Abstract:
The present invention provides an improvement over conventional electric circuit monitoring devices in that it provides a device and method to passively monitor the performance of an electrical circuit to a load device, including faults that occur intermittently. The invention is capable of identifying the location and type of malfunction in the event of a fault.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to control and diagnosis of driver circuits and wiring harnesses for electrical load devices, including electromagnetic actuators and resistive devices such as lamps.  
         BACKGROUND OF THE INVENTION  
         [0002]    Electric load devices such as electromechanical actuators and lamps are used in a variety of applications in industrial controls, motor vehicles and other devices. Industrial applications include, for example, robotics and electrically controlled valves for chemical process systems. Vehicle applications may include fuel injection systems, electronic transmissions, evaporative purge control systems, antilock braking systems, intake/exhaust valve control systems, lighting systems and others. Typically a circuit will comprise the load device located in a remote area where control or power is needed with a remote driver that is connected to the driver with a wiring harness.  
           [0003]    A circuit for an electric load device is used primarily to control the device, but may also be used to monitor performance of the device. When a fault occurs in a circuit, the effect in an industrial setting will be machine downtime and a resulting loss in productivity. The effect on a motor vehicle can include unacceptable system performance and damage to related systems and components, or an increase in emissions of the vehicle. The increase in emissions has become important with the advent of government regulations that compel addition of on-board vehicle diagnostic systems to monitor emissions related components and control systems. The intent of the on-board diagnostic systems is to detect faults that lead to emissions increases.  
           [0004]    There is a need to identify a specific location of a fault once it has been detected to ensure that any fault can be quickly located and effectively repaired. This need to identify the location of a fault is important to minimize a loss of productivity associated with machine downtime in a factory, or to minimize costs to diagnose and repair a system on a vehicle.  
           [0005]    When a fault occurs in a system, there is a need to identify the type and location of the fault to facilitate repair. When a fault occurs on a vehicle a diagnostic fault indicator may be set. This fault indicator typically will identify the system where a fault has occurred, but will lack sufficient specificity to identify where a specific repair needs to occur. The diagnostic fault indicator will lead a repair technician to a system whose performance may be affected by an interaction of several components or subsystems. The technician may be compelled to work through multiple diagnostic procedures to locate and repair the fault. This consumes time and resources, and results in increased cost and decreased satisfaction to the vehicle owner.  
           [0006]    The ability to correctly detect and identify a fault is more difficult when the fault is intermittent, as may occur when there is water intrusion into a wiring harness or connector. A technician will spend time and resources in attempting to reproduce failure conditions to identify a fault or verify a repair. This can result in customer dissatisfaction and high costs to the customer or the manufacturer, due to multiple attempts to identify and repair intermittent faults in a circuit. This problem is apparent when a fault occurs that sets a general diagnostic code that lacks sufficient specificity to identify a needed repair.  
           [0007]    Electric load circuits can include devices such as insulated wires, connectors, drive transistors or relays, wiring junctions, and fuses. Faults in the circuit that can lead to undesirable operation of an electric load system include wiring harness shorts to ground, wiring harness open circuits, and wiring harness intermittent connections. Other faults include broken or abraded wires, and connector faults such as relaxation of terminals, or corrosion due to intrusion of water or contaminants.  
           [0008]    There are standard methods existing to diagnose and repair faults using off-board techniques such as connectivity tests and diagnostic trouble trees. These methods and tools are contained in service manuals, and are well known in the art. Off-board techniques require the employment of intrusive test methods, including the use of hand held scan tools used by a skilled technician. The prior art has sought to diagnose faults in electrical load circuits on-board the vehicle through the addition of current-monitoring devices that add cost and complexity to the circuit. These may be effective in diagnosing fault in a specific solenoid, but do not diagnose faults in the circuit leading to the electrical device. The prior art has also sought to identify the presence and location of faults with on-board intrusive methods and systems that send a signal through a circuit to a device and look for an subsequent output from the device. These methods can be disruptive when they occur during normal operation of the vehicle or the system. The prior art also has not addressed the issue of identifying the presence of an intermittent fault in a circuit, and the related result of being able to focus the repair efforts of a technician to a specific location in the system.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention is an improvement over conventional electric circuit monitoring devices in that it provides a device and method to passively monitor the performance of an electrical circuit to a load device, including faults that occur intermittently. The invention is capable of identifying the location and type of malfunction in the event of a fault. Accordingly, the invention provides a complete apparatus and method to control and diagnose driver circuits for electromagnetic actuators and resistive load devices, and detect faults therein.  
