Patent Publication Number: US-8994210-B2

Title: Driver circuit for an electric vehicle and a diagnostic method for determining when an electrical short circuit to a ground voltage is present between a contactor coil and a voltage driver

Description:
BACKGROUND 
     The inventor herein has recognized a need for an improved driver circuit for an electric vehicle and a diagnostic method for determining when an electrical short circuit to a ground voltage is present between a contactor coil and a voltage driver. 
     SUMMARY 
     A driver circuit for an electric vehicle in accordance with an exemplary embodiment is provided. The driver circuit includes a first voltage driver having a first input line and a first output line. The first input line is coupled to a microprocessor. The first output line is coupled to a first side of a contactor coil of a contactor. The driver circuit further includes a second voltage driver having a second input line, a second output line, and a second voltage sense line. The second input line is coupled to the microprocessor. The second output line is coupled to a second side of the contactor coil. The second voltage sense line is coupled to the microprocessor. The microprocessor is configured to generate a first pulse width modulated signal on the first input line to induce the first voltage driver to output a second pulse width modulated signal on the first output line that is received by the first side of the contactor coil to energize the contactor coil. The microprocessor is further configured to iteratively measure a voltage on a first side of a contact in the contactor over time to obtain a first plurality of voltage values. The microprocessor is further configured to determine a first filtered voltage value based on the first plurality of voltage values. The microprocessor is further configured to iteratively measure a voltage on a second side of the contact in the contactor over time to obtain a second plurality of voltage values. The microprocessor is further configured to determine a second filtered voltage value based on the second plurality of voltage values. The microprocessor is further configured to iteratively measure a voltage on the second voltage sense line over time to obtain a third plurality of voltage values indicative of an amount of electrical current flowing through the second voltage driver. The microprocessor is further configured to determine a first filtered current value based on the third plurality of voltage values. The microprocessor is further configured to stop generating the first pulse width modulated signal to de-energize the contactor coil if both the first filtered voltage value is substantially equal to the second filtered voltage value, and the first filtered current value is less than a threshold current value, indicating that an electrical short circuit to a ground voltage is present between the contactor coil and the second voltage driver. 
     A diagnostic method for a driver circuit for an electric vehicle in accordance with another exemplary embodiment is provided. The driver circuit has a first voltage driver, a second voltage driver, and a microprocessor. The first voltage driver has a first input line and a first output line. The first input line is coupled to the microprocessor. The first output line is coupled to a first side of a contactor coil of a contactor. The second voltage driver has a second input line, a second output line, and a second voltage sense line. The second input line is coupled to the microprocessor. The second output line is coupled to a second side of the contactor coil. The second voltage sense line is coupled to the microprocessor. The method includes generating a first pulse width modulated signal on the first input line utilizing the microprocessor to induce the first voltage driver to output a second pulse width modulated signal on the first output line that is received by the first side of the contactor coil to energize the contactor coil. The method further includes iteratively measuring a voltage on a first side of a contact in the contactor over time to obtain a first plurality of voltage values utilizing the microprocessor. The method further includes determining a first filtered voltage value based on the first plurality of voltage values utilizing the microprocessor. The method further includes iteratively measuring a voltage on a second side of the contact in the contactor over time to obtain a second plurality of voltage values utilizing the microprocessor. The method further includes determining a second filtered voltage value based on the second plurality of voltage values utilizing the microprocessor. The method further includes iteratively measuring a voltage on the second voltage sense line over time to obtain a third plurality of voltage values indicative of an amount of electrical current flowing through the second voltage driver utilizing the microprocessor. The method further includes determining a first filtered current value based on the third plurality of voltage values utilizing the microprocessor. The method further includes stopping the generating of the first pulse width modulated signal to de-energize the contactor coil if both the first filtered voltage value is substantially equal to the second filtered voltage value, and the first filtered current value is less than a threshold current value, indicating that an electrical short circuit to a ground voltage is present between the contactor coil and the second voltage driver, utilizing the microprocessor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an electric vehicle having a driver circuit in accordance with an exemplary embodiment; 
