Abstract:
A programmable fuse and fuse panel are described. Unlike conventional fuses and fuse panels, the trip values of the fuses of the panel—i.e., the current values at which the fuse trips—are field programmable. One of many advantages includes the ability to adaptively set the trip value of a fuse—depending on the operating needs of a load device—without having to physically exchange the fuse. In an embodiment, electronic fuses are used.

Description:
RELATED APPLICATION 
     This application claims priority to the provisional application 60/875,853 entitled “AUTOMATIC FUNCTION WITH SELECTABLE FUSE RATING FOR SINGLE FUSES AND FUSE PANELS” filed on Dec. 20, 2006, the content of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The technical field of this disclosure generally relates to providing fuse and fuse panels that are field programmable. Some embodiments of the field programmable fuses and fuse panels are based on electronic fuses. 
     BACKGROUND 
     In a typical power distribution system, such as for residential homes, a fuse panel with a number of fuses are used. The trip value of each fuse is selected to protect each load device connected to the fuse. When a new load device is to be connected to the panel, a free fuse with a proper trip value for the new load device is selected. 
     Fuse panels of today are based on a number of different technologies such as melting wire types, heat activated types and electronic types. No matter the type, the fuse “trips” or breaks the circuit to the load device when the current provided to the load device exceeds the trip value. 
       FIG. 12  illustrates a conventional fuse panel  1200  that includes a plurality of individual fuses  1210 . In this particular example, there are six (6) fuses  1210  with differing trip values. The first two fuses have the trip values set at 2 amperes (or 2 A), the second 2 fuses have their trip value set at 5 A and the third set of fuses have their trip value set at 10 A. Each fuse provides power from an external power source  1240  to the respective load devices  1250 . 
     The fuses  1210  can be electronic type fuses.  FIG. 13  illustrates a conventional electronic fuse  1210 . The conventional electronic fuse  1210  includes an electronic switch  1310  coupled to a shunt  1330  to deliver power from the external source connected at input  1212  (see also  FIG. 12 ) to the load device connected at output  1214 . The electronic fuse  1210  also includes a voltage comparator  1320  that measures a voltage drop across the shunt  1330 . The voltage drop across the shunt  1330  is related to an amount of current flowing through the shunt  1330  to the load device  1250 . If the voltage drop across the shunt  1330  is at or above a threshold level, the comparator  1320  outputs a signal to the electronic switch  1310  to turn off. By setting the threshold voltage, an appropriate trip value is set for the electronic fuse  1210 . 
     A major disadvantage with the conventional fuse and fuse panels is that the trip value of each fuse must be determined during the production of the panel and remains fixed. For electronic fuses such as those illustrated in  FIG. 13 , threshold voltage is fixed during the production. This requires that each panel be tailored for a number of load devices at specific current values. This creates a problem when a new load device is desired to be added but there is no free fuse available with the correct trip values. Referring back to  FIG. 12 , it is seen that both 2 A fuses are already occupied. If another 2 A load device is desired to be connected, it will impossible with the conventional fuse panel. This is despite the fact that there are fuses with other trip values available such as the 5 A and 10 A fuses. 
     Conventionally, this problem can be addressed by rebuilding the panel or by adding a new panel altogether. Both of these solutions are inefficient and costly. 
     SUMMARY 
     In an example embodiment, a field programmable fuse includes an electronic fuse. The electronic fuse is configured to deliver a load current from an external source to a load device. The electronic fuse comprises one or more field selectable trip value inputs such that a trip value of the electronic fuse is set based on values applied to the selectable trip value inputs. When an amount of the load current delivered to the load device exceeds the trip value set for the electronic fuse, the electronic fuse is configured to cease delivering the load current to thereby protect the load device. 
     The electronic fuse can include a shunt, a comparator, and an electronic switch. The shunt or the comparator can be variable—i.e., field programmable. The shunt delivers the load current from an external source to the load device, the comparator measures a voltage drop across the shunt, and the electronic switch switches ON and OFF the delivery of the load current from the external source to the shunt. When the voltage drop across the shunt is above or substantially at a predetermined threshold, the voltage comparator outputs a TURN OFF signal to the electronic switch. Upon receipt of the TURN OFF signal from the voltage comparator, the electronic switch switches OFF the delivery of the load current. 
     In an embodiment, the shunt is a variable shunt that is configured to vary its impedance value based on the trip value set for the electronic fuse. In a variant of the embodiment, the programmable fuse includes a trip controller which controls the impedance value of the variable shunt based on inputs to the trip value inputs. 
