Abstract:
Single fault tolerant isolated dual bus power input circuits and systems are provided. One input circuit comprises a first bus and a second bus configured to be coupled to first and second power sources, respectively. The first bus includes first input and return lines, the first input or return line including a switch. The second bus includes second input and return lines, the second input or return line including two switches coupled in series. A system includes multiple power sources coupled to an electronic device via the input circuit discussed above. Another system includes multiple power sources, an electronic device, and an input circuit coupling the electronic device to the power sources. The input circuit includes multiple input lines coupling the electronic device to a respective power source, wherein each input line includes a switch coupled between the electronic device and each respective power source.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    The United States Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided by the terms of Contract No. NNJ06TA25C and Sub-Contract No. RH6-118204 awarded by Orion. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to power input circuits, and more particularly relates to isolated dual bus power input circuits that are single fault tolerant. 
       BACKGROUND OF THE INVENTION 
       [0003]    In aerospace applications, efficiency and reliability are important factors in designing electronic systems. That is, an ideal electronic system includes features that enable the electronic system to be light weight and consume a minimal amount of power, while also providing features that enable the electronic system to operate in the unlikely event of a partial system malfunction. 
         [0004]      FIG. 1  is a schematic diagram of a prior art electronic system  100  having a plurality of power sources  105 ,  110  connected to an electronic device  115  via an input circuit  120  having a high side isolation, dual bus configuration. 
         [0005]    In aerospace applications, power sources  105 ,  110  are typically 28 volt power supplies. In other applications, power sources  105 ,  110  may provide a greater or smaller amount of voltage. 
         [0006]    Electronics device  115  may be, for example, a line-replaceable unit (LRU) including a load  1152 . Examples of an LRU include, but are not limited to, a radio, a global positioning system (GPS), a radar system, and the like auxiliary devices. As discussed above, electronic device  115  is connected to power sources  105 ,  110  via input circuit  120 . 
         [0007]    Input circuit  120  includes a primary bus  122  having an input line  1222  and a return line  1224  connecting power source  105  to load  1152 . Input line  1222  includes a diode  1226  having an anode connected to the positive terminal of power supply  105  and a cathode connected to a node  1228 , which is connected to the input (V in ) terminal of load  1152 . Return line  1224  connects the negative terminal of power source  105  to the return (RTN) terminal of load  1152 . 
         [0008]    Input circuit  120  further includes a secondary (or redundant) bus  132  having an input line  1322  and a return line  1324  connecting power source  110  to load  1152 . Input line  1322  includes a diode  1326  connected to the positive terminal of power supply  110  and a cathode connected to node  1228 . Return line  1324  connects the negative terminal of power source  110  to the RTN terminal of load  1152 . 
         [0009]      FIG. 2  is a schematic diagram of a prior art electronic system  200  having a plurality of power sources  205 ,  210  connected to an electronic device  215  via an input circuit  220  having a high/low side isolation, dual bus configuration. In the design illustrated in  FIG. 2 , power sources  205 ,  210  and electronic device  215  (including load  2152 ) are similar to power sources  105 ,  110  and electronic device  115  (and load  1152 ), respectively, discussed above with reference to  FIG. 1 . The difference between system  100  and system  200  is that input circuit  120  has a high side isolation, dual bus configuration while input circuit  220  has a high/low side isolation, dual bus configuration. 
         [0010]    Input circuit  220  includes a primary bus  222  having an input line  2222  and a return line  2224  connecting power source  205  to load  2152 . Input line  2222  includes a diode  2226  having an anode connected to the positive terminal of power supply  205  and a cathode connected to a node  2228 , which is connected to the V in  terminal of load  2152 . 
         [0011]    Similar to return line  1224  in  FIG. 1 , return line  2224  connects the negative terminal of power source  205  to the RTN terminal of load  2152 . However, in contrast to return line  1224 , return line  2224  includes a diode  2250  having an anode connected to the RTN terminal of load  2152  and a cathode connected to the negative terminal of power source  205 . 
