Patent Publication Number: US-2009218997-A1

Title: Power supply circuit

Description:
BACKGROUND 
     The present disclosure relates generally to power management. 
     Many devices require electrical power to operate. For example, data communication devices use supply voltage or current to perform desired functions, such as processing, transmitting, and/or receiving data. Some power systems, subsystems, or devices may be sized for peak power demand. 
     However, such systems or devices may involve larger power supplies that may require heavier or larger current carrying conductors for power delivery. Larger conductors may increase cost as well as size of devices. Other systems or devices, such as data communication systems or devices, may not receive sufficient power or prevent a component from using peak power. Such techniques may adversely impact quality and/or range of communications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  illustrates a data communication system; 
         FIG. 2  illustrates a device that may be used in a system, such as the system of  FIG. 1 ; 
         FIG. 3  illustrates a power supply circuit that may be used with the device of  FIG. 2 ; 
         FIG. 4  illustrates a current pattern over time; 
         FIG. 5  illustrates a method for supplying power; and 
         FIG. 6  illustrates a method for providing a power supply circuit. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     By way of introduction, the example embodiments described below include a power supply circuit and associated methods. For example, the power supply circuit is used in conjunction with a load device, such as a data communication device. The power supply circuit may limit current from a main power supply below a desired current and still provide a peak power to the load device. 
     According to a first aspect, a current limiter is configured to limit current drawn from a main power supply to a maximum value. A load device is coupled with an output of the current limiter. The load device is configured to periodically draw a first current during operation. The maximum value is below a value of the first current. A capacitor or alternate charge storage device is coupled with the load device. The charge storage device is configured to supply additional current to the load device to satisfy the first current value. A linear voltage regulator is coupled between the charge storage device and the load device. 
     According to a second aspect, a current limiter has an input and an output. The input of the current limiter is configured to couple with a main power supply. A diode is coupled with the input of the current limiter. A capacitor is coupled with the output of the current limiter. A low dropout voltage regulator is coupled with the capacitor and the output of the current limiter. An output of the low dropout voltage regulator is configured to supply a substantially noise free power to a load device. 
     According to a third aspect, a host device is provided. A plurality of modules are configured to couple with the host device. Each of the plurality of modules includes a current limiter configured to limit power from the host device. A data communication device is coupled with an output of the current limiter. The data communication device is configured to periodically draw a first power. A capacitor is coupled with the data communication device. The capacitor is configured to store power from the host device and supplement the current limiter to satisfy a value of the first power. A linear voltage regulator is coupled between the capacitor and the data communication device. The linear voltage regulator is configured to step down a voltage. 
     According to a fourth aspect, a load device is operated. The load device periodically draws a first current during operation. A current drawn from a main power source is limited to a limited current value. The limited current value is below a value of the first current. Additional current from a capacitor is supplied to satisfy a desired current during the operation of the load device. Also, a substantially constant and substantially noise free voltage is supplied to the load device. 
     According to a fifth aspect, a current limiter having an input and an output is provided. The input of the current limiter is configured to couple with a main power supply. A capacitor is coupled with the output of the current limiter. A linear voltage regulator is coupled with the capacitor and the output of the current limiter. A load device is coupled with an output the linear voltage regulator. The output of the linear voltage regulator is configured to provide a supply power to the load device. 
     The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments. 
     Example Embodiments 
     Data communication devices, such as a GSM-based wireless modem, present a time varying bursty power load during operation. For example, GSM power consumption includes heavy power bursts lasting one or more milliseconds in duration, such as during transmission, and significantly less power consumption otherwise, such as during a receiving mode. A power supply circuit is used to limit current from a main power supply during the heavy power bursts, which allows for smaller or lighter cabling, wiring, and/or connections. For example, power connections to a plurality of data communication devices within a host device, such as a router, may be reduced in size and/or ratings by the power supply circuit. Even though current from a main power source is limited, the power supply circuit is able to provide a desired current or power to the data communication device for operation, including during peak power demand periods. 
       FIG. 1  shows a data communication system  100  (hereinafter referred to as “system  100 ”). The system  100  is an Internet protocol-based system, an Intranet system, a telephony system, a cellular based system, a wireless or wired audio/visual data communication system, and/or any known or future data communication system. 