     The variable shunt can include a plurality of shunt devices and a plurality of bypass gates. The plurality of bypass gates provide a capability to selectively bypass one or more of the shunt devices. The plurality of bypass gates are arranged to bypass different combinations of the plurality of shunt devices based on different trip value settings. The plurality of shunt devices can be arranged in series with each other, in parallel with each other, or in a combination of both. 
     In an embodiment, the comparator is a variable comparator  220  that is configured to measure a voltage drop across the shunt and to output the TURN OFF signal to the electronic switch  210  when the voltage drop across the shunt is above or substantially at a threshold voltage. In this embodiment, the threshold voltage is varied based on the trip value set for the electronic fuse. A trip value controller can be used to control the threshold voltage level. 
     The electronic fuse can also include a voltage divider, which can be variable—i.e., field programmable. The variable voltage divider outputs a divided voltage. The divided voltage output by the variable voltage divider is a portion of the voltage drop across the shunt. The portion of the voltage drop output as the divided voltage is based on the trip value set for the electronic fuse. A trip value controller can be used to control the portion of the voltage drop output as the divided voltage based on the trip value set for the electronic fuse. 
     The voltage divider can include a first impedance group and second impedance group in series with each other. The impedance group has a first impedance value and the second impedance group has a second impedance value. The voltage drop across the shunt is divided between the first and second impedance groups. Either the voltage drop over the first impedance group or the second impedance group is output as the divided voltage. 
     The comparator outputs the TURN OFF signal to the electronic switch  210  when the divided voltage is above or substantially at a predetermined threshold. Upon receipt of the TURN OFF signal from the voltage comparator, the electronic switch switches OFF the delivery of the load current. One or both of the first and second impedance groups can vary their impedance values based on the trip value set for the electronic fuse. 
     One or both impedance groups can include a plurality of impedance devices and a plurality of bypass gates to provide a capability to selectively bypass one or more of the plurality of impedance devices. The plurality of bypass gates are arranged to bypass different combinations of the plurality of impedance devices based on different trip value settings. The impedance devices can be connected in series, in parallel, or a combination of both. 
     In an embodiment, the field programmable fuse can include a programming connector. The programming director includes one or more programming pins coupled to the field selectable trip value inputs of the electronic fuse. Each programming pin is field settable—i.e., field programmable—to take on one of a plurality of electrical values. The trip value of the electronic fuse is determined by a combination of the electrical values set on the programming pins. 
     The electrical values can be any one of electrically open, ground, power, and one or more voltage values other than the ground and the power. The programming connector can include at least one impedance device coupled to a programming pin such that the electrical value of the coupled programming pin is set to be a voltage other than the ground and the power. The impedance devices can be connected to ground or to the power. 
     In an embodiment, the load device can be connected to the electronic fuse or via the programming connector. 
     In an embodiment, multiple programmable fuses can be arranged to form a fuse panel. The fuse panel can include a combination of programmable fuses and fixed fuses. The programmable fuses can be programmed simultaneously. 
     In an embodiment, the trip value inputs are physically spaced apart from each other and the load device can include a load select blade with differing physical sizes such that when inserted, one or more of the trip value inputs come into physical contact with the load select blade. The combination of the trip value inputs that come into contact with the load select blade determines the trip value of the electronic fuse. The load select blade can be integrated into a single physical piece with a load input of the load device or with the power output of the electronic fuse. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIGS. 1A and 1B  illustrate example embodiments of field programmable fuses; 
         FIGS. 2A ,  2 B and  2 C illustrate example embodiments of electronic fuses with variable (field programmable) shunts, comparators and voltage dividers, respectfully; 
         FIGS. 3A and 3B  illustrate example implementations of the variable shunts; 
         FIGS. 4A and 4B  illustrate example embodiments of voltage dividers that include a plurality of impedance groups; 
         FIGS. 5A and 5B  illustrate example implementations of the impedance groups; 
         FIGS. 6-9  illustrate example embodiments of programming connectors including programming pins that are set to various electrical values to set the trip value of the programmable fuse; 
         FIG. 10  illustrates an example embodiment of a fuse panel; 
         FIG. 11  illustrates an example embodiment of a mechanical implementation of a fuse panel setup; 
         FIG. 12  illustrates a conventional fuse panel; and 
         FIG. 13  illustrates a conventional electronic fuse. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. That is, those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. 
     In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
     Thus, for example, it will be appreciated by those skilled in the art that block diagrams herein can represent conceptual views of illustrative circuitry embodying the principles of the technology. Similarly, it will be appreciated that any flow charts, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 
     Modifying the trip value—a value of current at which a fuse trips—for an electronic fuse may be done in several ways. These include bypassing parts of the shunt and bypassing parts of the signal that is connected to the comparator. Another way is to use programming pins as inputs to a programming controller to modify the trip value of the electronic fuse. 
