 describes a prior electric arc welder embodiment having a voltage reduction capability for safety purposes. As a way to introduce the detailed description of certain improved embodiments described herein,  FIG. 2  is provided to illustrate a schematic block diagram of an example embodiment of a prior voltage reduction capability implemented in the prior electric arc welder embodiment (as described in the preferred embodiment section and drawings of U.S. Pat. No. 7,238,917 which are incorporated herein by reference) which may also be implemented in the electric arc welding system  900  of  FIG. 1 , for example. The welder shown in  FIG. 2  is of the type used for AC or DC welding for MIG welding, TIG welding, stick welding and submerged arc welding in both CC and CV modes. 
         [0018]    The welder of  FIG. 2  includes power source  10  having a three phase input  12  and output terminals  14 ,  16  connected to welding cables  30 ,  32 , respectively. The welding operation is schematically illustrated as an electrode E, which can be a consumable wire directed toward workpiece WP connected to ground terminal  34 . Gap G is located between electrode E and workpiece WP and is used in standard welding technology. The average welding current is measured by shunt  36 . When welding is performed by the welder, power source  10  is activated to provide power at terminals  14 ,  16 . 
         [0019]    Power source  10  is preferably an inverter based power source having an ON terminal  18  controlled by the logic on input line  20 . A logic one or starting signal on line  20  activates power source  10  to provide welding power at terminals  14 ,  16 . A logic zero on line  20  (no starting signal) turns power source  10  off or down to a very low open circuit voltage. Power source  10 , when activated, has an open circuit voltage across terminals  14 ,  16  which is high. When the power source is deactivated by a logic zero on line  20 , the open circuit voltage of power source  10  is zero. To turn the power source fully on, switch  40  or a contact from the trigger of the welding gun is closed in accordance with standard technology. 
         [0020]    The welder of  FIG. 2  relates to the concept of maintaining the power source at zero open circuit voltage until switch  40  is closed and there is a low resistance across gap G. This low resistance indicates that the welder is in a condition preparatory to beginning the welding operation. A resistance across gap G greater than the set given amount indicates that the gap is still open and there is a demand for no open circuit voltage or a low OCV. An open circuit voltage is not required or desired in a welding operation until the welding process is to be initiated. This condition of the gap is recognized as a low resistance across gap G. Indeed, the resistance is often zero by electrode E touching workpiece WP to start the welding process. The open circuit voltage of the power source  10  is maintained at zero or a low level (which is equivalent to zero) until there is a detected indication that a welding operation is being initiated. This event is accomplished by determining the resistance across gap G. 
         [0021]    A more specific use of the welder of  FIG. 2  is creating “an enable signal” when (a) the welding operation is initiated by a low resistance in gap G (creating a “start signal”) and (b) trigger switch  40  is closed. The closing of switch  40  is a positive act after or when the electrode approaches or contacts workpiece WP. Power source control device D is used to reduce the open circuit voltage of power source  10  until the resistance in gap G is below a given amount, which given amount is generally less than 100 ohms, 50 ohms, or 30 ohms according to the desired setting of device D. Device D includes an input transformer  60  having a primary winding  62  and a secondary winding  64 . Winding  64  is a single turn of cable  30 , which cable is passed through a tube. About the tube is a toroid with three turns wound upon it, which constitutes the primary winding  62 . The tube as defined above could be a conductor such as copper or aluminum so that cable  30  electronically terminates at both ends of the tube. This is known transformer technology, where one turn is a low resistance strap. Primary winding  62  is energized at a high frequency by a low voltage signal created by oscillator  70 . The set frequency is generally greater than 50 kHz and preferably in the range of 60 to 90 kHz. In practice, oscillator  70  is set at 85 kHz. The current of this signal is limited to a low value. In accordance with an embodiment of the present invention, the signal current is less than 40 ma. 
