Electronic apparatus having battery charge circuit and charge control method therefor

On embodiment provides an electronic apparatus including: a controller configured to perform a power management of the electronic apparatus; a battery capable of counting cycles of a charging; and a charge circuit configured to perform the charging to the battery by using DC power supplied from an AC power supply device, wherein the controller is configured to cause the charge circuit to step down a charge voltage of the battery every predetermined number of the counts.

TECHNICAL FIELD

An embodiment of the invention relates to an electronic apparatus and a charge control method which is applied to the electronic apparatus.

BACKGROUND ART

A PC (Personal Computer) becomes configured so that a main battery is of the built-in type. Therefore, the user cannot intentionally replace the battery. In order to enable a PC to be used for a long period of time, consequently, it is important to extend the life of a battery which decreases in characteristic over time.

For example, a Li-ion battery has characteristics in which the cycle characteristic is improved by lowering the charge voltage. However, if the current/voltage of charging a battery is constant, the cycle characteristic can not be improved.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment will be described with reference toFIGS. 1 to 7. First, the configuration of an electronic apparatus of the embodiment will be described with reference toFIG. 1. The electronic apparatus may be realized as one of various electronic apparatuses such as a notebook personal computer and a tablet terminal. Hereinafter, a case is supposed where the electronic apparatus is realized as a notebook personal computer10.

FIG. 1is a perspective view of the computer10in a state where a display unit is opened, as viewed from the front side. The computer10includes a computer body11and the display unit12. A display device such as a liquid crystal display device (LCD)31is incorporated in the display unit12. A camera (Web camera)32is placed in an upper end portion of the display unit12. The computer10is configured to be powered by a battery20.

The display unit12is swingably attached to the computer body11so as to be moved between an opened position at which the upper surface of the computer body11is exposed, and a closed position at which the upper surface of the computer body11is covered with the display unit12. The computer body11has a housing shaped in a thin box. On the upper surface, a keyboard13, a touch pad14, a finger print sensor15, a power switch16for powering ON/OFF the computer10, and speakers18A,18B are placed.

Furthermore, a power supply connector (DC power supply input terminal)21is disposed in the computer body11. The power supply connector21is disposed in a side surface, for example, the left side surface of the computer body11. An external power supply device is detachably connected to the power supply connector21. An AC adapter may be used as the external power supply device. An AC adapter is a power supply device which converts a commercial power supply (AC power) into DC power.

In some types, the battery20is detachably mounted on, for example, a rear end portion of the computer body11. In the embodiment, however, it is assumed that the battery20is built in the computer10.

The computer10is driven by power from the external power supply device or that from the battery20. When the external power supply device is connected to the power supply connector21of the computer10, the computer10is driven by the power from the external power supply device. The computer10is driven by the power from the battery20during a period when the external power supply device is not connected to the power supply connector21of the computer10. Moreover, the power from the external power supply device is used also for charging the battery20.

Furthermore, the computer body11is provided with some USB ports22, an HDMI (registered trademark) (High-definition multimedia interface) output terminal23, and an RGB port24.

FIG. 2shows the system configuration of the computer10.

The computer10includes a CPU111, a system controller112, a main memory113, a graphics processing unit (GPU)114, a sound CODEC115, a BIOS-ROM116, a solid state drive (SSD)117, an optical disk drive (ODD)118, a HDMI control circuit119, a wireless LAN module121, an embedded controller/keyboard controller IC (EC/KBC)130, a system power supply circuit141, a charge circuit142, and the like.

The CPU111is a processor which controls the operations of the components of the computer10. The CPU111executes various types of software which are loaded from the SSD117onto the main memory113. The software includes an operating system (OS)201, and the like.

Moreover, the CPU111also executes a basic input output system (BIOS) stored in the BIOS-ROM116which is a non-volatile memory. The BIOS is a system program for hardware control.