         FIG. 2  is a schematic of a first voltage driver utilized in the driver circuit of  FIG. 1 ; 
         FIG. 3  is a schematic of a second voltage driver utilized in the driver circuit of  FIG. 1 ; 
         FIG. 4  is a schematic of a first set of voltage pulses output by the driver circuit of  FIG. 1 ; 
         FIG. 5  is a schematic of a second set of voltage pulses output by the driver circuit of  FIG. 1 ; 
         FIG. 6  is a schematic of a signal output by the driver circuit of  FIG. 1 ; 
         FIG. 7  is a schematic of a third set of voltage pulses output by the driver circuit of  FIG. 1 ; 
         FIG. 8  is a schematic of a fourth set of voltage pulses output by the driver circuit of  FIG. 1 ; 
         FIG. 9  is a schematic of another signal output by the driver circuit of  FIG. 1 ; 
         FIG. 10  is a schematic of a fifth set of voltage pulses output by the driver circuit of  FIG. 1 ; 
         FIG. 11  is a schematic of a sixth set of voltage pulses output by the driver circuit of  FIG. 1 ; 
         FIG. 12  is a schematic of another signal output by the driver circuit of  FIG. 1 ; and 
         FIGS. 13-15  are flowcharts of a diagnostic method in accordance with another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-3 , an electric vehicle  10  having a driver circuit  40  in accordance with an exemplary embodiment is provided. The electric vehicle  10  further includes a battery pack  30 , a main contactor  50 , a grounding contactor  52 , a pre-charge contactor  54 , an electrical current sensor  60 , a resistor  70 , a high voltage inverter  90 , an electric motor  91 , electrical lines  100 ,  102 ,  104 ,  106 ,  108 ,  114 ,  116 ,  118 , a vehicle controller  117 , an electrical current sensor  119 , and a power supply  121 . An advantage of the driver circuit  40  is that the driver circuit  40  performs a diagnostic algorithm to determine when an electrical short circuit to a ground voltage is present between a contactor coil and a voltage driver. 
     Before explaining the structure and operation of the electric vehicle  10 , a brief explanation of some of the terms utilized herein will be provided. 
     The term “filtered voltage value” refers to a voltage value that is determined based on a plurality of voltage values. A filtered voltage value can be determined utilizing a filter equation. 
     The term “filtered current value” refers to a current value that is determined based on a plurality of voltage values or a plurality of current values. A filtered current value can be determined utilizing a filter equation. 
     The term “filter equation” refers to an equation that is used to calculate a value based on a plurality of values. In exemplary embodiments, a filter equation can comprise a first order lag filter or an integrator for example. Of course, other types of filter equations known to those skilled in the art could be utilized. 
     The term “high voltage” refers to a voltage greater than an expected voltage during a predetermined operational mode of the driver circuit. For example, if an expected voltage at a predetermined location in the driver circuit is 4 volts (e.g., 12 volts at a 30% duty cycle) in a predetermined operational mode of the driver circuit, an actual voltage of 4.5 volts at the predetermined location in the driver circuit could be considered a high voltage. 
     The term “high logic voltage” refers to a voltage in the driver circuit that corresponds to a Boolean logic value of “1.” 
     The battery pack  30  is configured to output an operational voltage to the high voltage inverter  90  which outputs operational voltages to the electric motor  91  via the electrical lines  118 . The battery pack  30  includes battery modules  140 ,  142 ,  144  electrically coupled in series with one another. 
     The driver circuit  40  is configured to control operational positions of the main contactor  50 , the grounding contactor  52 , and the pre-charge contactor  54 . The driver circuit  40  includes a microprocessor  170 , a first voltage driver  180 , a second voltage driver  182 , a third voltage driver  184 , a fourth voltage driver  186 , a fifth voltage driver  188 , and a sixth voltage driver  190 . 