         [0022]    Input transformer  60  induces a high frequency low voltage signal into the series circuit comprising cable  30 , electrode E, gap G, workpiece WP, shunt  36 , cable  32  and the internal resistance and inductance between terminals  14 ,  16  of power source  10 . Consequently, a high frequency signal is induced into this series circuit. The obtainable magnitude of this signal is determined by the resistance in gap G. This magnitude is sensed by output transformer  80  having a primary winding  82  and a secondary winding  84 . Winding  82  is a single turn winding such as secondary winding  64  of input transformer  60 . The high frequency signal induced into secondary winding  84  is directed to the tuned decoding detector  90  which detector is constructed in accordance with standard technology to provide a logic signal on output  92  when the resistance of gap G is below a given amount. Consequently, a logic 1 on output start signal line  92  indicates that electrode E is touching workpiece WP preparatory to and beginning a welding operation. A “start signal” in line  92  is created when gap G has a resistance less than a given amount. To accomplish this objective, there is an input transformer inducing a high frequency low voltage signal in the series circuit including gap G. Output transformer  80  detects and measures the magnitude of the signal at the set frequency. The magnitude of any signal at the set high frequency is measured by detector  90  and creates an output logic one or “start signal” on line  92 . How this start signal is used to start power source  10  is in accordance with another aspect of an embodiment of the present invention. The broad concept as described can be used with diverse starting logic for power source  10 . 
         [0023]    In accordance with an embodiment of the present invention, power source control device D utilizes a “start signal” on line  92 . This signal is used to control power source  10 . The “start signal” is one input of an ANDing circuit  100  having a second input  102  from contact  40   a  of the trigger switch. The term contact or switch will be used interchangeably for items  40  and  40   a.  Contacts  40  and  40   a  are the trigger switch contacts which are closed when a welding operation is initiated by an operator or by an automatic mechanism. Device D may include only contact  40   a.  However, the other contact  40  is also illustrated to show that power source  10  is not operated until there is a low resistance at gap G and the trigger is closed to initiate the welding operation. ANDing circuit  100  has output  104  for an “enabling signal” that is a logic one when the power source  10  is to be fully on. This enable signal does not occur unless the trigger switch  40   a  is closed. Thus, contact  40  is closed by means  40   b  to connect line  20 . 
         [0024]    Output  104  of ANDing circuit  100  is directed to starting circuit  110  in the form of an OR gate with one input being the “enabling signal” on line  104 . Thus, when line  104  is a logic one, output  112  of starting circuit  110  is a logic one. This starts power source  10  so it is at full power, i.e. welding power. With switch  40   a  closed, switch  40  is also closed. In most welder power sources, there is an internal low impedance branch between terminals  14 ,  16  as represented by the parallel circuit of capacitor  252  and resistor  254 . If device D is retrofitted on a power source without a low impedance between its output terminal, such circuit is added so the series circuit with gap G has a low impedance. 
         [0025]    Switch  40  in line  20  can be eliminated in practicing various embodiments of the present invention. However, it is used with an override network involving a welding current detector. After a “start signal” in line  92 , the welding cycle commences and welding current flows. As long as there is welding current, the power source should stay at the full on state. The full on state means it has a welding power which may be low, such as with TIG welding. When the welding current flows, transformers  60 ,  80  may saturate and become ineffective to maintain a logic one on line  92 . There is no “start signal” after the device D has accomplished its objective at the start of a welding cycle. To hold the power source on after the transformers saturate, the logic network includes an override segment in the form of comparator  120 . The voltage or input signal on line  122  is provided by welding current averaging circuit  124 . Consequently, the voltage on line  122  is representative of the average welding current of welder W. This average welding current is compared by detector  120  with the voltage on a second input  126 . This input has a voltage representing a low reference current x. By this logic network, when the average welding current represented by the voltage on line  122  is greater than a certain fixed lower amount, (and the transformers are saturated) comparator or welding current detector  120  produces a logic one on output line  130  which is a “welding current signal.” 
         [0026]    The welding current signal on line  130  can be used in two separate branches of device D. The first branch directs the welding current signal on line  130  to AND gate  140  having an input  142  represented by a logic one upon closing of trigger switch  40   a.  This action releases gate  140  for operation in accordance with the logic on input line  130 . Thus, the logic on line  144  is a “welding current signal” appearing when there is a welding current of at least a small amount. In this branch of the welding current signal processor feature used in device D, the logic on line  144  is enabled only when trigger switch contact  40   a  is closed. 