           [0010]    The present invention includes a circuit and methods that are able to control and monitor an electric load. It includes the electric load, a first switch electrically coupled to a power supply and one end of the electric load, and a second switch electrically coupled between the second end of the electric load and ground. The switches are controlled by a load drive controller that communicates with an external controller. Detection of a fault condition in the circuit occurs by comparing an electric potential at one end of the electric load with a first known potential, and by comparing an electric potential at the second end of the electric load with a second known potential. The circuit accomplishes the comparison using, for example, discrete electronic comparators. The inputs from the electric load and the first and second known potentials are appropriately biased with an effective amount of electric potential to enable detection of a type and location of a fault condition. The output from each of the comparators is communicated as an indication of a fault. This is a passive monitoring system. When a fault is detected, the circuit will operate to identify a location and type of fault, by controlling the switches and monitoring the output of the comparators. The output from the comparators can be communicated to an external controller to indicate the type and location of the fault.  
           [0011]    The present invention also comprises a method for controlling and monitoring an electric load. This includes providing a circuit comprising an electric load with a first switch electrically coupled between a power supply and the electric load. The circuit also includes a second switch electrically coupled between the electric load and ground, and a load drive controller operable to control each switch. The method operates by activating the switches. It then compares an electric potential at the first end of the electric load with a first known potential, and also compares an electric potential at the second end of the electric load with a second known potential. The method will then obtain an output from each comparison. The output can then be communicated to an external controller to indicate a fault. The method can also detect the type and location of any fault condition using the comparison of electric potentials. The electric potentials at the first and second ends of the electric load and the first and second known potentials are appropriately biased to detect the type and location of a fault condition. The outputs from the comparisons are then communicated and indicate the type and location of the fault.  
           [0012]    A feature of this invention is to provide a circuit to control an electric load and monitor for faults in the circuit. The circuit is also able to identify the type and location of a fault, and communicate this information.  
           [0013]    Another feature of this invention is to provide a method for controlling an electric load and monitoring for faults in the circuit. The method is also capable of identifying the type and location of a fault, and communicating this information.  
           [0014]    These and other features of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]    The invention may take physical form in certain parts and arrangement of parts, the preferred embodiment of which will be described in detail and illustrated in the accompanying drawings wherein:  
         [0016]    [0016]FIG. 1 is a schematic diagram of a circuit for controlling and diagnosing an electric load, in accordance with the present invention;  
         [0017]    [0017]FIG. 2 is a method for monitoring an electric load, in accordance with the present invention;  
         [0018]    [0018]FIG. 3 is a method for identifying an location and type of fault, in accordance with the present invention;  
         [0019]    [0019]FIG. 4 is a truth table, in accordance with the present invention;  
         [0020]    [0020]FIG. 5 is another truth table, in accordance with the present invention; and  
         [0021]    [0021]FIG. 6 is another schematic diagram of a circuit for controlling and diagnosing an electric load, in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Referring now to the drawings, wherein the showings are for the purpose of illustrating the preferred embodiment of the invention only and not for the purpose of limiting the same, FIG. 1 shows a schematic diagram of an electrical circuit  5  for control and diagnosis of an electric load  32  that has been constructed in accordance with the present invention. The electric load  32  has a first end  28  that is electrically coupled to a first switch  20 , which is placed in series between the first end  28  of the electric load  32  a first electrical potential  38 . There is a first resistor  24  placed in series between the first switch  20  and the first end  28  of the electric load  32 . There is a third resistor  42  placed in parallel with the series coupled first switch  20  and first resistor  24 , between the first electrical potential  38  and the first end  28  of the load  32 . A first connector  27  may be placed in between the first end  28  of the load  32  and the first resistor  24 .  