         [0012]    Input circuit  220  further includes a secondary (or redundant) bus  232  having an input line  2322  and a return line  2324  connecting power source  210  to load  2152 . Input line  2322  includes a diode  2326  having an anode connected to the positive terminal of power supply  210  and a cathode connected to node  2228 . 
         [0013]    Similar to return line  1324  in  FIG. 1 , return line  2324  connects the negative terminal of power source  210  to the RTN terminal of load  2152 . However, in contrast to return line  1324 , return line  2324  includes a diode  2336  having a cathode connected to the negative terminal of power supply  210  and an anode connected to the RTN terminal of load  2152 . 
         [0014]    While input circuits  120  and  220  are each fully capable of performing the functionality of their respective designs, input circuits  120  and  220  are heavier than they should be and consume more power than they should consume. Accordingly, it is desirable to provide single fault tolerant isolated dual bus power input circuits that consume less power than previous input circuits. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    Various embodiments provide input circuits for an electronic device configured to be coupled to a plurality of power sources. One input circuit comprises a first bus configured to be coupled to a first power source. The first bus includes a first input line and a first return line, and the first input line or the first return line comprises a first switch. The input circuit further comprises a second bus configured to be coupled to a second power source. The second bus includes a second input line and a second return line, and the second input line or the second return line comprises a second switch and a third switch coupled in series. 
         [0016]    Various embodiments also provide electronic systems. One system comprises a first power source including a first positive terminal and a first negative terminal, a second power source including a second positive terminal and a second negative terminal, an electronic device including an input terminal and a return terminal, and an input circuit coupling the electronic device to the first power source and the second power source. The input circuit comprises a first bus comprising a first input line coupling the input terminal and the first positive terminal, a first switch coupled between the input terminal and the first positive terminal, and a first return line coupling the return terminal and the first negative terminal. The input circuit further comprises a second bus comprising a second input line coupling the input terminal and the second positive terminal, a second switch and a third switch coupled in series between the input terminal and the second positive terminal, and a second return line coupling the return terminal and the second negative terminal. 
         [0017]    Another system comprises a plurality of power sources, an electronic device, and an input circuit coupling the electronic device to the plurality of power sources. The input circuit comprises a plurality of input lines, each input line coupling the electronic device to a respective power source and comprising a switch coupled between the electronic device and the respective power source. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0019]      FIG. 1  is a schematic diagram of a prior art electronic system having a plurality of power sources connected to an electronic device via a high side isolation, dual bus power input circuit; 
           [0020]      FIG. 2  is a schematic diagram of a prior art electronic system having a plurality of power sources connected to an electronic device via a high/low side isolation, dual bus power input circuit; 
           [0021]      FIG. 3  is a schematic diagram an electronic system comprising a plurality of power sources coupled to an electronic device via a high side isolation, dual bus power input circuit in accordance with one embodiment of the present invention; 
           [0022]      FIG. 4  is a schematic diagram an electronic system comprising a plurality of power sources coupled to an electronic device via a high/low side isolation, dual bus power input circuit in accordance with another embodiment of the present invention; 
           [0023]      FIGS. 5A-5G  are schematic diagrams illustrating the operation of the electronic systems of  FIG. 4 ; 
           [0024]      FIG. 6  is a schematic diagram a specific embodiment of the electronic system of  FIG. 3 ; and 
           [0025]      FIG. 7  is a schematic diagram a specific embodiment of the electronic system of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
         [0027]    Various embodiments of the present invention provide an electronic system comprising an improved high side isolation, dual bus power input circuit. Various other embodiments provide an electronic system comprising an improved high/low side isolation, dual bus power input circuit. 