     The system  100  includes, but is not limited to, a host device  104 , a network  108 , and user devices  112 . Additional, different, or fewer devices or components may be provided. For example, a proxy server, a billing server, a name server, a switch or intelligent switch, a computer or workstation, administrative components, such as an administrative workstation, a gateway device, a backbone, ports, network connections, and network interfaces may be provided. While the components in  FIG. 1  are shown as separate from one another, one or more of these components may be combined. 
     The host device  104  is a router, server, laptop computer, desktop computer, switch, workstation, or other data communication device. For example, the host device  104  is a router configured to connect with the network  108  via a connection  116 . The connection  116  is a wireless or wired connection. For example, the host device  104  is a GSM based router that wirelessly communicates with the network  108 . Other wireless communications, such as wideband code division multiple access (“WCDMA”), code division multiple access (“CDMA”), or Bluetooth, may be used. 
     The network  108  is the Internet, cellular network, an intranet, a local area network (“LAN”), a wide area network (“WAN”), a virtual private network (“VPN”), and/or any known or future network. The network may contain cellular basestations, servers, computers, or other systems, devices, or components for transferring and/or modifying data. 
     The host device  104  also communicates with the user devices  112  via a connection  120 . The connection  120  is a wired connection including cables, conductors, or other wiring. Alternatively, the connection  120  is a wireless connection or a network. The user devices  112  are workstations, phones, desktop or laptop computers, personal digital assistants (“PDAs”), processing devices, and/or other data communication devices that can be operated by a user. A user uses the user devices  112  to view websites or other digital forums, view messages, check email, initiate or receive phone calls, access the Internet, intranet, or other networks, and/or perform any other data processing. For example, the user devices  112  are adapted to receive and transmit 2G or 3G global system for mobile communications (“GSM”) communications. Other communication standards may be used. Alternatively, the user devices  112  may be intermediate devices, such as servers or switches, that communicate with user devices. Also, the host device  104  may be part of the user devices  112  or may be a separate user device. 
       FIG. 2  shows a host device  201 , such as the host device  104 . For example, the host device  201  is a router, such as the Cisco 1841, 2800, or 3800 series integrated service router provided by Cisco, Inc of San Jose, Calif. The host device  201  includes ports or slots  205  (hereinafter referred to as “slots”) and a housing. The host device may have a substantially rectangular housing with a relatively smaller height compared to the length and width. Alternatively, the housing may have other geometrical shapes. 
     The slots  205  are used to receive modules or data cards  213  (hereinafter referred to as “modules”). The slots  205  are located in a front, back, side, or inside of the host device  201 . The slots  205  receive the modules  213  and connect the modules  213  with a main power supply and processing circuitry of the host device  201 . The host device  201  may include one or more slots  205 . For example, the host device  201  includes at least about 3 slots  205 . 
     The modules  213  are or include PC or PCI cards, wireless data cards, integrated circuit cards, subscriber identity modules (“SIMs”), modems, or other data devices that connect with a host device. For example, the modules  213  are GSM wireless data modules, such as high speed wide area network (“WAN”) interface cards provided by Cisco, Inc. of San Jose, Calif. incorporating 3G Wireless mini peripheral component interconnect (“PCI”) express cards. Each module  213  is supplied with power from a main power supply of the host device  201 . For example, the host device  201  of one embodiment plugs into or receives power from a standard 110 VAC wall outlet or power supply. Other power sources may be used. The host device  201  converts the 110 VAC power to a lower voltage, such as a lower DC voltage to power each of the modules  213  and/or other circuitry. For example, cables, wiring, connections, and/or other conductors supply a converted voltage, such as 5 VDC, to each of the modules  213 . 
     Each of the modules  213  includes one or more components  209 . For example, the components  209  are embedded antennas, trace antennas, protruding antennas, and/or other antennas used to transmit and/or receive signals or data for each of the modules  213 . Separate antennas may be used between receive and transmit operations. Alternatively, the components  209  are antenna ports or connections that connect with respective antennas within or on the host device  201 . Different antennas and/or antenna connections may correspond to different modules  213 . Alternatively, multiple modules  213  may use or connect with a common antenna. 
