HK1076928B - Battery pack, battery protection processing apparatus, and startup control method of the battery protection processing apparatus - Google Patents

Description

Battery pack, battery protection processing device and start control method thereof

The present application claims priority from Japanese patent application No.2003-385372, filed 11/14/2003, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a battery pack of a secondary battery integrated with a processing circuit that performs processing including prevention of occurrence of an abnormality in the secondary battery, a protection processing device for performing protection processing, and a start-up control method of the battery protection processing device.

Background

In recent years, the number of portable electronic devices such as digital cameras on the market has increased. The performance of the secondary battery mounted on these electronic devices is very important. Such secondary batteries include lithium ion batteries.

In particular, if the lithium-ion secondary battery is overcharged, lithium ions are precipitated as metallic lithium on the negative electrode. It is known that in the worst case, the battery smokes, ignites, or explodes. If the battery is overdischarged, a small short circuit or capacity reduction may be experienced between the electrodes. When the positive and negative electrodes are short-circuited, it is also known that abnormal heat generation is caused by the flow of an overcurrent. In order to prevent overcharge, overdischarge, and short circuit (overcurrent), the lithium ion secondary battery is generally provided with a protection function for monitoring these abnormal states and a switch for preventing the abnormal states.

Fig. 1A and 1B are graphs showing changes in voltage and current when discharge and overcurrent occur in a lithium ion secondary battery.

Fig. 1A and 1B show examples of lithium ion battery cells used for home digital cameras and digital cameras. The fully charged voltage is assumed to be 4.2V, and the overdischarge detection voltage is assumed to be 3.0V. Fig. 1A shows a change in cell voltage during discharge with 2W power consumption. As shown in fig. 1A, the cell voltage drops to the overdischarge detection voltage after about 90 minutes from the full charge state. If the discharge load is released, the cell voltage temporarily rises, but thereafter gradually falls due to self-discharge. If the battery is not used for a long time, the cell voltage may be lowered to 0V. When the positive and negative electrodes are short-circuited, the cell voltage immediately decreases to about 1V, as shown in fig. 1B. At this time, an overcurrent of about 15A flows.

On the other hand, the above-described portable electronic devices using a secondary battery as a power source are increasingly provided with a remaining battery capacity display function. As shown in fig. 1A, particularly in a lithium-ion secondary battery, the cell voltage gradually and linearly decreases except immediately before and after discharge. Therefore, the remaining battery pack capacity cannot be accurately detected using only the cell voltage. The useful remaining service life can be accurately calculated by using the accumulated values of the charge and discharge currents, the battery cell temperature, and the like. In order to realize such a remaining battery capacity display function, there is a commercially available battery pack including a secondary battery and a circuit such as a microcontroller in the same component.

Fig. 2 shows an example of the internal structure of a conventional battery pack.

The conventional battery pack in fig. 2 includes: a battery cell 1 including a lithium ion secondary battery; protection switches SW11 and SW12 for charge and discharge control, each of which includes a MOSFET (metal oxide semiconductor field effect transistor) equivalently including a diode between a source and a drain according to the structure; a resistor Rs for current detection; a battery protection circuit 110; a microcontroller 120; a clock oscillator 130 for microcontroller operation; a thermistor 140 for detecting the temperature of the battery cell 1; and a communication I/F (interface) 150 for establishing communication with the electronic device with the battery pack.

In the battery pack, each of the protection switches SW11 and SW12 includes a FET and a diode. The protection switch SW11 may cut off the discharge current. The protection switch SW12 may cut off the charging current. Therefore, when the battery cell 1 is charged, the charger is connected to the positive terminal Eb1 and the negative terminal Eb 2. Also, the protection switch SW12 is turned on. The positive terminal Eb1 and the negative terminal Eb2 may be connected to a device serving as a discharge load. In this way, turning on the protection switch SW11 can provide power to the device. The battery protection circuit 110 is also integrated with various circuits for providing power to the microcontroller.

The microcontroller 120 is a circuit for calculating information required to display the remaining capacity of the battery unit 1 and operating according to the power supplied from the battery protection circuit 110. The battery protection circuit 110 controls the start timing for stable operation. The microcontroller 120 calculates necessary information under software control based on digitized values equivalent to the charge and discharge currents and the cell voltage provided by the battery protection circuit 110 and the temperature value detected by the thermistor 140. The microcontroller transmits information to the electronic device in which the battery pack is mounted through the communication I/F150 and the control terminal 4. The remaining capacity of the battery in the electronic device can thus be displayed.

However, as described above, the cell voltage of the secondary battery varies sharply with the situation. On the other hand, the microcontroller system is designed on the premise that the power supply voltage is stably supplied to the microcontroller. For this reason, as shown in fig. 2, the conventional battery pack provides a protection function using another circuit independent of the microcontroller, which monitors abnormalities of the secondary battery such as overcharge, overdischarge, and overcurrent. There is an example of such a circuit that mainly includes a dedicated voltage comparator as a main component to perform a protection function of the battery cell (see, for example, japanese patent No.3136677 (paragraphs [0011] to [0016], fig. 1)).

Fig. 3 schematically depicts the cell states of a conventional battery pack.

As shown in fig. 3, for example, when the voltage of the battery cell 1 is changed from 3.0 to 4.25V, the conventional battery pack maintains a normal state. In this state, if connected, both the protection switches SW11 and SW12 are turned on, thereby enabling the supply of power to the discharging load and the charging operation of the charger. When the voltage of the battery cell 1 exceeds 4.25V, an overcharged state occurs. The protection switch SW12 is turned off, thereby cutting off the charging. When the voltage of the battery cell 1 is lower than 3.0V and higher than or equal to 2.50V, an over-discharge state occurs. The protection switch SW11 turns off, thereby cutting off the discharge. However, in this state, power continues to be supplied to the microcontroller 120, keeping the microcontroller 120 running.

When the voltage of the battery cell 1 becomes lower than 2.50V, all discharge is stopped in case the capacity of the battery cell 1 is decreased. Accordingly, the microcontroller 120 stops operating. Thereafter, the battery cell 1 is charged with the voltage applied from the charger terminal. When the voltage exceeds a certain value, the microcontroller 120 starts to operate.

The current detection resistor Rs is used to detect the discharge current. When the discharge current exceeds 3.0A, an overcurrent state occurs. The protection switch SW11 is turned off to prevent discharging. These states also stop the operation of the microcontroller 120 and the like. Releasing the discharging load automatically restores the normal state.

As described above, the conventional battery pack is mounted independently of the protection circuit for the lithium ion secondary battery and the microcontroller for calculating the display of the remaining battery pack capacity. Recently, from the viewpoints of miniaturization, reduction in the number of components, and reduction in parts cost, it is desired to mainly use a microcontroller to perform the functions of the above-described protection circuit and integrate most of the circuits on a single semiconductor circuit board.

However, as described above, the secondary battery voltage is unstable with a change in the condition. The supply voltage is not constantly supplied to the microcontroller itself. It has been difficult to monitor the abnormal state of the secondary battery mainly under software control of the microcontroller. If the microcontroller implements part of the protection function, this is mainly done by dedicated hardware, such as a voltage comparator. A microcontroller is used as a complementary function to that hardware.

When the microcontroller mainly performs a protection function for the secondary battery, it is important to save power consumption of the microcontroller itself as much as possible and stably supply power to the microcontroller.

The battery pack may use a plurality of battery cells connected in series according to the magnitude of load applied to a connected device. As such, the overcharge and overdischarge states must be separately determined for each battery cell. However, when only the voltage comparator is used to detect the cell voltage as described above, it is necessary to provide a protection circuit including as many voltage comparators as the battery cells connected in series, thereby causing problems of increasing design cost and enlarging installation space.

Disclosure of Invention

The present invention has been made in view of the above. Accordingly, it is an object of the present invention to provide a battery pack that stably performs a secondary battery protection function and reduces circuit installation space and component costs, mainly using software control.

It is another object of the present invention to provide a battery protection processing device that stably performs a secondary battery protection function using mainly software control and reduces a circuit installation space and component costs.

It is still another object of the present invention to provide a control method capable of making a battery protection processing device to stably perform a secondary battery protection function and reduce a circuit installation space and component costs, mainly using software control.

According to an aspect of the present invention, there is provided a battery pack including a secondary battery integrated with a processing circuit that performs processing including prevention of occurrence of a failure in the secondary battery, the battery pack including: discharge current cutoff means for selectively cutting off a discharge current in the secondary battery; a charging current cut-off device for selectively cutting off a charging current in the secondary battery; protection processing means for controlling operations of the discharge current cutoff means and the charge current cutoff means in accordance with at least an interelectrode voltage between a positive electrode and a negative electrode of the secondary battery; and start-up enabling voltage detecting means for generating a detection signal when the power supply voltage supplied to the protection processing means reaches a minimum voltage for starting up the protection processing means, wherein the protection processing means performs an initialization process according to the detected detection signal from the start-up enabling voltage detecting means, the battery pack further comprising: and a stabilized driving voltage detection means for generating a detection signal when the power supply voltage reaches a minimum voltage of the stabilized driving protection processing means which is higher than the minimum voltage, wherein the protection processing means starts the protection processing in accordance with the detection signal from the stabilized driving voltage detection means.

