Abstract:
A circuit which is configured for connection between a voltage source and a load, and which is configured to function as an automatic, re-settable fuse with regard to providing current to the load. The circuit includes a switch and sensor, such as a field effect transistor (FET), which is connected to the voltage source and the load and which is configured to selectively provide current to the load, depending on whether an overload condition exists. There is circuitry in communication with the FET which is configured to periodically send pulses to the FET in an attempt to re-set the switch and sensor during an overload condition. The circuit is configured to stop providing current to the load during an overload condition, but is configured to provide current to the load upon the overload condition being rectified. The circuitry which is in communication with the field effect transistor and which is configured to periodically send pulses thereto includes a timing circuit and an oscillator. Also included is a circuit speed controller which is configured to control how often the pulses are provided to field effect transistor.

Description:
RELATED APPLICATION (PRIORITY CLAIM) 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/760,019, filed Jan. 18, 2006, which is hereby incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]    Fuses are used in electrical and electronic circuit protection. Typically, the fuse opens in response to a metallic element in the fuse melting due to heating effects when a certain current level is reached, to thus create an “open” in protected circuit, thereby preventing a short-circuit from damaging the protected components in the circuit. Some fuses return to normal when cooled (thus are automatic resettable), or by a manually resettable device. The conventional automatic resettable fuse does work, but for a limited number of cycles and thus needs to eventually be replaced. 
       SUMMARY OF THE INVENTION  
       [0003]    An embodiment of the present invention provides a circuit which operates as an auitomatic resettable high-speed fuse. The circuit requires a few economical components, resets itself after opening, and does not require a special current-sense resistor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0004]    The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference numerals identify like elements in which: 
           [0005]      FIG. 1  is a diagram of a circuit which is in accordance with an embodiment of the present invention, showing some of the components in block diagram form; and 
           [0006]      FIG. 2  is a diagram similar to  FIG. 1 , but showing specific components of the circuit in more detail. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0007]    While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. 
         [0008]      FIG. 1  illustrates a circuit  20  which is in accordance with an embodiment of the present invention. The circuit  20  is configured to operate as an automatic, resettable high-speed fuse. The circuit  20  requires a few economical components, resets itself after opening, and does not require a special current-sense resistor. The circuit  20  is preferably provided in a seven-way connector (not shown) of a trailer, such as the one shown in U.S. Pat. No. 6,450,833, which is concurrently owned by the assignee of the present provisional application. When used in the seven-way connector of the trailer, the circuit  20  is provided on six of the seven pins of the seven-way connector (the remaining pin being coupled to ground). The circuit  20  allows for the detection of an overload condition, such as a short circuit in the cabling  22 , for example, connected between the seven-way connector and a grounded load  25  (for example, the lights of the trailer or the ABS system of the trailer). 
         [0009]    The circuit  20  includes a switch and sensor  26  which is configured to selectively provide current to a load  25 , depending on whether a short circuit condition exists, which will be described in more detail hereinbelow. The circuit  20  also includes an oscillator  48  and timing circuit  61  which are configured to become operative during a short circuit condition and periodically send pulses to the switch and sensor  26 . The circuit  20  also includes a circuit speed controller  72  which is configured to effectively control how often the pulses are provided to the switch and sensor  26 , and a voltage regulator  74  which is configured to regulate and provide voltage to certain components of the circuit  20 , which will be described in more detail hereinbelow. The circuit  20  also includes a signature translation circuit  76  which is configured to generate a current signature which is used by a communication interface  78  and/or a light display  79 , thereby providing a perceivable indication of the absence/presence of a short circuit condition. 
         [0010]      FIG. 2  shows the circuit  20  in more detail. As shown, the switch and sensor  26  may consist of a field effect transistor (FET)  26  which is configured to operate as a switch and as a sense resistor to control current to the load  25 . FET  26  may be an IRF640 integrated circuit (“IC”) manufactured by International Rectifier and others. 
         [0011]    Voltage and current are supplied to the circuit  20  by the “circuit in”  28  from the cab of the trailer through the seven-way connector. The applied voltage to the circuit  20 , is for example, 12 volts. 
         [0012]    A resistor  30  is connected to the “circuit in”  28 . Resistors  32 ,  34  are connected to resistor  30 . The drain  36  of FET  26  is connected to resistor  30 . Resistor  34  is connected to the input of inverter  38  (one of a group of inverters in an IC package, commonly referred to as “CD4049UB”), and the output of the inverter  38  is connected to the gate  40  of FET  26 . The source  42  of FET  26  is connected to resistor  32  and to the load  25 . 