         [0028]    Turning now to the figures,  FIG. 3  is a schematic diagram of an electronic system  300  including a plurality of power sources  305 ,  310  coupled to an electronic device  315  via an input circuit  320  including a high side isolation, dual bus configuration. System  300  also includes a switch controller  325  coupled to input circuit  320  and configured to control the ON/OFF state of one or more switches (discussed below) included in input circuit  320 . 
         [0029]    In the embodiment illustrated in  FIG. 3 , power sources  305 ,  310  and electronic device  315  (including load  3152 ) are similar to power sources  105 ,  110  and electronic device  115  (and load  1152 ), respectively, discussed above with reference to  FIG. 1 . Among other elements, one difference between system  100  and system  300  is that input circuit  120  uses diodes  1226  and  1326  for high side isolation and input circuit  320  uses switches  3226 ,  3326 , and  3350  for high side isolation. 
         [0030]    Input circuit  320  includes a primary bus  322  including a return line  3224  and an input line  3222  coupling power source  305  to load  3152 . Specifically, return line  3224  couples the negative terminal of power source  305  to the RTN terminal of load  3152  and input line  3222  couples the positive terminal of power source  305  to the V in  terminal of load  3152 . 
         [0031]    Input line  3222  includes switch  3226  coupled to the positive terminal of power supply  305  and to a node  3228 , which is connected to the V in  terminal of load  3152 . 
         [0032]    Switch  3226  may be any type of semiconductor switch known in the art or developed in the future. In one embodiment, switch  3226  is an N-channel metal oxide semiconductor field-effect transistor (MOSFET). In another embodiment, switch  3226  is a P-channel MOSFET. In yet another embodiment, switch  3226  is an insulated gate bipolar junction transistor (IGBT). In still another embodiment, switch  3226  is a bipolar junction transistor. 
         [0033]    Input circuit  320  further includes a secondary (or redundant) bus  332  comprising a return line  3324  and an input line  3322  coupling power source  310  to load  3152 . Specifically, return line  3324  couples the negative terminal of power source  310  to the RTN terminal of load  3152  and input line  3322  couples the positive terminal of power source  310  to the V in  terminal of load  3152 . 
         [0034]    Input line  3322  includes switch  3326  coupled in series with switch  3350 , which coupled to the positive terminal of power supply  310 . Switches  3326  and  3350  may be any type of semiconductor switch known in the art or developed in the future. In one embodiment, switches  3326  and  3350  are N-channel MOSFETs. In another embodiment, switch  3326  and  3350  are P-channel MOSFETs. In yet another embodiment, switches  3326  and  3350  are IGBTs. In still another embodiment, switches  3326  and  3350  are bipolar junction transistors. 
         [0035]    Switch controller  325  may be any system, device, hardware (and software), and combinations thereof capable of controlling the ON/OFF state of switches  3226 ,  3326 , and  3350 . That is, switch controller  325  is configured to switch ON/OFF switches  3226 ,  3326 , and  3350  in accordance with the operation of system  300 . 
         [0036]    During operation, when system  300  is working properly switch  3226  is ON and switches  3326  and  3350  are both OFF such that power source  305  provides power to electronic device  315 . In the unlikely event that power source  305  and/or primary bus  322  malfunctions, switches  3326  and  3350  both turn ON, and switch  3226  turns OFF such that power source  310  provides power to electronic device  315 . In this manner, system  300  ensures that power is supplied to electronic device  315  and that the high side of input circuit  320  is isolated. Furthermore, because input circuit  320  uses switches  3226  and  3326  for high side isolation, input circuit  320  consumes less power and is lighter in weight because lower power dissipation means a smaller heat sink needed than previous input circuits. 
         [0037]      FIG. 4  is a schematic diagram of an electronic system  400  having a plurality of power sources  405 ,  410  coupled to an electronic device  415  via an input circuit  420  including a high/low side isolation, dual bus configuration. System  400  also includes a switch controller  425  coupled to input circuit  420  and configured to control the ON/OFF state of one or more switches (discussed below) included in input circuit  420 . 