According to another aspect of the present invention, there is also provided a battery protection processing device for performing a process of preventing abnormality of a secondary battery, the device including: discharge current cutoff means for selectively cutting off a discharge current in the secondary battery; a charging current cut-off device for selectively cutting off a charging current in the secondary battery; protection processing means for controlling operations of the discharge current cutoff means and the charge current cutoff means in accordance with at least an interelectrode voltage between a positive electrode and a negative electrode of the secondary battery; and start-up enabling voltage detecting means for generating a detection signal when the power supply voltage supplied to the protection processing means reaches a minimum voltage for starting up the protection processing means, wherein the protection processing means performs an initialization process according to the detected detection signal from the start-up enabling voltage detecting means, the battery protection processing means further comprising: and a stabilized driving voltage detection means for generating a detection signal when the power supply voltage reaches a minimum voltage of the stabilized driving protection processing means which is higher than the minimum voltage, wherein the protection processing means starts the protection processing in accordance with the detection signal from the stabilized driving voltage detection means.

According to another aspect of the present invention, there is provided a start-up control method for a battery protection processing apparatus that performs a process of protecting a secondary battery against occurrence of an abnormality by an operation of controlling a discharge current cut-off circuit to selectively cut off a discharge current of the secondary battery and controlling a charge current cut-off circuit to selectively cut off a charge current of the secondary battery according to a voltage between a positive electrode and a negative electrode of the secondary battery, the method including: when the power supply voltage supplied to the battery protection processing device reaches a minimum voltage for starting the battery protection processing device, the method performs an initialization process of the battery protection processing device, and further includes: after the initialization process, a protection process is started when the power supply voltage reaches a minimum voltage higher than the minimum voltage at which the battery protection process apparatus is stably driven.

In order to solve the above-described problems, the present invention provides a battery pack composed of a secondary battery integrated with a processing circuit that performs processing including prevention of occurrence of a failure in the secondary battery, the battery pack including: discharge current cutoff means for selectively cutting off a discharge current in the secondary battery; a charging current cut-off device for selectively cutting off a charging current in the secondary battery; protection processing means for controlling operations of the discharge current cutoff means and the charge current cutoff means in accordance with at least an interelectrode voltage between a positive electrode and a negative electrode of the secondary battery; and start-up enable voltage detection means for generating a detection signal when the power supply voltage supplied to the protection processing means reaches a minimum value of the start-up protection processing means, wherein the protection processing means performs an initialization process according to detection of the detection signal from the start-up enable voltage detection means.

In this battery pack, the protection processing means controls the operations of the discharge current cut-off means and the charge current cut-off means in accordance with at least the interelectrode voltage between the positive and negative electrodes of the secondary battery. For example, the charge current cut-off device cuts off the charge current when it is determined that the secondary battery is in an overcharged state. The discharge current cut-off device cuts off the discharge current when it is determined that the secondary battery is in an overdischarge state. In this manner, the secondary battery is protected from abnormal states such as overcharged and overdischarged states. The protection processing device is initialized when the power supply voltage supplied to the protection processing device reaches the lowest voltage for starting the protection processing device according to the signal detected by the start enabling voltage detection device. Therefore, the protection processing device stops operating in accordance with a decrease in the power supply voltage supplied from the secondary battery. Then, when the power supply voltage rises enough to enable the start-up, the protection processing device starts up. The protection processing device is initialized to stabilize the running state while starting.

Further, stable driving voltage detecting means for generating a detection signal when the power supply voltage of the protection processing means reaches a certain voltage higher than the minimum voltage and lower than or equal to the voltage at which the protection processing means is stably driven may be further provided. After the initialization process is completed, the protection processing means may configure a threshold voltage required for operation control of the discharge current cut-off means and the charge current cut-off means in accordance with detection of the detection signal from the stable driving voltage detecting means. In this manner, the power supply voltage rises much higher than the above-described minimum voltage, and then the data setting necessary for the secondary battery protection processing is performed more reliably to start the protection processing.

Also, the present invention provides a start-up control method for a battery protection processing apparatus that performs a process of protecting a secondary battery against occurrence of an abnormality by controlling an operation of a discharge current cutoff circuit to selectively cut off a discharge current of the secondary battery and a charge current cutoff circuit to selectively cut off a charge current of the secondary battery according to a voltage between a positive electrode and a negative electrode of the secondary battery, the method including: when the power supply voltage supplied to the battery protection processing device reaches a minimum voltage for starting the battery protection processing device, the initialization processing of the battery protection processing device is performed.

The start-up control method for the battery protection processing device performs initialization processing of the device when the power supply voltage supplied to the battery protection processing device reaches the lowest voltage at which the battery protection processing device is started up. Therefore, the battery protection processing device stops operating as the power supply voltage supplied from the secondary battery decreases. After that, when the power supply voltage rises enough to enable the start-up, the protection processing device starts up. The battery protection processing device is initialized to stabilize the operation state while starting.

Further, it is preferable that the threshold voltage required for the operation control of the discharge current cut-off circuit and the charge current cut-off circuit is configured and the protection process of the secondary battery is started when the power supply voltage reaches a certain voltage higher than the minimum voltage and lower than or equal to the voltage at which the protection process means is stably driven. In this manner, the power supply voltage rises much higher than the above-described minimum voltage, and then the data setting necessary for the secondary battery protection processing is performed more reliably to start the protection processing.

According to the battery pack of the present invention, when the power supply voltage rises enough to enable starting, the protection processing means for performing the protection processing of the secondary battery starts. The protection processing device is initialized to stabilize the running state while starting. Therefore, software control can be provided to stably perform protection processing for the secondary battery against large voltage variations. This makes it possible to protect the secondary battery more reliably, reduce the circuit mounting area and production cost, and easily achieve a high-precision protection process.

Further, when the power supply voltage for the protection processing means reaches a certain voltage higher than the lowest voltage at which the protection processing means is started and lower than or equal to a voltage at which the protection processing means is stably driven, stable driving voltage detection means for generating a detection signal is provided. After the initialization process is completed, the protection processing means may configure the threshold voltage required for the operation control of the discharge current cut-off means and the charge current cut-off means in accordance with the detection of the detection signal from the stable driving voltage detecting means. In this case, when the power supply voltage rises much higher than the minimum voltage, the secondary battery protection process is started. This makes it possible to perform the protection processing more reliably.

According to the start-up control method for the battery protection processing device of the present invention, the battery protection processing device starts up when the power supply voltage rises enough to enable start-up. The battery protection processing device is initialized to stabilize the operation state while starting. Therefore, software control can be provided to stably perform protection processing in which the secondary battery is subjected to a large voltage variation. So that it is possible to protect the secondary battery more reliably, reduce the circuit mounting area and production cost of the battery protection processing device, and easily perform the protection processing with high accuracy.

Also, it is possible to configure threshold voltages required for operation control of the discharge current cut-off circuit and the charge current cut-off circuit and start the secondary battery protection process when the power supply voltage supplied to the battery protection process device reaches a certain voltage higher than the lowest voltage at which the device is started and lower than or equal to a voltage at which the device is stably driven. In this case, when the power supply voltage rises much higher than the minimum voltage, the secondary battery protection process is started. So that the protection process can be performed more reliably.

Drawings

Fig. 1A and 1B are graphs showing changes in voltage and current when discharge and overcurrent occur in a lithium ion secondary battery;

fig. 2 shows an example of the internal structure of a conventional battery pack;

fig. 3 schematically depicts the cell states of a conventional battery pack;

fig. 4 illustrates an internal structure example of a battery pack according to an embodiment of the present invention;

fig. 5 is a block diagram showing an example of the internal structure of an integrated processing circuit;

FIG. 6 is a graph showing the change in cell voltage during charging;

fig. 7A to 7C show the relationship between the output signal of the reset circuit, and the power supply voltages of the battery cell and the microcontroller;

FIGS. 8A and 8B schematically illustrate the path of power provided during start-up and steady operation of the microcontroller;

FIG. 9 is a flow chart showing microcontroller processing at a moment after startup;

fig. 10 shows a state change of the cell voltage;

fig. 11 shows the flow of the state change control in detail;

fig. 12 shows an internal configuration example of the overcurrent detection circuit;

fig. 13 is a graph showing a change in consumption current during operation of the video camera;

fig. 14 shows an example of the internal structure of a fuel gauge (fuel gauge).

FIG. 15 illustrates a variation of the manner of operation of the microcontroller;

FIG. 16 is a flow chart showing the overall flow of the microcontroller process;

fig. 17 is a flowchart showing a battery protection process of the microcontroller;

fig. 18 is a flowchart showing a remaining battery capacity calculation process of the microcontroller; and

fig. 19 shows an example of the internal structure of a battery pack using a plurality of battery cells connected in series.

Detailed Description

Embodiments of the present invention will be described in further detail with reference to the accompanying drawings.

Fig. 4 shows an internal structure example of a battery pack according to an embodiment of the present invention.

The battery pack according to the present invention is an integrated assembly of a secondary battery and a circuit that performs a processing function to display the remaining capacity of the secondary battery and a protection function against an abnormal state of the secondary battery. The embodiment uses a lithium ion secondary battery having such discharge characteristics that the discharge voltage is relatively gentle and linearly decreased. For example, the use of such a secondary battery makes it possible to accurately detect the remaining battery capacity and display it according to the available remaining time.

The battery pack in fig. 4 has: a battery unit 1 including a lithium-ion secondary battery; an integrated processing circuit 2 formed on the same semiconductor substrate to control the operations of the above-described processing function for displaying the remaining battery capacity and the protection function; protection switches SW1 and SW2 for discharge control and charge control; a current detection resistor Rs; a capacitor C1 that stabilizes the output voltage; resistors Rth1 and Rth2 that set a threshold; and a thermistor 3 that detects the temperature of the battery cell 1.

