Abstract:
An apparatus and method for providing a primary and a secondary protection to a load in a power switching application uses an electronic circuit breaker to selectively permit a flow of current from an input to a load. The circuit breaker comprises a plurality of first switches coupled in parallel, and a plurality of fuses coupled to the plurality of first switches. In a disclosed embodiment, each first switch is coupled to a first fuse and to a second fuse. A controller opens and closes the plurality of first switches by commanding a driver current ON and OFF. The controller is operable to detect a fault condition and to open the plurality of first switches in response to the fault condition by commanding the driver current OFF. If the controller fails to open one of the first switches, one of the fuses coupled to the switch is operable to blow. In addition, the circuit breaker also comprises a charge pump that provides an electric current to a second plurality of switches to prevent the second plurality of switches form shorting the driver current.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application relates generally to vehicle power systems, and more particularly, to power switching applications. 
         [0002]    Vehicles, such as aircraft, typically have a primary power source that is used to provide power to various other vehicle systems. In the event of a fault condition, such as an electrical current exceeding a threshold, it is necessary to protect the various vehicle systems from the fault condition. 
         [0003]    An electronic circuit breaker can be used to selectively control a distribution of power to various vehicle systems, and also to protect a vehicle system from a fault condition. 
         [0004]    A switch or a plurality of switches can be used in an electronic circuit breaker to provide a switching function and to act as a primary protection from a fault condition. However, in the event of a switch failure, a circuit breaker may no longer be able to protect a vehicle system from a fault condition. 
         [0005]    There is a need for a secondary protection for an electronic circuit breaker for use in vehicle power switching applications. 
       SUMMARY OF THE INVENTION 
       [0006]    A circuit breaker comprises a plurality of first switches coupled in parallel and a plurality of fuses coupled to the plurality of first switches. In a disclosed embodiment, each first switch is coupled to a first fuse and a second fuse. A controller is operable to detect a fault condition and to open the plurality of first switches in response to the fault condition using a driver current. A first fuse and a second fuse coupled to a first switch are operable to blow if the controller fails to open the first switch associated with the first fuse and the second fuse. The circuit breaker also comprises a charge pump that provides a charge pump current to a plurality of second switches to prevent the plurality of second switches from shorting the driver current. If the charge pump stops providing the charge pump current, at least one of the plurality of second switches shorts the driver current, turning the circuit breaker OFF. 
         [0007]    These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  schematically illustrates an electronic circuit breaker according to one embodiment of the present invention. 
           [0009]      FIG. 2  schematically shows the electronic circuit breaker of  FIG. 1  in an example environment of an aircraft. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]    As shown in  FIG. 1 , an electronic circuit breaker  10  selectively controls a flow of current from a DC input voltage  12  to a load  14 . In one example, the electronic circuit breaker  10  is a solid state power controller for use in a vehicle, such as an aircraft. It is understood, however, that the electronic circuit breaker  10  can be used in a variety of other applications. 
         [0011]    A microprocessor  16  controls a driver  18  which provides a driver current to selectively turn a plurality of first switches  20 ,  22 , and  24  ON and OFF. A plurality of first fuses  26 ,  28 , and  30  are coupled to inputs  20   a,    22   a,  and  24   a  of the first switches  20 ,  22 , and  24 . A plurality of second fuses  32 ,  34 , and  36  are coupled to control inputs  20   c,    22   c,  and  24   c  of the first switches  20 ,  22 , and  24 . While the example embodiment in  FIG. 1  only has three first switches  20 ,  22  and  24 , it is understood that other quantities of first switches could be used, and that any additional first switches might also be coupled to at least one fuse and could be coupled to the other first switches in parallel. 
         [0012]    When the microprocessor  16  detects a fault condition, such as a current that exceeds a threshold, also known as an “overcurrent” condition, it commands the first switches  20 ,  22 , and  24  OFF. By turning OFF and preventing current from flowing to the load  14 , the switches  20 ,  22 , and  24  provide a primary protection to the load  14 . 