       FIGS. 1A and 1B  illustrate example embodiments of field programmable fuses  100 . In other words, the trip values of the programmable fuses  100  are not fixed upon production, but can be programmed in the field—that is, after production-many times over as the need arises. The field programmable fuses  100  can be tailored for AC only, for DC only, or for a combination of AC and DC systems. 
     In the example embodiments illustrated in  FIGS. 1A and 1B , the field programmable fuse  100  includes an electronic fuse  110 . The electronic fuse  110  is configured to provide power from an external source coupled to its power input  116  to a load device  130  that is coupled to its power output  112 . The electronic fuse  110  also includes one or more field selectable trip value inputs  115  such that the trip value of the electronic fuse  110  is set based on the values applied to the field selectable trip value inputs  115 . 
     Inputs to the trip value inputs  115  may be provided directly. Optionally, the programmable fuse  100  may also include a programming connector  120  with programming pins  135  connected to the trip value inputs  115 . The program connector  120  can make the process of selecting the trip value easier and less error prone. 
     The load device  130  may be connected directly to the electronic fuse  110  as illustrated in  FIG. 1B  or through the program connector  120  as illustrated in  FIG. 1A . When connected through the program connector  120  as in  FIG. 1A , the number of trip value inputs  115  may be reduced as will be demonstrated later. 
       FIG. 2A  illustrates an example embodiment of the electronic fuse  110 . The electronic fuse  110  includes an electronic switch  210  and a variable shunt  230  configured to deliver power from the external source coupled to the power input  116  to the load device  130  coupled to the power output  112 . The electronic fuse  110  also includes a comparator  220  coupled to the variable shunt  230  and is configured to measure a voltage drop across the variable shunt  230 . When the voltage drop across the variable shunt  230  is above or substantially at a pre-determined threshold, the voltage comparator  220  outputs a TURN OFF signal to the electronic switch  210 , at which the electronic switch  210  switches off the delivery of the load current. 
     In this particular embodiment, the variable shunt  230  (denoted by the angle sign) is configured to vary its impedance value based on the trip value settings provided at the trip value inputs  115 . By varying the impedance value of the variable shunt  230 , the trip value of the electronic fuse  110  is also varied. In this embodiment, the voltage drop across the variable shunt  230  is a product of the load current flowing through the variable shunt  230  and its impedance. If the impedance is lowered, the trip value is accordingly increased since the voltage drop across the variable shunt  230  is correspondingly lowered. Conversely, increasing the impedance of the variable shunt  230  decreases the trip value. 
       FIGS. 3A and 3B  illustrate example implementations of the variable shunt  230 . The variable shunt  230  includes a plurality of shunt devices  310  and a plurality of bypass gates  320 . The shunt devices  310  are operatively coupled to deliver the load current from the external source to the load device, and the bypass gates  320  are coupled to the plurality shunt devices  310  and provide a capability to selectively bypass one or more of the shunt devices  310 . While only two shunt devices  310  are illustrated in both  FIGS. 3A and 3B , it is to be noted that any number of shunt devices may be utilized. Similarly, the number of bypass gates  320  are not limited to the illustrated example implementations. 
     In  FIG. 3A , the plurality of devices  310  are connected in series. To provide selective bypassing capabilities, the plurality of bypass gates  320  are provided. By selectively activating gates  235  of the bypass gates  320 , an electrical pathway may be made to bypass either of shunt devices  310   1  or  310   2 . For proper operation, the load current from input  237  should pass through at least one of the shunt devices  310   1  and  310   2 . 
     For maximum flexibility, it is preferred that the impedances of each shunt device  310  be different. For example, the first shunt device  310   1  may have an impedance value of 1Ω and the second shunt device  310   2  may have an impedance value of 2Ω. With selective bypassing through activating different combinations of the bypass gates, different total impedance values for the variable shunt  230  may be achieved. 
     As an example, the load current may be made to flow only through the first shunt device  310   1  by deactivating the first bypass gate  320   1  and activating second and third bypass gates  320   2  and  320   3 . As another example, the load current may be made to flow only through the second shunt device  310   2  by activating first and second bypass gates  320   1  and  320   2  and deactivating the third bypass gate  320   3 . Finally, the low current may be made to flow through both first and second shunt devices  310   1  and  310   2  by deactivating the first and third bypass gates  320   1  and  320   3 . 