In the battery pack, the expansion-maintaining switches SW1 and SW2 each include a MOSFET that equivalently includes a diode between a source and a drain according to a structure. The protection switches SW1 and SW2 may cut off the discharging current and the charging current, respectively. When the battery cell 1 is charged, the charger is connected to the positive terminal Eb1 and the negative terminal Eb2, and the protection switch SW2 is turned on. When a device as a discharge load is connected to the positive terminal Eb1 and the negative terminal Eb2, if the protection switch SW1 is turned on, power can be supplied to the device.

Integrated processing circuit 2 is powered from two points, power terminals CPin1 and CPin2, which power terminals CPin1 and CPin2 may be selectively used in integrated processing circuit 2. The power supply terminal CPin1 is connected to the positive side of the battery cell 1 and supplies the voltage of the battery cell 1 (hereinafter referred to as the cell voltage) to the integrated processing circuit 2. The power supply terminal CPin2 is connected between the protection switches SW1 and SW 2. As will be explained later, the power supply terminal CPin2 can supply a voltage from a charger to operate the integrated processing circuit 2 when the cell voltage is extremely low. The operations of the protection switches SW1 and SW2 may be selected according to the output voltages of the output terminals DIS and CHG, respectively.

The integrated processing circuit 2 further comprises various input/output terminals. The input terminal ADCin is connected to the positive electrode side of the battery unit 1. The input terminals CSP and CSN are connected to both ends of a resistor Rs. The input terminal HVIN is connected between the positive terminal Eb1 and the protection switch SW 2. The input/output terminal UART is used for communication with a device mounted with a battery pack and is connected to a communication terminal of the device through the control terminal 4. The output terminal VAA outputs a reference voltage (operating voltage of the integrated processing circuit 2) of 3.4V. The reference voltage from the output terminal VAA is divided by the resistors Rth1 and Rth2 and applied to the input terminal ODI. The output terminal THRM outputs a control signal for the thermistor 3. The output signal from the thermistor 3 is supplied to the input terminal AINO.

Fig. 5 is a block diagram showing an example of the internal structure of the integrated processing circuit 2;

as shown in fig. 5, the integrated processing circuit 2 roughly includes a power supply circuit 10, an overcurrent detection circuit 20, and a microcontroller 30. The power supply circuit 10 further includes: a charge pump (charge pump) circuit 11 and a linear regulator 12 to supply a driving voltage to the microcontroller 30; and reset circuits 13 and 14 to reset microcontroller 30.

The charge pump circuit 11 selects the voltage supplied from one of the power supply terminals CPin1 and CPin2 and increases the voltage by 1.5 times or two times. The linear regulator 12 stabilizes the input voltage boosted by the charge pump circuit 11 to 3.4V. The output voltage from the linear regulator 12 is supplied as a drive voltage to the microcontroller 30. The output voltage is output from the output terminal VAA and is also supplied to the reset circuits 13 and 14.

The reset circuits 13 and 14 each have a comparator so as to compare the output voltage from the linear regulator 12 with a reference voltage. The reset circuits 13 and 14 change output values of a power-on reset signal (hereinafter, referred to as a signal POR) and a power failure warning signal (hereinafter, referred to as a signal PFW) according to a comparison result of the comparator, thereby controlling a start-up operation of the microcontroller 30. The reset circuit 13 configures the signal POR to an L level when the linear regulator 12 outputs a voltage greater than or equal to a minimum voltage (2.7V in the embodiment) required to activate the microcontroller 30. When the linear regulator 12 outputs a voltage greater than or equal to the minimum voltage (3.0V in the present embodiment) required to stably operate the microcontroller 30, the reset circuit 14 configures the signal PFW to the L level. Output signals from the reset circuits 13 and 14 are input to a reset terminal (not shown) that detects the reset timing of the microcontroller 30.

The overcurrent detection circuit 20 detects a current value from the voltage between the input terminals CSN and ODI. When an overcurrent is detected, the overcurrent detecting circuit 20 notifies these to the microcontroller 30 by way of an interrupt (CPU 31). Further, the overcurrent detection circuit 20 controls and operates the protection switches SW1 and SW2 to protect the battery cell 1. The internal structure of the overcurrent detecting circuit 20 will be explained later with reference to fig. 12.

The microcontroller 30 is configured to interconnect the following components via a data bus 43: a CPU (central processing unit) 31; a program memory 32; a ROM (read only memory) 33; a RAM (random access memory) 34; an EEPROM (electrically erasable programmable read only memory) 35; a timer 36; a monitoring timer 37; an AD converter 38; a fuel gauge 39; an I/O port 40; a communication I/F (interface) 41; and a FET driver 42. The microcontroller 30 includes clock oscillators 44a and 44b that generate instruction clocks of different frequencies (32kHz and 6MHz) to run the respective blocks.

The CPU31 reads and executes programs stored in the program memory 32 and EEPROM35 to control overall operation of the microcontroller 30. The program memory 32 is a nonvolatile memory medium and stores programs in advance to operate the respective parts of the microcontroller 30. The ROM33 stores data and the like necessary for the CPU31 to execute programs in advance. The RAM34 includes, for example, an SRAM (static RAM), and temporarily stores part of programs executed by the CPU31 and data necessary for the program execution process. Also, the microcontroller 30 has an EEPROM35 as a nonvolatile memory. The EEPROM35 is capable of not only storing software and configuration data executed by the CPU31, but also rewriting them if necessary.

Timer 36 measures the time required for the various parts of microcontroller 30. The watchdog timer 37 monitors commands executed by the CPU31 based on the time measured by the timer 36. The watchdog timer 37 automatically resets the microcontroller 30 when it is determined that the system is abnormally terminated.

The AD converter 38 converts signals from the input terminals ADCin, AINO, HVIN, and PCKP into digital signals and supplies them to the CPU 31. In this way, the microcontroller 30 can obtain information such as the charging and discharging voltages and temperatures of the battery unit 1, the presence or absence of a charger to be connected, and the presence or absence of a charging voltage to be applied.

The fuel gauge 39 is a circuit that calculates the amount of current flowing into the battery unit 1 from the voltage between the input terminals CSP and CSN and accumulates the current value. The accumulated current value is output to the CPU31 and used to calculate the remaining capacity of the battery cell 1. The internal structure of the fuel gauge 39 will be described later with reference to fig. 14.

The I/O port 40 is used for data input or output to various input/output terminals. For example, the I/O port 40 outputs a control signal from the CPU31 to the output terminal THRM to control the operation of the thermistor 3. The communication I/F41 is an interface circuit for communicating with a device in which the battery pack is mounted. The communication I/F41 mainly receives necessary information to display the remaining capacity of the battery unit 1 and transmits the information to the device.

The FET driver 42 is a driving circuit that controls the operations of the protection switches SW1 and SW2 for discharge and charge control. The FET driver 42 operates in accordance with control signals from the CPU31 and the overcurrent detection circuit 20.

In the integrated processing circuit 2, the microcontroller 30 performs processing for displaying the remaining capacity of the battery unit 1. Also, the protection function of the battery unit 1 is mainly performed under the control of the microcontroller 30. Specifically, the microcontroller 30 detects the overcharge and overdischarge states of the battery cell 1 using information such as the voltage and temperature obtained by the AD converter 38. The microcontroller 30 controls the protection switches SW1 and SW2 and the like for charging and discharging, thereby protecting the battery cell 1 from these abnormal states.

In order to perform the protection function, the microcontroller 30 needs to stably operate without malfunction. However, during normal operation, the microcontroller 30 uses the output voltage of the battery unit 1 as a power source at a proper time. The output voltage of the battery unit 1 changes abruptly depending on the situation. It is difficult to stably operate the microcontroller 30. In order to solve these problems to stably operate the microcontroller 30, the present invention controls the start-up operation of the microcontroller 30 based on the output signals from the reset circuits 13 and 14 in the power supply circuit 10. Also, the present invention selects a voltage as a power source supplied from the battery cell 1 and a charger connected to the battery pack according to the state of the battery cell 1. In this manner, the peripheral circuits such as the power supply circuit 10 and the microcontroller 30 become a single chip.

[ Start-Up control of microcontroller ]

The control operation at the time of start-up on the premise that the microcontroller 30 is stably operated is described below.

It is necessary for the microcontroller 30 to ensure stable operation because it controls the protection function for the battery unit 1. However, the secondary battery may be subject to a significant drop in battery voltage due to self-discharge and a short circuit due to overcurrent. This low voltage drop can cause the voltage supplied from the power supply circuit 10 to the microcontroller 30 to be lower than the operating voltage of the microcontroller 30 (3.4V in this embodiment). As such, the microcontroller 30 cannot stably operate. If the battery cell 1 is not used for a long time, the battery voltage may be reduced to 0V. As such, the battery cell 1 cannot be charged under the control of the microcontroller 30.

In order to stably operate the microcontroller 30, for example, the minimum operating voltage of the microcontroller 30 may be further reduced to a smaller value (e.g., 1.8V). The method may reduce the likelihood of causing unstable operation of the microcontroller 30. However, the method cannot solve the unstable state of the microcontroller 30 and cannot ensure stable operation of the protection function. Therefore, it is necessary to design the microcontroller 30 so that the protection function can be stably operated at all times in the case where the battery unit 1 is not used for a long period of time and the battery voltage is approximately 0V.

