Patent Abstract:
A system includes an input configured to connect to a power source providing an input voltage, an output configured to connect to a load and to transfer power from the power source to the load, a battery selectively coupled to the input to receive current from the power source, a detector configured to indicate whether the input voltage drops more than a threshold amount, and a processor configured to regulate the selective coupling of the battery to the input to regulate a charging current supplied to the battery, the processor configured to regulate the selective coupling such that if a first charge current induces a drop in the input voltage beyond the threshold amount, then the processor will change the charging current to a second charge current that is lower than the first charge current.

Full Description:
BACKGROUND 
     A battery charger is a type of system for use in charging a rechargeable battery so that the battery may be recharged or its charge maintained. Some battery charging systems are capable of providing power from a single power supply to both a load and to a battery. Examples of loads include modems, computers, telephones, and anything else capable of drawing electrical power. In such battery charging systems, the battery may be used to provide standby power to the load in the event of loss of power from the power supply. 
     Many types of power supplies are current limited, such as, for example, AC to DC power converters. For example, many AC to DC power converters include foldback current limiting protection circuitry. This protection circuitry limits the amount of current at increasing overloads. 
     In some situations, the power supply may be unable to provide sufficient power to both the load and to charge the battery. For example, the load may be temporarily increased so that a large amount of current is being drawn from the power supply. If the battery charger attempts to use the maximum charging current to power the increased load and the battery, it may draw too much current and cause the power supply to have a reduced output voltage. This may result in the supported load falling out of regulation. 
     As an example,  FIGS. 1-4  illustrate exemplary curves for four different types of power sources.  FIG. 1  illustrates a voltage versus current curve for a power supply with gradual current limit. As illustrated, the voltage gradually falls from 100% to about 90% of maximum as the current approaches 100% of the rating of the power supply. Beyond 100%, the voltage drops dramatically.  FIG. 2  illustrates an exemplary voltage versus current curve for a power supply with a hard current limit. As illustrated, this voltage stays at approximately 100% as the current approaches 100% of the rating of the power supply, but drops off to 0 beyond this point.  FIG. 3  illustrates an exemplary voltage versus current curve for an unregulated power supply while  FIG. 4  shows a curve for a fold-back current limit. All of the power supplies illustrated in  FIGS. 1-4  share the common feature that as the current is increased, the voltage drops as the power supply crosses 100% of the rating of the power supply. 
     In prior systems, a switch was used to provide power to the battery and the load. This switch had two levels, on or off. That is, if the switch was on, the battery was charged at a designed rate, and if it was off, the battery was not charged. In this system, when the power drawn by the load exceeded a threshold, the switch was turned off, thus turning off all charging power to the battery. Thus, if this high power condition persisted for a sufficient period of time, it could result in the battery becoming discharged and the system not having available standby power. This was true regardless of the amount of power drawn by the load over the threshold. Thus, the situation could arise where the switch was completely turned off even though the power drawn by the load only exceeded the threshold by a small amount. 
     SUMMARY 
     In general, in an aspect, the invention provides a method for use in a battery charging system, the method including providing power from a power source to a load, the provided power having an input voltage, providing current from the power source to a battery at a first level, monitoring a voltage associated with the input voltage to determine if the input voltage drops below a threshold voltage, and reducing the current supplied from the power source to the battery in response to detecting that the input voltage dropped more than the threshold amount such that the current supplied to the battery is provided at a desired level that is below the first level. 
     Implementations of the invention may include one or more of the following features. Reducing the current supplied from the power source to the battery includes: reducing the current provided from the first level to a second level; and gradually increasing the current supplied from the power source to the battery from the second level to the desired level. Gradually increasing the current supplied from the power source to the battery includes repeatedly reducing the desired level in response to determinations of drops in the input voltage below the threshold voltage during the gradual increasing of the current supplied to the battery and gradually increasing the current supplied to the battery from levels below the reduced desired levels toward a present desired level until the current supplied to the battery reaches the present desired level. Reducing the desired level includes reducing the desired level by a predetermined amount. Reducing the desired level includes reducing the desired level by an amount determined based on an amount of energy provided to the load. The method further includes: evaluating whether a time period has elapsed from a time when the desired level is reduced; and setting the desired level to a maximum desired level if the time period has elapsed. Gradually increasing the current supplied from the power source to the battery includes increasing the current by predetermined amounts. The desired level is greater than an initial level. 
