Patent Publication Number: US-9887057-B2

Title: Remote activated fuse and circuit

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This application relates generally to electronic protection circuitry. More, specifically, the application relates to a remote activated fuse and circuit for using the remote activated fuse. 
     Introduction to the Invention 
     Protection circuits are utilized in electronic circuits to isolate failed circuits from other circuits. For example, a protection circuit may be utilized to prevent a cascade failure of circuit modules in an electronic automotive engine controller. Protection circuits may also be utilized to guard against more serious problems, such as a fire caused by a power supply circuit failure. 
     One type of protection circuit is an ordinary glass fuse. The glass fuse includes a conductor that behaves like a short circuit during normal operation. When the current through the conductor exceeds a threshold, the conductor opens and current flow stops. 
     Another protection circuit is a thermal fuse that transitions between short circuit and open circuit modes of operation when the temperature of the thermal fuse exceeds a specified temperature. To facilitate these modes, thermal fuses include a conduction element, such as a fusible wire, a set of metal contacts, or a set of soldered metal contacts, that can switch from a conductive to a non-conductive state. A sensing element may also be incorporated. The physical state of the sensing element changes with respect to the temperature of the sensing element. For example, the sensing element may correspond to a low melting metal alloy or a discrete melting organic compound that melts at an activation temperature. When the sensing element changes state, the conduction element switches from the conductive to the non-conductive state by physically interrupting an electrical conduction path. 
     One disadvantage with existing fuses is they are only configured to activate (i.e., open) during a single fault condition, such as either when the current exceeds a threshold or when a temperature exceeds a threshold. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first aspect, a fuse includes first, second, and third terminals disposed on a substrate. Respective ends of one or more primary conductors of the fuse are connected to one of the first and the second terminals. The primary conductors have a first conductivity and are configured to open when a primary current between the first and second terminals exceeds a first pre-determined threshold. One or more secondary conductors of the fuse have respective first ends connected to the third terminal. The secondary conductors are configured to ignite when a secondary current through the secondary conductors exceeds a second pre-determined threshold. When ignited the secondary conductors open the primary conductors to thereby stop the primary current. 
     In a second aspect, a fuse-protected circuit includes a fuse housing and a component. The fuse housing includes first, second, and third terminals that are disposed on an outside surface of the housing. The first and second terminals are in series with a circuit to be protected. The fuse housing also includes a substrate. At least a portion of each of the first, second, and third terminals is also disposed on the substrate. Respective ends of one or more primary conductors are connected to one of the first and the second terminals. The primary conductors have a first conductivity and are configured to open when a primary current between the first and the second terminals exceeds a first predetermined threshold. The fuse housing also includes one or more secondary conductors with respective first ends connected to the third terminal. The secondary conductors are configured to ignite when a secondary current through the secondary conductors exceeds a second predetermined threshold. Ignition of the secondary conductors opens the primary conductors to thereby stop the primary current. The component includes a first end that is in electrical communication with the third terminal and a second end at a voltage potential that is different than the first terminal. The component facilitates current flow between the first terminal and the third terminal upon activation of the component, to thereby cause the secondary conductors to ignite and the primary conductors to open. 
     In a third aspect, a fuse includes a housing. First, second, and third terminals are disposed on an outside surface of the housing. The first and second terminals are in series with a circuit to be protected. A substrate is disposed within an interior of the housing. At least a portion of each of the first, second, and third terminals is also disposed on the substrate. One or more primary conductors and one or more secondary conductors are disposed within the housing. Respective ends of the primary conductors are connected to one of the first and the second terminals. The primary conductors have a first conductivity and are configured to open when a primary current between the first and the second terminals exceeds a first predetermined threshold. Respective first ends of the secondary conductors are connected to an electrode. The secondary conductors are configured to ignite when a secondary current through the secondary conductors exceeds a second predetermined threshold. Ignition of the secondary conductors opens the primary conductors to thereby stop the primary current. A component is also disposed with the housing. The component includes a first end that is in electrical communication with the third terminal disposed on the substrate and a second end in electrical communication with the electrode. The component facilitates current flow between the electrode and the third terminal upon activation of the component, to thereby cause the secondary conductors to ignite and the primary conductors to open. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the claims, are incorporated in, and constitute a part of this specification. The detailed description and illustrated embodiments described serve to explain the principles defined by the claims. 
         FIG. 1  is a schematic of a first exemplary circuit that may be utilized in connection with a first remote activated fuse embodiment. 
         FIG. 2  is a schematic of a second exemplary circuit that may be utilized in connection with the first remote activated fuse embodiment. 
         FIG. 3  illustrates an interior representation of the first remote activated fuse embodiment. 
         FIG. 4  illustrates an interior representation of a second remote activated fuse embodiment. 
         FIG. 5  is a schematic of an exemplary circuit that may be utilized in connection with the second remote activated fuse embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments described below describe fuses that are configured to open when a primary current that flows between first and second terminals of the device exceeds a threshold. The fuses are further configured to be remotely activated (i.e., opened) by allowing current flow through a third terminal of the fuse. 