The GPU114is a display controller which controls the LCD31employed as a display monitor of the computer10. The GPU114generates a display signal (LVDS signal) which is to be supplied to the LCD31, from display data stored in a video memory (VRAM)114A. Furthermore, the GPU114can also generate an analog RGB signal and an HDMI video signal from the display data. The analog RGB signal is supplied to an external display device through the RGB port24. The HDMI output terminal23can transmit an HDMI video signal (non-compressed digital video signal) and a digital audio signal to the external display device by means of one cable. The HDMI control circuit119is an interface which sends the HDMI video signal and the digital audio signal to the external display device through the HDMI output terminal23.

The system controller112is a bridge device which makes connection between the CPU111and each of the components. The system controller112incorporates a serial ATA controller for controlling the SSD117.

The EC/KBC130is a power management controller which executes power management of the computer10, and implemented as a one-chip microcomputer in which, for example, a keyboard controller for controlling the keyboard (KB)13, the touch pad14, and the like is incorporated. The EC/KBC130has a function to power ON and OFF the computer10in response to a manipulation by the user on the power switch16. The control of powering ON/OFF the computer10is executed by a cooperative operation of the EC/KBC130and the system power supply circuit141.

In the embodiment, it is possible to determine whether the battery20is in an overvoltage state or not, based on the state of the charge current. Specifically, when the battery20is charged, the firmware (F/W54) of the EC/KBC130determines the start/stop of the charging of the battery20while checking the state of a Charger IC143in the charge circuit142, and that of a Gas Gauge IC52in the battery20. The Charger IC143is an IC for controlling the charging. The Gas Gauge IC52is an IC which is configured so as to provide information relating to various conditions of battery cells in the battery20, to the host.

The system power supply circuit141is a power supply circuit which is configured so as to supply power (operation power Vcc) to components in the computer10by using the power (DC power) from the battery20or the power (DC power) from the AC adapter150. A power input terminal of the system power supply circuit141is connected to the power supply connector21. When the AC adapter150is connected to the power supply connector21through a power supply cable, therefore, the system power supply circuit141can receive the power (DC power) from the AC adapter150.

Upon reception of an ON signal sent from the EC/KBC130, the system power supply circuit141supplies operating power to the components of the computer10. Upon reception of an OFF signal sent from the EC/KBC130, the system power supply circuit141stops the supply of the operating power to the components.

The EC/KBC130can communicate with the charge circuit142and the battery20through a serial bus. The charge circuit142is a circuit for charging the battery20by using the DC power supplied from the AC adapter150. The charge circuit142includes the Charger IC143which is configured so as to control a charge current and voltage which are output from the charge circuit142to the battery20. The charge current is a regulated output current of the charge circuit142, and used for charging the battery20. The charge voltage is a regulated output voltage of the charge circuit142, and also called a battery voltage.

The EC/KBC130, the system power supply circuit141, the charge circuit142, and the Charger IC143operate also during a period when the computer10is powered OFF.

A charge control process in the embodiment will be described with reference to the block diagram ofFIG. 3.

The battery20includes a battery cell51, the Gas Gauge IC52, a Protection IC53, and the like. The charge circuit142is connected to the battery20through the + terminal (BATT+) of the battery20and the − terminal (BATT−) of the battery20. The battery20, the charge circuit142, and the EC/KBC130are interconnected through an I2C (I2C) bus which is a serial bus, and communicable with one another. Alternatively, an SM bus (System Management bus) may be used in place of the I2C bus.

The EC/KBC130includes the firmware (F/W)54. In the case where the following five conditions (1) to (5) are satisfied, the F/W54starts the charging of the battery20.

(1) There is no error status in the Charger IC143.

(2) There is no error status in the Gas Gauge IC52of the battery20.

(3) Communication between the EC/KBC130and the Gas Gauge IC52is normal.

(4) The battery20is not fully charged.

(5) The battery20is not at overvoltage.

The condition (3) functions as a precondition for the other conditions (1), (2), (4) and (5).