     In general, in another aspect, the invention provides a system including an input configured to connect to a power source providing an input voltage, an output configured to connect to a load and to transfer power from the power source to the load, a battery selectively coupled to the input to receive current from the power source, a detector configured to indicate whether the input voltage drops more than a threshold amount, and a processor configured to regulate the selective coupling of the battery to the input to regulate a charging current supplied to the battery, the processor configured to regulate the selective coupling such that if a first charge current induces a drop in the input voltage beyond the threshold amount, then the processor will change the charging current to a second charge current that is lower than the first charge current. 
     Implementations of the invention may include one or more of the following features. The processor is further configured to gradually increase the charging current in the absence of the input voltage dropping more than the threshold amount. The processor is configured to limit the charging current to a predetermined highest charging current. The processor is configured to: gradually increase the charge current to the battery from the second charge current to a desired charge current; repeatedly reduce the desired charge current in response to drops in the input voltage below the threshold amount during the gradual increasing of the charge current; and gradually increase the charge current supplied to the battery from levels below the reduced desired charge currents toward a present desired charge current until the current supplied to the battery reaches the present desired charge current. The processor is further configured to reduce the desired charge current by a predetermined amount. The processor is further configured to reduce the desired charge current by an amount determined based on amount of power provided to the load. The processor is further configured to: evaluate whether a time period has elapsed from a time when the desired charge current is reduced; and set the desired charge current to a maximum desired charge current if the time period has elapsed. The time period is at least as long as an expected maximum duration of a maximum current draw by the load. The processor is further configured to increase the charge current by predetermined increments. 
     In general, in another aspect, the invention provides an uninterruptible power supply (UPS) configured to couple to a power source that provides an input voltage and to a load, the UPS comprising an input configured to couple to the power source, an output configured to couple to the load, and a battery charger coupled to the input to receive the input voltage and comprising: a battery; a monitor connected and capable of monitoring a voltage associated with the input voltage and capable of determining that the input voltage drops below a threshold voltage; and a switch configured and coupled to provide power from the power source to the load and current from the power source to the battery, the switch being adjustable to provide a range of charge current amounts to the battery, where the monitor includes means for directing the switch to reduce the current supplied from the power source to the battery in response to detecting that the input voltage drops below the threshold such that the current supplied to the battery is provided at a reduced level below a desired level and greater than an initial level. 
     Implementations of the invention may include one or more of the following features. The directing means is further for directing the switch to increase the current from the power source to the battery from the reduced level toward the desired level in the absence of the input voltage dropping below the threshold voltage. The directing means is further for reducing the desired level in response to the input voltage dropping below the threshold voltage and for increasing the desired level to a maximum level in response to a time period elapsing from a time of a most recent reduction in the desired level without the input voltage dropping below the threshold voltage. 
     In accordance with implementations of the invention, one or more of the following capabilities may be provided. Battery charging may be accomplished without unacceptably affecting power provided to a load by a power source that powers the load and provides the battery charging. Battery charging may be accomplished in the presence of a varying load power demand. Battery charging current from a source can be adjusted to maximize, or nearly maximize, the current without substantially negatively affecting power provided to other devices from the source. An appropriate battery charging current from a power supply can be determined without knowing a current limit of the power supply or an output load current. Amounts of current allowed into a battery can be controlled. 
     These and other capabilities of the invention, along with the invention itself, will be more fully understood after a review of the following figures, detailed description, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a voltage versus current curve for a power supply with gradual current limit, in accordance with the prior art. 
         FIG. 2  illustrates an exemplary voltage versus current curve for a power supply with a hard current limit, in accordance with the prior art. 
         FIG. 3  illustrates an exemplary voltage versus current curve of an unregulated power supply, in accordance with the prior art. 
         FIG. 4  illustrates an exemplary voltage versus current curve for a supply with a fold-back current limit, in accordance with the prior art. 
         FIG. 5  is a simplified block diagram of an exemplary system for use in supplying power to a load and charging a battery. 
         FIG. 6  is a block flow diagram of a process for adaptively supplying power to the battery in the system shown in  FIG. 5 . 
         FIG. 7  is a simplified block diagram of a household telecommunications application of the system shown in  FIG. 5 . 
         FIGS. 8-9  are simplified block diagrams showing sample implementations of a battery charger portion of the system shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the invention provide techniques for adaptively charging a battery. For example, a battery of an uninterruptible power supply (UPS) may be charged based on an input voltage. The input voltage is monitored and if it dips more than a designated amount, indicating an inability of an input power source to provide a desired amount of power to a load and to supply the present amount of charging current, then the charging current is reduced. Other embodiments are within the scope of the invention. 