         [0013]    An input of inverter  44  (of IC CD4049UB) is connected to the output of inverter  38  between inverter  38  and the gate  40  of FET  26 . The output of inverter  44  is applied to a diode  46  which, in turn, is connected to the input of the oscillator  48 . As shown in  FIG. 2 , the oscillator  48  may consist of three inverters  50 ,  52 ,  54  in series, two resistors  56 ,  60 , and a capacitor  58 . In addition to being connected to resistor  56 , the output of inverter  54  (and effectively the output of the oscillator  48 ) is connected to the timing circuit  61 . 
         [0014]    As shown in  FIG. 2 , the timing circuit  61  may consist of a capacitor  62 , resistors  64 ,  66 , inverter  68  and diode  70 . Capacitor  62  is connected to the output of the oscillator  48  and to a grounded resistor  64 . Capacitor  62  is also connected to resistor  66 , and resistor  66  is connected to the input of inverter  68 . The output of inverter  68  is connected to diode  70 , and diode  70  is connected to the input of inverter  38 . Diode  70  is also connected to the circuit speed controller  72 , which as shown in  FIG. 2  may consist of a grounded capacitor  72  which is also connected to resistor  34  and to the input of inverter  38 . 
         [0015]    The “circuit in”  28  is also connected to the input of the voltage regulator  74  (IC MC7805/TO, for example). The output of the voltage regulator  74  is connected to the inverter package (IC CD4049UB) which includes inverters  38 ,  44 ,  50 ,  52 ,  54 ,  68  to supply power (typically 5 volts) to same in a conventional mariner. Inverters  38 ,  44 ,  50 ,  52 ,  54 ,  68  are grounded in a conventional manner. 
         [0016]    A voltage drop is measured across resistor  30  for use by the signature translation circuit  76  in generating a current signature, which is used by a communication interface  78  in the cab of the trailer and/or on a light display  79  on the trailer. The signature translation circuit  76  is preferably controlled by a microcontroller which has a memory built into it. A suitable microcontroller is sold by Freescale under Model No. HCS08. 
         [0017]    Now that the structure of the circuit  20  has been described, two operating conditions will be described, namely, a non-short condition and a short-circuit condition. 
         [0018]    In a non-overload condition such as during a non-short condition, the cable  22  and the load  25 , for example the cable and associated trailer lights, are functioning normally. In this condition, current flows through the resistor  30 , causing a lower voltage to be applied to the drain  36  of FET  26 . Current also flows through resistor  34  to apply a logical low voltage signal (“LOW”) to the input of inverter  38 . A logical high voltage signal (“HIGH”) is thus created on the output inverter  3   8  and applied to the gate  40  of the FET  42 . A HIGH on the gate  40  of FET  26  causes the flow of current through the FET  26  and the load  25  to be at normal (non-short) operating levels. 
         [0019]    The HIGH is also applied to the input of inverter  44 , thereby creating a LOW on its output. Diode  46  effectively allows this LOW to pass to the input of inverter  50 , thereby turning off the oscillator  48  and disabling the timing circuit  61 . As such, during normal operating conditions, the switch and sensor  26  (i.e., the FET  26  shown in  FIG. 2 ) causes the current to flow to the load  25 , and the oscillator  48  and timing circuit  61  are effectively not operational. 
         [0020]    In an overload condition such as when there is a short-circuit condition, the load  25 , for example the lights, are not functioning normally because of, for example, a short-circuit in the cabling  22  between the seven-way connector and the load  25 . In this condition, an excessive current flows through the resistor  30  as the current flows to ground instead of through the load  25 , causing a voltage to be applied the drain  36  of FET  26  which is higher than the voltage applied to the drain  36  of FET  26  in the non-short condition. The FET  26  acts as a voltage divider causing a higher voltage to be applied to resistor  34 . As a result, a HIGH is applied to the input of inverter  38 . The capacitor  72  also charges as a result of this increased voltage. A LOW is thus created on the output of inverter  38  and applied to the gate  40  of FET  42 . A LOW on the gate  40  of FET  26  effectively stops the flow of current through the FET  26  and, as a result, effectively stops current being supplied to the load  25 . 
         [0021]    The present circuit  20  also provides for a constant checking to verify that the short-circuit is still occurring. Once the short-circuit has been rectified, the circuit  20  automatically resets the FET  26  to allow current to flow therethrough such that current is supplied to the load  25 . 
         [0022]    To perform the check, the LOW on the output of inverter  38  is applied to the input of inverter  44 . The inverter  44  then creates a HIGH on the output and applies the HIGH to diode  46 . 