         [0038]    In the embodiment illustrated in  FIG. 4 , power sources  405 ,  410  and electronic device  415  (including load  4152 ) are similar to power sources  205 ,  210  and electronic device  215  (and load  2152 ), respectively, discussed above with reference to  FIG. 2 . Among other elements, one difference between system  200  and system  400  is that input circuit  220  uses diodes  2226 ,  2250 ,  2326 , and  2336  for high/low side isolation and input circuit  420  uses switches  4226 ,  4250 ,  4326 ,  4336 ,  4350 , and  4360  for high/low side isolation. 
         [0039]    Input circuit  420  includes a primary bus  422  including a return line  4224  and an input line  4222  coupling power source  405  to load  4152 . Return line  4224  connects the negative terminal of power source  405  to the RTN terminal of load  4152  and includes a switch  4250 . 
         [0040]    Switch  4250  may be any type of semiconductor switch known in the art or developed in the future. In one embodiment, switch  4250  is an N-channel MOSFET. In another embodiment, switch  4250  is a P-channel MOSFET. In yet another embodiment, switch  4250  is an IGBT. In still another embodiment, switch  4250  is a bipolar junction transistor. 
         [0041]    Input line  4222  includes switch  4226  coupled to the positive terminal of power supply  405  and to a node  4228 , which is connected to the V in  terminal of load  4152 . Switch  4226  may be any type of semiconductor switch known in the art or developed in the future. In one embodiment, switch  4226  is an N-channel MOSFET. In another embodiment, switch  4226  is a P-channel MOSFET. In yet another embodiment, switch  4226  is a PNP IGBT. In still another embodiment, switch  4226  is an NPN IGBT 
         [0042]    Input circuit  420  further includes a secondary (or redundant) bus  432  comprising a return line  4324  and an input line  4322  coupling power source  410  to load  4152 . That is, return line  4324  connects the negative terminal of power source  410  to the RTN terminal of load  4152 . Specifically, return line  4324  comprises a switch  4336  coupled to the RTN terminal of load  4152 . Switch  4336  is further coupled in series with a switch  4360  that is coupled to the negative terminal of power supply  410 . 
         [0043]    Switches  4336  and  4360  may be any type of semiconductor switch known in the art or developed in the future. In one embodiment, switches  4336  and  4360  are N-channel MOSFETs. In another embodiment, switch  4336  and  4360  are P-channel MOSFETs. In yet another embodiment, switches  4336  and  4360  are IGBTs. In still another embodiment, switches  4336  and  4360  are bipolar junction transistors. 
         [0044]    Input line  4322  connects the positive terminal of power source  410  to node  4228 , which is coupled to the V in  terminal of load  4152 . Specifically, input line  4322  comprises switch  4326  coupled to node  4228 . Switch  4326  is further coupled in series with switch  4350  that is coupled to the positive terminal of power supply  410 . 
         [0045]    Switches  4326  and  4350  may be any type of semiconductor switch known in the art or developed in the future. In one embodiment, switches  4326  and  4350  are N-channel MOSFETs. In another embodiment, switch  4326  and  4350  are P-channel MOSFETs. In yet another embodiment, switches  4326  and  4350  are IGBTs. In still another embodiment, switches  4326  and  4350  are bipolar junction transistors. 
         [0046]    Switch controller  425  may be any system, device, hardware (and software), and combinations thereof capable of controlling the ON/OFF state of switches  4226 ,  4250 ,  4326 ,  4336 ,  4350 , and  4360 . That is, switch controller  425  is configured to switch ON/OFF switches  4226 ,  4250 ,  4326 ,  4336 ,  4350 , and  4360  in accordance with the operation of system  400 . 