         [0027]    In an alternative, optional operation, as illustrated by dashed line  150 , the logic on line  144  merely reflects the logic on line  130 . When a logic one appears on line  144  there is a welding current above a given small amount. When this occurs, starting circuit  110  is activated to produce a starting signal or logic on line  112 . In this optional operation, when there is a welding current and the trigger switch is closed, switch  40  is closed and the power source is on. When the welding operation is stopped, trigger switch contact  40  is opened. Power source  10  is deactivated to a zero open circuit voltage awaiting the next starting operation implemented and controlled through device D. As can be seen, trigger switch  40  may be eliminated and is used primarily when the device D generates a welding current signal bypassing the remainder of the circuitry of device D. So whenever there is welding current and/or the transformers are saturated, the power source is still held on. 
         [0028]    As can be appreciated from  FIG. 2 , device D turns on power source  10  when the resistance across gap G is below a given amount, which is accomplished by inducing a high frequency, low voltage signal in a series circuit including the gap and measuring the magnitude of the signal by a tuned detector (receiver) to create a start signal in line  92 . Otherwise, the power source remains off with a zero open circuit voltage. It is possible to use transformers that do not saturate, then the start signal will be held during welding and there is no need for the override portion of the logic network. 
         [0029]    Again, the welder of  FIG. 2  was previously disclosed in U.S. Pat. No. 7,238,917. Improvements and modifications to the voltage reduction device capability of U.S. Pat. No. 7,238,917 will now be described herein in accordance with  FIGS. 3-7 . 
         [0030]      FIG. 3  illustrates a schematic block diagram of an example embodiment of an improved voltage reduction device implemented in a first embodiment of a welding power source  300  that may be implemented in the electric arc welding system  900  of  FIG. 1 .  FIG. 3  shows an input power side of the power source  300 , being on the primary side of a welding transformer  310 , and an output power side of the power source, being on the secondary side of the welding transformer  310 . 
         [0031]    The input power side of the power source  300  in  FIG. 3  includes the primary winding  311  of the single phase welding transformer  310  along with an input power contact relay CR having an energizing coil  321  and a set of electrical relay contacts  322 . The primary winding  311  and the relay contacts  322  are in series with an input power source V IN  when V IN  is applied to the input of the power source  300 . The input power side also includes an auxiliary transformer  330  having a primary side connected to V IN  and a secondary side connected to a main ON/OFF switch  340  of the power source  300 . The main ON/OFF switch  340  is accessible to a user on the front panel of the power source  300 , in accordance with an embodiment of the present invention. 
         [0032]    As can be seen in  FIG. 3 , the secondary side of the auxiliary transformer  330  includes a secondary winding  332  in series with the ON/OFF switch  340 , the relay coil  321 , and a voltage reduction device (VRD) switch  350 . In order for the relay coil  321  to be energized by the secondary winding  332  of the auxiliary transformer  330 , both the ON/OFF switch  340  and the VRD switch  350  must be closed. When the relay coil  321  is energized, the contacts  322  of the contact relay CR are closed and current is able to flow from V IN  through the contacts  322 , through the primary winding  311  of the welder transformer  310 , and back to V IN  (and vice versa). 
         [0033]    The power source  300  also includes a VRD power supply  360  which connects to and derives power from the secondary side of the auxiliary transformer  330  on the input power side of the power source  300 , as shown. The VRD power supply  360  is part of the VRD device and provides electrical power to the various VRD components in the power source  300  as needed. The various VRD components that power may be supplied to in various embodiments may include the VRD switch  350 , a VRD control logic  370 , an oscillator circuit  380 , and a tuned receiver circuit  390 , the operation of which are described in more detail later herein. In accordance with an embodiment of the present invention, all of the VRD components are located internally within the power source  300 , making it difficult for a user to override the VRD functionality described herein. 