         [0023]    The diode  46  blocks the HIGH, thereby enabling oscillator  48  and timing circuit  61 . Oscillator  48  periodically (e.g., every few tenths of a second) sends a pulse to inverter  38  through inverter  68 , attempting to reset FET  26 . If the short-circuit persists, FET  26  “blows” again; this process takes approximately 25 μs, for example. If the short-circuit does not persist, the current rises in 25 μs. 
         [0024]    Inverter  50  converts the LOW on its input to a HIGH on its output. The HIGH is applied to the input of inverter  52 , and the inverter  52  converts the HIGH to a LOW, supplying the LOW to the input of inverter  54 , which converts the LOW back to a HIGH. 
         [0025]    This HIGH is applied to capacitor  62  which induces a HIGH on the input of inverter  68 . Inverter  68  converts the signal to a LOW and applies the LOW to diode  70 . As a result of the LOW passed by diode  70 , a LOW is generated by capacitor  72  for a predetermined amount of time as the capacitor  72  discharges. This LOW is applied to the input of inverter  38 , and the inverter  38  creates a HIGH and applies it to the gate  40  of the FET  42 . A HIGH on the gate  40  of FET  26  allows for the flow of current through the FET  26  and for current to be supplied to the load  25 . If the short-circuit persists, an excessive current flows through the resistor  30  as the current flows to ground instead of through the load  25 , causing a voltage to be applied to the drain  36  of FET  26  which is higher than the voltage applied to the drain  36  of FET  26  in the non-short condition. The FET  26  acts as a voltage divider causing a higher voltage to be applied to resistor  34 . As a result, a HIGH is applied to the input of inverter  38 . The capacitor  72  also recharges as a result of this increased voltage. A LOW is thus created on the output of inverter  38  and applied to the gate  40  of FET  42 . A LOW on the gate  40  of FET  26  effectively stops the flow of current through the FET  26  and, as a result, effectively stops current being supplied to the load  25 . 
         [0026]    The HIGH on the output of inverter  54  is also is fed back to the input of inverter  50 , and the inverter  50  converts the HIGH to a LOW. The LOW is applied to the input of inverter  52 , which converts the LOW to a HIGH. The HIGH is applied to the input of inverter  54 , which converts the HIGH to a LOW. The LOW does not induce a HIGH to be passed by capacitor  62 . The LOW on the output of inverter  54  is fed back to the input of inverter  50 , thereby repeating the cycle discussed above. Therefore, pulses of HIGH are sent to capacitor  62  so that the check on FET  26  can be repeatedly performed. 
         [0027]    As a result, when FET  26  is closed, i.e., the fuse “blows”, the circuit  20  periodically (e.g., every few tenths of a second) sends a signal enabling the FET  26 , attempting to reset the FET  26 . If the short persists, the FET  26  blows again; this process can take microseconds, for example. If the short does not persist, the circuit  20  enables the FET  26  and returns the FET  26  to the normal condition. 
         [0028]    The speed of the circuit  20  can be tuned by modifying capacitor  72 , which low-pass filters the signal from the drain  36  of FET  26 . 
         [0029]    Because of the fast response, no heating effects take place, so persistent shorts can be tolerated continuously without damage to the system. An indicator (identified with reference numerals  78  and  79 , and discussed above) can be provided, therefore, enabling an operator to quickly identify a malfunctioning circuit. This identification also aids in the determination that the circuit  20  having the short-circuit has been rectified, such as when the communication interface  78  indicates that the short-circuit condition no longer exists or when the light display  79  is no longer illuminated. 
         [0030]    The exact current flowing through the system can be monitored via resistor  30 . This provides for the ability to establish a current signature. With such a current signature, metrics can used to assist its prognostics, trend analysis (current change over time due to corrosion, for example), and maintenance assistance that can be translated and available to both driver and remote information via signature translation circuit  76  and communication interface  78 . 
         [0031]    With regard to what exact elements can used in the implementation of what is shown in  FIGS. 1 and 2 , capacitor  58  could be a 10 μF, 25V tantium capacitor, capacitor  62  could be a 1.5 nF, 100V ceramic capacitor, and capacitor  72  could be a 0.1 μF, 100V ceramic capacitor, all of which are made by Kemet. Each of diodes  46  and  70  could be a IN4148 general purpose diode, and as discussed above FET  26  could be a IRF640/TO MOSFET made by International Rectifier. Each of resistors  34 ,  64  and  66  could be a 100 Kohm, ⅛ Watt resistor, each of resistors  56 ,  60  could be a 1 Mohm, ⅛ Watt resistor, and resistor  32  could be a 10 Kohm, ⅛ Watt resistor, all of which are made by Yageo. 
         [0032]    While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention. For example, while specific discreet elements are shown in  FIGS. 1 and 2 , it should be understood that different elements can be used, or the circuit can be implemented in more of a microprocessor-type implementation.