     The microprocessor  170  is configured to generate control signals for controlling operation of the first voltage driver  180 , the second voltage driver  182 , the third voltage driver  184 , the fourth voltage driver  186 , the fifth voltage driver  188 , and the sixth voltage driver  190 . The microprocessor  170  is further configured to execute a software program stored in a memory device  171  for implementing a diagnostic algorithm associated with the driver circuit  40  as will be explained below. The memory device  171  is configured to store software algorithms, values, and status flags therein. The microprocessor  170  is operably coupled to a Vcc voltage source that supplies an operational voltage (e.g., 5 Volts) to the microprocessor  170 . 
     Before explaining the diagnostic algorithm associated with the driver circuit  40  in accordance with an exemplary embodiment, the structure and operation of the driver circuit  40  will be explained. 
     Referring to  FIGS. 1 and 2 , the first voltage driver  180  and the second voltage driver  182  are utilized to energize the main contactor coil  502  to induce the contact  500  to have a closed operational position, and to de-energize the main contactor coil  502  to induce the contact  500  to have an open operational position. 
     Referring to FIGS.  1  and  4 - 6 , during operation, when the microprocessor  170  outputs both the initial voltage pulse  602 , and the first signal  702  on the input lines  202 ,  262 , respectively, of the first and second voltage drivers  180 ,  182 , respectively; the voltage drivers  180 ,  182  energize the main contactor coil  502  to induce the contact  500  to have a closed operational position. In particular, in response to the first voltage driver  180  receiving the initial voltage pulse  602 , the first voltage driver  180  outputs the initial voltage pulse  652  to energize the main contactor coil  502 . 
     After generating the initial voltage pulse  602 , the microprocessor  170  outputs the pulse width modulated signal  603  having the voltage pulses  604 ,  606 ,  608 ,  610  with a duty cycle of about 30%. Of course, the duty cycle of the voltage pulses  604 ,  606 ,  608 ,  610  could be less than 30% or greater than 30%. 
     Further, after generating the initial voltage pulse  602 , the microprocessor  170  continues outputting the first signal  702  which has a high logic voltage while generating the voltage pulses  604 ,  606 ,  608 ,  610 . The first signal  702  turns on the transistor  280  in the second voltage driver  182 . 
     In particular, in response to the first voltage driver  180  receiving the pulse width modulated signal  603 , the first voltage driver  180  outputs the pulse width modulated signal  653  (shown in  FIG. 5 ) to maintain energization the main contactor coil  502 . The pulse width modulated signal  653  includes the voltage pulses  654 ,  656 ,  658 ,  660  with a duty cycle of about 30%. Of course, the duty cycle of the voltage pulses  654 ,  656 ,  658 ,  660  could be less than 30% or greater than 30%. 
     When the microprocessor  170  stops outputting the pulse width modulated signal  603  and the first signal  702  on the input lines  202 ,  262 , respectively, of the first and second voltage drivers  180 ,  182 , respectively, the voltage drivers  180 ,  182  de-energize the main contactor coil  502  to induce the contact  500  to have an open operational position. 
     Referring to  FIGS. 1 and 2 , the first voltage driver  180  includes a driver circuit  201 , an input line  202 , an output line  204 , and a voltage sense line  206 . The input line  202  is coupled to both the microprocessor  170  and to the driver circuit  201 . The output line  204  is electrically coupled to a first side of the main contactor coil  502 . The voltage sense line  206  is coupled to both the output line  204  and to the microprocessor  170 . 
     In one exemplary embodiment, the driver circuit  201  includes transistors  220 ,  222 . The transistor  220  has: (i) a base (B) coupled to a node  230  that is further coupled to the microprocessor  170 , (ii) a collector (C) coupled to a power supply  121  via power supply lines  207 ,  209 , and (iii) an emitter coupled to a node  232  which is further coupled to the output line  204 . The electrical current sensor  119  is electrically coupled in series with the power supply lines  207 ,  209 , and is configured to generate a signal when the power supply  121  is supplying an amount of electrical current on the power supply line  207  that is greater than a threshold current level. The signal from the electrical current sensor  119  is received by the microprocessor  170 . 