     The plurality of shunt devices  310  may also be coupled in parallel with each other as illustrated in  FIG. 3B . In this implementation, the total impedance of the variable shunt  230  can be achieved by activating/deactivating different combinations of the bypass gates  320   1  and  320   2 . 
     While  FIGS. 3A and 3B  illustrated series implementation and parallel implementation in isolation, having a combination of both fall within the scope of the disclosure. Also, having any number of shunt devices  310  and bypass gates  320  fall within the scope of the disclosure. 
     Referring back to  FIG. 2A , it is shown that the trip value inputs  115  may be provided directly to the inputs  235  of the variable shunts  230 . In an alternative, the electronic fuse  110  may include a trip value controller  270  which takes as inputs the values set on the trip value inputs  115  and outputs control signals to the inputs  235  of the variable shunt  230 . An advantage of the trip value controller  270  is that it can minimize the number of trip value inputs  115  that are required to interface with an external programming controller while providing a fine granularity of trip value settings within the electronic fuse  110 . 
     For explanation purposes,  FIG. 3A  shows three bypass gates  320  that can be individually activated to bypass either the first or the second shunt device  310   1  or  310   2 . If the gate inputs  235  of the bypass gate  320  are directly coupled to the trip value inputs  115 , then three trip value inputs  115  will be required. However, referring back to  FIG. 2A , if the inputs  235  are connected to the trip value controller  270 , then only two trip value inputs  115  will be required assuming that the trip value inputs  115  take on a binary signal. This is because there are only three combinations possible in  FIG. 3A . If the trip value input  115  can take on more than two electrical values—such as power, ground and some intermediate value—then the number of trip value input  115  can be reduced to one for both  FIGS. 3A and 3B . 
     In addition to or instead of the variable shunt  230 , the field programming capability may be provided by the variable comparator  220  as illustrated in  FIG. 2B . In this embodiment, the comparator  220  is variable in a sense that the threshold voltage at which the TURN OFF signal is provided is varied according to the trip value set based on the inputs provided to the trip value inputs  115 . If it is desired to increase the trip value, the threshold voltage may be increased. If it is desired to decrease the trip value, then the threshold voltage may be decreased. 
     The trip value inputs  115  may be provided directly to the variable comparator  220  via the comparator inputs  225  as shown in  FIG. 2B , or may be provided through the trip value controller  270  as understood from the previous description. 
     In both  FIGS. 2A and 2B , the comparator  220  outputs the TURN OFF signal based on the threshold voltage drop across the whole of the shunt  230 . In another embodiment, a variable voltage divider  240  may be provided as illustrated in  FIG. 2C . The variable voltage divider  240  provides a divided voltage to the comparator  220 . The voltage divider  240  outputs a portion of the voltage drop measured across the shunt  230  as the divided voltage. By varying the divided voltage output—that is by varying the portion of the voltage drop across the shunt  230  that is output to the comparator  220  according to the inputs provided to the voltage divider inputs  245  through trip value inputs  115 —the trip value of the electronic fuse  110  may be selectively set. 
       FIGS. 4A and 4B  illustrate example implementations of the voltage divider  240 . In both embodiments, the voltage divider  240  includes first and second impedance groups  410  and  420  connected in series. The first impedance group  410  has a first impedance value and the second impedance group  420  has a second impedance value. Both the first and second impedance values  410 ,  420  can be varied based on the trip value settings. In  FIG. 4A , the voltage drop across the first impedance group is output as the divided voltage and in  FIG. 4B , the voltage drop across the second impedance group  420  is output as the divided voltage. 
     One or both of the impedance groups  410 ,  420  may be implemented as illustrated in  FIGS. 5A and 5B . The impedance groups include a plurality of impedance devices  510  along with a plurality of bypass gates  520  connected to selectively bypass the impedance devices  510 . The impedance devices  510  may be connected in series or in parallel with each other. It is also contemplated that various combinations of serial and parallel combinations are within the scope of the disclosure. The structure of the impedance groups  410 ,  420  are similar to the plurality of shunt devices  310  as illustrated in  FIGS. 3A and 3B . Thus, detailed description of the operations of the impedance groups will be omitted. 
     Again, the trip value controller  270  may be optionally provided to control the operations of the impedance groups  410 ,  420 . 
     Referring back to  FIGS. 1A and 1B , the programmable fuse  100  optionally includes the programming connector  120  coupled to the electronic fuse  110 . The programming connector  120  includes a plurality of programming pins  135  that are field settable to take on one of a plurality of electrical values. The trip value of the electronic fuse  110  is determined by a combination of the electrical values set on the programming pins  135 . 
