Battery charger that employs current sharing to simultaneously power an application and charge a battery

[0001] The invention relates to the charging of batteries in electrical devices. In particular, it relates to a method, an apparatus, and an article of manufacture for controlling the quantity of current allocated towards battery charging simultaneous with the supply of current to an application load.

[0002] Many electrical devices are designed to be operable under battery power. Often, these electrical devices may be powered by an external power source or one or more batteries. Devices operable under battery power often provide circuitry for charging the batteries. This circuitry may be either internal to the device, integrated with an external power source circuit, or external to both the device and the external power source circuit.

[0003] The recent popularity of portable electronic devices such as portable computers, MP3 players, handheld video games, cellular telephones, and the like, has greatly increased the number of devices operable with rechargeable batteries. Consumers have become accustomed to the constant availability of the conveniences offered by these devices and may be reluctant to discontinue use in order to recharge the batteries. On the other hand, consumers prefer that the batteries always be fully charged such that the consumer may unplug the device at any time and have maximum runtime.

[0004] Accordingly, it is beneficial to have a method and a device to power an application load while charging a battery.

[0011] Various embodiments of the present invention will be described in detail with reference to the drawings, where like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention.

[0012] Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” includes plural reference, and the meaning of “in” includes “in” and “on.” The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. The term “coupled” means at least either a direct electrical connection between the items connected, or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means at least either a single component or a multiplicity of components, either active and/or passive, that are coupled together to provide a desired function. The term “signal” means at least one current, voltage, charge, temperature, data, or other signal. The term “maximum” means at least either a maximum defined by programmed parameters, circuit configuration, safety considerations, and/or the like.

[0013] Briefly stated, the invention relates circuitry for controlling powering of a load and charging of a battery from a power source by a smart power supply. The smart power supply controls the maximum current for battery charging based in part upon variables such as the maximum rate of charge of the battery and maximum source current. Accordingly, the smart power supply is capable of providing the power requested by the load, and use the remaining power for battery charging.

[0014] FIG. 1 illustrates an embodiment of a power supply (100) and associated devices. The associated devices include power source 10, battery 20, and application load 30. Power supply 100 includes battery charger control circuit 110 and battery charger and power source circuit 120.

[0015] Battery charger control circuit 110 is configured to control the charging of battery 20 via state machine 112. State machine 112 is operable to at least partially control charging of battery 20 via control signal 130 and battery charger and power source circuit 120. In one embodiment, state machine 112 calculates control signal 130 based upon the value(s) of register 114. However, in other embodiments, state machine 112 may calculate the value of control signal 130 by a multitude of inputs and various means instead of or in addition to the values of register 114. In one embodiment, control signal 130 includes information about the maximum current available from the power source 10, the desired current with which to charge the battery 20, and/or the like.

[0016] Register 114 is operable to store operational parameters, default values, and other configuration data for state machine 112 to use in determining its output or controlling its operation. Battery charger control circuit 110 is connected to battery charger and power source circuit 120 via control signal 130 to control the charging of battery 20.

[0017] Battery charger and power source circuit 120 contains circuitry to connect application load 30 to battery 20 and/or power source 10 for obtaining operating power. These connections may be implemented by a variety of methods known in the art including, but not limited to, switches, transistors, relays, and the like. Likewise, these connections may be controlled by state machine 112. Battery charger and power source circuit 120 also contains circuitry to connect power source 10 to battery 20 for charging. This circuitry may consist of current regulators and/or voltage regulators configured to operate, in part, under the control of state machine 112 via control signal 130. In one embodiment, state machine 112 signals battery charger and power source circuit 120 to indicate an algorithm for supplying current to battery 20.

[0018] In response to the information received via control signal 130 and other factors, power source circuit 120 may increase or decrease the amount of current supplied to battery 20. For instance, battery charger and power source circuit 120 may adjust the amount of current supplied to battery 20 based, in part, on information about the maximum current available from the power source 10, the desired current with which to charge the battery 20, and/or the like. Battery charger and power source circuit 120 may utilize control signal 130, in part, to determine an appropriate charging current for battery 20. In this manner, power supply 100 is able to power application load 20 while maximizing charging current to battery 20, and accurately determine and calculate the value of control signal 130.

