Abstract:
Methods and systems for charging energy storage devices are disclosed. Often the charging circuit may have different levels of power available to charge the energy storage device depending on the state of other subsystems of the electronic system. The present invention provides a source power limiting charging system. Often the losses of the charging system and losses due to the power requirements of support systems are not well known and/or are variable. Controlling source power to the charging system maximizes the amount of power delivered to the energy storage device for a given value of these losses and avoids power contention with the other elements of the electronic system. Therefore, the power drawn from the power source by a controllable power limiting charging circuit is controlled to be less than a source power limit.

Description:
BACKGROUND 
       [0001]    1. Background Field 
         [0002]    The present invention relates to power charging systems for energy storage devices. 
         [0003]    2. Relevant Background 
         [0004]    In many electronic systems, in particular data storage systems, unexpected power failures may cause loss of data or other problems. Thus, many such electronic systems include a backup power system to provide temporary power to the electronic system during a power failure. Typically, the electronic system performs shut down operations to prevent data loss.  FIG. 1  is a block diagram of an electronic system  100 , having a power source  110 , a functional device  120 , and a conventional backup power system  130 . Functional device  120  performs the main function of electronic system  100 . Power source  110  provides power to functional device  120  and to backup power system  130 . Backup power system  130  is configured to store energy from power source  110  and to provide power to functional device  120  in case power source  110  fails. 
         [0005]    Backup power system  130  includes a power path control circuit  131 , a charging circuit  133 , an energy storage device  135 , and a discharge circuit  137 . When power source  110  is available, power path control circuit  131  is configured to pass power from power source  110  to charging circuit  133  and to functional device  120 . The discharge circuit  137  is configured to prevent power transfer from energy storage device  135  to functional device  120 . Charging circuit  133  modifies the power from power source  110  as necessary to charge energy storage device  135 . Generally, energy storage device  135  is a battery, capacitor, inductor, or other device capable of storing energy. 
         [0006]    If power source  110  fails, power path control circuit  131  and discharge circuit  137  are configured to allow power to pass from energy storage device  135  to functional device  120  through discharge circuit  137  and power path control circuit  131 . Generally, functional device  120  is informed that power is being supplied by backup power system  130  so that appropriate measures can be performed to prevent data loss in functional device  120 . For example, if functional device  120  includes volatile memory, the contents of the volatile memory can be written to non-volatile memory such as Flash RAM or disk drives. 
         [0007]    In many electronic systems, power source  110  only provides a limited amount of power. For example for some systems, power source  110  is supplied through a standard bus, such as PCI, where a limited amount of power is available to each device. Generally, backup power system  130  draws more power when energy storage device  135  is discharged and gradually draws less power as energy storage device is charged. However, functional device  120  may have other components that also require additional power upon activation. Thus, when electronic system  100  is initially activated, there may be contention between functional device  120  and backup power system  130  for power from power source  110 . Hence there is a need for a method and system for controlling the power draw of a charging circuit to prevent power contention with a functional device. 
       SUMMARY 
       [0008]    Electronic systems often have a limited amount of power available and thus require management of the power of individual subsystems. One functional block often present in electronic systems is a charging system with an energy storage device. Often the charger circuit may have different levels of power available to charge the energy storage device depending on the state of other subsystems of the electronic system. The present invention provides a source power limiting charging system. Often the losses of the charging system and losses due to the power requirements of support systems are not well known and/or are variable. Controlling source power to the charging system maximizes the amount of power delivered to the energy storage device for a given value of these losses and avoids power contention with the other elements of the electronic system. 
         [0009]    In accordance with the present invention a power system includes an energy storage device and a power limiting charging circuit. The power limiting charging circuit is configured to draw a limited amount of source power from a power source to charge the energy storage device. Specifically, the power limiting charging circuit receives a power limit parameter that defines a source power limit. Power limited charging circuit draws an amount of source power that is less than the source power limit and provides a charge power to the energy storage device. Some embodiments of the present invention also include a power sensing circuit between the power source and the power limited charging circuit to sense source power information, which may include source current value of a source current or a source voltage value of a source voltage. 
         [0010]    The present invention will be more fully understood in view of the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a simplified block diagram of an electronic system with a conventional backup power system. 
           [0012]      FIG. 2  a simplified block diagram of an electronic system in accordance with one embodiment of the present invention. 
           [0013]      FIG. 3  is block diagram of a power sensing circuit in accordance with one embodiment of the present invention. 
           [0014]      FIG. 4  is block diagram of a controllable power limiting charging circuit in accordance with one embodiment of the present invention. 
           [0015]      FIG. 5  is a flow diagram for a charge control circuit in accordance with one aspect of the present invention. 