         [0047]    During operation, when system  400  is working properly switches  4226  and  4250  are both ON, and switches  4326 ,  4350 ,  4336 , and  4360  are each OFF such that power source  405  provides power to electronic device  415 . In the unlikely event that power source  405  and/or primary bus  422  malfunctions, switches  4326 ,  4350 ,  4336 , and  4360  each turn ON, and switches  4226  and  4250  are both turned OFF such that power source  410  provides power to electronic device  415 . In this manner, system  400  ensures that power is supplied to electronic device  415  and that the high side and low side of input circuit  420  are isolated. Furthermore, because input circuit  420  uses switches  4226 ,  4250 ,  4326 ,  4336 ,  4350 , and  4360  for high/low side isolation, input circuit  420  consumes less power and is lighter in weight because lower power dissipation means a smaller heat sink needed than previous input circuits. 
         [0048]      FIGS. 5A-5G  are schematic diagrams illustrating the isolating operation of electronic system  400 . That is, electronic system  400  ensures that power is no exchanged between primary bus  422  and secondary or redundant bus  432 . Specifically, switches  4226 ,  4250 ,  4326 ,  4336 ,  4350 , and  4360  are configured in a manner the prevents connection between primary bus  422  and secondary bus  432  if a fault occurs on any one device on primary bus  422  or secondary bus  432 . 
         [0049]    Notably, one skilled in the art will appreciate that the discussion above with reference to  FIGS. 5A-5G  are also applicable to electronic system  300 , and electronic systems  600  and  700 , each of which is discussed below. Furthermore, for discussion purposes, only the diode portion of switches  4226 ,  4250 ,  4326 , and  4336  are illustrated in  FIGS. 5A-5G . 
         [0050]      FIG. 5A  illustrates the isolating operation of electronic system  400  when electronic system  400  is functioning properly. In  FIG. 5A , switch  4350  and/or  4360  are switched OFF (i.e., open) such that there is no connection between primary bus  422  and secondary bus  432 . That is, with switch  4350  and/or  4630  turned OFF, there is no power exchange between primary bus  422  and secondary bus  432 . 
         [0051]      FIG. 5B  illustrates the situation in which there is a short (i.e., fault  1 ) or other type of malfunction in switch  4226 . In this situation, secondary bus  432  cannot be driven by primary bus  422  because switch  4350  and/or switch  4360  being turned OFF breaks any connection (e.g., power exchange) between primary bus  422  and secondary bus  432 . 
         [0052]      FIG. 5C  illustrates the situation in which there is a short (i.e., fault  2 ) or other type of malfunction in switch  4250 . Similar to the situation illustrated in  FIG. 5B , secondary bus  432  cannot be driven by primary bus  422  because switch  4350  and/or switch  4360  being turned OFF breaks any connection (e.g., power exchange) between primary bus  422  and secondary bus  432 . 
         [0053]      FIG. 5D  illustrates the situation in which there is a short (i.e., fault  3 ) or other type of malfunction in switch  4326 . Similar to the situation illustrated in  FIGS. 5B and 5C , secondary bus  432  cannot be driven by primary bus  422  because switch  4350  and/or switch  4360  being turned OFF breaks any connection (e.g., power exchange) between primary bus  422  and secondary bus  432 . 
         [0054]      FIG. 5E  illustrates the situation in which there is a short (i.e., fault  4 ) or other type of malfunction in switch  4336 . Similar to the situation illustrated in  FIGS. 5B-5D , secondary bus  432  cannot be driven by primary bus  422  because switch  4350  and/or switch  4360  being turned OFF breaks any connection (e.g., power exchange) between primary bus  422  and secondary bus  432 . 
         [0055]      FIG. 5F  illustrates the situation in which there is a short (i.e., fault  5 ) or other type of malfunction in switch  4350 . In this situation, secondary bus  432  cannot be driven by primary bus  422  because switch  4360  being turned OFF creates an open circuit that breaks any connection (e.g., power exchange) between primary bus  422  and secondary bus  432 . 