         [0023]    A second end  30  of the electrical load  32  is electrically coupled to a second switch  22 , which is placed is series between the second end  28  and a second electrical potential  40 . There is a second resistor  26  placed in series between the second switch  22  and the second end  30  of the electric load  32 . There is a fourth resistor  44  placed in parallel with the series coupled second switch  22  and second resistor  26 , between the second end  30  of the load  32  and the second electrical potential  40 . A second connector  29  may be placed in between the second end  30  of the load  32  and the second resistor  26 . The circuit will also contain other elements (not shown) that enable the circuit to accommodate electrical noise, including internally generated noise due to switching or from an external source. The circuit may also contain additional elements (not shown) that enable assembly and operation of the circuit  5 . These additional elements (not shown) are known to one skilled in the art.  
         [0024]    In a typical embodiment, the load  32  can be an inductive device, such as an electromagnetic solenoid, or a resistive device, such as a lamp. The first electrical potential  38  may be battery voltage, as would be found in a vehicle, or other system voltage typically found in an industrial setting. The second electrical potential  40  can be ground, neutral, or other appropriate level, depending on the system. The load  32  is energized by activating switches  20 ,  22 . The first and second resistors  24 ,  26  are sized to be approximately equal in resistance levels and small to create a minimum amount of voltage drop in the circuit. The intent in sizing the first and second resistors  24 ,  26  is to have the electrical potential level at the first end  28  of the load  32  equal to the electrical potential level at the second end  30  of the load  32  under normal conditions when switches  20 ,  22  are deactivated, in the absence of a fault. A small amount of current will pass through third and fourth resistors  42 ,  44  when the load  32  is de-energized, i.e. when the switches are deactivated. The third and fourth resistors  42 ,  44  are sized to be large enough as to not activate the load  32 . The third and fourth resistors  42 ,  44  are intended to appropriately bias the electrical potential levels at the first end  28  and the second end  30  of the load  32  with an effective amount of electric potential to enable detection of one of a type of fault conditions, as will be discussed below. The first and second resistors  24 ,  26  should be selected to be about {fraction (1/100)} of the resistance of the load  32 , or in the range of 0.1 Ω. The third and fourth resistors  42 ,  44  should be about 100 times the resistance of the load, or in the range of 10 kΩ.  
         [0025]    The switches  20 ,  22  can be transistors (FET or bipolar), electromagnetic relays, or other devices. The circuit may also contain one or more electrical connectors  28 ,  30 , conductive wire (not detailed), electrical splices (not shown), junction boxes (not shown) or other devices used in connecting load devices to electrical power in a system. The use of alternative devices to switch is known to one skilled in the art.  
         [0026]    A load drive controller  10  is operably attached to the first and second switches  20 ,  22 . The load drive controller  10  is operable to receive a control signal on a control line  12  from an external controller  7 , and generate control signals  16 ,  18  to control the switches  20 ,  22  and therefore control the power delivered to the load  32 . The load drive controller  10  is also able to send results on a fault detection line  14  to the external controller  7 , based upon other inputs the controller  10  may receive. Another input is discussed below.  
         [0027]    Detection of a fault condition in circuit  5  occurs by comparing an electric potential at the first end of the electric load  34  with a first known potential  60 , and by comparing an electric potential at the second end of the electric load  36  with a second known potential  62 . This comparison can be accomplished by providing a comparison circuit  51  which is comprised of a plurality of comparators  52 ,  54 . Each comparator  52 ,  54  is preferably a digital device that provides an output that is a logic high signal or logic low signal in response to a comparison of a first and a second input. The first input to each of the comparators is electrically coupled with the electric load  32 , either at the first end  28  or the second end  30 . The second input to each of the comparators is the first known potential  60  or the second known potential  62 . The first known potential  60  and the second known potential  62  are created using a voltage divider device comprised of fifth, sixth, and seventh resistors  46 ,  48 ,  50  placed in series between the first electrical potential  38  and the second electrical potential  40 . There is a first node  60  at the junction between fifth resistor  46  and sixth resistor  48 . This node  60  is electrically coupled to the second input of the first comparator  52 . There is a second node  62  at the junction between sixth resistor  48  and seventh resistor  50 . This node  62  is electrically coupled to the second input of the second comparator  52 . The fifth, sixth and seventh resistors  46 ,  48 ,  50  each have substantially the same resistance value. The input impedance and bias current of the comparison circuit  51  determines the actual values. An acceptable range of resistance for each of the fifth, sixth and seventh resistors  46 ,  48 ,  50  is 1 kΩ to 100 ΩkΩ. The resistance of fifth, sixth and seventh resistors  46 ,  48 ,  50  is driven by electronic design practices understood by one skilled in the art. The outputs  56 ,  58  of the comparators  52 ,  54  are electrically coupled to the load drive controller  10 , which is able to communicate any fault detection to an external controller  7 .  