         [0013]    Each of the first switches  20 ,  22 , and  24  has an input ( 20   a,    22   a,  and  24   a ), an output ( 20   b,    22   b,  and  24   b ), and a control input ( 20   c,    22   c,  and  24   c ). In one example the first switches  20 ,  22 , and  24  are MOSFETs, and each input  20   a,    22   a,  and  24   a  is a MOSFET drain, each output  20   b,    22   b,  and  24   b  is a MOSFET source, and each control input  20   c,    22   c,  and  24   c  is a MOSFET gate. In another example, the first switches  20 ,  22 , and  24  are IGBTs. 
         [0014]    During normal operation, if the first switches  20 ,  22 , and  24  are ON, an equal amount of current will flow through each of the first switches, which are connected in parallel. If one of the first switches fails to turn OFF, the plurality of first fuses  26 ,  28 ,  30  provide a secondary protection. For example, if all first switches are commanded OFF, but only switches  20  and  22  turn OFF and switch  24  remains ON, all current will flow through switch  24 . This could happen if the switch  24  failed to turn off, or if the input  24   a  was shorted to the output  24   b.  In this case, the increased flow of current through fuse  30  would exceed a threshold, and fuse  30  would blow and prevent additional current from flowing through first switch  24  to the load  14 . In this example, the fuse  30  provides secondary protection. 
         [0015]    In another example, one of the control inputs  20   c,    22   c,  or  24   c  is shorted to its associated input  20   a,    22   a,  or  24   a.  In this example the plurality of second fuses  32 ,  34 , or  36  provide a secondary protection by shorting if a current flowing through the second fuses exceeds a threshold. In one example, the plurality of first and second fuses  26 ,  28 ,  30 ,  32 ,  34 , and  36  are made of a specially sized and constructed bond wire that melts if coupled to a current that exceeds a threshold. The specific amount of time it takes for the bond wire to melt depends on the magnitude of the current that exceeds the threshold. However it is understood that the plurality of first fuses and second fuses could be made of other materials. 
         [0016]    The microprocessor  16  uses a plurality of inputs  38 ,  40 ,  62  and  66  to detect a fault condition and to monitor the electronic circuit breaker  10 . The microprocessor  16  also communicates with a system controller  106  to send and receive data and instructions. The microprocessor  16  uses inputs  38  and  40  to measure a voltage drop across a current sensing resistor  42 . The microprocessor  16  can use this voltage measurement to determine the magnitude of an output current flowing to the load  14 . If the output current exceeds a threshold, the microprocessor  16  commands the first switches  20 ,  22 , and  24  OFF. 
         [0017]    The microprocessor can also measure an input voltage and an input current to the electronic circuit breaker  10 . One example where it is useful to detect an input voltage or current is when the electronic circuit breaker  10  is OFF state, and no current flows to the current sensing resistor  42 . In this scenario, the current sensing resistor  42  cannot be used to measure an output voltage or an output current. 
         [0018]    To measure an input voltage, microprocessor  16  uses resistors  44 ,  46 ,  48 , and  50  as a first voltage divider. Resistors  44 ,  46 , and  48  collectively act as a first resistor in this first voltage divider, and resistor  50  acts as a second resistor. The microprocessor  16  uses output  64  to turn on a switch  60  which shorts the resistor  50  to ground. Then the microprocessor  16  uses input  62  to measure an input voltage. This voltage measurement enables the microprocessor  16  to determine the magnitude of an input voltage and an input current to the electronic circuit breaker  10 . When not measuring the input voltage, the microprocessor  16  uses output  64  to turn the switch  60  OFF so that resistor  50  is no longer shorted to ground, and the first voltage divider comprising resistors  44 ,  46 ,  48 , and  50  is no longer active. 
         [0019]    The microprocessor  16  can also detect an input current to the control inputs  20   c,    22   c,  and  24   c  of the first switches  20 ,  22 , and  24 . The microprocessor  16  uses an input  66  coupled to a second voltage divider comprising a first resistor  68  and a second resistor  70 . This enables the microprocessor  16  to measure an input voltage and an input current to the control inputs  20   c,    22   c,  and  24   c  of the first switches  20 ,  22 , and  24 . 