         [0056]    Similarly,  FIG. 5G  illustrates the situation in which there is a short (i.e., fault  6 ) or other type of malfunction in switch  4360 . In this situation, secondary bus  432  cannot be driven by primary bus  422  because switch  4350  being turned OFF creates an open circuit that breaks any connection (e.g., power exchange) between primary bus  422  and secondary bus  432 . 
         [0057]      FIG. 6  is a schematic diagram of an electronic system  600  including a plurality of power sources  605 ,  610  coupled to an electronic device  615  via an input circuit  620  including a high side isolation, dual bus configuration. System  600  also includes a switch controller  625  coupled to input circuit  620  and configured to control the ON/OFF state of one or more switches (discussed below) included in input circuit  620 . 
         [0058]    In the embodiment illustrated in  FIG. 6 , power sources  605 ,  610  and electronic device  615  (including load  6152 ) are similar to power sources  105 ,  110  and electronic device  115  (and load  1152 ), respectively, discussed above with reference to  FIG. 1 . Among other elements, one difference between system  100  and system  600  is that input circuit  120  uses diodes  1226  and  1326  for high side isolation and input circuit  620  uses switches  6226  and  6326  for high side isolation. 
         [0059]    Input circuit  620  includes a primary bus  622  including a return line  6224  and an input line  6222  coupling power source  605  to load  6152 . Specifically, return line  6224  couples the negative terminal of power source  605  to the RTN terminal of load  6152  and input line  6222  couples the positive terminal of power source  605  to the V in  terminal of load  6152 . 
         [0060]    Input line  6222  includes switch  6226  coupled to the positive terminal of power supply  605  and to a node  6228 , which is connected to the V in  terminal of load  6152 . In the embodiment illustrated in  FIG. 6 , switch  6226  is an N-channel metal oxide semiconductor field-effect transistor (MOSFET) device including a source coupled to the positive terminal of power supply  605  and a drain coupled to node  6228 . 
         [0061]    Input circuit  620  further includes a secondary (or redundant) bus  632  comprising a return line  6324  and an input line  6322  coupling power source  610  to load  6152 . Specifically, return line  6324  couples the negative terminal of power source  610  to the RTN terminal of load  6152  and input line  6322  couples the positive terminal of power source  610  to the V in  terminal of load  6152 . 
         [0062]    Input line  6322  includes a switch  6326  coupled in series with a switch  6350  that is coupled to the positive terminal of power supply  610 . In the embodiment illustrated in  FIG. 6 , switches  6326  and  6350  are both N-channel MOSFET devices with their sources serially coupled to one another. The drain of switch  6350  is coupled to the positive terminal of power supply  610  and the drain of switch  6326  is coupled to node  6228 . 
         [0063]    Switch controller  625  may be any system, device, hardware (and software), and combinations thereof capable of controlling the ON/OFF state of switches  6226 ,  6326 , and  6350 . That is, switch controller  625  is configured to switch ON/OFF switches  6226 ,  6326 , and  6350  in accordance with the operation of system  600 . 
         [0064]    During operation, when system  600  is working properly switch  6226  is ON and switches  6326  and  6350  are both OFF such that power source  605  provides power to electronic device  615 . In the unlikely event that power source  605  and/or primary bus  622  malfunctions, switches  6326  and  6350  both turn ON, and switch  6226  turns OFF such that power source  610  provides power to electronic device  615 . In this manner, system  600  ensures that power is supplied to electronic device  615  and that the high side of input circuit  620  is isolated. Furthermore, because input circuit  620  uses switches  6226  and  6326  for high side isolation, input circuit  620  consumes less power and is lighter in weight than previous input circuits. 
         [0065]      FIG. 7  is a schematic diagram of an electronic system  700  having a plurality of power sources  705 ,  710  coupled to an electronic device  715  via an input circuit  720  including a high/low side isolation, dual bus configuration. System  700  also includes a switch controller  725  coupled to input circuit  720  and configured to control the ON/OFF state of one or more switches (discussed below) included in input circuit  720 . 