As described above, the charge circuit142includes the Charger IC143. The Charger IC143is an IC for controlling the charging of the battery20. The Charger IC143includes a Charger IC Fault register58indicating whether there is an error status in the Charger IC143or not.

As to the condition (1), the F/W54refers to the Charger IC Fault register58to determine whether there is an error status in the Charger IC143or not.

The battery cell51is configured, for example, by three cells each of which is a 1-series cell, and which are connected in parallel (1-series and 3-parallel) as shown inFIG. 3.

In the case where plural battery cells are connected in parallel as shown inFIG. 3, for example, an overvoltage occurs when the voltages of the battery cells are unbalanced.

The Gas Gauge IC52is connected to the positive and negative electrodes of the battery cell51. The Gas Gauge IC52is a communication IC which communicates with the EC/KBC130through the I2C bus, whereby battery information can be sent to the EC/KBC130. For example, the battery information is information indicating the value of the present charge current (hereinafter, referred to as charge current information), and information indicating whether the battery cell51is fully charged or not (hereinafter, referred to as full-charge information). Moreover, the Gas Gauge IC52performs a control related to the charging in the battery20. Specifically, the Gas Gauge IC52calculates the remaining amount of the battery cell51. For example, the remaining amount of the battery cell51is a ratio of the charged amount to the full-charge capacity.

The Gas Gauge IC52includes a charge current detector55, a full-charge detector56, and a Gas Gauge IC Flag register60. The charge current detector55detects the charge current flowing through a charging line in the battery20. The charging line is a line which connects the + terminal (BATT+) of the battery20and the − terminal (BATT−) of the battery20to each other. The Gas Gauge IC52can send the charge current information detected by the charge current detector55, to the EC/KBC130.

The charge current detector55detects the charge current by using, for example, a detection circuit61. The detection circuit61has a charge current detection resistor R1and a comparator62. The detection circuit61detects the charge current based on the voltage across the charge current detection resistor R1.

The full-charge detector56detects whether the battery cell51is in a fully charged state or not. The full-charge detector56includes a Gas Gauge IC Fault register59which stores full-charge information. The full-charge detector56stores the full-charge information indicating whether the battery cell51is fully charged or not, in the Gas Gauge IC Fault register59. The Gas Gauge IC52can send the full-charge information stored in the Gas Gauge IC Fault register59, to the EC/KBC130. Thus, as to the condition (4), the F/W54can refer to the Gas Gauge IC Fault register59to determine whether the battery20is fully charged or not.

The Gas Gauge IC52further includes the Gas Gauge IC Flag register60indicating whether there is an error status in the Gas Gauge IC52or not. As to the condition (2), the F/W54can refer to the Gas Gauge IC Flag register60to determine whether there is an error status in the Gas Gauge IC52or not.

In the case where at least the above-described four conditions are satisfied, the F/W54notifies the Charger IC143to start the charging, and the Charger IC143outputs the charge current to the battery20, thereby starting the charging.

The Protection IC53is connected to the positive and negative electrodes of the battery cell51. The Protection IC53turns ON or OFF a switch S1which is disposed in the charging line. For example, the switch S1is an FET.

The Protection IC53is an IC for monitoring the voltage of the battery cell51. Specifically, the Protection IC53detects whether the voltage of the battery20(battery cell51) is at overvoltage or not, based on the voltage across the battery51(hereinafter, referred to as battery cell voltage). In the case where the battery cell voltage exceeds a preset predetermined threshold during charging, more specifically, the Protection IC53determines that the voltage of the battery20(battery cell51) is an overvoltage. In the case where an overvoltage is detected, the Protection IC53performs a control for changing the ON state of the switch S1to the OFF state.

Hereinafter, the overvoltage of the battery20which is detected by the Protection IC53is referred to merely as the overvoltage, and the overvoltage of the battery20which is determined by the F/W54is referred to as the overvoltage state.