         [0020]    The microprocessor  16  controls the driver  18  to selectively turn the first switches  20   22 , and  24  ON and OFF. The driver  18  amplifies an internal supply voltage  72  to provide an electric current to the first switches  20 ,  22 , and  24 . In one example the internal supply voltage  72  is a 10 volt DC voltage. Of course, other voltages may be used. The driver control  78  is an output from microprocessor  16  that turns the driver  18  ON or OFF. The driver  18  performs an amplifying function, as it amplifies the internal supply voltage  72  to a driver output voltage that is greater than the input voltage  72 . In one example, the driver  18  is an operational amplifier. 
         [0021]    When sufficient voltage is present at the control inputs  20   c,    22   c,  and  24   c,  the first switches  20 ,  22 , and  24  turn ON. When no voltage or insufficient voltage is present at the control inputs  20   c,    22   c,  and  24   c,  the first switches  20 ,  22 , and  24  turn OFF. If the increased driver output voltage mentioned above facilitates a voltage at the control inputs  20   c,    22   c,  and  24   c  of sufficient magnitude, each of the first switches  20 ,  22 , and  24  turn ON. When the driver  18  is OFF, the plurality of first switches are also OFF. A resistor  98  is coupled to an output of the driver to keep the driver current applied to the control inputs  20   c,    22   c,  and  24   c  at a moderate level. 
         [0022]    The microprocessor  16  also controls a charge pump  76  that enables the driver  18  to turn the first switches  20 ,  22 , and  24  ON. The charge pump includes a second plurality of switches  80  and  82 , capacitors  84  and  86 , diodes  88  and  90 , and resistors  92  and  94 . Inputs  80   a  and  82   a  of the second plurality of switches  80  and  82  are coupled to the driver current. An output  80   b  of the switch  80  is coupled to a control input  82   c  of the switch  82 . In one example the switch  80  is a JFET and switch  82  is a transistor, and the input  80   a  is a JFET drain, the output  80   b  is a JFET source, the control input  80   c  is a JFET gate, the input  82   a  is a transistor collector, the output  82   b  is a transistor emitter, and the control input  82   c  is a transistor base. 
         [0023]    The microprocessor  16  has a square wave output signal  74  that controls the charge pump  76 . If the square wave output signal  74  is OFF, then the charge pump  76  is OFF and the switch  80  is ON. When the switch  80  is ON, the driver current flows from the driver  18  through the switch  80  to a control input  82   c  of the switch  82 , turning the switch  82  ON. When the switch  82  is ON, the driver current flows from the driver  18  through the switch  82  to ground. Thus, if the square wave output signal  74  is OFF, the driver current is shorted to ground by the switch  82 , and the plurality of first switches  20 ,  22 , and  24  remain OFF. 
         [0024]    If the microprocessor  16  determines it should turn the first switches  20 ,  22 , and  24  OFF, it turns the driver  18  and the charge pump  76  OFF. Additionally, the charge pump  76  provides additional protection if the driver  18  fails to stop providing a driver current to the first switches  20 ,  22 , and  24 , because even if the driver  18  is producing a driver current, if the charge pump  76  is OFF then the driver current will be shorted and the first switches  20 ,  22 , and  24  will be turned OFF. 
         [0025]    When the square wave output signal  74  is ON, current flows to the capacitor  84 . From the capacitor  84  current flows through a diode  88  to ground and to a diode  90 . The diode  90  is oriented to only permit a flow of positive current towards the capacitor  84 , and to prevent a positive flow of current away from the capacitor  84 . However, this orientation does allow a flow of negative current away from the capacitor  84  to a capacitor  86 . The capacitor  86  stores this negative charge and transmits the negative charge to the control input  80   c  of the switch  80 , which turns the switch  80  OFF, and prevents the switch  82  from shorting the driver current to ground. Thus, when the charge pump  76  is ON, the driver current can flow to the control inputs  20   c,    22   c,  and  24   c  without being shorted to ground. 