         [0034]    As current flows through the primary winding  311  when the contacts  322  of the contact relay CR are closed, the secondary winding  312  of the welding transformer  310  may be energized on the secondary side of the power source  300 . The secondary side of the power source  300  may include one or more output control power switching devices such as silicon controlled rectifiers (SCR&#39;s), IGBT&#39;s, or FET&#39;s, for example, as are well known in the art. As an example,  FIG. 3  shows an SCR  395  connected to the secondary winding  312  of the welding transformer  310 . The SCR  395  is shown generically and may represent a plurality of SCR&#39;s in an output configuration. The oscillator circuit  380  is connected to the output of the SCR  395  as shown on the electrode side E of the output current path of the power source  300 . The tuned receiver circuit  390  is connected to the secondary winding  312  on the workpiece side W of the output current path of the power source  300 . However, other configurations are possible as well, in accordance with other embodiments of the present invention. For example, the oscillator circuit  380  may instead be on the workpiece side W and the tuned receiver circuit  390  may be on the electrode side E. Furthermore, both the oscillator circuit  380  and the tuned receiver circuit  390  may be implemented in series on either the electrode side E or on the workpiece side W, for example. 
         [0035]    The output side of the power source  300  also includes a voltage feedback circuit  375  and a current feedback circuit  376  providing signals being representative of output voltage and output current to the input of the VRD control logic  370 . The output voltage may be sampled across the welding output terminals A and B of the power source  300 , and the output current may be sampled through a shunt device  396  in the welding output current path. In accordance with various embodiments of the present invention, the voltage feedback circuit  375  may provide a signal  373 , which may be a RMS voltage signal or a logical (high/low) output voltage condition signal for example, to the VRD control logic  370 . Furthermore, in accordance with various embodiments of the present invention, the current feedback circuit  376  may provide a signal  374 , which may be an average current of the welding output to the VRD control logic  370  or a logical (high/low) output current condition signal for example, to the VRD control logic  370 . Other types of signals being representative of the output voltage and the output current are possible as well. 
         [0036]    The output side of the power source  300  further includes an output controller  399  and the VRD control logic  370 . Just as the voltage feedback circuit  375  and the current feedback circuit  376  provide signals to the VRD control logic  370 , the tuned receiver circuit  390  provides a signal  376  to the VRD control logic  370  which may be a resistance level signal or a logical (high/low) load/no-load condition signal. The signal  376  provided by the tuned receiver circuit  390  defines a load condition or a no-load condition at the output of the welding power source  300 . A load condition corresponds to a relatively low resistance between the electrode E and the workpiece W (e.g., when welding), whereas a no-load condition corresponds to a relatively high open circuit resistance value between the electrode E and the workpiece W (e.g., when not welding). 
         [0037]    The oscillator circuit  380  and the tuned receiver circuit  390  operate in much the same manner as the corresponding oscillator and decode detector circuit components of  FIG. 2  herein. The oscillator circuit  380  induces an oscillating signal (e.g., at 80 kHz) in the welding output current path and the tuned receiver circuit  390 , which is tuned to the frequency of the oscillating signal, receives the induced oscillating signal in the welding output current path. Both the inducing and the receiving are accomplished via transformer coupling to the welding output circuit path within the power source  300 . Such transformer coupling is described in detail in U.S. Pat. No. 7,238,917. The level of detection or sensing by the tuned receiver circuit  390  depends on the load or resistance between the electrode E and the workpiece W. The level of detection may be compared to a threshold value to define a load condition or a no-load condition of the welding output. A trigger switch signal  377  from, for example, a welding gun may also serve as an input to the VRD control logic  370 , in accordance with an embodiment of the present invention. 
         [0038]    The VRD control logic  370  operates on some or all of the input signals to produce an output enable signal  371  that is provided to the output controller  399 . For example, in accordance with an embodiment of the present invention, the output controller  399  may disable the output side of the power source  300  (e.g., by turning off the SCR  395 ) when the load/no-load signal  376  indicates a no-load condition. Similarly, the output controller  399  may enable the output side of the power source  300  (e.g., by turning on the SCR  395 ) when the load/no-load signal  376  indicates a load condition. In this manner, when the welder is not currently being used for welding but is connected to an input power source V IN  and the on/off switch  340  is on, a higher resistance (no-load condition) is detected and the output of the power source  300  is disabled. 