       FIG. 5  illustrates an exemplary system  100  for use in supplying power to a load and charging a battery. As illustrated, the system  100  includes a power source  102 , a battery charging system  104  (e.g., that may be part of a UPS), and a load  106 . The power source  102  may be any of a variety of types of power source, for example an AC to DC power supply that may be plugged into an AC wall outlet. The load  106  is capable of drawing DC power from the power source  102  or a battery  112 , and may be, for example, a modem connected to a telecommunications system. 
     The battery charging system  104 , as illustrated, includes a battery  112 , a power monitoring subsystem  114 , and current controlled charger with a switch  116 . The battery  112  is a rechargeable battery, of which many types exist and may be used. The switch  116  is capable of adjusting the current supplied to the battery  112  and allows the battery to supply power to the load in the event of a failure of the power supply  102 . For example, the switch  116  is a Pulse Width Modulated (PWM) switch capable of adjusting the amount of current provided to the battery  112  in accordance with an opening and closing duty cycle of the switch  116 . The switch  116  may be adjustable across a range of 0 to 100 percent, where when set at 0, all power is provided to the load  106  and none to the battery  112 , and when set to 100%, a predetermined maximum allowable current is delivered to the battery  112 . When the switch  116  is set at 60%, the battery is delivered 60% of its design maximum current leaving the remaining current available for the load  106 . This setting may be referred to as the switch level. The switch  116  as shown in  FIG. 5  is a simplification of various possible implementations.  FIGS. 8-9  show exemplary embodiments of a battery charger including the battery  112  and exemplary embodiments of the switch  116 , here systems  140  and  150 . In the system  140 , a single switch  142  with an inductor  144  is used to limit the current to the battery  112  when a PWM signal is applied to the switch  142 . When the switch  142  is held on, the battery  112  is allowed to power the load through the inductor  144  with minimal loss. In the system  150 , a separate current limiting supply  152  is included to limit the current to the battery  112  as directed by a PWM signal. 
     As illustrated, the power monitoring subsystem  114  includes circuitry for monitoring the voltage of the power provided to the load  106  and adjusting the level of the switch  116  so that more or less power is supplied to the battery  112 . The power monitoring subsystem  114  includes a comparator  124  and a processor  122 . The comparator  124  is connected to a reference voltage  128  and to the power supply  102 , that is here the same as the input to the system  104  and the input to the load  106 . The comparator  124  is configured to compare the input voltage (V in )  130  from the power supply  102  with the reference voltage  128  and indicate to the processor  122  whether the input voltage  130  is below the reference voltage  128  (i.e., drops more than a threshold amount below the expected maximum input voltage). The value of the reference voltage  128  is predetermined based upon knowledge of the input voltage  130  of the supply  102  and an acceptable amount of voltage drop in the supply voltage corresponding to an acceptable decrease in power to the load  106 . The reference voltage  128  may be provided by the processor  122  or other circuitry (not shown). Additionally, in other examples this reference voltage may be adjusted dynamically by the processor  122 , e.g., based on changes in power demand by the load  106  or on measurements of the power supply under no load conditions. 
     The processor  122  is coupled to the comparator  124  to receive the output of the comparator  124 . The processor  122  may include a central processing unit (CPU) and memory that stores software instructions for execution by the CPU, or other configurations such as all hardware, or firmware, or combinations of these, such that the processor  122  is configured to perform the functions described. The processor  122  is configured to control the switch  116  by regulating a PWM signal provided to the switch  116  to adjust the level of the switch corresponding to the PWM signal level/value. The PWM signal controls the switch  116  to close and open according to a duty cycle of the PWM signal. The PWM signal has a maximum duty cycle corresponding to the maximum amount of charging current to be provided to the battery  112 . 
     The processor  122  is configured to control the PWM signal between a PWM-MIN level and a PWM-MAX level. These levels may change, although the processor  122  is preferably programmed with a non-changing highest allowable value for the PWM-MAX level. The PWM-MIN level may be, for example, 0%, although other levels higher than 0 are acceptable, e.g., in cases where a parasitic load is attached to the battery  112  and it is desired not to discharge the battery  112 . The PWM-MIN value may be static or dynamically derived, e.g., depending on the state of the system such as the current drawn by a parasitic load on the battery  112  to ensure some charging current for a dead battery, and/or to ensure that a dead battery is not provided with too much charging current. The PWM-MAX level may be static or dynamically derived, e.g., based upon the current drawn by the load  106  (with higher load currents corresponding to lower PWM-MAX values), or the condition of the battery  112  (e.g., to avoid providing a large charging current to a dead battery), or the maximum charge current allowed by the battery, and/or other factors. 