           [0016]      FIG. 6  is a block diagram of an energy storage device in accordance with one aspect of the present invention. 
           [0017]      FIG. 7  a simplified block diagram of an electronic system in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    As explained above, backup power systems may have power contention issues with the functional device in an electronic system. However, in accordance with the present invention, a power limiting backup power system makes use of a power limiting charging circuit to limit the amount of power drawn from the power source. Specifically, the amount of power used by a power limiting backup power system can be controlled by a power limit parameter P_LIM.  FIG. 2  shows a block diagram of an electronic system  200  that includes a power source  210 , a functional device  220 , and a power limiting backup power system  230  in accordance with one embodiment of the present invention. Power source  210  provides power to functional device  220  and power limiting backup power system  230 . If power source  210  fails, power limiting backup power system  230  provides power to functional device  220 . Unlike conventional backup power systems, power limiting backup power system  230  is controlled by a power limit parameter P_LIM. Specifically, power limit parameter P_LIM defines a source power limit. In some embodiments of the present invention, power limit parameter P_LIM is provided by functional device  220 . Power limiting backup power system  230  draws no more power than the source power limit as explained below. Furthermore, power limiting backup power system  230  also receives an energy storage device full parameter ESD_F, which is used to determine when to transition from a charging mode to a maintenance mode as described below. Generally, energy storage device full parameter ESD_F should define an amount of energy that allows functional device  220  to shut down without error. Thus, in some embodiments of the present invention, energy storage device full parameter is provided by functional device  220 . 
         [0019]    Power limiting backup power system  230  includes a power path control circuit  231 , a power sensing circuit  233 , a controllable power limiting charging circuit  235 , an energy sensing circuit  236 , an energy storage device  237 , and a discharge circuit  239 . 
         [0020]    When power source  210  is available, power path control circuit  231  is configured to pass power from power source  210  to functional device  220  and pass power from power source  210  to controllable power limiting charging circuit  235  through power sensing circuit  233 . Discharge circuit  239  is configured to prevent power transfer through discharge circuit  239 . Controllable power limiting charging circuit  235  modifies the power from power source  210  as necessary to charge energy storage device  237 . Power sensing circuit  233  measures the power drawn from power source  210  by controllable power limiting charging circuit  235  and provides power usage information PUI to controllable power limiting charging circuit  235 . Controllable power limiting charging circuit  235  prevents the power usage from exceeding power limit parameter P_LIM. Generally, controllable power limiting charging circuit  235  can reduce the power usage from power source  210  by reducing charge voltage V_C, charge current I_C, or a combination of charge voltage V_C and charge current I_C. 
         [0021]    In some embodiments of the present invention, power sensing circuit  233  may be placed between power source  210  and power path control circuit  231 . In these embodiments power sensing circuit can sense the combined power usage of both power limiting backup power system  230  and functional device  220 . Furthermore, some embodiments of the present invention may include another power sensing circuit in between power path control circuit  231  and functional device  220  to sense the power usage of functional device  220 . 
         [0022]    Energy sensing circuit  236  measures the amount of energy stored in energy storage device  237  and provides energy storage information ESI to controllable power limiting charging circuit  235 . In one embodiment of the present invention energy sensing circuit  236  includes a current sensor and a voltage sensor. 
         [0023]    For clarity, the voltage, current, and power from power source  210  to controllable power limiting charging circuit  235  is referred to as source voltage V_S, source current I_S and source power P_S. Conversely, the voltage, current, and power provided by controllable power limiting charging circuit  235  to energy storage device  237  is referred to as charge voltage V_C, charge current I_C, and charge power P_C. 
         [0024]    In some embodiments of the present invention, power usage information PUI includes both the value of source voltage V_S and the value of source current I_S. In other embodiments, power usage information PUI is the value of source power P_C. In still other embodiments of the present invention, the power usage information PUI only includes the value of source current I_S because the value of source voltage is predefined and not variable or can be independently determined by controllable power limiting charging circuit  235 . Similarly energy storage information may include different types of information depending on the implementation of energy storage device  237 . For example for capacitor based energy storage devices, energy storage information ESI may be the voltage of the energy storage device  237 . For other embodiments, energy storage information ESI may be a current measurement or a power measurement. Generally, energy storage information ESI is correlated with energy storage device full parameter ESD_F. 
         [0025]    If power source  210  fails, power path control circuit  231  and discharge circuit  239  are configured to pass power from energy storage device  237  to functional device  220 . Furthermore, controllable power limiting charging circuit  235  stops charging energy storage device  237 . In some embodiments of the present invention energy storage device  237  also powers some or all parts of power limiting backup power system  230  when power source  210  is unavailable. 