         [0039]    Furthermore, the VRD control logic  370  operates on some or all of the input signals to produce an input disable signal  372  that is provided to the VRD switch  350  on the input power side of the power source  300 . For example, in accordance with an embodiment of the present invention, the VRD switch  350  (which is normally closed) may be opened when the load/no-load condition signal  376  indicates a no-load condition and the high/low output voltage condition signal  373  indicates a high output voltage condition. In this manner, the contact relay  322  is opened when the VRD switch  350  is opened, disallowing current to flow through the primary winding  311  of the welder transformer  310 . Therefore, output power cannot be generated on the secondary or output side of the power source  300 . 
         [0040]    In this manner, an extra measure of safety is provided. For example, even if the output of the power source  300  is being commanded to be disabled by the output controller  399  because of a no-load condition being detected, an output voltage could still appear across the output terminals A and B if a failure or defect occurs in the output side of the power source  300 . For example, if the SCR  395  were to fail by shorting, a relatively high output voltage level could still appear across the terminals A and B, which can be potentially dangerous during a non-welding (no-load) situation. However, the high output voltage condition is sensed and the VRD control logic  370  commands the VRD switch  350  to open, shutting down the input power side of the power source  300 . 
         [0041]    When the VRD switch  350  is opened, because of a high output voltage condition, and the on/off switch  340  is still closed, power is still able to be supplied to the VRD power supply  360 . As a result, the various components of the VRD device are still being supplied with electrical power and are able to operate. In accordance with an embodiment of the present invention, to reset (i.e., close) the VRD switch  350 , the on/off switch  340  has to be toggled off and then on again. This resets the VRD switch  350  and enables the input power side of the power source  300 , unless the VRD control logic  370  is still sensing a no-load condition and a high output voltage condition, in which case the VRD switch  350  will immediately open again. Such a situation may indicate that the power source  300  requires servicing, repair, or replacement. 
         [0042]      FIG. 4  illustrates a schematic block diagram of an example embodiment of an improved voltage reduction device implemented in a second embodiment of a power source  400  of the electric arc welding system  900  of  FIG. 1 . The power source  400  of  FIG. 4  is very similar to the power source  300  of  FIG. 3  except that the output power side of the power source  400  of  FIG. 4  is configured a little differently as a single phase full bridge configuration. Instead of having a single secondary winding as in  FIG. 3 ,  FIG. 4  shows a welding transformer  410  having two secondary windings  412  and  413  and two SCR&#39;s  495  and  496 . The output controller  399  is configured to enable and disable such a configuration of output components. The VRD components of  FIG. 4  are the same as that of  FIG. 3 , however, and VRD capability and operation are the same. 
         [0043]      FIG. 5  illustrates a schematic block diagram of an example embodiment of an improved voltage reduction device implemented in a generic embodiment of a power source  500  of the electric arc welding system  900  of  FIG. 1 .  FIG. 5  is intended to illustrate that the VRD device of  FIG. 3  and  FIG. 4  may be implemented in many other types of power sources having various power converter configurations including single phase configurations and multi-phase configurations (e.g., three-phase configurations) and inverter or chopper configurations, for example.  FIG. 5  shows the auxiliary transformer  330  with the on/off switch  340 , the VRD switch  350 , and the relay coil  321  in series with each other on the secondary side of the auxiliary transformer  330 , as in  FIG. 3  and  FIG. 4 , for disabling the input power side of the generic power source  500 .  FIG. 5  also shows the output controller  399  for enabling and disabling the output power side of the generic power source  500 . Again, the VRD components of  FIG. 5  are the same as that of  FIG. 3  and  FIG. 4 , and VRD capability and operation are the same. 