       FIG. 3  is a circuit diagram of a module  300 , such as one of the modules  213 . The module  300  includes a power supply circuit  312  (hereinafter referred to as “circuit  312 ”) and a load device  316 . Fewer, more, or different components may be provided. For example, the module  300  may include a SIM card holder or circuitry, an antenna, an antenna connection or port, one or more processors, such as a general processor, application-specific integrated circuit (“ASIC”), digital signal processor, field programmable gate array (“FPGA”), digital circuit, analog circuit, or combinations thereof, one or more memories, and/or other circuitry or components. Different components may be integrated or remain separate. 
     A main power supply, source, or output  304  connects with the circuit  312  via a connection  308 . Power is provided to the load device  316  from the main power supply via the circuit  312 . For example, the main power supply  304  provides 5 VDC power to the module  300  and other devices or components of an associated host device, such as the host device  104  or  201 . The connection  308  is a wire, trace, connector, or other conductor. Power or current via  308  allocated to module  300  is limited according to a system power budget and/or according to current ratings of conductors delivering the power. For example, the connection  308  may be rated at about 1 Ampere. 
     The load device  316  is a modem, processor, data communication device, or other device that periodically draws different power levels during operation. The load device  316  of one embodiment may be a low voltage digital component or integrated circuit and/or an analog component or circuit. For example, the load device  316  may be a wireless GSM modem operating from a 3.3 VDC power source. The load device intermittently or periodically requires, pulls, uses, or draws peak power or current during its operation. Peak or a higher current is drawn during these operation intervals in order to support the peak power demand. For example, higher peak power bursts or pulses may draw a higher current during transmission modes of the load device compared to that of receive or other modes. 
       FIG. 4  shows a current pattern over time that corresponds to the power consumption or current draw of the load device  316 . High power or current intervals, periods, or bursts  400  are periodically repeated during operation of the load device  316 . Each of the high power bursts may have a duration of at least about one millisecond. For example, a duty cycle of the peak demand is typically less than about 20% of the total combined peak and non-peak periods. Therefore, an average current or power  408  is less than the peak current or power of the high power bursts  400 . Alternatively, the high power bursts  400  may have shorter or longer duration timings. During these periods, a higher current, such as 2.5 A, is desired by the load device  316  to operate at a peak capacity. For example, the high power or current periods correspond to transmission of data or a transmit processing. During intermediate intervals or periods  404 , the load device  316  uses less power or current. The intermediate intervals or periods  404  may correspond to receive operations or other modes. The high power bursts  400  and the intermediate intervals or periods  404  may have a constant or varying periodic pattern during operation of the load device  316 . 
     Referring back to  FIG. 3 , the circuit  312  is used to provide an ample, sufficient, or desired amount of power or current to the load device  316  for operation as well as limit current drawn from the main power supply  304 . The circuit  312  includes a diode  320 , a current limiter  324 , a capacitor  328 , and a voltage regulator  332 . Fewer, more, or different components may be provided. Less, at, or more than the peak desired power may be provided. 
     The anode of the diode  320  couples with the connection  308 , and the cathode of the diode  320  couples with the current limiter  324 . An output of the current limiter  324  couples with the capacitor  328 . The other end of the capacitor  328  is coupled with a ground or other return path. The connection point of the capacitor  328  and the output of the current limiter  324  is also coupled with an input to the voltage regulator  332 . An output of the voltage regulator  332  is coupled with the load device  316 . The connections of the components may be made using traces, such as copper, gold, silver, or other elements, vias, or other conductors. The components of the circuit  312  may be discrete components or integrated components. 
     The diode  320  is a Schottky diode, other type of diode, or another device configured to pass current in a forward direction and block current in a reverse direction. For example, the diode  320  is a Schottky diode. The diode  320  allows current to pass from the main power supply  304  to other components. The diode  320  also acts as a protection device to prevent or prohibit reverse current from flowing from other components, such as the capacitor  328 , to the main power supply  304 . The diode  320  of one embodiment may provide a voltage drop of about 0.3 volts or more. 
     The current limiter  324  may be a fixed or configurable current limiter. For example, the current limiter  324  is a configurable current limiter integrated circuit (“IC”), such as the MIC2544 from Micrel Semiconductor, Inc. of San Jose, Calif. The current limiter  324  allows a maximum current to be drawn into its input. The value of the maximum limited current is less than or below a desired maximum current value according to the allocated budget for module  300  for operation of the load device  316 . For example, the current limiter  324  is set to limit the current from the main power supply to at most about 1 A. Because of the maximum current value, the load device  316  may draw at most about 5 Watts average power from the main power source  304 . Other maximum current values or powers may be set. The current limiter  324  may be configured before or during manufacturing or by a user during operation of the module  300  or load device  316 . For example, the current limiter  324  may be programmed or set on an assembly line and/or by a user via a computer or processor commands. 