     The transistor  222  has: (i) a base (B) coupled to the node  230  that is further coupled to the microprocessor  170 , (ii) a collector (C) coupled to electrical ground, and (iii) an emitter coupled to the node  232 . When the microprocessor  170  applies a high logic voltage to node  230 , the transistor  220  is turned on and the transistor  222  is turned off and a voltage (e.g., 12 volts) from the power supply  121  is applied to the node  232  and the output line  204  which is further applied to a first end of the main contactor coil  502 . Alternately, when the microprocessor  170  stops applying the high logic voltage to node  230 , the transistor  220  is turned off and the transistor  222  is turned on and a ground voltage is applied to the node  232  and the output line  204  which is further applied to the first end of the main contactor coil  502 . 
     Referring to  FIGS. 1 and 3 , the second voltage driver  182  includes a driver circuit  261 , an input line  262 , an output line  264 , a voltage sense line  266 , and a voltage sense line  268 . The input line  262  is coupled to both the microprocessor  170  and to the driver circuit  261 . The output line  264  is electrically coupled to a second side of the main contactor coil  502 . The voltage sense line  266  coupled to both the output line  264  and to the microprocessor  170 . When the main contactor coil  502  is energized, the voltage sense line  268  receives a voltage indicative of a first current in the main contactor coil  502  and is coupled to the microprocessor  170 . 
     In one exemplary embodiment, the driver circuit  261  includes a transistor  280  and a resistor  282 . The transistor  280  has: (i) a gate (G) coupled to the microprocessor  170 , (ii) a drain (D) coupled to a node  284  that is further coupled to both the voltage sense line  266  and to the output line  264 , and (iii) a source (S) coupled to a resistor  282 . The resistor  282  is coupled between the source (S) and electrical ground. A node  286  at a first end of the resistor  282  is further coupled to the microprocessor  170  through the voltage sense line  268 . When the microprocessor  170  applies a high logic voltage to the gate (G), the transistor  280  turns on and allows electrical current from the main contactor coil  502  to flow through the transistor  280  and the resistor  282  to ground. Alternately, when the microprocessor  170  stops applying the high logic voltage to the gate (G), the transistor  280  turns off and does not allow electrical current to flow through the main contactor coil  502 , the transistor  280 , and the resistor  282 . 
     Referring to  FIG. 1 , the third voltage driver  184  and the fourth voltage driver  186  are utilized to energize the grounding contactor coil  512  to induce the contact  510  to have a closed operational position, and to de-energize the grounding contactor coil  512  to induce the contact  510  to have an open operational position. 
     Referring to FIGS.  1  and  7 - 9 , during operation, when the microprocessor  170  outputs both the initial voltage pulse  802 , and the first signal  902  on the input lines  302 ,  362  of the third and fourth voltage drivers  184 ,  186 , respectively; the voltage drivers  184 ,  186  energize the grounding contactor coil  512  to induce the contact  510  to have a closed operational position. In particular, in response to the third voltage driver  184  receiving the initial voltage pulse  802 , the third voltage driver  184  outputs the initial voltage pulse  852  to energize the grounding contactor coil  512 . 
     After generating the initial voltage pulse  802 , the microprocessor  170  outputs the pulse width modulated signal  803  having the voltage pulses  804 ,  806 ,  808 ,  810  with a duty cycle of about 30%. Of course, the duty cycle of the voltage pulses  804 ,  806 ,  808 ,  810  could be less than 30% or greater than 30%. 
     Further, after generating the initial voltage pulse  802 , the microprocessor  170  continues outputting the first signal  902  which has a high logic voltage while generating the voltage pulses  804 ,  806 ,  808 ,  810 , to continue to turn on a transistor, like the transistor  280 , in the fourth voltage driver  186 . 
     In particular, in response to the third voltage driver  184  receiving the pulse width modulated signal  803 , the third voltage driver  184  outputs the pulse width modulated signal  853  (shown in  FIG. 8 ) to energize the grounding contactor coil  512 . The pulse width modulated signal  853  includes the voltage pulses  854 ,  856 ,  858 ,  860  having a duty cycle of about 30%. Of course, the duty cycle of the voltage pulses  854 ,  856 ,  858 ,  860  could be less than 30% or greater than 30%. 