         [0044]      FIG. 6  illustrates a schematic diagram of an example embodiment of a voltage reduction device (VRD) control logic  370  and associated logic truth table implemented in the voltage reduction devices of  FIGS. 3-5 . The VRD control logic  370  includes an AND gate  610  and an inverter  620 . As seen in the logic truth table, when the load/no-load condition signal  376  indicates a no-load condition (e.g., a logic “0”) and the high/low condition signal  373  indicates a high output voltage condition (e.g., a logic “1”), the signal  372  is a logic “1” and the VRD switch is opened (i.e., a logic “1” commands the VRD switch to open in this embodiment), disabling the welder input side of the power source. Furthermore, the signal  371  to the output controller is a logic “0” which tells the output controller to disable the welder output side of the power source. As an example, a no-load condition may exist when the resistance between the welding output terminals A and B is greater than 100 ohms. Similarly, a high output voltage condition may exist when the voltage between the welding output terminals A and B is greater than 50 volts RMS (i.e., V T &gt;50 V RMS ). 
         [0045]    Continuing with the logic truth table, when a no-load condition exists and a low output voltage condition exists, the welder input is enabled but the welder output is disabled. When a load condition exists and a low output voltage condition exists, both the welder input and the welder output are enabled. This may correspond to a situation where the electrode E is being touched to the workpiece W forming a short. When a load condition exists and a high output voltage condition exists, both the welder input and the welder output are enabled. This may correspond to an active welding situation, for example, where an arc exists between the electrode E and the workpiece W. 
         [0046]    Therefore, according to the logic of  FIG. 6 , the load/no-load condition signal  376  determines whether or not the welder output is enabled or disabled. Both the load/no-load condition signal  376  and the high/low voltage condition signal  373  determine whether or not the welder input is enabled or disabled via the VRD switch. Of course, in accordance with various embodiments of the present invention, the trigger switch signal  377  and/or the current feedback signal  374  may be included in the control logic as well (e.g., see U.S. Pat. No. 7,238,917). 
         [0047]      FIG. 7  is a flowchart of an example embodiment of a method  700  for providing voltage reduction capability in the electric arc welder  900  of  FIG. 1  using the voltage reduction devices of  FIGS. 3-5  and the voltage reduction control logic  370  of  FIG. 6 . In step  710 , the on/off switch  340  is closed (and the VRD switch  350  is normally closed), enabling the input power side of the welding power source. In step  720 , if the resistive load on the output terminals A and B is less than a threshold value R thres  (e.g., 100 ohms) indicating a load condition then, in step  730 , the output power side of the welding power source is enabled and, in step  740 , a user may proceed to weld. 
         [0048]    If, however, in step  720 , the resistive load on the output terminals A and B is greater than the threshold value R thres  indicating a no-load condition then, in step  750 , the output power side of the welding power source is disabled. Furthermore, in step  760 , if the output voltage (e.g., the RMS output voltage V RMS ) is not greater than a threshold value V thres  indicating a low output voltage condition then, in step  770 , since the output power side is disabled and the output voltage is low, the welder is in a proper no-load safety condition. 
         [0049]    However, in step  760 , if the output voltage (e.g., the RMS output voltage V RMS ) is greater than the threshold value V thres  indicating a high output voltage condition then, in step  780 , the input power side of the welding power source is also disabled. This provides an extra measure of safety in case a failure were to occur on the output power side of the welding power source, allowing power to get to the output terminals A and B (e.g,. if the SCR  395  in  FIG. 3  were to short). In step  790 , the on/off switch  340  is reset (i.e., turned off and then on again) in an attempt to reset the welder to re-enable the input power side by causing the VRD switch  350  to close. The method  700  reverts back to step  760  to check if the high output voltage condition still exists. If so, the VRD switch  350  is immediately opened again. 
         [0050]    In summary, an embodiment of the present invention comprises a method of providing a voltage reduction capability in a welding power source. The method includes sensing an induced signal, from within a welding power source, to generate a sensed signal being indicative of a load condition or a no-load condition between an electrode output terminal and a workpiece output terminal of the welding power source. The method further includes detecting an output voltage, from within the welding power source, being indicative of a low output voltage condition or a high output voltage condition across the electrode output terminal and the workpiece output terminal. The method also includes disabling an input power side of the welding power source, from within the welding power source, when the sensed signal is indicative of a no-load condition and the output voltage is indicative of a high output voltage condition. In accordance with an embodiment of the present invention, the sensed signal is indicative of a no-load condition when a resistance between the output terminals is greater than about 100 ohms, and the output voltage is indicative of a high output voltage condition when the output voltage level is greater than about 50 V RMS . The method may further include disabling an output power side of the welding power source, from within the welding power source, when the sensed signal is indicative of a no-load condition. The induced signal is an oscillating signal induced in an output current path of the welding power source, in accordance with an embodiment of the present invention, and the output voltage is a root-mean-square (RMS) voltage. The step of disabling the input power side of the welding power source may be accomplished by automatically opening a voltage reduction device (VRD) switch on the input power side which is in series with a main ON/OFF switch of the welding power source and a coil of an input power contact relay of the welding power source. 