[0019] FIG. 2 illustrates an embodiment of power supply 200 and associated devices. FIG. 2 may be employed as an embodiment of power supply 100 of FIG. 1. Battery charger and power source circuit 220 may include power routing and current supply circuit 228, I_diff interface 222, I_min interface 224, and status signal generator 226.

[0020] Power source 10 may comprise a wall type AC adapter, a USB host, a firewire host, a 12 volt DC adapter (automobile type), and/or the like. Battery 20 may include a nickel-cadmium battery, a nickel-metal-hydride battery, a lithium-ion battery, a lithium-polymer battery, and/or the like. In an embodiment of the invention, battery 20 comprises a lithium-ion battery, and power sources 10 include a wall type AC adapter and a USB host.

[0021] Battery charger control circuit 210 includes register 214 and state machine 212. Register 214 may be a single register or multiple registers. Example parameters to be stored include an I_limit variable to indicate the maximum current that power source 10 is able to deliver and an I_prog variable to indicate the maximum current with which battery 20 may be charged. In one embodiment, for simplified digital design, these variables may be digitized with each binary count representing a magnitude of current. For example, in one embodiment, each increase in binary count indicates an additional 100 milliamps of current.

[0022] Register configuration interface 242 allows for updating and reading of registers 214 by microprocessor 240 or other control circuit. Although register configuration interface 242 is illustrated as connecting the microprocessor 240 to registers 214 in FIG. 2, in other embodiments, microprocessor 240 may be connected to the battery charger control circuit 210 in any manner which allows it to read or modify registers 214. For example, in one embodiment, microprocessor 240 may also be connected to registers 214 via state machine 212.

[0023] State machine 212 may be connected to: registers 214 for retrieval and updating of operational data; power source busses 12 for determining status of power source 10; and to battery charger and power source circuit 220 for controlling battery charging and determining battery and battery charging status. The embodiment illustrated in FIG. 2 includes registers 214 containing an I_limit register for storing a value representing the maximum current that power supply 10 is configured to supply and an I_prog register for storing a value representing the desired charging rate at which the battery 20 is to be charged.

[0024] In the embodiment as illustrated by FIG. 2, battery charger control circuit 210 is connected to battery charger and power source circuit 220 via control signal I_diff, signal I_min, and signal Status. Signal I_diff informs battery charger and power source circuit 220 of the difference between the maximum current power source 10 is able to deliver (I_limit) and the desired current with which battery 20 may be charged (I_prog). Accordingly, I_diff represents the maximum amount of current that application load 30 may consume before there is insufficient current to charge battery 20 at its desired charging rate. Signal I_min notifies battery charger and power source circuit 220 of the minimum value of I_limit and I_prog. This represents the maximum current with which to charge battery 20. Signal Status allows battery charger control circuit 220 to be aware of battery or battery status information. For example, this information may indicate the voltage at the battery 20 terminals, the charging state, the actual charging current for battery 20, and/or the like. Signals I_diff, I_min, and Status may each be single discrete signals lines, busses of multiple signal lines, multiplexed and demultiplexed on to one or more shared signal paths, and/or any other means of communicating a signal between the state machine 212 and battery charger and power source circuit 220.

[0025] In one embodiment, an asynchronous circuit, microcontroller, microprocessor and/or the like may perform the functions of state machine 212. Likewise, values stored in registers 214 may be have default values that may be reprogrammable or permanently configured. Default or permanently configured values may be configured by means such as pull-up and pull-downs, and the like.

[0026] Power routing and current supply circuit 228 is operable to connect application load 30 to one or more of battery 20 and/or power source 10 for obtaining operating power and/or regulating power to the application load 30. These connections may be implemented by a variety of methods known in the art including, but not limited to, switches, transistors, relays, and/or the like. For the system illustrated by FIG. 2, a three-way switch is particular well suited for supplying power to application load 30.

[0027] Power routing and current supply circuit 220 also includes circuitry to connect power source 10 to battery 20 for charging of battery 20. This circuitry may include current regulators, voltage regulators, current sensors, and voltage sensors, and/or the like, configured to operate under the control the I_diff and I_min signals for providing power to application load 30 and battery 20. In addition, status signal generator 226 is arranged to provide signal Status to battery charger control circuit 220. In one embodiment, battery charger control circuit 220 uses signal Status to determine if battery 20 is in trickle-charge or full-rate charge mode and status signal generator 226 includes an analog comparator configured to indicate if the voltage of battery 20 is above or below a trickle charging threshold level.