         [0026]    A resistor  92  is coupled in parallel to the capacitor  86 . If the charge pump  76  turns OFF, the resistor  92  provides a path to ground to get a stored voltage out of the capacitor  86 . A resistor  94  is coupled to the output  80   b  and to the control input  82   c.  If the charge pump  76  turns OFF, the resistor  94  ensures that the switch  82  is able to turn off by providing a path to ground for the control input  82   c.    
         [0027]    Diodes  52 ,  54 ,  56 , and  58  perform a clamping function in the electronic circuit breaker  10 . A typical diode is biased to only permit a flow of current in one direction. A zener diode initially permits a flow of current only in a first direction, however if sufficient voltage is supplied to a zener diode, it may permit a flow of current in a second direction that is opposite the first direction. In the example shown in  FIG. 1 , diodes  52 ,  54 , and  56  are zener diodes, and diodes  58 ,  88 , and  90  are regular diodes. 
         [0028]    It is common in an aircraft application to work with an inductive load. If power is turned off to an inductive load, such as the load  14 , it is possible to receive a high inductive kick back. An aircraft is an example environment where it is possible to receive a high inductive kick back, because in an aircraft a ground connection is typically really a “neutral” connection, due to the fact that when an aircraft flies it is not in contact with an earth ground connection. A neutral connection is connected to other components in an aircraft, and therefore an inductive load  14  has the potential to provide an inductive kickback to its own input  12  and to provide a voltage spike at an input of a switch. 
         [0029]    The first switches  20 ,  22 , and  24  are rated for specific voltages, and a high inductive kick back or a voltage spike could potentially damage the first switches  20 ,  22 , and  24 . The diodes  52 ,  54 , and  56  are zener diodes oriented to only permit a flow of current in a first direction away from the first switches  20 ,  22 , and  24 . However if an input voltage increases to a certain level, the diodes  52 ,  54 , and  56  become conductive and permit a flow of current in a second direction opposite the first direction towards the control inputs  20   c,    22   c,  and  24   c  to turn the first switches  20 ,  22 , and  24  ON to limit a voltage drop across the first switches  20 ,  22 , and  24  and to prevent damage of the first switches  20 ,  22 , and  24 . 
         [0030]    An additional zener diode  96  is coupled to the driver current and to ground, and is oriented to only permit a flow of current in a first direction towards the control inputs  20   c,    22   c,  and  24   c.  The zener diode  96  is, however, operable to conduct current in a second direction opposite the first direction to ground a voltage spike or an excessive current at the control inputs  20   c,    22   c,  and  24   c.  If for some reason one of the second fuses  32 ,  24 , or  36  failed to blow, the zener diode  96  ensures that a voltage at the control inputs  20   c,    22   c,  and  24   c  does not increase beyond a maximum voltage that the first switches  20 ,  22 , and  24  can handle. 
         [0031]    A plurality of resistors  100 ,  102 , and  104  perform a decoupling function to prevent the first switches  20 ,  22 , and  24  from oscillating due to an input capacitance of the diodes  52 ,  54 ,  56 , and  58 . 
         [0032]    A resistor  108  limits a flow of current from the internal supply voltage  72  to the driver  18 . A capacitor  109  acts as a filter for the driver  18 , so that when the driver  18  is switched ON or OFF the driver current does not disturb the switch  82 . 
         [0033]    Additionally, the microprocessor can use the input  62  to determine if the diodes  52 ,  54 , and  56  have failed. For example, if diode  52  fails and is for some reason shorted, then the resistor  44  would also be shorted. This would affect the data from the first voltage driver as measured by input  62 . Thus, the microprocessor  16  is able to detect a variation in voltage from the first voltage divider to determine if one of the diodes  52 ,  54 , or  56  has failed. 
         [0034]    As shown in  FIG. 2 , an aircraft  110  contains an electronic circuit breaker  10  that connects a DC input voltage  12  to a load  14 . The electronic circuit breaker  10  is coupled to an internal supply voltage  72 . The electronic circuit breaker communicates with a system controller  106  to send and receive data and instructions. 
         [0035]    It is understood that although the example electronic circuit breaker  10  of  FIG. 1  is configured for a DC application, it would be possible for one of ordinary skill in the art to adapt the electronic circuit breaker  10  to an AC application. 
         [0036]    Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.