     When the microprocessor  170  stops outputting the pulse width modulated signal  803 , and the first signal  902  on the input lines  302 ,  362 , respectively, of the third and fourth voltage drivers  184 ,  186 , respectively, the voltage drivers  184 ,  186  de-energize the grounding contactor coil  512  to induce the contact  510  to have an open operational position. 
     Referring to  FIGS. 1 and 2 , the third voltage driver  184  includes a driver circuit  301 , an input line  302 , an output line  304 , and a voltage sense line  306 . The input line  302  is coupled to both the microprocessor  170  and to the driver circuit  301 . The output line  304  is electrically coupled to a first side of the grounding contactor coil  512 . The voltage sense line  306  is coupled to both the output line  304  and to the microprocessor  170 . In one exemplary embodiment, the structure of the driver circuit  301  is identical to the structure of the driver circuit  201  discussed above. Further, the driver circuit  201  is coupled to the power supply  121  via a series combination of a respective first power supply line (not shown), a respective electrical current sensor (not shown), and a respective second power supply line (not shown). 
     Referring to  FIGS. 1 and 3 , the fourth voltage driver  186  includes a driver circuit  361 , an input line  362 , an output line  364 , a voltage sense line  366 , and a voltage sense line  368 . The input line  362  is coupled to both the microprocessor  170  and to the driver circuit  361 . The output line  364  is electrically coupled to a second side of the grounding contactor coil  512 . The voltage sense line  366  coupled to both the output line  364  and to the microprocessor  170 . When the grounding contactor coil  512  is energized, the voltage sense line  368  receives a signal indicative of a second current in the grounding contactor coil  512  and is coupled to the microprocessor  170 . In one exemplary embodiment, the structure of the driver circuit  361  is identical to the structure of the driver circuit  261 . 
     The fifth voltage driver  188  and the sixth voltage driver  190  are utilized to energize the pre-charge contactor coil  522  to induce the contact  520  to have a closed operational position, and to de-energize the pre-charge contactor coil  522  to induce the contact  520  to have an open operational position. 
     Referring to FIGS.  1  and  10 - 12 , during operation, when the microprocessor  170  outputs both the initial voltage pulse  1002 , and the first signal  1102  on the input lines  402 ,  462 , respectively, of the fifth and sixth voltage drivers  188 ,  190 , respectively; the voltage drivers  188 ,  190  energize the pre-charge contactor coil  522  to induce the contact  520  to have a closed operational position. In particular, in response to the fifth voltage driver  188  receiving the initial voltage pulse  1002 , the fifth voltage driver  188  outputs the initial voltage pulse  1052  to energize the grounding contactor coil  512 . 
     After generating the initial voltage pulse  1002 , the microprocessor  170  outputs the pulse width modulated signal  1003  having the voltage pulses  1004 ,  1006 ,  1008 ,  1010  with a duty cycle of about 30%. Of course, the duty cycle of the voltage pulses  1004 ,  1006 ,  1008 ,  1010  could be less than 30% or greater than 30%. 
     Further, after generating the initial voltage pulse  1002 , the microprocessor  170  continues outputting the first signal  1102  which has a high logic voltage while generating the voltage pulses  1004 ,  1006 ,  1008 ,  1010 , to continue to turn on a transistor, like the transistor  280 , in the sixth voltage driver  190 . 
     In response to the fifth voltage driver  188  receiving the pulse width modulated signal  1003 , the fifth voltage driver  188  outputs the pulse width modulated signal  1053  to energize the pre-charge contactor coil  522 . The pulse width modulated signal  1053  includes the voltage pulses  1054 ,  1056 ,  1058 ,  1060  having a duty cycle of about 30%. Of course, the duty cycle of the voltage pulses  1054 ,  1056 ,  1058 ,  1060  could be less than 30% or greater than 30%. 