       FIG. 1  is a schematic of an exemplary fuse-protected circuit  100 . The exemplary circuit  100  includes a power source  105 , a first fuse embodiment  110 , an exemplary RLC circuit  115 , and a FET device  120 . The fuse  110  includes a housing with first, second, and third terminals ( 130 A,  130 B,  135 ) that are disposed on the outside of the housing. The first, second, and third terminals ( 130 A,  130 B,  135 ) are in electrical contact or communication with circuitry positioned within the housing. The circuitry is described in detail below. 
     The fuse  110  is connected in series with the RLC circuit  115  and the FET  120 . The first terminal  130 A of the fuse  110  is connected to a first side of the power source  105 . The second terminal  130 B of the fuse  110  is connected into the RLC circuit  115 . During normal operation, (i.e., non-fault condition), current flows between the first terminal  130 A and the second terminal  130 B of the fuse  110 . During a fault condition, the fuse  110  opens, thus preventing current flow through the RLC circuit  115  and the FET  120 . A fault may occur when, for example the FET  120  shorts. In this case, the current through the fuse  110  will exceed a threshold. This in turn, will cause a primary conductor  305  ( FIG. 3 ) within the fuse  110  to open. 
     The third terminal  135  of the fuse facilitates remote activation of the fuse  100 . In one implementation, when the third terminal  135  is connected to a potential different from the potential at the first and second terminals ( 130 A and  130 B), current will flow through the third terminal  135  and will cause the fuse  110  to open. That is, the fuse  110  can be made to open even though the primary current is below the threshold current necessary to cause the primary conductor  305  to open. 
     In one implementation, the third terminal  135  is coupled to a component  125  that exhibits opened and closed conduction states. When the component  125  is activated, the third terminal  135  is brought to a potential that is different than the potential at the first and second terminals ( 130 A,  130 B). For example, the component  125  may be a passive device such as a pressure, temperature, humidity, etc. sensing switch. The component  125  may be an active device such as a transistor switch configured to change conduction state base on a sensed voltage. The component  125  may correspond to a bimetal strip, or a different device that changes conduction states based on a temperature. The component  125  may be external to the fuse  110 , though in some implementations the component  125  could be positioned within the housing of the fuse  110 . 
     In one implementation, the component is an anomalous negative-temperature-coefficient (aNTC) device  205  ( FIG. 2 ) such as vanadium dioxide incorporating doping compounds. Referring to  FIG. 2 , the aNTC device  205  comprises a material with a resistance that varies with temperature. The aNTC device  205  may be characterized as having a high resistance below a threshold temperature and a low resistance above the threshold temperature. The aNTC device  205  may be placed adjacent to a critical component, such as a FET  120  so as to trigger the fuse  110  when the temperature of the FET  120  exceeds a threshold temperature. This facilitates opening of the fuse  110  potentially before damage occurs to the circuit  200  as a result of an imminent failure of the FET  120 . It should be emphasized that the circuits of  FIGS. 1, 2, and 5  (described below) are only shown for illustrative purposes and that the fuse embodiments illustrated in the figures can be configured to protect different circuit configurations. 
       FIG. 3  illustrates an interior view of a first fuse embodiment  300  that may correspond to the fuse  110  illustrated in  FIG. 1 . The fuse  300  includes a substrate  302 , first, second, and third terminals ( 130 A,  130 B, and  135 ), primary conductors  305 , and a secondary conductor  310 . The terminals ( 130 A,  130 B, and  135 ) are disposed on the substrate  302  and may be plated to facilitate soldering of the fuse  300  to a circuit board. 
     On implementation, respective ends of the primary conductors  305  are connected to the first and second terminals ( 130 A,  130 B). The primary conductors  305  may comprise copper, tin, zinc, or a combination thereof, or a different conductive material having a first conductivity. For example, the primary conductors may correspond to copper wires. The primary conductors  305  are sized and/or numbered to open when a primary current  315  between the first and second terminals ( 130 A,  130 B) exceeds a first pre-determined threshold. The threshold at which the primary conductors  305  open may be adjusted by changing the dimensions of the primary conductors  305  and/or the number of primary conductors  305 . The threshold may also be changed by varying the composition of the primary conductors  305 . 
     The secondary conductor  310  has a first end connected to an electrode  303  that is disposed on the substrate  302  and a second end connected to the third terminal  135 . The secondary conductor  310  is positioned across the primary conductors  305 . For example, the secondary conductor  310  may be arranged perpendicularly with respect to the primary conductors  305 . The secondary conductor  310  is configured to ignite (i.e., cause an exothermic reaction) when a secondary current  320  through the secondary conductor  310  exceeds a second predetermined threshold current. The second predetermined threshold current at which the secondary conductor  310  ignites may be the same as or different from the primary conductor current  315  at which the primary conductors  305  open. For example, the secondary conductor  310  may comprise an exothermic reactive material such as a palladium/aluminum (Pd/Al) wire, which ignites when the current flow though the material exceeds a threshold and continues to burn until the reactive materials are exhausted. Ignition of the secondary conductor  310  causes the primary conductors  305  to melt and thereby open. 