An example of the embodiment is explained below by assuming a case where the battery voltage becomes 0V. Similar control is provided when the battery voltage drops to a stop microcontroller 30 (off state).

Fig. 6 is a graph showing the voltage change of the battery cell 1 during charging.

When charging the battery cell 1, the charger is connected to the positive terminal Eb1 and the negative terminal Eb 2. Fig. 6 shows not only the change in the cell voltage when charging is started from 0V but also the change in the output current value from the charger.

When the battery voltage is extremely low, for example, 0V, the battery cell 1 may deteriorate or a small amount of short circuit may occur between the electrodes, causing problems in reliability and safety. In view of this, as shown in fig. 6, it is a common practice to set the charging current supplied from the charger as low as about 50 to 100mA immediately within a given period of time after the start of charging. Since the initial charging current is thus applied, the battery voltage gradually rises. After a given period of time, the charger went into normal operation and output a constant current of 680 mA. The lithium ion secondary battery cell used in the present example exhibited a discharge capacity of 680mAh according to the 5-hour capacity measurement. The cell was charged with a constant current of 1C (680 mA). When the cell voltage reaches 4.25V, i.e., the voltage for overcharge detection, the protection switch SW2 is turned off (or output control is provided from the charger) to keep the cell voltage thereafter at 4.25V.

According to the present embodiment, the microcontroller 30 is supplied with a supply voltage of 3.4V. The battery cell 1 is supplied with a full charge voltage of 4.2V and a discharge end voltage of 3.0V. Therefore, the discharge termination voltage is lower than the power supply voltage of the microcontroller 30. The discharge voltage of the battery unit 1 needs to be boosted and supplied to the microcontroller 30. For this purpose, the power supply circuit 10 is provided with a charge pump circuit 11 and a linear regulator 12. That is, the voltage input to the charge pump circuit 11 rises by two times or 1.5 times. The voltage is regulated to 3.4V in the linear regulator 12.

In addition, timing must be provided to stably start and operate the microcontroller 30. To this end, reset circuits 13 and 14 are provided to use comparators to compare the output voltage from the linear regulator 12 with a reference voltage.

Fig. 7A to 7C show the relationship among the output signals of the reset circuits 13 and 14, and the power supply voltages of the battery unit 1 and the microcontroller 30.

The charger is connected to the positive terminal Eb1 and the negative terminal Eb2 to start charging. As shown in fig. 6, the charger provides an initial charging current of 50 to 100 mA. Therefore, as shown in fig. 7A, the cell voltage gradually rises. For example, when the cell voltage reaches 1.2V, the power supply circuit 10 starts. At this time, the charge pump circuit 11 increases the input voltage by two times. As shown in fig. 7B, the voltage of 2.4V (timing T41) is supplied to the microcontroller 30.

The power supply circuit 10 is configured to start up when the voltage supplied to the microcontroller 30 reaches the minimum voltage Vpor (2.7V) required to start up the microcontroller 30 or reaches a voltage slightly lower than the minimum voltage. After the charging is started, the cell voltage may be unstably increased due to a short circuit between the contacts of the battery cell 1 or a small short circuit inside the cell. In view of this, the capacity of the capacitor C1 connected to the output terminal of the linear regulator 12 is configured to compensate for voltage fluctuations and stabilize the output voltage.

When the output voltage from the power supply circuit 10 does not reach the voltage Vpor, the signals POR and PFW from both the reset circuits 13 and 14 reach the H level, as shown in fig. 7C. When the output voltage from the power supply circuit 10 thereafter reaches the voltage Vpor, the signal POR from the reset circuit 13 reaches the L level (timing T42). The timing is used to provide reset timing for the microcontroller 30. When the supplied supply voltage reaches around the voltage Vpor, the microcontroller 30 starts. Because of the insufficient applied voltage, the microcontroller 30 may continue to operate erratically, with irregular results. To solve these problems, the system of the microcontroller 30 is reset at the timing when the signal POR reaches the L level. Subsequent operation of the microcontroller 30 can thus be reliably stabilized.

In the above-described timing T42, for example, for protection processing, the system is configured to initialize only the register or the RAM34 in the CPU31 without initializing the battery unit 1. When the cell voltage further rises, the voltage supplied to the microcontroller 30 reaches Vpfw (3.0V), i.e., a minimum voltage at which the microcontroller 30 is stably operated. At this time, the signal PFW from the reset circuit 14 reaches the L level (timing T43). It is determined that the microcontroller 30 can operate normally. The system starts reading the configuration values of the protection battery cell 1. The protection function starts running.

As described above, the microcontroller 30 does not start up until the power supply voltage supplied to the microcontroller 30 reaches a value sufficient for start-up. The microcontroller 30 is automatically initialized just after start-up. In addition, the microcontroller 30 does not start the protection process of the battery unit 1 until the power supply voltage reaches a value enabling stable operation. This control prevents the microcontroller 30 from starting in an unstable state, thereby working erratically and running the protection function incorrectly. Also, such control is performed by using a minimum analog circuit such as the reset circuits 13 and 14. The circuit can be easily integrated on the same semiconductor substrate as the microcontroller 30.

When the cell voltage is set to 0V or the like, the voltage supplied from the power supply terminal CPin1 cannot start the microcontroller 30. However, after starting the charging, the charger stably provides its output. When the cell voltage is less than or equal to a specific value (e.g., 2.2V) in the above-described integrated processing circuit 2, the system starts the microcontroller 30 using the output voltage of the charger, i.e., the voltage supplied from the power supply terminal CPin 2.

FIGS. 8A and 8B schematically illustrate the paths of power provided during start-up and stable operation of microcontroller 30;

fig. 8A shows a power supply path when charging is started with the cell voltage set to 2.2V or less. At this time, the microcontroller 30 is in an inactive (off) state. Both protection switches SW1 and SW2 are on. When the power supply terminal CPin2 is selected for input to the charge pump circuit 11, power can be supplied to the microcontroller 30 and started.

After the microcontroller 30 starts up, a time period is required until the power supply voltage is stabilized to some extent. During this period, the microcontroller 30 operates at the voltage provided by the charger. The CPU31 performs processing to detect that the cell voltage reaches a certain value (2.5V in the present embodiment) according to the output signal from the AD converter 38. At this time, the power supply terminal CPin1 is selected for input to the charge pump circuit 11. As shown in fig. 8B, the charge pump circuit 11 is supplied with the output voltage from the battery unit 1. This voltage generates a supply voltage for the microcontroller 30. In this manner, when the operation becomes stable after the start, the power supply terminal CPin1 is selected for input to the charge pump circuit 11. If the charger is removed, power may be continuously supplied from the battery unit 1 to the microcontroller 30.

The sense voltage is used to provide timing to select the power supply terminal CPin1 for input to the charge pump circuit 11. It is desirable for the microcontroller 30 to set the detection voltage higher than the cell voltage (2.5V in the embodiment) to determine that the battery cell 1 is in an overdischarge state (to be described). This makes it possible to stably operate the microcontroller 30.

Fig. 9 is a flowchart showing the processing of the microcontroller 30 immediately after startup.

When the signal POR from the reset circuit 13 reaches the L level in step S601, the process proceeds to step S602. In step S602, the microcontroller 30 starts initializing the registers and the RAM34 in the CPU 31. At this time, the system performs only the minimum processing required after the microcontroller 30 is started and does not start the protection processing of the battery unit 1.

In step S603, the process detects the level of the signal PFW from the reset circuit 14. When the signal PFW reaches the L level, the CPU31 performs normal processing for the microcontroller 30, such as protecting the battery cell 1 and calculating the remaining battery capacity. The program performs the following initial processing.

In step S604, the process clears the configuration value of the watchdog timer 37. The watchdog timer 37 included in the microcontroller 30 has a function of protecting the microcontroller 30 from unstable operation. During startup with the power supply voltage rising, neither the microcontroller 30 nor the watchdog timer 37 is initially set. It is necessary to prevent this state to realize the protection function of the battery unit 1 mainly by using the microcontroller 30 itself. Immediately after the start of the microcontroller 30, the steady operation of the microcontroller 30 clears the configuration value of the watchdog timer 37, for example, the time interval, to determine that the unstable operation and enable the watchdog timer 37 is valid. When the initial configuration value is cleared, the monitoring timer 37 transmits an activation signal to the CPU31, thereby notifying the monitoring timer 37 of the activation.

In step S605, when the signal PFW reaches the L level in step S603, the timer 36 is allowed to count a time interval of 300 msec from the timing. During this period, the microcontroller 30 is forced into a wait state. At this step, as shown in fig. 7B, the power supply voltage supplied to the microcontroller 30 may be further raised after the start-up. The microcontroller 30 needs to be stably operated by increasing the power supply voltage as much as possible. For this reason, the microcontroller 30 is in a wait state long enough for the instruction clock frequency of the microcontroller 30. Then, the following processing is performed.

At step S606, the process reflects various configuration values assigned to the active software to start execution of the protection process against abnormal states of the battery cell 1, such as overcharge and overdischarge. The reflected configuration values include, for example, the voltage and temperature of the battery cell 1 to detect abnormal states such as overcharge and overdischarge. These states are detected based on the values input to the AD converter 38. At step S607, the process initializes register values configured inside the microcontroller 30, e.g., the CPU 31.