     When the microprocessor  170  stops outputting the pulse width modulated signal  1003 , and the first signal  1102  on the input lines  402 ,  462 , respectively, of the fifth and sixth voltage drivers  188 ,  190 , respectively; the voltage drivers  188 ,  190  de-energize the pre-charge contactor coil  522  to induce the contact  520  to have an open operational position. 
     The fifth voltage driver  188  includes a driver circuit  401 , an input line  402 , an output line  404 , and a voltage sense line  406 . The input line  402  is coupled to both the microprocessor  170  and to the driver circuit  401 . The output line  404  is electrically coupled to a first side of the pre-charge contactor coil  522 . The voltage sense line  406  is coupled to both the output line  404  and to the microprocessor  170 . In one exemplary embodiment, the structure of the driver circuit  401  is identical to the structure of the driver circuit  201  discussed above. Further, the driver circuit  401  is coupled to the power supply  121  via a series combination of a respective first power supply line (not shown), a respective electrical current sensor (not shown), and a respective second power supply line (not shown). 
     The sixth voltage driver  190  includes a driver circuit  461 , an input line  462 , an output line  464 , a voltage sense line  466 , a voltage sense line  468 . The input line  462  is coupled to both the microprocessor  170  and to the driver circuit  461 . The output line  464  is electrically coupled to a second side of the pre-charge contactor coil  522 . The voltage sense line  466  coupled to both the output line  464  and to the microprocessor  170 . When the pre-charge contactor coil  522  is energized, the voltage sense line  468  receives a signal indicative of a third current in the pre-charge contactor coil  522  and is coupled to the microprocessor  170 . In one exemplary embodiment, the structure of the driver circuit  461  is identical to the structure of the driver circuit  261 . 
     The main contactor  50  is electrically coupled in series with the battery pack  30 , the current sensor  60  and the inverter  90 . In particular, a positive voltage terminal of the battery pack  100  is electrically coupled to the current sensor  60  via the electrical line  100 . The current sensor  60  is electrically coupled to a first end of the contact  500  of the main contactor  50  via the electrical line  102 . Also, a second end of the contact  500  is electrically coupled to the inverter  90  via the electrical line  106 . When the main contactor coil  502  is energized, the contact  500  has a closed operational position and electrically couples a positive voltage terminal of the battery pack  30  to the inverter  90 . When the main contactor coil  502  is de-energized, the contact  500  has an open operational position and electrically de-couples the positive voltage terminal of the battery pack  30  from the inverter  90 . 
     The grounding contactor  52  is electrically coupled in series between the battery pack  30  and the inverter  90 . A negative voltage terminal of the battery pack  30  is electrically coupled to a first end of the contact  510  of the grounding contactor  52  via the electrical line  114 . Also, a second end of the contact  510  is electrically coupled to the inverter  90  via the electrical line  116 . When the grounding contactor coil  512  is energized, the contact  510  has a closed operational position and electrically couples a negative voltage terminal of the battery pack  30  to the inverter  90 . When the grounding contactor coil  512  is de-energized, the contact  510  has an open operational position and electrically de-couples the negative voltage terminal of the battery pack  30  from the inverter  90 . 
     The pre-charge contactor  54  is electrically coupled in parallel to the main contactor  50 . A first end of the contact  520  is electrically coupled to the electrical line  102  via the electrical line  104 . A second end of the contact  520  is electrically coupled to the electrical line  106  via the resistor  70  and the electrical line  108 . When the pre-charge contactor coil  522  is energized, the contact  520  has a closed operational position and electrically couples a positive voltage terminal of the battery pack  30  to the inverter  90 . When the pre-charge contactor coil  522  is de-energized, the contact  520  has an open operational position and electrically de-couples the positive voltage terminal of the battery pack  30  from the inverter  90 . 
     The electrical current sensor  60  is configured to generate a signal indicative of a total amount of current being supplied by the battery pack  30  to the electric motor  90 . The microprocessor  170  receives the signal from the electrical current sensor  60 . The electrical current sensor  60  is electrically coupled in series between a positive voltage terminal of the battery pack  30  and a first end of the contact  500 . 