     The electrical values can be any one of open (i.e., not connected), ground, power, and one or more voltage values other than the ground and the power.  FIGS. 6-9  illustrate various implementations of setting the electrical values to the programming pins  135 . In  FIGS. 6A-6D  for example, the programming pins  135  are set to take on one of two electrical values—connected to ground or open. Various combinations of the electrical values applied to the programming pins  135  determine the trip value setting. In  FIGS. 7A-7D , the programming pins may take on one of power or open. In  FIG. 8 , the programming pins may take on one of three values—open, connected to power and connected to ground.  FIG. 9  illustrates that intermediate voltages may also be provided by providing impedance devices  910  connected to either the ground or the power. Combining the features of  FIGS. 6A-6D ,  7 A- 7 D,  8  and  9  are within the scope of the disclosure. 
       FIG. 10  illustrates an embodiment of a fuse panel  1000 . The fuse panel  1000  includes a plurality of programmable fuses  100 . While not specifically shown, the fuse panel  1000  can also include one or more fixed fuses. The fuse panel  1000  is generic in that the trip values of the programmable fuses  100  are not fixedly set at the time of production. With this fuse panel, as long as there is a programmable fuse  100  available, another load device  130  may be added. Thus, the expense and difficulty associated with the conventional fuse panels are avoided. Each programmable fuse  100  can be individually programmed apart from other fuses. Also, a subset, that is two or more of the programmable fuses  100 , less than the whole, can be simultaneously field programmable. 
     The fuses  100  and the fuse panel  1000  can be implemented mechanically, for example, as a fuse panel connector implemented as an edge connector directly on a printed circuit board (PCB).  FIG. 11  illustrates an embodiment of this concept. On one side of the PCB  1160 , programming fingers  1130 ,  1140  are located. A plug is implemented as a blade  1110  on each side. The width of the blade  1110  determines the amount of current that can be used. 
     In  FIG. 11 , three blades  1110  of varying widths are illustrated. In general, the wider the blade width, the higher current than can be used. The trip value programming is performed by the blade  1110  connecting to the one or more programming fingers  1130  and  1140  to a power or to ground. In this embodiment, if the 10 A blade  1110   2  is connected, the programming finger  1130  is connected to the power  1120  (providing a signal to the “A” trip value input) while the programming finger  1140  is left unconnected (providing no signal to the “B” trip value input). When the 20 A blade  1110   3  is connected, both programming fingers are connected to power to provide signals to the “A” and “B” trip value inputs  115  of the electronic fuse  110 . Conversely, when a 5 A blade is connected, no programming finger are connected. This implementation has the advantage that an intuitive indication of the current setting is provided. 
     It should be noted that other connector alternatives are possible. For example, instead of being connected to power, the programming fingers  1130  and  1140  may be made to connect to a ground or some other voltage when a blade  1110  of proper width is connected depending on the application. The load select blade  1110  may be integrated into a single physical piece with a load input of the load device  130 . Alternatively, the load select blade  1110  may be integrated into a single physical piece with the power output  112  of the programmable fuse  100 . 
     Again referring back to  FIGS. 1A and 1B , the electronic fuse  110  can optionally include a reset (R/S) input  118  to provide a capability to reset the electronic fuse  110 . When the trip value of the electronic fuse  110  is exceeded, the electronic fuse  110  switches off. For example, the comparator  220  can output the TURN OFF signal to the electronic switch  210  in  FIGS. 2A-2C . When the R/S input  118  is activated under this type of a conditions, the electronic fuse  110  switches ON. 
     The R/S input  118  may be used for safety as well. For example, when no load device is connected to the electronic fuse  110 , the R/S input  118  may be used to cause the comparator  220  to output the TURN OFF signal to the electronic switch  210 . In this way, no power is output when there is no load on the electronic fuse  210  promoting safety. When a mechanical implementation such as illustrated in  FIG. 11  is considered, determining whether or not a load device is connected will be possible simply by determining whether or not the load select blade  1110  is absent or present. The R/S input  118  is not the only way to implement the safety feature. In general, it is sufficient to detect whether or not a load device  130  is connected and to prevent the power from reaching the power output  112  of the electronic fuse  110  when there is no load device  130  connected. 
     The following advantages are realized by one or more of the disclosed embodiments. These include being able to provide a generic programmable fuse panel designed for all types of outputs, trip values that are decided in the field by the loads or the settings, maximizing the fuse utilization, and being able to free fuse positions for any load devices independent of the current needed. 
     While described with reference to the example embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments. The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that these and other variations are possible. The invention is defined in the following claims and their equivalents.