     The capacitor or charge storage device  328  (hereinafter referred to as the “capacitor  328 ”) may be a metal-insulator-metal (“MIM”) capacitor, ceramic capacitor, a tantalum capacitor, a discrete capacitor, other capacitor, a rechargeable battery, and/or another device operable to hold and supply a charge or current. For example, the capacitor  328  is a 33 milliFarad (“mF”) capacitor, such as the BZ055A from AVX Corp. of Myrtle Beach, S.C. Alternatively, other capacitance values may be used. The capacitor  328  charges up during low power demand periods, such as during the intermediate intervals  404  of the load device  316 , and provides reservoir power or current during periods of heavy power consumption, such as during the peak or high power intervals  400  of the load device  316 . 
     The capacitor  328  has a low equivalent series resistance (“ESR”) and a size compatible with spacing and arrangement on or in the circuit  312  and/or module  300 . The capacitor  328  has a large capacitance so that it can supply adequate current during the high power bursts  400 . For example, the capacitor  328  of one embodiment provides at least about 1.5 A during the high power intervals  400  of the load device  316 . Therefore, during the high power intervals  400 , the current limiter  324 , which provides a limited maximum current, and the capacitor  328 , in combination, supply an adequate, sufficient, or desired amount of power or current to the load device  316 , such as 2.5 Amperes. The adequate or sufficient amount of power or current may be more, less, or at the desired power or current. 
     The voltage regulator  332  is a linear regulator, a low dropout (“LDO”) regulator, or other voltage regulator that provides a substantially noise or jitter free output. For example, the voltage regulator  332  is a LDO regulator that can respond quickly to changing load current demands while receiving power from the current limiter  324  and the capacitor  328 . The voltage regulator  332  steps down the voltage at the input to a lower voltage used to operate the load device  316 . For example, the voltage regulator  332  converts at least about 5 VDC to about 3.3 VDC. By using at least about 5 VDC, the main power supply  304  is able to provide a range of voltages to various components of the module  300 . Also, because the load device  316  is powered at about 3.3 VDC, a higher voltage from the main power supply  304 , such as 5 VDC, is beneficial because other components, such as the diode  320 , can be used even though they generate voltage drops. 
     The voltage regulator  332  maintains a substantially constant and noise free output voltage even though the input voltage may vary. Using a linear voltage regulator allows for a substantially noise free output signal, which is beneficial in transmission or reception operations, such as operations by transceivers. On the other hand, a switching power supply or boost converter may not provide a relatively noise free output, which may impact the performance of the load device  316 . 
     In operation, the circuit  312  limits current from the main power supply  304 . The current from the main power supply  304  is below a desired current that the load device  316  uses during high power bursts  400 . However, the capacitor  328  supplies additional current to the load device  316  during the high power bursts to satisfy the desired current and compensate for the limited current. This may allow for ideal or peak operation of the load device  316  as well as a reduced size and/or rating of the main power supply connections, such as the connection  308 . The reduced size or ratings of the connections decreases cost and helps in reducing size of a host device, such as the host device  104  and  201 , especially when a plurality of modules  300  are connected with the host device. Also, power is conserved from the main power supply  304 . 
       FIG. 5  shows an exemplary method for supplying power. Fewer or more acts may be provided. In act  501 , a load device, such as the load device  316 , is enabled or operated. For example, one or more modules, such as the modules  213  or  300 , are placed in a host device, such as the host device  104  or  201 . The host device is turned on for communications. For example, a wireless router connected with a site network, system, and/or devices wirelessly transmits and receives data from an external network, such as the network  108 . The host device supplies power to the module(s). The load devices periodically pull more power or current in high power bursts or intervals, such as the high power bursts  400 . For example, during transmission processing, the load devices may desire at least 2.5 A for at least one or more millisecond power bursts. The current for the high power bursts allows the load devices to transmit in a maximum range or allows for a higher quality transmission. 