     Referring to  FIGS. 1 ,  4 - 7 , and  13 - 16 , a flowchart of diagnostic method for the driver circuit  40  of the electric vehicle  10  when at least one of the main contactor coil  502 , the grounding contactor coil  512 , and the pre-charge contactor coil  522  are energized will now be explained. The diagnostic method determines when an electrical short circuit to a ground voltage is present between a contactor coil and a voltage driver. For purposes of simplicity, the following diagnostic method will be explained with reference to the main contactor coil  502  and the first and second voltage drivers  180 ,  182  for controlling the main contactor coil  502 . However, it should be understood that the following diagnostic method can be utilized with grounding contactor coil  512  and/or the pre-charge contactor coil  522  and the associated voltage drivers therewith. 
     At step  1300 , the electric vehicle  10  utilizes the driver circuit  40  having the first voltage driver  180 , the second voltage driver  182 , the electrical current sensor  119 , and the microprocessor  170 . The first voltage driver  180  has the input line  202 , the output line  204 , and the power supply line  207 . The input line  202  is coupled to the microprocessor  170 . The output line  204  is coupled to a first side of the contactor coil  502  of the contactor  50 . The electrical current sensor  119  is electrically coupled to the power supply line  207 . The second voltage driver  182  has the input line  262 , the output line  264 , and the voltage sense line  268 . The input line  262  is coupled to the microprocessor  170 . The output line  264  is coupled to a second side of the contactor coil  502 . The voltage sense line  268  is coupled to the microprocessor  170 . After step  1300 , the method advances to step  1302 . 
     At step  1302 , the microprocessor  170  generates a first pulse width modulated signal  603  on the input line  202  to induce the first voltage driver  180  to output a second pulse width modulated signal  653  on the output line  204  that is received by the first side of the contactor coil  502  to energize the contactor coil  502 . After step  1302 , the method advances to  1304 . 
     At step  1304 , the microprocessor  170  generates a first signal  702  on the input line  262 , while generating the first pulse width modulated signal, to induce the second voltage driver  182  to receive an electrical current from the contactor coil  502  on the output line  264  which energizes the contactor coil  502 . After step  1304 , the method advances to step  1306 . 
     At step  1306 , the electrical current sensor  119  makes a determination as to whether an amount of electrical current on the power supply line  207  is greater than a threshold current level. If the value of step  1306  equals “yes”, the method advances to step  1320 . Otherwise, the method advances to step  1322 . 
     At step  1320 , the electrical current sensor  119  generates a first signal indicating that the power supply  121  is supplying an amount of electrical current on the power supply line  207  that is greater than a threshold current level. The first signal is received by the microprocessor  170 . After step  1320 , the method advances to step  1322 . 
     Referring again to step  1306 , if the value of step  1306  equals “no”, the method advances to step  1322 . At step  1322 , the microprocessor  170  iteratively measures a voltage on a first side of the contact  500  in the contactor  50  over time to obtain a first plurality of voltage values. After step  1322 , the method advances to step  1324 . 
     At step  1324 , the microprocessor  170  determines a first filtered voltage value based on the first plurality of voltage values. In one exemplary embodiment, the first filter equation is a first order lag filter equation. For example, in one exemplary embodiment, the first filter equation is as follows: first filtered voltage value=first filtered voltage value Old +(voltage value of one of first plurality of voltage values−first filtered voltage value Old )*Gain Calibration . It is noted that the foregoing equation is iteratively calculated utilizing each of the voltage values of the first plurality of voltage values. 
     At step  1326 , the microprocessor  170  iteratively measures a voltage on a second side of the contact  500  in the contactor  50  over time to obtain a second plurality of voltage values. The step  1326  may be substantially simultaneously performed with the step  1322 . After step  1326 , the method advances to step  1328 . 