[0028] As is known in the art, typical lithium ion batteries are commonly charged in a multi-phase process which generally includes: a trickle charge phase, a full-rate constant current phase, and a constant voltage phase. During a trickle charge phase, a reduced amount of current is supplied to the battery to gradually increase the voltage of the battery cell. After reaching threshold voltage level V_tr, the battery is supplied with an increased amount of current to more quickly charge the battery during the full-rate constant current phase. Upon reaching voltage V_cv the battery is charged in a constant voltage mode until the charge cycle for the battery ends.

[0029] According to one example, the trickle charge operation proceeds as follows. The threshold level is set to approximately 3 Volts for a typical 4.2 Volt lithium ion battery cell. When the battery voltage is above this threshold, battery 20 is charged at a “full-rate” charging current. However, if battery 20 is below this threshold, battery 20 is “trickle charged” until it reaches the threshold voltage. Likewise, Status signal generator 226 may include an analog-to-digital converter, and/or the like.

[0030] In one embodiment, power routing and current supply circuit 228 is operable to receive control signals I_diff and I_min via I_diff interface 222 and I_min interface 224 respectively. Interfaces 222 and 224 may consist of digital-to-analog converters operable to convert the digital outputs of state machine 212 to analog signals. In other embodiments, I_diff interface 222 and I_min interface 224 may reside in battery charger control circuit 210 or power routing and current supply circuit 228 may be configured to receive digital inputs.

[0031] FIG. 3 is a circuit diagram illustrating an embodiment of battery charging circuit 300 of battery charger and power source circuit 220 of FIG. 2 as configured to supply current to battery 20 under the control of the I_diff and I_min and Status signals. In this embodiment, application load 30 draws load current I_load. Load current sense circuit 310 outputs a proportional signal Loadsense. Battery charging current I_charge is supplied to battery 20 by pass transistor 320. Charge current sense circuit 330 outputs a proportional signal Chgsense. Signals Loadsense and Chgsense may be either current signals, voltage signals, and/or the like.

[0032] Charge feedback amp 340 operates an error amp to control current Icharge based on the difference between lower of the voltages V_chgref and V_cvfb and charging reference voltage V_ccfb. Charge feedback amp 340 increases or decreases the power to battery 20 via pass transistor 320 and charging current sense circuit 330. During both trickle mode and full-rate charge mode, charger control 350 controls the charging current to battery 20 based upon feedback voltage V_ccfb. Charger control 350 receives signals Loadsense and Chgsense as well as digital inputs I_diff, I_min, and Sense to control charging of battery 20 via output V_ccfb. Charger control 350 calculates output voltage V_ccfb such that, in one embodiment, during CC full-rate mode, current Icharge is regulated as follows. If Iload-Idiff is less or equal to zero, current Icharge is regulated to Imin. If Iload-Idiff is greater than zero, current Icharge is regulated to Imin-(Iload-Idiff). In one embodiment, charger control circuit 350 includes embodiments of I_diff interface 222, I_min interface 224 of FIG. 2.

[0033] The voltage of battery 20 is monitored by constant voltage amp 360 via resistor divider network 370, 380. When the voltage of battery 20 increases, the constant voltage feedback voltage V_cvfb increases relative to constant voltage reference voltage V_cvref. When the voltage of battery 20 reaches constant voltage phase voltage threshold V_cv, the output of constant voltage feedback amp 360 falls below Vchgref. Accordingly, charge feedback amp 340 begins supplying power to battery 20 via pass transistor 320 and charge current sense circuit 330 based on the output of charge feedback amp 340. Further, signal Sense is provided to inform state machine 212 of FIG. 2 of the battery charging status.

[0034] FIG. 4 is a flow chart for the operation and control provided by battery charger control circuit 210. After start block 400, the process proceeds to decision block 410, where the voltage of battery 20 is measured and battery charger control circuit 210 determines, as discussed above, whether battery 20 is to be trickle charged.