     The processor  122  is configured to implement a ramp timer. The ramp timer is run when the processor  122  initially issues the PWM signal or increases the PWM signal level. The ramp timer runs for a designated an amount of time for which a new PWM signal level is used before potentially increasing the PWM signal level. The ramp timer preferably runs for a time that is long enough to allow the processor  122  sufficient time to accurately determine the PWM signal level when the input voltage dips, and to allow the charge current corresponding to the PWM signal to reach a steady state. An example of the time provided by the ramp timer is 1 ms. 
     The processor  122  is also configured to implement a PWM-MAX timer. The PWM-MAX timer is reset every time that the PWM signal level is decreased due to an unacceptable drop in the input voltage, corresponding to a decrease in the PWM-MAX level. When the PWM-MAX timer expires, the processor  122  resets PWM-MAX level to the predetermined or dynamically calculated PWM-MAX value. This timer guards against using a low charge current when the load has reduced its current consumption. The PWM-MAX timer is preferably set for a time period that corresponds to the peak load current duration. An example of this value may be 30 seconds for a telecommunication system that supports a telephone ringing operation. 
     Although the above elements of the power supply  102 , the load  106 , and the battery charging system  104  are illustrated as separate entities, two or more these elements in other embodiments may be combined, e.g., in a single entity. 
     In operation, referring to  FIG. 6 , with further reference to  FIG. 5 , a process  200  for adapting battery charging current using the system  100  includes the stages shown. The process  200 , however, is exemplary only and not limiting. The process  200  may be altered, e.g., by having stages added, removed, or rearranged. The process  200  attempts to maximize, or nearly maximize, the amount of current supplied by the source  102  to the battery  112  without unacceptably depriving the load  106  of power. The process  200  helps ensure that the load  106  receives sufficient power to operate acceptably. The process  200  regulates the PWM signal between a minimum level, PWM-MIN, and a maximum level, PWM-MAX. The present PWM signal level is ramped from the PWM-MIN value toward the PWM-MAX value. If during the ramping up, or after achieving the PWM-MAX level, a drop in the input voltage more than a threshold amount is detected, then the PWM-MAX level is adjusted to below the present PWM signal level and the PWM signal level is set to a lower value and ramped up toward the new PWM-MAX level. If the PWM-MAX level is reached, then the system remains charging at this level until the PWM-MAX timer expires. When the PWM-MAX timer expires, the PWM-MAX level can be increased, as high as a highest allowable level, and the PWM signal increased toward this new, increased PWM-MAX level. 
     At stage  202 , the PWM-MAX level is set. The PWM-MAX level is preferably set to a default value, e.g., 60% of the highest allowable PWM-MAX level. 
     At stage  204 , the PWM-MAX timer is set. This timer may be programmed based on the load  106 , and in particular the longest anticipated peak load current duration. 
     At stage  206 , the ramp timer is set. The ramp timer value may be set to a default value such as 1 ms, or may set based on parameters of the system  100 , e.g., the speed of the processor  122  for evaluating input voltage dips, etc. 
     At stage  208 , the PWM-MIN level is set and the PWM signal is issued at the PWM-MIN level. Initially, the PWM-MIN level may be set to a default value, such as 0%, or to a static or dynamically derived value higher than 0% (e.g., to accommodate parasitic loads on the battery  112 ). For subsequent visits to stage  208 , the PWM-MIN level may be reset to a static value, or to a dynamically derived value, e.g., based on system parameters, and/or based on the PWM signal level that induced an input voltage dip as discussed below, and/or other factors. 
     At stage  210 , an inquiry is made as to whether the input voltage  130  drops unacceptably low during running of the ramp timer. The ramp timer is started and the processor  122  monitors the output of the comparator  124 . If this output indicates that the input voltage  130  has dropped below the reference voltage  128 , then the process proceeds to stage  212 , and otherwise proceeds to stage  214  upon expiration of the ramp timer. 
     At stage  212 , the PWM-MAX timer is started and the PWM-MAX level is reset to a lower level than the present value of PWM-MAX. The PWM-MAX level is reset to a level below the present PWM signal level. For example, the new PWM-MAX level may be a fixed amount lower than the present PWM level, such as 5% so that if the present PWM signal level that induced the voltage drop is 50%, the new PWM-MAX level is 45%. Other values fixed reductions could be used. Non-fixed amounts could be used, such as a percentage, e.g., 50%, of the present PWM level. Other non-fixed amounts could be used, as well as combinations of fixed and non-fixed amounts (e.g., 75% of the present PWM signal minus 5%). With the new PWM-MAX level, the process  200  returns to stage  208  for resetting, as appropriate and/or desired, of the PWM-MIN level. The PWM-MIN level may be reset to the default value, or may be based upon factors such as the present PWM signal level that induced the input voltage drop. For example, with a PWM signal level of 50% inducing the drop, the PWM-MIN level may be reset to a level below the new PWM-MAX level, but above the initial PWM-MIN level, such as 20% below the new PWM-MAX level (with appropriate floors being used, e.g., 0% or higher, e.g., due to parasitics, etc.). The change may be static (e.g., fixed percentage increase, fixed percentage of the present value) or dynamically determined. 
