Abstract:
A controller area network (CAN) data link is provided including a first node, a second node, and a transformer circuit connected between the first and second nodes to provide electrical isolation. The transformer circuit provides the requisite electrical isolation and is reliable under high temperatures.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/342,371, filed Dec. 27, 2001, the contents of which are hereby incorporated by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to controller area networks (CANs), and more particularly to a CAN implementation including a transformer for isolation.  
         BACKGROUND  
         [0003]    Controller area networks are used in a number of industries, such as the automotive industries, for providing connections between simple industrial devices, such as sensors or actuators, and higher-level devices, such as an electronic control module (ECM). A standard implementation of an isolated CAN data link is described in “Volume I: DeviceNet Communication Model and Protocol,” Open DeviceNet Vendor Association, Inc., Release 2.0, 1997, p. 1-1. A standard CAN data link may include a CAN controller, a transceiver, an isolation module, and an isolated power supply. The CAN controller includes a device that handles incoming and outgoing CAN messages. The CAN controller may be part of a microprocessor or peripheral. The transceiver includes a bus driver and/or receiver and is connected on one side to the CAN and on the other side to the CAN controller via the isolation module. The isolation module isolates control logic (such as the CAN controller) from noise, voltage surges, and spikes. The isolation module typically includes optocouplers, which may use diodes. The isolated power supply provides voltage to both the transceiver and the isolation module.  
           [0004]    The use of optocouplers for electrical isolation is relatively expensive. Nonetheless, the standard implementation of the isolated CAN data link, using optocouplers for isolation, can be effective in certain applications. There are, however, situations when the standard implementation is insufficient. In particular, the conventional CAN data link may become unreliable at high heats because the optocoupler malfunctions. Most optocouplers cannot function reliably at higher operating temperatures, such as 120° C. In automotive applications, temperatures of up to 120° C. may occur, for example, due to mud build-up or other factors. In order to counter this problem, the industry standard currently uses hermetic sealing of the optocouplers. Another option is to use fuel coolant as a heat sink. Both of these methods are, however, expensive to implement.  
           [0005]    Thus, the prior art does not provide an inexpensive isolation design that can be utilized in all working environments. The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.  
         SUMMARY OF THE INVENTION  
         [0006]    In one aspect of the present invention, a controller area network (CAN) data link is provided including a first node, a second node, and a transformer circuit connected between the first and second nodes to provide electrical isolation.  
           [0007]    In another aspect of the invention, a method is provided for providing electrical isolation in a controller area network. A first and a second node are provided. A transformer circuit is also provided. A first end of the transformer circuit is coupled with the first node. A second end of the transformer circuit is coupled with the second node.  
           [0008]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an exemplary embodiment of the invention and together with the description, serve to explain the principles of the invention. In the drawings:  
         [0010]    [0010]FIG. 1 is a schematic diagram of an isolated CAN data link, consistent with one exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    [0011]FIG. 1 illustrates an exemplary isolated CAN data link  100 , consistent with one exemplary embodiment of the present invention. CAN data link  100  includes a first node, such as a CAN controller  110 , a second node, such as a transceiver  120 , an isolation module  130 , and an isolated power supply  140 . CAN controller  110  generally functions as described above. Components of the isolated CAN data link may be implemented using DeviceNET CAN components, or other suitable commercial or proprietary components. DeviceNET components are one type of commercially available CAN components. For example, CAN controller  110  of the exemplary embodiment may be implemented by DeviceNET component 82527, or any other suitable device. Transceiver  120  also generally functions as described above and may be implemented with DeviceNET component 82C251, or any other suitable device.  
         [0012]    In one embodiment of the invention, isolation module  130  may be implemented using a transformer circuit, which may include, for example, two R-C circuits  131 - 132  and  134 - 135 , two transistors  133  and  138 , an LED  136 , and a transformer  137 . Implementation of the R-C circuits and the LED are known in the art. The transistors  133  and  138  may be implemented by any suitable transistor, such as, for example, MMBT2369s which are used for switching applications. These transistors  133  and  138  may include NPN transistors, operating as current amplifiers, although any suitable device may be used. The transformer  137  may be implemented by any appropriate transformer, such as, for example, an Elytone Electronics transformer as is typically used in telephone line applications. By means of example only, the exemplary embodiment uses a YT-6561 Transformer (180 uH, 0.9 ohms).  
         [0013]    By reference to FIG. 1, one end of R-C circuit  131 - 132  is coupled with CAN controller  110 . The other end is coupled with the base of transistor  133 . The emitter of transistor  133  is grounded and the collector is coupled with one end of R-C circuit  134 - 135 . Also coupled with the collector and the same end of R-C circuit  134 - 135  is one end of a diode  136 . The other end of R-C circuit  134 - 135  is coupled with one edge of the transformer  137 . The other end of diode  136  is coupled with the other edge of the transformer  137  and to a voltage VCC. One edge of the other side of the transformer  137  is grounded. The other edge of that side of the transformer  137  is coupled with the base of transistor  138 . The emitter of transistor  138  is grounded and the collector of transistor  138  is coupled with transceiver  120  and to isolated voltage supply  140 . These components operate so as to isolate logic components from noise, voltage surges, and spikes.  
       INDUSTRIAL APPLICABILITY  
       [0014]    By using transformers rather than optocouplers in the isolated CAN data-link, the CAN is less susceptible to failure or unreliability at high temperatures. Further, transformers are generally less expensive than optocoupler devices. The system, however, still provides sufficient electrical isolation as may be required in the industry, such as by the DeviceNET standards. While the DeviceNET CAN components and standards have been illustrated here, it should be understood that the present invention is applicable to other CAN devices and standards.  
         [0015]    It will be readily apparent to those skilled in this art that various changes and modifications of an obvious nature may be made, and all such changes and modifications are considered to fall within the scope of the appended claims. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.