As described above, the F/W54starts the charging based on the above-described five conditions. In the case where the five conditions are satisfied, for example, the F/W54instructs the Charger IC143to output the charge current to the battery20, thereby starting the charging.

Next, a process of detecting the overvoltage state of the battery20by the F/W54will be described.

In the case where the following four sub-conditions (1) are satisfied, as to the condition (5), the F/W54detects the overvoltage state of the battery20. In this case, the charging of the battery20is stopped.

(1) The F/W54does not detect an abnormal state.

(3) The charge current value is equal to or smaller than 50 mA.

(4) The Charger IC143does not reduce the charging because of a high load.

The four sub-conditions will be specifically described.

As to the sub-condition (1), the F/W54refers to an Error Latch Flag57, and, at this time, can determine whether the charging is stopped because the battery20is in the overvoltage state, or not.

As to the sub-condition (2), the F/W54can communicate with the Charger IC143to determine whether the battery20is being charged or not. Alternatively, the F/W54may refer to the Error Latch Flag57to determine whether the battery20is being charged or not. In the case where the charging is being performed, and the F/W54refers to the Charger IC Fault register58of charger IC143to determine that there is no error information relating to the charging, the F/W54may determine that the sub-condition (2) is satisfied. Namely, the F/W54may determine that the battery20is being charged, based on the fact that the battery20is normally charged.

During a period when the battery20is charged by the Charger IC143, the Gauge IC52can detect the charge current supplied to the battery cell51. The Gauge IC52and the EC/KBC130are connected to each other through a communication line, and therefore the F/W54can periodically acquire information of the charge current from the Gauge IC52.

As described above, in the case where the overvoltage of the battery cell51is detected, the Protection IC53turns OFF the switch S2. If the battery cell51is at overvoltage, therefore, the charging line is interrupted by the switch S2, and therefore the charge current value detected by the Gauge IC52is substantially zero. The sub-condition (3) (i.e., the charge current value is equal to or smaller than 50 mA) is whether the switch S1is in the OFF state or not, namely, whether the Protection IC53detects the overvoltage of the battery cell51or not.

The sub-condition (4) is that the charge circuit142is not in a high load state in which the power available for charging the battery20is not limited. The term “is not in a high load state” means that, in the DC power supplied from the AC adapter, for example, the power available for charging the battery20is not limited. Specifically, the sub-condition (4) is whether the charge current value is not controlled by the Charger IC143so that the charge current value is smaller than a preset maximum value of the charge current. In the case where the power supplied from the AC adapter to the computer10is 30 W, and the maximum power which can be supplied for charging the battery20is 15 W, when 20 W is used for driving the system of the computer10, specifically, the power available for charging the battery20is limited to 10 W. In the case where the power supplied to the battery20for charging the battery20is smaller than the maximum power which can be supplied for charging the battery20as described above, or where the value of the available charge current is reduced, the sub-condition (4) is not satisfied. The F/W54can communicate with the Charger IC143through the communication line to check whether the Charger IC143reduces the charge current or not.

As described above, by providing the sub-condition (4), it is possible to prevent the overvoltage which is caused in the case where the charging is reduced, from being erroneously detected. In other words, a situation where the overvoltage state is erroneously detected in a place where detection of the overvoltage is usually inhibited, and the charging is stopped can be prevented from occurring.

In the case where the charge current is reduced, the charge current is reduced (the charge current value is smaller than the maximum value of the charge current), and therefore the possibility of causing problems such as that heat is generated by step charging is low. In the case where the charge current is reduced, when the charging is unstopped, therefore, it is possible to prevent the problem in that the charging is not correctly performed, from occurring.

In the case where all of the four sub-conditions (1) to (4) are satisfied in this way, the F/W54determines that the battery20is in the overvoltage state, and stops the charging of the battery20by the charge circuit142(Charger IC143).

By using the characteristics in which, in a lithium-ion battery, the cycle characteristic is improved by lowering the charge voltage, a control of switching the charge voltage in accordance with the cycle count is included.