         [0066]    In the embodiment illustrated in  FIG. 7 , power sources  705 ,  710  and electronic device  715  (including load  7152 ) are similar to power sources  205 ,  210  and electronic device  215  (and load  2152 ), respectively, discussed above with reference to  FIG. 2 . Among other elements, one difference between system  200  and system  700  is that input circuit  220  uses diodes  2226 ,  2250 ,  2326 , and  2336  for high/low side isolation and input circuit  720  uses switches  7226 ,  7250 ,  7326 ,  7336 ,  7350 , and  7360  for high/low side isolation. 
         [0067]    Input circuit  720  includes a primary bus  722  including a return line  7224  and an input line  7222  coupling power source  705  to load  7152 . Return line  7224  connects the negative terminal of power source  705  to the RTN terminal of load  7152  and includes switch  7250 . In the embodiment illustrated in  FIG. 7 , switch  7250  is an N-channel MOSFET device including a source coupled to the negative terminal of power source  705  and a drain coupled to the RTN terminal of load  7152 . 
         [0068]    Input line  7222  includes switch  7226  coupled to the positive terminal of power supply  705  and to a node  7228 , which is connected to the V in  terminal of load  7152 . In the embodiment illustrated in  FIG. 7 , switch  7226  is an N-channel MOSFET device including a source coupled to the positive terminal of power supply  705  and a drain coupled to node  7228 . 
         [0069]    Input circuit  720  further includes a secondary (or redundant) bus  732  comprising a return line  7324  and an input line  7322  coupling power source  710  to load  7152 . That is, return line  7324  connects the negative terminal of power source  710  to the RTN terminal of load  7152 . Specifically, return line  7324  comprises switch  7336  coupled to the RTN terminal of load  7152 . Switch  7336  is further coupled in series with switch  7360 , which is coupled to the positive terminal of power supply  710 . 
         [0070]    In the embodiment illustrated in  FIG. 7 , switches  7360  and  7336  are serially coupled via the drain of switch  7360  and the source of switch  7336 . The source of switch  7360  is coupled to the negative terminal of power source  710 , and the drain of switch  7336  is coupled to the RTN terminal of load  7152 . 
         [0071]    Input line  7322  connects the positive terminal of power source  710  to node  7228 , which is coupled to the V in  terminal of load  7152 . Specifically, input line  7322  comprises switch  7326  coupled to node  7228 . Switch  7326  is further coupled in series with switch  7350 , which is coupled to the positive terminal of power supply  710 . 
         [0072]    In the embodiment illustrated in  FIG. 7 , switches  7350  and  7326  are serially coupled via their respective sources. The drain of switch  7350  is coupled to the positive terminal of power source  710 , and the drain of switch  7326  is coupled to node  7228 . 
         [0073]    Switch controller  725  may be any system, device, hardware (and software), and combinations thereof capable of controlling the ON/OFF state of switches  7226 ,  7250 ,  7326 ,  7336 ,  7350 , and  7360 . That is, switch controller  725  is configured to switch ON/OFF switches  7226 ,  7250 ,  7326 ,  7336 ,  7350 , and  7360  in accordance with the operation of system  700 . 
         [0074]    During operation, when system  700  is working properly switches  7226  and  7250  are both ON, and switches  7326 ,  7350 ,  7336 , and  7360  are each OFF such that power source  705  provides power to electronic device  715 . In the unlikely event that power source  705  and/or primary bus  722  malfunctions, switches  7326 ,  7350 ,  7336 , and  7360  each turn ON, and switches  7226  and  7250  are both turned OFF such that power source  710  provides power to electronic device  715 . In this manner, system  700  ensures that power is supplied to electronic device  715  and that the high side and low side of input circuit  720  are isolated. Furthermore, because input circuit  720  uses switches  7226 ,  7250 ,  7326 ,  7336 ,  7350 , and  7360  for high/low side isolation, input circuit  720  consumes less power and is lighter in weight than previous input circuits. 
         [0075]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.