Under its own control, the microcontroller 30 performs the protection function of the battery unit 1. Various configuration values for the protection function can be freely changed by using a nonvolatile memory (EEPROM 35 in the present embodiment). Each manufactured microcontroller 30 may have different characteristics. The non-volatile memory may store values reflecting correction values corresponding to various configuration values of each microcontroller 30. The stored value may also be used to run the microcontroller 30. Furthermore, as will be explained later, the microcontroller 30 may be stopped due to the lowered cell voltage. In view of this, the nonvolatile memory stores various configuration values required for processing after restart, immediately before the microcontroller 30 stops (for example, when the cell voltage becomes lower than a certain voltage). After a reboot, the stored configuration values may be read for processing.

However, it takes a while to read the configuration values stored in the nonvolatile memory and reflect them on the operation of the CPU 31. This is inappropriate for the purpose of stably operating the protection function immediately after the start-up. To address this problem, the CPU31 is allowed to run using configuration values preset in the active software immediately after the microcontroller 30 starts up. I.e. the configuration values used at this stage are pre-stored in the program memory 32. These values are read into the CPU31 as a process is executed by software in the program memory 32. After a given timing, the CPU31 rereads the configuration values stored in the nonvolatile memory for operation. Under such control, the protection function can be continuously and stably operated immediately after the start-up. In addition, the degree of freedom of the respective values can be improved and versatility can be provided thereto.

For example, the configuration values stored in the nonvolatile memory may be reflected in the timing when the power supply voltage of the microcontroller 30 reaches a certain value. That is, in step S608, it is determined whether the power supply voltage supplied to the microcontroller 30 is greater than or equal to 2.5V from the cell voltage detected by the AD converter 38. If the result is affirmative, the process proceeds to step S609. In step S609, the process initializes registers necessary for changing the configuration values. At step S610, the process reflects the configuration values read from the EEPROM35 and continues the protection process for the battery cell 1. Thereafter, the microcontroller 30 transitions to a normal operating state. In step S611, the process selects the power supply terminal CPin1 for input to the charge pump circuit 11 that supplies power to the battery unit 1.

The above process makes it possible to reliably and stably start and operate the microcontroller 30 and accurately operate the protection function even when the cell voltage is reduced too small to drive the microcontroller 30.

[ control of State Change of Battery cell ]

How the microcontroller 30 controls the protection function for the battery unit 1 is explained in detail below. The protection function causes the AD converter to detect the cell voltage value and track the state. The microcontroller 30 stably performs processing suitable for the state mainly under software control.

Fig. 10 illustrates a state change according to a cell voltage.

Fig. 10 shows a state that varies with the cell voltage from the starting point in time series from when the battery cell 1 is fully charged. Secondary batteries require that the cell voltage should be within a certain range during normal use so as not to shorten the life, reduce the capacity, or deteriorate the quality of the battery itself. It is suggested to use the lithium ion secondary battery in a range of a cell voltage between 3.0 and 4.2V. In terms of cell voltage, the overcharge and overdischarge states are defined as normal operating states above and below approximately the corresponding cell voltage ranges above. The overcharged state indicates an excessively high cell voltage. The over-discharge state indicates an insufficient cell voltage.

For example, as shown in fig. 10, in the normal operation state, the battery unit 1 is fully charged. The normal operating state allows the charger to further charge and also allows for discharge due to connection to a discharging load. That is, the protection switches SW1 and SW2 are turned on under the control of the microcontroller 30. When the discharge is such that the cell voltage is less than or equal to a certain value from the state, the over-discharge state is effective to terminate any discharge, thereby protecting the battery cell 1. The protection switch SW1 is open.

Since the microcontroller 30 itself is operated by the cell voltage as a power supply, the cell voltage at which the operation of the microcontroller 30 is terminated is further reduced. At this time, the state changes to the off state to stop the microcontroller 30.

As described above, connecting the charger raises the cell voltage to some extent to start the microcontroller 30. After the start, the state becomes an overdischarge state. Immediately after the startup, a startup processing state is performed to immediately execute the startup processing as described with reference to fig. 9. In this state, only charging is allowed to turn off and on the protection switches SW1 and SW2, respectively. The power supply is set to the charger side (i.e., the power supply terminal CPin 2). When the charging is such that the cell voltage is greater than or equal to a certain value, the power supply is switched to the power supply terminal CPin 1. The battery unit 1 serves as a power source. When the cell voltage further exceeds a certain value, the normal state is restarted. The protection switch SW1 is also turned on to allow charging and discharging.

After the battery cell 1 is fully charged, the charging is further continued to change the state to the overcharged state. The protection switch SW2 is turned off to allow only discharge. When the discharge makes the cell voltage less than or equal to a certain value, the overcharge state becomes a normal state.

In the above state change, the cell voltage value that determines the state change is configured with the characteristics of the battery cell 1 taken into full consideration. Thus, it may be desirable to use different thresholds depending on the direction of change of state. Since the processing corresponding to the state change is performed under software control, the threshold value can be easily finely adjusted without using a complicated circuit.

In addition to the above state, the state may be converted into an overcurrent state in which a short circuit between electrodes or in a cell causes an excessively high discharge current. The overcurrent detecting circuit 20 determines a change in the overcurrent state. The microcontroller 30 controls the recovery from this state.

Fig. 11 shows the flow of the state change control in detail; referring to fig. 11, specific thresholds of cell voltage and discharge current and necessary processing during state change are explained below.

(1) Detecting overcharge state and recovery

The CPU31 of the microcontroller 30 determines the overcharge state of the battery cell 1 via the cell voltage Vcell detected by the AD converter 38. As shown in fig. 11, the overcharged state is detected when the cell voltage Vcell reaches 4.25V. The FET driver 42 changes the control voltage to be output to the output terminal CHG to turn off the protection switch SW 2. This will forcibly stop charging the battery unit 1.

Concurrently with the process, the CPU31 writes the change to the overcharged state in the EEPROM35 as a state change record. For example, during the remaining battery capacity calculation process for the battery unit 1, the calculated value may be corrected using the record in accordance with an error phenomenon or a detection failure in the battery unit 1.

When the cell voltage Vcell becomes lower than 4.15V, the microcontroller 30 detects a change from the overcharged state to the normal state. The protection switch SW2 is restored to the on state. The same detection voltage can be used for the change to the overcharged state and the recovery to the normal operation state. When the change to the overcharged state turns off the protection switch SW2, the cell voltage Vcell immediately decreases to detect the change in the normal operation state. This restarts the charging. The cell voltage Vcell rises again to change to the overcharged state, causing an irregular hunting condition that repeatedly changes between the overcharged and normal operating states. In order to prevent such a situation, the detection voltage for recovering to the normal operation state is set to be lower than the detection voltage during the change, referred to as 4.2V, that is, the full charge voltage of the lithium ion secondary battery.

According to the above process, the microcontroller 30 can accurately detect the occurrence of the overcharge state and stop the charging operation. Such a situation that ions are isolated or smoke and ignite on the electrodes of the battery cell 1 can be reliably prevented, thus ensuring safety. It is also possible to detect a fault in a charger connected to the battery pack.

In the above description, the state change is detected only from the cell voltage Vcell. In addition, safety can be further improved by detecting a state change using temperature information on the battery cell 1. The temperature information is detected by the thermistor 3 and obtained from the AD converter 38. For example, when the temperature information value exceeds 60 ℃, charging is not allowed. In other words, it is preferable to lower the threshold voltage by about 0.1V when the temperature information value exceeds 60 c to detect overcharge.

(2) Detecting over-discharge state and recovery

When the cell voltage Vcell becomes lower than 2.6V, a change from the normal operation state to the over-discharge state is detected. The detection turns off the protection switch SW1 to cut off the discharge current. The change to the over-discharge state is written to the EEPROM35 as a record, like the change to the over-charge state described above.

The lithium ion secondary battery uses a discharge end voltage set to 3.0V. When the device operates using the battery unit 1 as a power source, the device may be configured so as to stop the operation according to the detection of the discharge end voltage. The microcontroller 30 uses the detection voltage to detect an overdischarge state. If the detection voltage is set equal to the discharge end voltage, the timing of stopping the operation of the connected device corresponds to the timing of turning off the protection switch SW 1. The process of stopping the running apparatus cannot be normally completed, causing an error. To solve this problem, the over-discharge state detection voltage is set to be slightly lower than the discharge termination voltage. After the device normally stops operating, the protection switch SW1 is turned off to cut off the discharge current.

When the state changes to the overdischarge state, the cell voltage Vcell may further decrease, causing a change to the off state, which stops the microcontroller 30 from operating. In view of this, the EEPROM35 stores information necessary for the microcontroller 30 to restart after the timing to change to the over-discharge state. Such information includes, for example, values temporarily stored in RAM34 of microcontroller 30. The CPU31 reads the stored information at a timing when the CPU31 stably supplies the power supply voltage to the microcontroller 30 after the microcontroller 30 is restarted. The information can be used for operation (corresponding to step S610 in fig. 9).

On the other hand, when the detection cell voltage Vcell becomes higher than 2.65V and the charger is connected for charging in process, a change from the overdischarge state to the normal operation state is determined. It is known that a lithium ion secondary battery temporarily increases a cell voltage immediately after stopping discharge. Therefore, if the detection voltages use the same value to detect a change from the normal operation state to the overdischarge state and to detect a return to the normal operation state, an irregular hunting situation may be caused that repeatedly changes between these states. In order to reliably prevent the occurrence of irregular swing, a period of time is required between the transition to the over-discharge state and the return to the normal operation state. For this reason, the detection voltage for detecting the return to the normal operation state is set to be slightly higher than the detection voltage for detecting the over-discharge state. Furthermore, the state is not restored to the normal operation state until the charging is started.