FIG. 4shows the functional configuration of main portions of the embodiment which operates on the configuration ofFIG. 3.

In the Gas Gauge IC52, disposed are a CELL voltage monitoring block52a, a charge/discharge controlling core block52bincluding a charge controlling block52b1, and a cycle counting block52cincluding a cumulative discharge counter (not shown). In the example, a battery cell51a(3-series type) which is different in type from the battery cell51is connected to the Gas Gauge IC52through the block52a. Devices Q2, Q3are used for, when an abnormal current is disposed to flow out from the battery cell51a, enabling the CELL voltage monitoring block52ato transmit a voltage drop due to the current to the charge/discharge controlling core block52b, thereby leading to an interruption operation.

The cycle counting block52cdetects the number of charging and discharging cycles. One cycle is defined as follows.

In the case of a battery having a rating of 4,000 mAh, when the cumulative discharge amount in the battery driving reaches 4,000 mAh, for example, the cycle count is set to +1. The cumulative discharge amount is calculated by accumulating the value of the discharge current flowing through a resistor R.

The cycle counting block52cnotifies the charge/discharge controlling core block52bof the cycle number, and the charge controlling block52b1of the charge/discharge controlling core block52bsets the charge voltage and current according to the cycle count.

The charge voltage according to the cycle is determined as shown inFIGS. 5 and 6. In the example, the charging reducing period according to the cycle count is divided into 3 blocks.

(1) In the period of m1 cycles after the user starts the use, the charge controlling block52b1lowers by x mV/Cell every n cycles. When lowered every n cycles, there is an effect that the user hardly senses the full-charge capacity reduction.

(2) In consideration of a certain degree of elapse of passing of the user use period, during a period of (m1−m2) cycles, the charge controlling block52b1switches the lowering width of reduction of the charge voltage to y mV/Cell (y>x) every n2 cycles.

(3) After m2 cycles, there is no effect on the life of the battery, and therefore the charge controlling block52b1sets the value of the charge voltage constant.

Step S61: The charge controlling block52b1determines whether n cycles have passed or not. If passed, the flow transfers to next step S62, and, if not, the determination is repeated.

Step S62: The charge controlling block52b1determines whether a total of m1 cycles have passed or not. If passed, the flow transfers to next step S64, and, if not, the flow transfers to next step S63.

Step S63: The charge controlling block52b1lowers the charge voltage value by x mV/Cell, and the flow returns to step S61.

Step S64: The charge controlling block52b1determines whether a total of m2 cycles have passed or not. If passed, the flow ended, and, if not, the flow transfers to step S65.

Step S65: The charge controlling block52b1lowers the charge voltage value by y mV/Cell, and the flow then returns to step S61.

The charge voltage and current values which are set by the charge controlling block52b1are received by the EC/KBC130via the I2C communication with the Gas Gauge IC52, and charge setting is performed on the power supply circuit block (Charger IC)143.

The charge current value in a usual lithium-ion battery performs 0.7 C charging with respect to the design capacity. In the 0.7 C charging, the charge current value in a battery pack of 1 C=design capacity=4,000 mAh is 4,000 mAh×0.7=2.8 A. Although the C rate varies depending on the characteristics of a cell, the 0.7 C charging will be described here.

In the case of the 0.7 C charging with respect to the design capacity, when the cycles proceed, the battery deteriorates, and the full charge capacity (FCC) changes. In the case where the FCC is lowered, when the charge current in charging is fixed, the battery is charged by the charge current value of 0.7 C or more, and the life of the battery is affected. At the start of charging, therefore, the FCC at the start of charging is set to 1 C, when the charge current is FCC×0.7, whereby a control of always keeping the charge current to 0.7 C is included. When the 0.7 C charging is kept, the life of the battery is enhanced.