         [0028]    In operation, the circuit functions by providing an output to the external controller  7  indicating electrical integrity of the circuit  5 . This can be in the form of a continuous result, or a result that is sent only when a fault is detected. The system is intended to function as follows. The load drive controller  10  will generate signals  16 ,  18  commanding the switches  20 ,  22  to close, thus activating the load  32 . This is done in response to a control signal  12  from the external controller  5 . If there are no faults in the circuit, the outputs  56 ,  58  of the comparators  52 ,  54  will both be logic low signals. When the drive controller  10  generates signals  16 ,  18  commanding the switches  20 ,  22  to open and thus deactivating the load  32 , the outputs  56 ,  58  of the comparators  52 ,  54  will both be logic high signals if there are no fault conditions. This can be best described in a truth table as shown in FIG. 4, which demonstrates normal operation of circuit  5 .  
         [0029]    If a fault occurs in circuit  5 , one or both of the outputs  56 ,  58  of the comparators  52 ,  54  will no longer provide an expected response to the control signals  20 ,  22 . Outputs  56 ,  58  that indicate a fault in circuit  5  are shown in FIG. 5. The load drive controller  10  will then communicate a first result on the fault detection line  14  indicating that a fault has been detected. The configuration of circuit  5  allows continuous monitoring, both during the time when the load  32  is being powered and when it is not being powered. Therefore, the circuit  5  will be able to detect permanent or intermittent faults. The faults that the circuit will detect include an open circuit (e.g. a broken wire or connector), an internal short in a load, a short in a connector, an open circuit in a switch, a short to a first or second potential, among others. The intermittent faults that the circuit will detect include a weakened connector terminal, a broken or abraded wire, a corroded terminal, among others. The detection of the fault condition will be communicated to the external controller  7  as a first result. No intrusive action will be taken by the external controller  7  or the load drive controller  10  during normal operation.  
         [0030]    The invention can also identify of a type of fault condition and its corresponding location, after a fault has been detected, using the circuit  5  as described in FIG. 1. The load drive controller  10  will send a combination of signals  16 ,  18  intended to indicate the type and location of fault detected. The control signals  16 ,  18  to the switches  20 ,  22  are shown in FIG. 5, along with the second outputs  56 ,  58  of the comparators  52 ,  54 . The second output from the comparators  52 ,  54  will be provided to the load driver controller  10 , which in turn can communicate the type and location of fault as a second result to the external controller  7 . The external controller  7  can then use the information to generate actions to prevent further damage to the circuit  5  and the system including, for example, disabling all power to the circuit  5  or the load  32 . A technician can also use this information to identify and repair the circuit  5  offline. To identify the type of fault condition and its corresponding location, the load drive controller  10  will control the circuit  5  in an intrusive manner, i.e. it will supply circuit  5  with atypical control signals  16 ,  18 . It is thus able to identify the type and location of faults in the circuit. This will be described in greater detail.  
         [0031]    Referring now to FIG. 2, the invention also includes a method for controlling and monitoring an electric load  32 , using the circuit  5 . Monitoring of the electric load  32  is passive under normal operation, but will become active if a fault is detected in the circuit  5 . The process includes providing circuit  5  that includes an electric load  32  with a first  28  and a second  30  end. There is a first switch  20  electrically coupled between a first electric potential  38  and the first end  28  of the electric load  32 , and a second switch  22  electrically coupled between the second end  36  of the electric load  32  and a second electric potential  40 . A load drive controller  10  is operable to control each of the switches  20 ,  22 . The controller  10  activates the load  32  by sending control signals  16 ,  18  and closing both switches  20 ,  22 , in response to a command signal on a control line  12  from an external controller  7 . The circuit  5  then compares an electric potential at the first end  28  of the electric load  32  with a first known potential  60 , and also compares an electric potential at the second end  30  of the electric load  32  with a second known potential  62 . Outputs  56 ,  58  are obtained from each of the comparisons, and a fault condition is detected in the circuit  5  based upon the outputs  56 ,  58 . The fault condition is then communicated to an external controller  7  as a first result. Each output  56 ,  58  is preferably a digital signal, and is either a logic low signal or a logic high signal.  