To detect the charge start, the CPU31 obtains the signal level and the voltage value at the input terminal HVIN from the input terminal PCKP through the AD converter 38 for determination. The input terminal PCKP is used to detect the charger connection. The input terminal HVIN is connected to the positive terminal Eb 1.

According to the above process, the microcontroller 30 can accurately detect the occurrence of the over-discharge state and stop the discharge operation. This makes it possible to reliably prevent a small amount of short circuits and capacity degradation inside the electrodes. Further, it is possible to ensure safety and prevent the life of the battery unit 1 from being shortened.

(3) Detecting a disconnected state and recovering

When the cell voltage Vcell is further lowered from the over-discharge state, the microcontroller 30 cannot operate. The discharge current in the over-discharge state is cut off. Therefore, the cell voltage Vcell slowly decreases due to the power consumption of the microcontroller 30 and the power supply circuit 10. In order to prevent the battery cell 1 from being further discharged, the microcontroller 30 transitions to the off state to stop the operation when the cell voltage Vcell becomes less than 2.2V.

In this state, the microcontroller 30 cannot start up using the battery cell 1 because the cell voltage Vcell decreases. The power supply terminal CPin2 needs to be selected for input to the charge pump circuit 11 so as to be supplied with power from the charger at the next start-up.

As shown in fig. 9, as the voltage supplied to the microcontroller 30 rises, the off state is restored to the over-discharge state in accordance with the reset timing and the start-up process initialization timing supplied from the reset circuits 13 and 14. Immediately after start-up, the microcontroller 30 operates using the voltage from the charger as a power supply. When the voltage is stabilized to some extent, for example, when the cell voltage Vcell exceeds 2.5V, the power supply terminal CPin1 is selected for input to the charge pump circuit 11. The state is completely restored to the over-discharge state.

The above process can minimize power supply reduction in the battery unit 1. The microcontroller 30 may start normally after charging is started. The protection process for the battery unit 1 can be stably started.

(4) Detecting overcurrent conditions and recovering

If the contacts of the battery unit 1 are short-circuited, an excessively high discharge current flows, causing the battery unit 1 to heat abnormally. To prevent this problem, the resistor Rs is used to detect the discharge current. When an overcurrent occurs, the protection switch SW1 is turned off to cut off the discharge current.

The overcurrent detecting circuit 20 is used to detect an overcurrent and control the protection switch SW 1. The overcurrent detection circuit 20 is provided as dedicated hardware, independent of the microcontroller 30. The reason is that a quick and stable switching to the protection switch SW1 is required when a short circuit occurs. If the microcontroller 30 detects an overcurrent due to the occurrence of a short circuit under software control. An interrupt occurs in the microcontroller 30 after the short circuit occurs. The instruction clock of the microcontroller 30 runs. Depending on the state of the instructions of microcontroller 30 just prior to initiating interrupt processing, the time at which control is provided to open protection switch SW1 changes and causes a large delay. Therefore, the protection switch SW1 needs to operate independently of the state of the instructions in the microcontroller 30.

As will be described later, the start charging trigger recovers from the overcurrent state. When the overcharge state changes to the overcurrent state, the protection switch SW2 is also turned on to enable charging. After the change to the overcurrent state, the control of turning on the protection switch SW2 may be directly provided by the overcurrent detecting circuit 20 as the control of turning off the protection switch SW1, or the control of turning on the protection switch SW2 may also be provided by the processing of the CPU 31.

Fig. 12 shows an internal configuration example of the overcurrent detection circuit 20.

As shown in fig. 12, the overcurrent detection circuit 20 includes a comparator 21, a digital delay circuit 22, a latch circuit 23, and an and gate 24. The input terminals of the comparator 21 are connected to the input terminals ODI and CSN, respectively. The comparator 21 sets the output signal to H level when the voltage between the input terminals is greater than or equal to a certain value. In this example, a threshold of 3.4A is indicated to detect a change in the overcurrent condition. The resistance values of the resistors Rth1 and Rth2 are configured so as to enable voltage comparison of the threshold current of 3.4A in the comparator 21.

The digital delay circuit 22 delays the output signal from the comparator 21 for 5 milliseconds. When the input signal transitions to the L level within 5 milliseconds from the rising timing of the H level, the digital delay circuit 22 resets the output signal. In this way, the digital delay circuit 22 is prevented from detecting a momentary overcurrent in 5 milliseconds or less.

The latch circuit 23 latches the output from the digital delay circuit 22 according to the clock signal from the clock oscillator 44a or 44 b. The latched signal is provided to FET driver 42. When this signal reaches the H level, the protection switch SW1 is forced to open. The latch signal is further supplied to the CPU31 through an and gate where a clock signal is input at the other input terminal. This signal interrupts the CPU 31.

The overcurrent detection circuit 20 can promptly open the protection switch SW1 according to the overcurrent detection of the comparator 21, regardless of the command state of the microcontroller 30. This can improve the effect of protecting the battery unit 1.

Electronic devices such as video cameras and digital still cameras use motors to drive lenses and to move magnetic tapes. It is well known that drive motors generate very large inrush currents at all times. Similar inrush currents also occur when using flashlights. The comparator 21 can quickly detect an overcurrent. However, the occurrence of the rush current may be incorrectly regarded as the occurrence of the overcurrent, thereby turning off the protection switch SW 1. To avoid this, a digital delay circuit 22 is used in case of detecting a momentary overcurrent in 5 milliseconds or less. This can prevent malfunction due to a rush current and ensure stable operation of the protection function.

Detecting the overcurrent causes the overcurrent detection circuit 20 to interrupt the microcontroller 30. When detecting the occurrence of an interrupt, the central processor 31 of the microcontroller 30 writes a state indicating the occurrence of an overcurrent in a register (RAM 34 in this example) to store an abnormal state. After the occurrence of the interrupt, the CPU31 can read the configuration value from the register to recognize the overcurrent occurrence. This makes it possible to smoothly perform a subsequent recovery process from the overcurrent state under the control of the microcontroller 30. The read configuration values are recorded in the EEPROM35 as records, and can be used for failure detection. If an overcurrent occurs repeatedly, it can be determined that a large discharge current is used for a device connected to the battery pack or the battery cell 1 is highly likely to be short-circuited, for example.

Returning now to fig. 11, the recovery process from the overcurrent state is described in more detail below.

One possible method of recovering from an over-current condition to a normal operating condition is to detect the release of a discharging load for automatic recovery. However, consider the case when the battery pack is placed in a pocket and a metal such as a key makes contact with the electrodes causing a short circuit. In this case, the metal and the electrode may repeatedly contact and separate, thereby causing a failure called a chain short. If the above recovery method is used, the overcurrent state and the normal operation state of the battery unit 1 are repeated, thereby causing abnormal heat generation. When an overcurrent occurs, the cell voltage becomes lower than the operating voltage of the microcontroller 30. If this situation is repeated, the microcontroller 30 is not operating steadily.

In view of the above, the configuration is such that recovery from an overcurrent state occurs only when charging is performed as in fig. 11. That is, when the detection signals from the input terminals PCKP and HVIN detect the connection of the charger and the application of the charging voltage, control is provided to return the overcurrent state to the normal operation state.

No charging occurs for a long time after the overcurrent is detected. In this case, when the cell voltage Vcell becomes less than 2.2V, control is provided to stop the operation of the microcontroller 30.

In the battery pack according to the embodiment of the present invention as described above, the protection functions of the battery cell 1 include the charge current cut-off control in the over-charged state and the discharge current cut-off control in the over-discharged state. These control operations can be stably performed under the control of the microcontroller 30. Further, the overcurrent detecting circuit 20 detects an overcurrent state and provides discharge current cut-off control in this state. The operation of the overcurrent detection circuit 20 is independent of the control operation provided by the microcontroller 30. Therefore, the protection operation can be reliably performed against the overcurrent.

As such, the software control of the microcontroller 30 is mainly used to perform the protection function of the battery cell 1, thereby reducing the circuit size and the production cost. In addition, the threshold voltage for detecting an abnormal state can be easily finely adjusted. These advantages make it possible to control very precisely in correspondence with the characteristics of the battery unit 1.

Microcontroller-based optimization of cell protection process and remaining capacity calculation process

As described above, the protection function for the battery cell 1 is performed by detecting the overcharged and overdischarged states according to the cell voltage detection. The protection function further detects an overcurrent state based on the discharge current detection to provide cutoff control of the charge current and the discharge current corresponding to the respective states. For the processing of the microcontroller 30, the CPU31 obtains a cell voltage value through the AD converter 38. The CPU31 determines a normal operation state, an overcharge state, and an overdischarge state. Preferably, based on these states, the CPU31 controls the operation of the protection switches SW1 and SW2 through the FET driver 42. It is preferable to obtain not only the cell voltage but also information on the temperature of the battery cell 1 detected by the thermistor 3 through the AD converter 38. The temperature information may also be used to control the operation of protection switches SW1 and SW2 to protect against abnormal heating.

During these processes, the CPU31 of the microcontroller 30 reads information on the voltage and temperature of the battery cell 1 from the AD converter 38 at given intervals. The CPU31 executes processing according to these values. For example, consider the case where a device is connected to a battery pack and powered from battery unit 1. In order to safely protect the battery cell 1, it is desirable to read the voltage or temperature of the battery cell 1 from the AD converter 38 using as short an interval as possible.