         [0051]    Another embodiment of the present invention comprises a device for providing a voltage reduction capability in a welding power source. The device includes means for inducing an oscillating signal, from within a welding power source, in an output current path of the welding power source. The device further includes means for sensing the induced oscillating signal, from within the welding power source, to generate a sensed signal being indicative of a load condition or a no-load condition between an electrode output terminal and a workpiece output terminal of the welding power source. The device also includes means for detecting an RMS output voltage, from within the welding power source, being indicative of a low output voltage condition or a high output voltage condition across the electrode output terminal and the workpiece output terminal. The sensed signal is indicative of a no-load condition when a resistance level between the output terminals is greater than a defined threshold value, and the output voltage level is indicative of a high output voltage condition when the RMS output voltage is greater than a defined threshold value, in accordance with an embodiment of the present invention. The device further includes means for disabling an input power side of the welding power source, from within the welding power source, when the sensed signal is indicative of a no-load condition and the RMS output voltage is indicative of a high output voltage condition. The device may also include means for enabling an output power side of the welding power source, from within the welding power source, when the sensed signal is indicative of a load condition. The device may further include means for supplying electrical power to at least the means for inducing, the means for sensing, and the means for disabling, even when an input power contact relay of the welding power source is not energized. The electrical power is derived from the input power side of the welding power source through an auxiliary transformer, in accordance with an embodiment of the present invention. 
         [0052]    A further embodiment of the present invention comprises an apparatus for providing a voltage reduction capability in a welding power source. The apparatus includes a tuned receiver circuit configured within the welding power source to receive an oscillating signal induced in the welding output current path within the welding power source and to generate a logical load condition signal therefrom. The apparatus further includes a voltage sensing circuit configured within the welding power source to detect a voltage between an electrode output terminal and a workpiece output terminal of the welding power source and to generate a logical output voltage condition signal. The apparatus also includes a voltage reduction device (VRD) switch in series with a main ON/OFF switch of the welding power source and a coil of an input power contact relay of the welding power source on an input power side of the welding power source. The apparatus further includes a voltage reduction device (VRD) control logic circuit configured within the welding power source to open the VRD switch when the logical load condition signal indicates a no-load condition and the logical output voltage condition signal indicates a high output voltage condition. The apparatus may also include an oscillator circuit configured within the welding power source to induce the oscillating signal in the welding output current path. The VRD control logic circuit may be further configured within the welding power source to command an output controller of the welding power source to enable an output power side of the welding power source when the logical load condition signal indicates a load condition. The apparatus may further include a VRD power supply configured to provide electrical power to at least one of the tuned receiver circuit, the voltage sensing circuit, the VRD control logic circuit, the oscillator circuit, and the VRD switch. In accordance with an embodiment of the present invention, the VRD power supply is operatively connected to an auxiliary transformer of the welding power source on an input power side of the welding power source. The VRD power supply is capable of deriving electrical power from a secondary side of the auxiliary transformer whether or not the input power contact relay is energized, and when the main ON/OFF switch of the welding power source is closed. The logical load condition signal is indicative of a no-load condition when a resistance level between the output terminals is greater than a defined threshold value. The logical output voltage condition signal is indicative of a high output voltage condition when the voltage is greater than a defined threshold value. 
         [0053]    While the claimed subject matter of the present application has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the claimed subject matter. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the claimed subject matter without departing from its scope. Therefore, it is intended that the claimed subject matter not be limited to the particular embodiment disclosed, but that the claimed subject matter will include all embodiments falling within the scope of the appended claims.