     In some implementations, in the region where the secondary conductor  310  crosses the primary conductors  305 , the secondary conductor  310  is raised above the substrate  302  to allow the secondary conductor  310  to heat more rapidly than would occur if the secondary conductor  310  were to be in contact with the substrate  302 . For example, an insulating air gap or an insulating material may be provided between the secondary conductor  310  and the substrate  302 . In this regard, a higher current may be required to ignite the secondary conductor  310  if it were in contact with the substrate  302 . 
     To further facilitate opening of the primary conductors  305 , the secondary conductor  310  may be in direct contact with the primary conductors  305 . For example, in one implementation, the primary conductors  305  may form the shape of an arc as they extend between the first and the second terminals ( 130 A,  130 B). The secondary conductor  310  may be configured to contact the primary conductors  305  at their apex, which may be centered between first and second terminals ( 130 A,  130 B). 
     In another implementation, the primary conductors  305  may be interwoven within the secondary conductor. For example, even numbered primary conductors  305  may be positioned below the secondary conductor  310  and odd numbered primary conductors  305  may be positioned above the secondary conductor  310 . 
     In yet another implementation, instead of a single continuous conductor, each primary conductor  305  is split in a middle region and comprises a first section and a second section. The first section couples the first terminal  130 A to the secondary conductor  310 . The second section couples the second terminal  130 B to the secondary conductor  310 . This configuration forces primary current flow  315  to flow through a portion of the secondary conductor  310 , thus guaranteeing interruption in the primary current path when the secondary conductor  310  is ignited. 
     In another implementation, the primary conductors  305  may be interwoven within the secondary conductor (see the embodiment shown in  FIG. 4 , for example). For example, even numbered primary conductors  305  may be positioned below the secondary conductor  310  and odd numbered primary conductors  305  may be positioned above the secondary conductor  310 . 
     In other implementations, the secondary conductor  310  is connected to the third terminal  135  and a fourth terminal (not shown). A potential may be provided across the third terminal  135  and the fourth terminal to cause the secondary conductor  310  to ignite and thereby open the primary conductors  305 . 
       FIG. 4  illustrates an interior view of a second fuse  400  embodiment. The fuse  400  includes a substrate  302 , first, second, and third terminals ( 130 A,  130 B, and  135 ), primary conductors  305 , and a secondary conductor  310 . The respective members are generally arranged as described above and possess the features described above with respect to the first fuse embodiment  300 . 
     However, in the second fuse  400  embodiment, the secondary conductor  310  extends between the first electrode  303  and the second electrode  402 . A first end of a resilient conductive member  405  is connected to the third terminal  135 . A second end of the resilient conductive member  405  is configured to contact the second electrode  402  when the resilient conductive member  405  is above a threshold temperature. Below the threshold temperature, the second end of the resilient conductive member  405  is spaced apart from the second electrode  402 . When in contact, a path for the secondary current  320  to flow to the third electrode is provided. It is understood that the resilient conductive member  405  could also be connected to the second electrode  402  and configured to contact the third terminal  135  when the temperature of the resilient conductive member  405  exceeds the temperature threshold. In some implementations, the resilient conductive member  405  is a bimetal strip that changes shape with a temperature change. 
     In alternate implementations, the resilient conductive member  405  may be replaced with a component  125  that exhibits open and closed conduction states. When the component is activated, the second electrode  402  is brought to the potential present at the third terminal  135 . The component  125  may be a passive device such as a pressure, temperature, humidity, etc. sensing switch. The component  125  may be an active device such as a transistor switch configured to change conduction state base on a sensed voltage. The component  125  may correspond to a bimetal strip, or a different device that changes conduction states based on temperature. 
       FIG. 5  is a schematic of an exemplary fuse-protected circuit  500  that utilizes the second fuse embodiments  400 . The exemplary circuit  500  also includes a power source  105 , an exemplary RLC circuit  115 , and a FET device  120 . The various components are generally arranged as described above. However, in this case, the third electrode  135  may be directly connected to a node with a potential different than the potential at the first and second electrodes ( 130 A,  130 B). That is, an external switch or NTC device is not required. To facilitate an alternate means of activating the fuse  400 , the fuse  400  may be placed adjacent to or in contact with a critical component such as the FET device  120 . Excessive heat generated by such a component causes the resilient conductive member of the fuse  400  to close and thereby ignite the secondary conductors within the fuse  400 . This in turn causes the primary conductors to open. 
     While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the claims. For example, while various elements are described as being coupled or connected to one another, the term does not necessarily imply direct coupling or connection in that various intermediary elements may be added between the elements of the embodiments without significantly changing the behavior of the elements. Any such modifications are understood to fall within the scope of protection afforded by the claims. Accordingly, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the claims. Therefore, the embodiments described are only provided to aid in understanding the claims and do not limit the scope of the claims.