         [0026]    In some embodiments of the present invention, portions of power limiting backup power system  230  may be included in functional device  220 . For example control functions of controllable power limiting charging circuits  235  may be carried out by controllers (such as microprocessors or microcontrollers) on functional device  220 . 
         [0027]      FIG. 3  is a simplified block diagram of a power sensor  300  that can be used as power sensing circuit  233  ( FIG. 2 ). Power sensor  300  includes a current sensor  310  that measures the value of source current I_S and a voltage sensor  320  that measures the value of source voltage V_S. The values measured by current sensor  310  and voltage sensor  320  are provided to controllable power limiting charging circuit  235  as power usage information PUI. Current sensors and voltage sensors are well known in the art. Any of the well known conventional current sensors and voltage sensors can be used with the present invention. 
         [0028]      FIG. 4  is a block diagram of a controllable power limiting charging circuit  400  which can be used in place of controllable power limiting charging circuit  235  ( FIG. 2 ). Controllable power limiting charging circuit  400  includes a charge control circuit  410  and a power regulator  420 . Charge control circuit  410  receives energy storage information, ESI, power usage information PUI, energy storage device full parameter ESD_F, and power limit P_LIM. Charge control circuit  410  controls the function of power regulator  420  using one or more power regulator control signals PR_CS. Depending on the implementation of power regulator  420 , Charge control circuit  410  may use power regulator control signals PR_CS with variable voltage, variable current, or a combination of variable voltages and currents, to control power regulator  420 . Charge control circuit  410  can be implemented for example with a microcontroller, discrete circuitry, field-programmable gate arrays, or an application specific integrated circuit. For example, in a specific embodiment of the present invention, charge control circuit  410  is implemented using two microcontrollers (part number ST72F344K4T6) from ST Microelectronics. In some embodiments of the present invention, part or all of charge control circuit  410  can be placed on functional device  220 . 
         [0029]    In many embodiments of the present invention, charge control circuit  410  also controls power path control circuit  231  and discharge circuit  239 . In a specific embodiment of the present invention, charge control circuit  410  can be powered by power source  210  or energy storage device  237 . Specifically, when power source  210  provides greater voltage than energy storage device  237 , then power source  210  powers charge control circuit  410 . However, when energy storage device  237  provides greater voltage than power source  210 , then energy storage device  237  powers control circuit  410 . The performance of charge control circuit  410  is described below and shown in  FIG. 5 . 
         [0030]    Power regulator  420  can be implemented using a variety of circuits. For example, power regulator  420  can be an inverting or non-inverting switching regulator such as a SEPIC (single ended primary inductor converter), a buck regulator, a buck-boost regulator, a boost regulator, a flyback regulator, or a linear regulator such as a low dropout regulator or a inverting or non-inverting switched capacitor regulator. Power regulator  420  receives source power P_S (from power source  210  ( FIG. 2 )) and provides charge power P_C (to energy storage device  237  ( FIG. 2 )). Charge control circuit  410  controls power regulator  420  with one or more power regulator control signals PR_CS. In a specific embodiment of the present invention, power regulator  420  is an LTC3770 buck regulator manufactured by Linear Technology. 
         [0031]      FIG. 5  is a flow diagram  500  for charge control circuit  410 . On power up, flow diagram  500  begins at RECEIVE POWER INFORMATION  510  and receives power information such as power limitation parameter P_LIM, power usage information PUI (such as the value of source voltage V_S and the value of source current I_S), energy storage device full parameter ESD_F, energy storage information (such as the value of charge voltage V_C). The values of source voltage V_S and/or source current I_S can be used to determine the state of power source  210 . For example if the value of source voltage V_S or source current I_S is zero or below certain thresholds then charge control circuit  410  can determine that power source  210  is not available. For example in one embodiment of the present invention, when the value of source voltage V_S is less than the value of charge voltage V_C as provided by energy storage device  237 , then charge control circuit  410  considers power source  210  to be unavailable. If charge control circuit  410  determines that power source  210  is unavailable, charge control circuit  410  transitions to POWER DISCHARGE MODE  570 . IN POWER DISCHARGE MODE  570 , discharge circuit  239  and power path control circuit  231  are configured to allow energy storage device  237  to supply power to functional device  220 . Furthermore, in some embodiments of the present invention, energy storage device  237  also provides power to some or all parts of power limiting backup power system  230 . When power source  210  becomes available, charge control circuit  410  returns to RECEIVE POWER INFORMATION  510 . 