In a battery pack in which the design capacity is 5,700 mAh, for example, the charge current value is 5,700 mAh×0.7=3.99 A. When FCC=3,000 mAh at 600 cycles, the charge current value is 3,000 mAh×0.7=2.1 A, or reduced from 3.99 A to 2.1 A.

The core block52bin the battery20calculates the value of the full-charge capacity, and, at the start of next charging, the value of the charge current of 0.7 C with respect to the FCC. The Gas Gauge IC52indicates the calculated charge current value to the EC/KBC130via the I2C communication. In accordance with the charge current value, the EC/KBC130sets the indicated charge current in the power supply circuit block143, and charges the battery pack.

The charge control at a certain cycle count will be described with reference toFIG. 7. An example in which the charge control is performed on a PC having cylinder cells and the cycle count is 50 will be described. The abscissa inFIG. 7shows the time at the cycle count, and the ordinate shows the charging value. In the ordinate, the portion above the dash-dot line shows the behavior of the voltage, and that below the dash-dot line shows the behavior of the corresponding current.

In the case of a battery pack of 3-series (three cylinder cells are connected in series) and 2-parallel (two cylinder cells are connected in parallel), conditions are as follows.

When the standard charge voltage is 12.6 V (4.2 V/Cell×3 series), 50 cycles and between 0 to m1 cycles, and therefore −x mV/n cycles are applied. As the reduction width of the charge voltage per cell, for example, the lowering value of the charge voltage is 50/n cycles×x mV=30 mV, and the charge voltage of 4.2 V is 4.2 V−30 mV=4.17 V.

From the reduction value of the voltage per cell, the charge voltage of the battery pack is 4.17 V/Cell×3 series=12.51 V. With respect to the charge current value, the charging is performed by 0.7 C of the FCC.

The CELL voltage monitoring block which is in the Gas Gauge IC detects the cell voltage. When the cell voltage in charging reaches 4.17 V, information is informed to the core block, and a new charge current is transmitted to the EC/KBC while reducing step by step, for example, in steps of 128 mA from the charge current (FCC×0.7).

The EC/KBC sets the changed charge current value into the power supply circuit block, and the battery is charged by the changed charge current value. Each time when the cell voltage reaches 4.17 V, the charge current is lowered, and, when lowered below the charge termination current, the control is performed with determining that the battery is fully charged.

InFIG. 7, v and i indicate embodiments of long life controls of the voltage and the current, and the corresponding broken lines indicate an existing charge control. An ECO utility202(seeFIG. 4) which is one of power supply management application programs in the main memory113instructs the EC/KBC130which is a controller of the embodiment, to switch normal charging/ECO mode charging.

In order to solve the problem, the embodiment includes the control in which the charge voltage is lowered in accordance with the detection of charging and discharging cycles in the battery. As the control of reducing the charge voltage, the charge voltage calculation control is included in which the charge voltage is not uniformly reduced every cycle, but, in a certain cycle interval, a period when the charge voltage is kept constant, and a control of reducing the charge voltage in predetermined cycles are disposed, so that the user hardly senses a severe full-charge capacity reduction.

Also regarding the charge current value, although charging may be performed by a constant charge current value with respect to the design capacity, the charge control is performed with a charge current value corresponding to the full-charge capacity every battery cycle. Here are performed the fixed/variable hybrid charge voltage control according to the battery cycle, and the charge control at a charge current value corresponding to the full-charge capacity for every cycle.

In a Li-ion/polymer battery long-life charge control, as described above, the charge voltage (variable and fixed combination control) and the charge current value (FCC×0.7) control are performed, whereby the life of a battery pack can be improved. The battery life is extended as compared with an existing product.

The invention is not limited to the embodiment, and may be further implemented by modifying in various manners without departing from the spirit of the invention.

Moreover, plural components disclosed in the above-described embodiment may be appropriately combined with each other, whereby various inventions may be formed. For example, some components may be omitted from the whole components indicated in the embodiment, and moreover components of different embodiments may be adequately combined with each other.