     At stage  214 , with no input voltage drop below the threshold voltage  128  detected during the ramp timer&#39;s run, an inquiry is made as to whether the PWM-MAX timer has expired. The processor  122  determines whether the PWM-MAX timer had been activated and has run its course. If not, then the process  200  proceeds to stage  218  and otherwise proceeds to stage  216 . 
     At stage  216 , with the PWM-MAX timer having been activated and now expired, the processor  122  resets the PWM-MAX level. The PWM-MAX level is reset to the predetermined or dynamically derived level as any load-current demand increase that induced a reduction in available charge current should have passed. The process  200  proceeds to stage  218 . 
     At stage  218 , an inquiry is made as to whether the present PWM signal level is at the PWM-MAX level. If not, then the process  200  proceeds to stage  220  and otherwise proceeds to stage  222 . 
     At stage  220 , the PWM signal level is reset/increased. At this point, it has been determined that the present PWM signal level has not induced an unacceptable voltage drop and that the PWM-MAX level has not been reached. The PWM signal is thus reset to a higher level to provide for more charge current for the battery  112 . The new PWM signal level may be a fixed amount higher than the present PWM signal level, e.g., 1% (e.g., present signal level is 50% and new level is 51%), 2%, 5%, 10%, or other amount. Further, the amount may be higher on subsequent visits to stage  216 , e.g., with an initial increase being 1%, the next increase being 2%, the next 5%, etc. The new PWM signal level may also be a non-fixed amount higher than the present level such as a percentage of the present PWM signal, e.g., 105%, or higher by a combination of fixed and non-fixed amounts. The change may be static (e.g., fixed percentage increase, fixed percentage of the present value) or dynamically determined. 
     At stage  222 , with no voltage dip induced during the PWM-MAX timer&#39;s run and with the PWM signal at the PWM-MAX level, an inquiry is made as to whether the PWM signal level is at the highest allowable PWM-MAX level. If so, then the process  200  returns to stage  210  for further monitoring for an input voltage drop, and otherwise proceeds to stage  224 . 
     At stage  224 , the PWM-MAX level is increased. The level may be increased by a fixed amount, e.g., 5%, a non-fixed amount, or a combination of fixed and non-fixed amounts that may be static or dynamically determined. The increase is capped by the predetermined highest allowable PWM-MAX level. Indeed, the PWM-MAX level may be set directly to the highest allowable level. Using the process  200 , if the PWM-MAX level has been set or reset to a value below the highest allowable level, the PWM-MAX level may eventually be set to (or return to) the highest allowable level if unacceptable input voltage drops do not result from increasing the charge current (i.e., the power supply can provide the highest allowable charge current and still acceptably power the load  106 ). With the PWM-MAX level reset, the process  200  proceeds to stage  216  for increasing of the PWM signal level and further evaluation of the input voltage  130  relative to the reference voltage  128 . 
       FIG. 7  illustrates an exemplary embodiment of a system  300  for a telecommunications modem deployed in a household. The system  300  includes a power source  302  that may be, for example, an AC to DC power converter. The system  300  includes a modem  306  connected to a fiber optic cable or coaxial cable for providing telecommunications services, such as those available from a person&#39;s local telephone or cable carrier. The modem  306  is deployed in the house of a user and connected to telephone wiring  308  of the house. The telephone wiring  308  is connected to one or more telephones  322  in the house. End users may use the telephones  322  to place and receive telephone calls in the same manner as used with the plain old telephone system (POTS). Additionally, the modem  306  is here connected to one or more computers  324  via a router  326 , enabling the end user to utilize services, such as high speed Internet access services provided by a telecommunications carrier. 
     Additionally, the system  300  includes a UPS  304  that includes a battery charging system  304  similar to the system  104  shown in  FIG. 5 . The UPS  304  is deployed so that in the event of a power failure, the modem  306  may resort to battery backup. Thus, in the event of a power failure, end users may still be able to communicate using their standard home telephones  322 . 
     Other embodiments are within the scope and spirit of the invention. For example, due to the nature of software, functions described above can be implemented using software, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. 
     Further, while the description above refers to “the invention,” the description may include more than one invention.

Technology Classification (CPC): 7