[0035] If the battery 20 voltage is below voltage threshold V_tr, the process proceeds to block 420, where the I_min value is set to the value of I_prog to represent the maximum I_charge for battery 20. Further, at block 420, I_diff is set to I_limit minus a constant to represent the maximum I_load before there is insufficient current to supply I_charge at the preferred rate. Because during trickle charging I_charge may be quite low, a value of 100 milliamps is used as the constant in one embodiment. In one embodiment, neither I_min nor I_diff are negative; if the discussed calculations produce a negative result, the value is set to zero. The process then moves to block 430.

[0036] At block 430, battery charger 220 is placed in trickle charging mode and is informed of the value of I_min and I_diff. Battery charger 220 then charges battery 20 at a fraction of the I_min value if current I_load less than current I_diff. 1/10^th of I_min is a suitable fraction for current I_charge; however a fraction other than 1/10 may be used within the scope and spirit of the invention. If I_load is greater than I_diff, charging current I_charge is reduced, as discussed below, to give priority to application load 30.

[0037] If at decision block 410, the voltage of battery 20 is above voltage threshold V_tr, the process proceeds to decision block 440 to determine if the voltage of battery 20 has reached voltage mode threshold V_cv. Battery 20 is charged in constant voltage mode if its voltage reaches V_cv, which, for a common lithium ion battery cell, is typically set to approximately 4.2 volts. If the voltage of battery 20 is above V_cv, the process proceeds to decision block 470, for constant voltage charging as discussed below. After constant voltage charging is complete, the process proceeds to return block 480 where other processing is resumed. Accordingly, if the voltage of battery 20 is above V_tr but below V_cv then the process goes to block 450 for the setup of a full-rate charge. At block 450, the I_min value is set to the smaller of the I_limit or I_prog value, and identifies the desired charging rate of battery 20 if sufficient current is available. The I_diff value is also set to I_limit minus I_prog to calculate the maximum I_load current that may be supplied prior to reduction of I_charge. The process then advances to block 460, where battery charger 220 is placed in full-rate mode and notified of the calculated values of I_diff and I_min.

[0038] In one embodiment, battery charger and power source circuit 220 is operable to charge battery 20 based on signals I_min and I_diff as follows. Battery charger 220 charges battery 20 with I_charge current which is equal to I_min current if application load 30 draws less than I_diff current. If application load 30 draws more than I_diff current, then I_charge is reduced to give priority to application load 30. In one embodiment, I_charge is reduced by the amount that the application load 30 draws that is in excess of I_diff. Charging continues until the voltage of battery 20 reaches V_cv as determined by block 440 upon which time the process proceeds to block 470.

[0039] FIG. 5a is a waveform showing the voltage at battery 20 while being charged by an embodiment of the invention. Prior to start time 510, no current or voltage is supplied to battery 20. At start time 510, voltage waveform 570 is at zero as battery 20 is fully discharged. Because the battery voltage is below V_tr, battery 20 is charged in trickle charge mode during time trickle charge period 520. At full-rate start time 530 the battery voltage has reached V_tr. Accordingly, battery 20 is charged in a current limited full-rate mode during full-rate period 540. At constant voltage start time 550, battery 20 is nearly charged to capacity and it begins self regulating its charging current I_charge. Because I_charge asymptotically approaches zero due to battery 20 self regulation, current limitations based upon control signal 130 output of state machine 112 have limited importance during constant voltage charging period 560. In one embodiment, current limitations based upon control signal 130 employed during the constant voltage phase, and in another embodiment, they are not employed during the constant voltage phase.

[0040] FIG. 5b is a waveform showing the current I_charge into battery 20 while being charged by an embodiment of the invention. Prior to start time 510, no current or voltage is supplied to battery 20; thus I_charge is at zero. At start time 510, charging is initiated. Because the voltage of battery 20 is less than V_tr during trickle charge time 520, I_charge is limited to the trickle charging current during time trickle charge period 520.

[0041] At full-rate start time 530 the voltage of battery 20 has reached V_tr. Accordingly, battery 20 is charged in a current limited full-rate mode during full-rate period 540. Current I_charge supplied during full-rate period 540 is generally greater than the current supplied during trickle charge period 520. At constant voltage start time 550, battery 20 is nearly charged to capacity and any current limitations of the full-rate mode may be removed for constant voltage charging period 560. During this time, the battery charging current asymptotically goes to zero.

[0042] The above specification, examples and data provide a description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.