         [0032]    To activate the load  32 , the external controller  7  will send a command signal to the load drive controller  10  on the control line  12 , shown in step  110 . The load drive controller  10  will set both control signals  16 ,  18  to on, thus activating switches  20 ,  22 . This will serve to couple the power supply  38  to the load  32 , as shown in step  112 . In step  114 , the load drive controller  10  will continuously monitor the outputs  56 ,  58  of the comparators  52 ,  54 . No action is taken as long as both outputs  56 ,  58  are low when the control signals  16 ,  18  are on.  
         [0033]    To deactivate the load  32 , the external controller  7  will send a command signal on the control line  12  to the load drive controller  10 , as shown in step  120 . The load drive controller  10  will set the control signals  16 ,  18  to off, thus deactivating switches  20 ,  22 . This will serve to disconnect the power supply  38  to the load  32 , as shown in step  122 . In step  124 , the load drive controller  10  will continuously monitor the outputs  56 ,  58  of the comparators  52 ,  54 . No action is taken as long as both outputs  56 ,  58  are high when the control signals  16 ,  18  are off. This method of monitoring the circuit  5  is passive, and provides an ongoing indication of the integrity of the circuit  5  during normal operation.  
         [0034]    If a fault is detected, as shown in step  140 , a first result, representing fault detection, will be sent to the external controller  7  on a fault detection line  14 , as shown in step  150 . This first result is comprised of the outputs  56 ,  58  of the comparators  52 ,  54 , and is sent whether the fault is continuous or is intermittent. The external controller  7  will then decide on appropriate actions to deal with a fault, as shown in step  152 . These actions in step  152  can include actions outside the circuit  5 , such as signaling to the operator that a fault has occurred, disabling all control to the load drive controller  10 , or storing the fault information for further diagnostic analysis. There may also be other actions to protect the circuit  5  or the load  32  or to maintain operation of the system that have not been described.  
         [0035]    Referring now to FIG. 3, once a fault has been detected in step  140  (shown in FIG. 2), the method will then act intrusively to diagnose a location and type of fault. The method begins by interpreting the outputs  56 ,  58  of the comparators  52 ,  54 , as shown in step  154 . When the signals  16 ,  18  are both on and the corresponding outputs  56 ,  58  are both high, shown in step  156 , then the method will diagnose a short circuit in the load  32 , or a short circuit in a connector  28 ,  30  or another part of the circuit  5 . This is shown in step  158 , and in Table 1, below. A second result, representing the type and location of the fault, is then communicated to the external controller  7 , and there will be no further diagnostic action in the circuit. This result can then be retrieved by a repair technician and used to repair the circuit  5 .  
                               TABLE 1                               Output 56   Output 58           Control   Control   of   of   Type and       signal 16 to   signal 18 to   Comparator   Comparator   Location of       Switch 20   Switch 22   52   54   Fault                   On   On   High   High   Internal short                       to load 32,                       or short circuit                       between con-                       nector 27 and                       connector 29                  
 
         [0036]    When the corresponding outputs  56 ,  58  are not both high or both low, intrusive actions are taken to identify a type of fault and a location of a fault in the electric load  32 . when output  56  is low and output  58  is high, as shown in step  164 , the load drive controller  10  will set control signal  16  to off, thus deactivating switch  20 , and also set control signal  18  to on, thus activating switch  22 . Diagnosis will occur by reading the outputs  56 ,  58 , as shown in step  168 , and interpreting the results, as shown in step  170 . The results are also summarized below in Table 3.  
                               TABLE 3                       Control   Control   Output 56   Output 58           signal 16   signal 18   of   of           to Switch   to Switch   Comparator   Comparator   Type and Location       20   22   52   54   of a Fault                   Off   On   Low   Low   Connector 27 short                       to 1 st  potential 38       Off   On   Low   High   Connector 29 short                       to 1 st  potential 38       Off   On   High   Low   Connector 27 or 29                       short to 2 nd  potential                       40       Off   On   High   High   2 nd  Switch 22 open                       circuit                  
 
         [0037]    When output  56  is high and output  58  is low, as shown in step  184 , the load drive controller  10  will set control signal  16  to on, thus activating switch  20 , and also set control signal  18  to off, thus deactivating switch  22  (step  186 ). Diagnosis will occur by reading the outputs  56 ,  58  (step  188 ) and interpreting the results (step  190 ). The results are also summarized below in Table 4.  