     At step  1328 , the microprocessor  170  determines a second filtered voltage value based on the second plurality of voltage values. In one exemplary embodiment, the second filter equation is a first order lag filter equation. For example, in one exemplary embodiment, the second filter equation is as follows: second filtered voltage value=second filtered voltage value Old +(voltage value of one of second plurality of voltage values−second filtered voltage value Old )*Gain Calibration . It is noted that the foregoing equation is iteratively calculated utilizing each of the voltage values of the second plurality of voltage values. 
     At step  1330 , the microprocessor  170  iteratively measures a voltage on the voltage sense line  268  over time to obtain a third plurality of voltage values indicative of an amount of electrical current flowing through the second voltage driver  182 . The step  1330  may be substantially simultaneously performed with the step  1326 . After step  1330 , the method advances to step  1332 . 
     At step  1332 , the microprocessor  170  determines a first filtered current value based on the third plurality of voltage values. In one exemplary embodiment, the first filtered current equation is a first order lag filter equation. For example, in one exemplary embodiment, the first filtered current equation is as follows: first filtered current value=first filtered current value Old +((voltage value of one of second plurality of voltage values/resistance of resistor  282 )−first filtered current value Old ))*Gain Calibration . It is noted that the foregoing equation is iteratively calculated utilizing each of the voltage values of the second plurality of voltage values. The first filtered current value is indicative of an amount of electrical current flowing through the contactor coil  502 . After step  1332 , the method advances to step  1340 . 
     At step  1340 , the microprocessor  170  determines a difference value based on the first and second filtered voltage values. In one exemplary embodiment, the difference value is calculated utilizing the following equation: difference value=first filtered voltage value−second filtered voltage value. After step  1340 , the method advances to step  1342 . 
     At step  1342 , the microprocessor  170  makes a determination as to whether the microprocessor  170  received the first signal from the electrical current sensor  119  indicating that an excess current is being supplied on the power supply line  207 , and whether the difference value is greater than a predetermined threshold value indicating that the contact  500  has an open operational position, wherein both of the foregoing conditions further indicate that the first voltage driver  180  is shorted to a ground voltage. It should be noted that the first voltage driver  180  can either be directly shorted to a ground voltage, or indirectly shorted to a ground voltage through other components in the driver circuit  40 . If the value of step  1342  equals “yes”, the method advances to step  1344 . Otherwise, the method advances to step  1346 . 
     At step  1344 , the microprocessor  170  stops generating the first pulse width modulated signal  603  and the first signal  702  to de-energize the contactor coil  502 . After step  1344 , the method is exited. 
     Referring again to step  1342 , if the value of step  1342  equals “no”, the method advances to step  1346 . At step  1346 , the microprocessor  170  makes a determination as to whether the first filtered voltage value is substantially equal to the second filtered voltage value indicating that the contact  500  has a closed operational position, and whether the first filtered current value is less than a threshold current value indicating that a low level of current is flowing through the second voltage driver  182 , wherein both of the foregoing conditions indicate that an electrical short circuit to a ground voltage is present between the contact  500  and the second voltage driver  182 . If the value of step  1346  equals “yes”, the method advances to step  1348 . Otherwise, the method is exited. 
     At step  1348 , the microprocessor  170  stops generating the first pulse width modulated signal  603  and the first signal  702  to de-energize the contactor coil  502 . After step  1348 , the method is exited. 
     The driver circuit  40  and the diagnostic method provide a substantial advantage over other circuits and methods. In particular, the driver circuit  40  and the diagnostic method provide a technical effect of determining when an electrical short circuit to a ground voltage is present between a contactor coil and a voltage driver. 
     The above-described diagnostic method can be at least partially embodied in the form of one or more computer readable media having computer-executable instructions for practicing the methods. The computer-readable media can comprise one or more of the following: hard drives, RAM memory, flash memory, and other computer-readable media known to those skilled in the art; wherein, when the computer-executable instructions are loaded into and executed by one or more computers or microprocessors, the one or more computers or microprocessors become an apparatus for practicing the methods. 
     While the claimed invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the claimed invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the claimed invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the claimed invention is not to be seen as limited by the foregoing description.