On the other hand, the microcontroller 30 not only protects the battery unit 1 as described above, but also calculates the remaining capacity of the battery unit 1 and transmits the calculated information to the device through communication with the device. These processes make it possible for the display mounted on the apparatus to display the remaining capacity of the battery unit 1 and the remaining time available.

In order to perform the remaining battery capacity calculation process as in the above-described protection process, the CPU31 needs to obtain the voltage, the charge and discharge current, the discharge termination voltage (actually approximated by the detection voltage in the over-discharge state), and the temperature of the battery cell 1 through the AD converter 38. The remaining battery capacity calculation process further requires the power (current) consumed by the connection means and the discharge end voltage (minimum operating voltage) uniquely given by the device. The remaining battery capacity calculation process transmits the values calculated from these information units to the device through the communication I/F41. The above-mentioned

The device is operated using the battery unit 1 for a relatively long period of time, for example over an hour. For example, about 10 hours of continuous shooting may be performed on a video camera (video camera) or about 1 hour of continuous shooting may be performed on a digital camera. Thus, for example, it is preferable to update the display of the remaining battery capacity at intervals of 1 minute or 5 to 10 minutes. This can fully satisfy the display accuracy required by the user.

Therefore, the remaining battery capacity calculation process does not have to transmit the calculated value to the device in as short a time as required for the protection process. In an extreme case, the remaining battery capacity calculation processing and the processing of transmitting the calculated value to the device need be performed only when the processing is required. In view of this, the present embodiment performs these processes by issuing an external interrupt to the microcontroller 30, for example, using communication from the device. At this time, information is obtained from the AD converter 38. The interval for configuring the external interrupt is longer than the execution interval of the protection process to stabilize the operation and reduce the power consumption.

Calculating the remaining battery capacity requires detecting the power (or current) consumed by the device operating or discharging. In order to perform the remaining battery capacity calculation process within a given time interval as described above, it is necessary to be able to read the detected power consumption value within the given time interval.

Information required to detect power consumption is described below. Fig. 13 is a graph showing a change in consumption current during operation of the video camera.

Fig. 13 illustrates the change in current consumed by a camera using a motor to drive a tape. The camera is an example of a device connected to the battery pack. As shown in fig. 13, the camera is turned on at timing T101. The internal circuit starts operation at timing T102. Then, the motor is initialized at timing T103. The driving motor generates a rush current to thereby instantaneously increase a consumption current greatly. At the start of recording on the magnetic tape at timing T104, the motor is also driven to generate a rush current and increase a consumption current.

As such, when the camera operates, the consumption current drastically changes in a short period of time. For example, when a lens is driven or a flash is used, a digital camera also receives a sharp change in consumption current due to generation of a rush current. However, it is important to measure the average current consumption of the device, not the short term current variations, so that the remaining battery capacity can be calculated very accurately.

Conventionally, in order to detect the average consumption current, the current is converted into a voltage using a resistor inserted in series with the battery cell. The voltage waveform is detected by an AD converter. A calculation is performed to average the detected values. However, this approach complicates the handling of the average run of the microcontroller. Very accurate operation requires increasing the frequency of processing or increasing the size of the memory to store the sensed values. Another method that can be used is to provide a filter at the input of the AD converter and to measure the average value with this filter. However, this method requires a mounting area to mount a relatively large external part and increases production costs.

In contrast, the present embodiment provides a fuel gauge 39 in the microcontroller 30 to detect the average consumed current. This facilitates the process of detecting the consumption current by the microcontroller 30. Fig. 14 shows an internal configuration example of the fuel gauge 39.

As shown in fig. 14, the fuel gauge 39 includes: a differential amplifier 39a whose input terminals are connected to both ends of the current detection resistor Rs; a capacitor Cint connected between the output terminal and the inverting input terminal of the differential amplifier 39 a; a resistor Rint inserted in series between the battery cell side of the resistor Rs and the inverting input terminal of the differential amplifier 39 a; comparators 39b and 39c whose inputs are the output from the differential amplifier 39a and the reference voltage Vref; and a charge counter 39d and a discharge counter 39e connected to the outputs of the comparators 39b and 39c, respectively.

The fuel gauge 39 uses a resistor Rs to detect the consumption current as a voltage. The input to the differential amplifier 39a is inverted and fed back through the capacitor Cint. In this configuration, the differential amplifier 39a functions as an integrator of the input voltage. The output from the differential amplifier 39a is input to the non-inverting input terminal of the comparator 39b and the inverting input terminal of the comparator 39 c. The reference voltage Vref is input to the inverting input terminal of the comparator 39b and the non-inverting input terminal of the comparator 39 c. Thus, the comparators 39b and 39c having the opposite polarities, respectively, perform the comparison operation.

When the charging current flows, the input voltage from the differential amplifier 39a exceeds the reference voltage. In this case, the comparator 39b resets the input voltage and outputs a pulse signal. When the input voltage of the differential amplifier 39a increases, the output frequency of the comparator 39b increases. The charge counter 39d counts the output pulses of the comparator 39b in a given time interval. This operation measures the accumulated value (charge) of the charging current flowing through the resistor Rs during the period. Likewise, when the discharge current flows, the input voltage from the differential amplifier 39a may be smaller than the reference voltage. In this case, the comparator 39c resets the input voltage and outputs a pulse signal. The discharge counter 39e counts the output pulses of the comparator 39c for a given time interval. This operation measures the accumulated value of the discharge current flowing through the resistor Rs.

With this fuel gauge 39, the microcontroller 30 reads the count values of the charge counter 39d and the discharge counter 39e at given time intervals for conversion into the consumed power and the power charged in the battery unit 1, respectively. The remaining battery capacity calculation process may be performed. The fuel gauge 39 outputs an average value of the consumed power or the charged power. The processing load of the CPU31 for displaying the remaining battery capacity can be greatly reduced. Further, the fuel gauge 39 can be realized in a simple circuit structure as shown in fig. 14, so that the circuit mounting area, power consumption, and production cost can be reduced. This is advantageous for stably implementing the protection function and the remaining capacity calculation function on the microcontroller 30 for the battery unit 1.

For example, when the voltage of the battery cell 1 is slowly decreased, it is advantageous to extend the unit time required for accumulating the current. This makes it possible to accurately detect the consumed current per unit time and improve the accuracy of displaying the remaining battery capacity. However, it is disadvantageous to significantly extend the timing of updating the remaining battery capacity displayed on the device. Therefore, it is desirable to configure the CPU31 with an interval to obtain the consumption current value from the fuel gauge 39, while taking into account the balance between the accuracy of measuring the consumption current and the convenience of the remaining battery capacity display. Intervals of about 2 seconds are suitable for powering portable devices such as digital video cameras and digital still cameras. When the power is supplied to the device, the CPU31 may execute the remaining battery capacity calculation processing and the processing of transferring the calculated value to the device according to the interrupt processing in an interval of 2 seconds. The CPU31 can perform the protection processing for the battery unit 1 in a shorter interval.

If the powered device is not connected or disconnected, the power consumption of the battery unit 1 is very small and the unit voltage slowly decreases. In this case, it is not necessary to determine the over-charged or over-discharged state as frequently as supplying power to the apparatus. If the interval for reading the voltage and the temperature from the AD converter 38 is set sufficiently longer than the command clock frequency of the microcontroller 30, safety can be ensured.

Generally, a time period of several milliseconds is required to obtain information on the voltage and temperature of the battery cell 1 through the AD converter 38 and determine the overcharge or overdischarge state. This embodiment allows the CPU31 to perform protection processing on the battery unit 1 in the power saving mode when the device is not connected or connected and disconnected, greatly reducing power consumption. The power saving mode makes it possible to perform the protection process at intervals of 2 seconds in the same manner as the remaining battery capacity calculation process.

Fig. 15 illustrates a variation of the way microcontroller 30 operates.

In fig. 15, the microcontroller 30 is in "active" mode as its mode of operation when the powered device is connected to the battery pack and turned on. When the device is disconnected or not connected, the microcontroller 30 is in a "power saving mode" as its mode of operation. The active mode is enabled to run with a high frequency clock of 6 MHz. The power saving mode enables operation with a low frequency clock of 32kHz, thereby further improving power consumption effectiveness.

The active mode is roughly divided into a "communicable state" and a "non-communicable state". The communicable state performs communication between the apparatus and the microcontroller 30, and according to the clock of the timer 36, effects corresponding to an interrupt every 2 seconds. In other words, the communicable state is effective in response to an interrupt from the connected apparatus. When the communication interruption occurs, the CPU31 reads information from the AD converter 38 and the fuel gauge 39. The CPU31 provides control to turn on or off the protection switches SW1 and SW2 corresponding to each of overcurrent, overcharge, and normal operation states. The CPU31 calculates information required to display the remaining battery capacity and transmits the information to the device via the communication I/F41. When information has been transmitted and communication with the device is terminated, the state changes to a non-communicable state.

In the incommunicable state, the CPU31 reads information from the AD converter 38 in an interval of 0.2 seconds timed by the timer 36. The CPU31 provides control corresponding to the recognized state to turn on or off the protection switches SW1 and SW 2. At this time, the CPU31 does not perform the process of reading information from the fuel gauge 39.