         [0032]    While in RECEIVE POWER INFORMATION  510 , when charge control circuit  410  determines that the power source  210  is available, charge control circuit  410  also determines whether energy storage device  237  is full. In accordance with one embodiment of the present invention, energy storage device full parameter ESD_F is a voltage parameter. Energy storage device  237  is considered full if the voltage of energy storage device  237  is equal to or greater than energy storage device full parameter ESD_F. 
         [0033]    If power source  210  is available and energy storage device  237  is not full, then charge control circuit  410  transitions to CALCULATE POWER AVAILABILITY  520  and calculates a power availability value P_AV, which is equal to the source power limit (as defined by power limit parameter P_LIM) minus the amount of power currently being drawn from power source  210 , which is provided by or can be calculated from power usage information PUI. Then, charge control circuit  410  transitions to CALCULATE NEW CONTROL SIGNALS  530 . 
         [0034]    In CALCULATE NEW CONTROL SIGNALS  530 , charge control circuit  410  calculates new values for power regulator control signal(s) PR_CS. In some embodiments of the present invention, the new values for power regulator control signal(s) are calculated so as to reduce the magnitude of power availability value P_AV to zero. In other embodiments of the present invention a more iterative approach is used so that the new values for power regulator control signal(s) reduces the magnitude of power availability value P_AV by some amount each iteration. 
         [0035]    Then, in DRIVE NEW CONTROL SIGNALS  540 , charge control circuit  410  drives power regulator control signal(s) PR_CS to the new values. After which, charge control circuit  410  transitions back to RECEIVE POWER INFORMATION  510 . 
         [0036]    In RECEIVE POWER INFORMATION  510 , if charge control circuit  410  detects that power source  210  is available and that energy storage device  237  is full, charge control circuit  410  transitions to CALCULATE HOLD CONTROL SIGNAL  550 . In CALCULATE HOLD CONTROL SIGNAL  550 , charge control circuit  410  calculates hold values for power regulator control signal(s) PR_CS so that the energy in energy storage device  237  is maintained. The hold values to maintain charge in energy storage device  237  depends on the implementation of energy storage device  237 . For example, if energy storage device  237  is a battery, charge control circuit  410  would configure power regulator  420  to provide a trickle charge or a float voltage to energy storage device  237 . If energy storage device  237  is formed using capacitors, charge control circuit  410  would configure power regulator  420  to maintain the voltage in energy storage device  237  or provide a small current to compensate for leakage in the capacitors. Then, control circuit  410  drives the hold values on power regulator control signal(s) PR_CS in DRIVE HOLD CONTROL SIGNAL  560 . Charge control circuit  410  then transitions to RECEIVE POWER INFORMATION  510 . 
         [0037]      FIG. 6  is a block diagram of a energy storage device  600  which can be used in place of energy storage device  237 . Energy storage device  600  includes capacitors  610 ,  620 , and  630  coupled in series between power input output terminal P_IO and ground. In a specific embodiment of the present invention capacitors  610 ,  620 , and  630  are manufactured by Cooper Bussman and have a part number of B1860-2R5107-R. 
         [0038]      FIG. 7  shows a block diagram of an electronic system  700 . Because electronic system  700  is very similar to electronic system  200  ( FIG. 2 ), the same reference numerals are used for identical elements. For brevity, the description of identical elements is not repeated. Electronic system  700  includes a power source  210 , a functional device  220 , and a power limiting backup power system  730 . Power limiting backup power system  730  differs from power limiting backup power system  230  ( FIG. 2 ) by including an isolation circuit  738  between controllable power limiting charging circuit  235  and energy sensing circuit  236 . For certain types of energy storage devices, and/or power regulators, the power regulator is not capable of initializing while connected to the energy storage device  237 . Thus, isolation circuit  738  is activated to isolate energy storage device  237  from controllable power limiting charging circuit  235 . After energy sensing information ESI is received by controllable power limiting charging circuit  235 , power regulator  420  is initialized to match certain conditions (such as the voltage) of energy storage device  237 . Then isolation circuit  738  is deactivated which recouples energy storage device  237  to controllable power limiting charging circuit  235 . 
         [0039]    In the various embodiments of the present invention, novel methods and systems have been described for charging a energy storage device with a controllable power usage of the power source. By limiting the power drawn from the power source, contention between a functional device and a backup power system can be greatly reduced. The various embodiments of the structures and methods of this invention that are described above are illustrative only of the principles of this invention and are not intended to limit the scope of the invention to the particular embodiments described. For example, in view of this disclosure those skilled in the art can define other energy storage devices, switches, power sensing circuits, controllable power limiting charging circuits, charge control circuits, and so forth, and use these alternative features to create a method, or system according to the principles of this invention. Thus, the invention is limited only by the following claims.