     In act  505 , a current or power from a power supply of the host device, such as the main power supply  304 , is limited. For example, current drawn by module  300  during a high or peak power interval from the host power supply  304  is limited. A current limiter, such as the current limiter  324 , may be used. A maximum current limit value is set prior to operation of the load device. Alternatively, the maximum current limit value may be set or changed during operation by a user or by a dynamic set of logic. For example, a feedback circuit, sensors, or other indicators may be used to dynamically change the maximum current limit. A maximum current limit value may be set to at most about 1 A. Other current values may be used. 
     In act  509 , supplemental power or current is supplied to the load device. During intermediate intervals  404 , load device current demand is less than the current limiter&#39;s available 1 Ampere capacity. During these intermediate periods  404 , a capacitor, such as the capacitor  328 , is recharged using remaining available current from the current limiter. For example, during intermediate intervals  404 , the load device may be supplied with current drawn solely from the power supply of the host device. The capacitor provides supplemental current to voltage regulator  332  for delivery to the load device during high or peak power load bursts. During high or peak power bursts, such as the intervals  400 , supplemental current from the capacitor combined with the limited current satisfies or provides a desired, adequate, or ample amount of current or power to the load device. Without the supplemental current, the load device may have to operate at less than optimum level because the limited current value is below a desired current value for operation during the high power intervals. The supplemental current may be at least about 1.5 A in one embodiment. Alternatively, other additional current values may be used. The additional current or charge may be prevented from flowing to the power supply of the host device. For example, a diode, such as the diode  320 , may be used to prohibit reverse current. 
     In act  513 , a substantially constant and substantially noise free voltage is supplied to the load device. For example, a substantially constant and noise free voltage is applied to the load device while current varies between low and high power intervals. The substantially constant and noise free voltage is a stepped down voltage from the power supply of the host device. For example, 5 VDC of the host power supply is converted to about 3.3 VDC. A voltage regulator, such as the voltage regulator  332 , may be used to provide the substantially constant and noise free voltage. Reduction of noise in the supply power may benefit the operation of the load device, such as allow for better quality in modem operations. 
       FIG. 6  is a method for manufacturing or providing a power supply circuit. Fewer or more acts may be provided. In act  600 , a current limiter, such as the current limiter  324 , is provided. The current limiter may be attached or soldered on a printed circuit board associated with a module, such as the module  213  or  300 . For example, the printed circuit board is an integral part of the module or may be attachable and removable from the module. The current limiter is configured to attach with a main power supply, such as the main power supply  304 . 
     In act  604 , a diode, such as the diode  320 , is connected with an input of the current limiter. For example, the cathode of the diode is connected with the input of the current limiter, and the anode of the diode is configured to connect with the main power supply or connections thereof. Alternatively, the diode may be connected at the output of the current limiter before a capacitor connection. A capacitor, such as the capacitor  328 , is connected with an output of the current limiter, in act  608 . The other end of the capacitor is connected with a ground or other return path connection. 
     In act  612 , the output of the current limiter and the end of the capacitor connected with the output of the current limiter are connected with an input of a linear voltage regulator, such as the voltage regulator  332 . In act  616 , an output of the linear voltage regulator is connected with a load device, such as the load device  316 . 
     The connections made between the components may be made by soldering, printing, etching, or other manufacturing processes. The order of connections may be changed to produce a similar circuit. Various components may be placed on different sides or inner layers of a circuit board. 
     The logic, software or instructions for implementing the processes, methods and/or techniques discussed above are provided on computer-readable storage media or memories or other tangible media, such as a cache, buffer, RAM, removable media, hard drive, other computer readable storage media, or any other tangible media. The tangible media include various types of volatile and nonvolatile storage media. The functions, acts or tasks illustrated in the figures or described herein are executed in response to one or more sets of logic or instructions stored in or on computer readable storage media. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firmware, micro code and the like, operating alone or in combination. Likewise, processing strategies may include multiprocessing, multitasking, parallel processing and the like. In one embodiment, the instructions are stored on a removable media device for reading by local or remote systems. In other embodiments, the logic or instructions are stored in a remote location for transfer through a computer network or over telephone lines. In yet other embodiments, the logic or instructions are stored within a given computer, central processing unit (“CPU”), graphics processing unit (“GPU”) or system. 
     While the invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.