                               TABLE 4                       Control   Control   Output 56   Output 58           signal 16   signal 18   of   of       to Switch   to Switch   Comparator   Comparator   Type and Location       20   22   52   54   of a Fault                   On   Off   Low   Low   Connector 29 short                       to 2 nd  potential 40       On   Off   Low   High   Connector 27 or 29                       short to 1 st  potential                       38       On   Off   High   Low   Connector 27 short                       to 2 nd  potential 40       On   Off   High   High   1 st  Switch 20 open circuit                  
 
         [0038]    In this embodiment, the load drive controller  10  is operably coupled to the external controller  7 , such that the load drive controller  10  is responsive to input from the external controller  7 . This input includes information to activate the switches  20 ,  22  to control and monitor the load  32  and to identify the type and location of a fault. This operable connection will also enable the load drive controller  10  to communicate to the external controller  7  either a first result that represents the first output of the comparators, or a second result that represents the second output of the comparators.  
         [0039]    The external controller  7  may instead comprise a switch activated by an operator, such as when operating a lamp or robotic device. In this configuration, the fault detection line  14  can be directly coupled to a fault indicator lamp instead of to the external controller  7 . The method shown in FIG. 3 of interpreting the comparator output (step  154 ), setting control signals (step  166  or  168 ) and diagnosing a type and location of fault (step  170  or step  190 ) can be accomplished by the load drive controller  10  or by other external methods.  
         [0040]    [0040]FIG. 6 shows another embodiment of the invention wherein the functions of the comparison circuit  51  and the load drive controller  10  are accomplished in a control device  8 . Control device  8  can comprise the load drive controller  10 , the external controller  7 , and the comparison circuit  51 , as well as other functions. In this embodiment control device  8  is designed to perform the same functions as the discrete components shown in FIG. 1. For example, when the comparison circuit  51  is internal to the control device  8  it can take the form of an electronic circuit or an algorithm that is designed to perform the same functions as the comparison circuit  51  to achieve the same result. The use of algorithms and up-integrated components to compare voltage levels is known to one skilled in the art. In this embodiment the electric potentials at node  1   34  and node  2   36  are input directly to the control device  8 , using an analog to digital converter (not shown). The load  32  and other elements of circuit  4  will be analogous to those shown in circuit  5  (FIG. 1). For example, the other inputs to the comparators, i.e. the first known potential  60  and the second known potential  62 , can be created within the control device  8 . In this embodiment the control device  8  will perform the functions of operating the switches  22 ,  24  and comparing the electrical potentials at node  1   34  and node  2   36  with the first known potential  60  and the second known potential  62 .  
         [0041]    The invention may be used to monitor load devices in vehicle systems including, inter alia, braking systems, fuel injectors, EGR valves, transmission solenoids, purge control valves, cam phasers, headlamps, taillamps, and signal lamps. The invention may also be used to monitor load devices in industrial settings such as control solenoids and lamps, among others.  
         [0042]    System requirements, circuit design factors or communications protocols may drive the designer to configure the circuit differently. For example, the load drive controller  10  may be up-integrated into the external controller  7 ; the outputs  56 ,  58  from the comparators  52 ,  54  may be communicated directly to the external controller  7 ; or, the load drive controller  10  may have other diagnostic and control capabilities in addition to those mentioned in the invention. In addition, some or all of the elements of the circuit  5  may be integrated into the load  32 , the external controller  7 , or the connectors  27 ,  29 . The components of circuit  5  may or may not be discrete elements.  
         [0043]    The circuit  5  can also include other elements, not shown. These may include additional connectors, splices, or fusible links, for example. The invention for diagnosis and control of the circuit will include monitoring those devices that are part of the function of a circuit that controls the load.  
         [0044]    Circuit design factors and communications protocols may also drive changes to the circuit in other ways also. The invention encompasses the various alternative designs. For example, the inputs to the comparators can be reconfigured to provide different outputs in response to control signal inputs.  
         [0045]    The invention has been described with specific reference to the preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention.