Abstract:
A method of implementing a power-based current limiting circuit in an information handling system includes providing a power supply having an output voltage operating range that can vary between a first voltage output level and a second voltage output level. The power supply output voltage is coupled to a load module via a switch. A power output of the power supply supplied to the load module is detected as a function of the load module current and the output voltage. Lastly, the switch is controlled between a first state and a second state in response to the detected power output.

Description:
BACKGROUND  
         [0001]    The present disclosure relates generally to information handling systems, and more particularly to a method and apparatus for implementing a power-based current limiting circuit in an information handling system.  
           [0002]    As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.  
           [0003]    In conjunction with information handling systems, such as with notebook computers, high power external modules are often powered from unregulated main power source in the notebook computers to avoid efficiency losses. For instance, in one known notebook computer, a plug-in module inserted into a corresponding bay of the notebook computer can be powered from the main system power rail. However, the main system power rail or supply voltage can vary in voltage from between eight (8) volts and twenty (20) volts.  
           [0004]    To protect the module from internal faults and the computer system from excessive power draw, the notebook computer system usually employs a fuse. The is fuse interrupts power delivery when excessively high current is detected. Since input voltage varies greatly and the module device in the bay draws constant power, its normal current will vary inversely proportionally with the input voltage. Such large variations in fault currents make it difficult, if not impossible, to design a robust fault protection circuit.  
           [0005]    The problem is even more severe for ultra-portable notebook computer systems, where the fuse designed for the lowest battery voltage (e.g., 8 V) causes a system shutdown at the highest AC adapter voltage (e.g., 20 V) due to a power budget limitation in the AC power adapter.  
           [0006]    In prior systems, two types of fuses were used to interrupt fault current to an external device. A first type includes a mechanical fuse, based on physical properties of certain materials such as polymer in a polyswitch. A second type included a solid state current-limiting switch, such as a MAX1838, manufactured by Maxim Integrated Products, Inc. of Sunnyvale, Calif. These devices were inserted in the current path between the system power source and the module. If a fault occurred in the module or if an unsupported module is inserted requiring more power than the system can supply, the supply current would be interrupted.  
           [0007]    [0007]FIG. 1 illustrates a graph representation of supply current to supply voltage of a module in a system using a conventional fuse. In the prior systems, both types of fuse devices are triggered at preset constant current value, as indicated by reference numeral  10  (for example, 2.2 A). However, selecting a proper trip current can be an impossible task if voltage variations are wide and the system has very limited power budget (e.g., as in an ultra-portable notebook computer). With the constant current value fuse, any current above the constant current value results in a module fault. Similarly, any current below the constant current value renders the system okay.  
           [0008]    Accordingly, it would be desirable to provide method for improved fault protection in an information handling system absent the disadvantages found in the prior methods discussed above.  
         SUMMARY  
         [0009]    According to one embodiment, a method of implementing a power-based current limiting circuit in an information handling system includes providing a power supply having an output voltage operating range that can vary between a first voltage output level and a second voltage output level. The power supply output voltage is coupled to a load module via a switch. A power output of the power supply supplied to the load module is detected as a function of the load module current and the output voltage. Lastly, the switch is controlled between a first state and a second state in response to the detected power output. An information handling system having a power-base current limiting circuit is also disclosed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 illustrates a graph representation of supply current to supply voltage of a module in a system using a conventional fuse;  
         [0011]    [0011]FIG. 2 illustrates a block diagram view of an information handling system having a method and apparatus for implementing a power-based current limiting circuit in an operating system according to an embodiment of the present disclosure;  
         [0012]    [0012]FIG. 3 illustrates a graph representation of supply current to supply voltage of a module in a system using a power-base fuse/switch according to an embodiment of the present disclosure; and  
         [0013]    [0013]FIG. 4 illustrates a schematic block diagram view of a power-based current limiting circuit according to one embodiment of the present disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0014]    According to one embodiment of the present disclosure, a method and system apparatus are disclosed for implementing a power-based current limiting circuit an information handling system. The method and system can be better understood by reference to the flow charts, drawing figures, and additional discussion included herein.  
         [0015]    [0015]FIG. 2 depicts a high level block diagram of an information handling system  100  in which the disclosed technology is practiced. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components.  
         [0016]    The particular information handling system  100  depicted in FIG. 2 is a portable computer which includes a processor  105 . An Intel Hub Architecture (IHA) chip  110  provides system  100  with memory and I/O functions. More particularly, IHA chip  110  includes a Graphics and AGP Memory Controller Hub (GMCH)  115 . GMCH  115  acts as a host controller that communicates with processor  105  and further acts as a controller for main memory  120 . GMCH  115  also provides an interface to Advanced Graphics Port (AGP) controller  125  which is coupled thereto. A display  130  is coupled to AGP controller  125 . IHA chip  110  further includes an I/O Controller Hub (ICH)  135  which performs numerous I/O functions. ICH  135  is coupled to a System Management Bus (SM Bus)  140  which is coupled to one or more SM Bus devices  145 .  
         [0017]    ICH  135  is coupled to a Peripheral Component Interconnect (PCI) bus  155  which is coupled to mini PCI connector slots  160  which provide expansion capability to portable computer  100 . A super I/O controller  170  is coupled to ICH  135  to provide connectivity to input devices such as a keyboard and mouse  175  as shown in FIG. 1. A firmware hub (FWH)  180  is coupled to ICH  135  to provide an interface to system BIOS  185  which is coupled to FWH  180 . A General Purpose I/O (GPIO) bus  195  is coupled to ICH  135 . USB ports  200  are coupled to ICH  135  as shown. USB devices such as printers, scanners, joysticks, etc. can be added to the system configuration on this bus. An integrated drive electronics (IDE) bus  205  is coupled to ICH  135  to connect IDE drives  210  to the computer system. In addition, a network interface card (N IC) provides connectivity to a network, for example, the Internet or other computer network.  
         [0018]    Referring now to FIG. 3, according to one embodiment of the present disclosure, an ultra-portable 15 W computer with a 50 W power supply can be viewed as having a solution space, indicated by reference numeral  300 , in which a module fault can be detected over a full range of operating voltages for the system. The solution space  300  includes a fault detection region  302  bordered between an upper limit of a normal operation for the module and a lower limit of a system down region. The upper limit of the normal operation for the module is indicated by reference numeral  304 . The lower limit of the system down region is indicated by reference numeral  306 . Below the upper limit  304  of the normal operation, over the range of supply voltages, the module operates in the normal operating range  303  and the system is ok. Above the lower limit  306  of the system down region, the module and/or AC adapter shuts down due to an overload condition and furthermore, the system goes down.  
         [0019]    According to one embodiment, a method is provided for detection of a module fault within the solution space for an information handling system. In particular, a power-based fuse/switch is included within the information handling system to implement a power-based current limiting circuit. The power-based current limiting circuit has a curve representation similar to that shown in FIG. 3 and indicated by reference numeral  308 . With a conventional fuse, as shown in FIG. 1, it is impossible to stay within solution space  300  of FIG. 3 at a full range of operating voltages for the information handling system. However, the problem of the conventional fuse is overcome with the power-based current limiting circuit of the present embodiments.  
         [0020]    Turning now to FIG. 4, further in conjunction with the embodiments of the present disclosure, the power-based current limiting circuit  400  includes a current interrupting device based on monitoring power consumed by a module. FIG. 4 is a block diagram of such current interrupting device.  
         [0021]    System power  402  provides the supply voltage. Input differential amplifier  404  amplifies a voltage drop across a Current Sense Resistor (CSR)  406 , thus producing a voltage proportional to the current consumed by the load (i.e., the module)  408 . Multiplier  410  multiplies the voltage output of the differential amplifier  404  by the voltage seen on the load terminal  408 , thus producing a voltage proportional to power consumed by the load. Comparator  412  receives at an inverting input  414  the multiplier  410  output and at a non-inverting input  416  a reference voltage input. Comparator  412  determines if consumed power is greater than the maximum allowed. Low pass filter  418  filters out transients, thus preventing false tripping of the device  400 . Lastly, a Schmitt trigger  420  ensures that there is no instability. The output of the Schmitt trigger  420  control switch device  422 , according to the solution space  300  of FIG. 3.  
         [0022]    According to another embodiment, the Schmitt trigger  420  can be replaced by a reset-able latch to make sure that the switch  422  is fixed in the OFF position until power is cycled.  
         [0023]    Although only a few exemplary embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the embodiments of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the embodiments of the present disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.