In the active mode, the protection process for the battery cell 1 is performed in a period of 0.2 seconds. The remaining battery capacity calculation processing is performed in correspondence with the communication interruption in a period of 2 seconds. These control operations can always stably perform the protection process against the variation of the cell voltage. Furthermore, it becomes possible to provide the improved battery with important processing, such as communication with the device and calculation of information required to display the remaining battery capacity, with reduced power consumption and sufficient accuracy.

The active mode makes it possible to perform the protection processing and the remaining battery capacity calculation processing for the battery unit 1 in a given cycle. It is desirable to set this period to be an even multiple of the period in which only the protection processing is performed. If these periods have an odd multiple relationship, the control stability of the microcontroller 30 is sacrificed. The even-multiple relationship can simplify control by maintaining stability.

When communication is interrupted after 2 seconds counted by the timer 36 have elapsed, the non-communicable state is changed to a communicable state. When no communication interruption occurs after 2 seconds have elapsed, the state changes to the sleep state. In the sleep mode, the microcontroller 30 reads information from the AD converter 38 and the fuel gauge 39 in a period of 2 seconds. The microcontroller 30 provides control to turn on or off the protection switches SW1 and SW2 according to the recognized state and calculates information required for the remaining capacity display. The calculated values are stored in, for example, an EEPROM35 for each calculation process, and are updated by new calculated values. When a communication interruption occurs, the communication interruption enables the active mode and changes the non-communicable state to a communicable state.

As described above, the microcontroller 30 controls the transition between the active mode and the power saving mode. To this end, the microcontroller 30 determines whether a device is connected or whether a connected device is turned on by detecting whether communication with the device occurs within a given interval. I.e. when no communication with the device takes place within a given period of time, the microcontroller 30 presents a reduction of the discharge load of the battery unit 1 and allows operation in a power saving mode.

The energy saving mode extends the interval to perform the protection process for the battery unit 1, thereby extending the time during which the AD converter 38 stops operating. Thus, power consumption can be greatly saved.

The overcurrent detection circuit 20 always detects the overcurrent even when the microcontroller 30 operates in the power saving mode. If an overcurrent is detected, the protection switches SW1 and SW2 are controlled according to the state. At this time, the microcontroller 30 interrupts. For example, when an interrupt is detected, microcontroller 30 temporarily resumes from the sleep state to set an overcurrent state in RAM 34.

Even when the battery pack does not supply power to the device, the overcurrent detection circuit 20 needs to be always operated in addition to the protection process of the battery cell 1 by the microcontroller 30. Therefore, reducing the power consumption of the microcontroller 30 is very important to provide a stable protection function for the battery unit 1.

In particular, in order to ensure stable operation of the protection function of the battery unit 1, a monitoring timer 37 is provided to the microcontroller 30. The monitoring timer 37 always monitors the timing of executing the protection processing. If the protection process is not performed within a given 2 seconds or more, the supervision timer 37 assumes an unstable operation of the microcontroller 30 and resets it. Accordingly, the respective operation modes reset the count value of the watchdog timer 37 at the termination of each protection process (i.e., the determination according to the state of the cell voltage and the control of the protection switches SW1 and SW2 corresponding to the state). In this way, it is possible to always avoid the unstable operation of the microcontroller 30 itself and normally operate the protection function for the battery cell 1.

[ Total processing of microcontroller after restart ]

The overall process flow of the microcontroller 30 including the protection of the battery unit 1 and the calculation of the remaining battery capacity is described below with reference to a flowchart.

Fig. 16 is a flowchart showing the entire flow of the microcontroller 30 processing.

In step S1301, the cell voltage is raised to increase the power supply voltage supplied to the microcontroller 30. When the supply voltage reaches a certain value, the microcontroller 30 starts up according to a timed signal from the power supply circuit 10. The processing after the startup corresponds to the processing shown in fig. 9, and the description thereof is omitted.

In step S1302, the timer 36 starts counting time. After 2 seconds have elapsed, the process proceeds to step S1303.

In step S1303, the CPU31 determines whether a communication interruption occurs during the count of 2 seconds. If no interrupt occurs, the process proceeds to step S1304. If an interrupt has occurred, the process proceeds to step S1307.

The process performs steps S1304 to S1306 in the power saving mode. In step S1304, the process executes a subroutine, i.e., a protection process for the battery unit 1 (hereinafter referred to as a battery protection process). The subroutine program determines whether an abnormal state occurs in the battery cell 1 according to the cell voltage detection result. The subroutine program controls charging and discharging according to the state. This subroutine will be described later with reference to fig. 17.

In step S1305, the process executes a subroutine for remaining battery capacity detection. The subroutine calculates information required to display the remaining battery capacity in the devices to be connected. This subroutine will be described later with reference to fig. 18.

In step S1306, the process resets the count value of the monitoring timer 37. The process returns to step S1302 to determine whether another communication interruption occurs during 2 seconds.

If a communication interruption occurs during 2 seconds, the process is performed in the active mode. In step S1307, the battery protection process is executed as in step S1304.

In step S1308, the remaining battery capacity calculation processing is executed as in step S1305.

In step S1309, the process transmits information necessary for display of the remaining capacity, such as the value calculated in step S1308, to the device via the communication I/F41. This information includes, for example, the current voltage and temperature of the battery cell 1, the accumulated remaining discharge current and power consumption calculated from the accumulated current value, and the temperature coefficient specific to the battery cell 1.

In step S1310, the process resets the count value of the monitoring timer 37.

In step S1311, the process determines whether an interval of 0.2 seconds has elapsed after the occurrence of the communication interruption (corresponding to step S1303) from the count of the timer 36. If that period has elapsed, the process proceeds to step S1312.

In step S1312, the process determines whether an interval of 2 seconds has elapsed after the occurrence of the communication interruption. If not, the process proceeds to step S1313. If the 2-second interval has elapsed, the process returns to step S1303 to determine whether a communication interruption has occurred.

In step S1313, the battery protection process is executed as in steps S1304 and S1307. The battery protection process is performed at intervals of 0.2 seconds. On the other hand, the remaining battery capacity calculation processing of step S1308 is performed at intervals of 2 seconds.

Although not shown, the overcurrent detecting circuit 20 always detects an overcurrent in the battery cell 1 regardless of the operation of the microcontroller 30. When detecting an overcurrent, the overcurrent detecting circuit 20 turns off and on the protection switches SW1 and SW2, respectively. Further, the overcurrent detecting circuit 20 interrupts the microcontroller 30 due to the occurrence of an overcurrent.

According to the flowchart, in the microcontroller 30, the CPU31 monitors an interrupt from the overcurrent detecting circuit 20 during processing, if necessary. When an interruption due to an overcurrent is detected, the CPU31 rewrites the information indicating the state mode (safe mode) stored in the RAM34, thereby indicating the overcurrent state.

Fig. 17 is a flowchart showing the battery protection process (corresponding to steps S1304, S1307, and S1313 in fig. 16) performed by the microcontroller 30.

The CPU31 first reads the security mode stored in the RAM34 to recognize the current protection state (corresponding to steps S1401, S1407, S1415, and S1419).

If the over-discharge state is currently in effect at step S1401, the process proceeds to step S1402.

In step S1402, the process reads the cell voltage (Vcell) from the AD converter 38. If the cell voltage is lower than 2.2V, the process proceeds to step S1403, otherwise to step S1404.

In step S1403, the process assumes that the cell voltage is extremely low and turns off the microcontroller 30 itself.

In step S1404, the process reads not only the cell voltage from the AD converter 38 but also information indicating whether the charger is on and whether the charging voltage is applied. If the cell voltage is higher than 2.65V and charging is started, the process proceeds to step S1405, otherwise the subroutine is terminated.

At step S1405, the process transmits a control signal to the FET driver 42 to turn on the protection switch SW 1. At this time, the protection switch SW2 is turned on.

In step S1406, the process rewrites the secure mode in the RAM34, thereby indicating normal operation and terminating the subroutine.

In step S1407, if the normal operation state is currently performed according to the read security mode, the process proceeds to step S1408.

In step S1408, if the cell voltage read from the AD converter 38 is lower than 2.6V, the process proceeds to step S1409, otherwise to step S1412.

In step S1409, the process transmits a control signal to the FET driver 42 to turn off the protection switch SW 1. At this time, the protection switch SW2 is turned on.

In step S1410, the process overwrites the security mode in the RAM34, thereby indicating an overdischarge state.

Thereafter, the cell voltage may be further reduced, thereby turning off the microcontroller 30. In preparation for the case of step S1411, the process copies the configuration values stored in the RAM34 or the like to the EEPROM35 for saving. This configuration value is related to the current operating state. Then, the subroutine terminates.

In step S1412, if the cell voltage is higher than 4.25V, the process proceeds to step S1413, otherwise the subroutine is terminated.

In step S1413, the protection switch SW2 is turned off.

In step S1414, the process overwrites the secure mode in the RAM34, thereby indicating an overcharged state, and then terminates the subroutine.

In step S1415, if the overcharge state is currently performed according to the read safety mode, the process proceeds to step S1416.

In step S1416, if the cell voltage read from the AD converter 38 is lower than 4.15V, the process proceeds to step S1417, otherwise the subroutine is terminated.

In step S1417, the process turns on the protection switch SW 2.

In step S1418, the process rewrites the secure mode in the RAM34, thereby indicating a normal operation state and terminating the subroutine.

If it is determined in step S1415 that the overcharge state is not currently active, the process determines that the overcurrent state should be currently active, and then proceeds to step S1419.

In step S1419, if the cell voltage read from the AD converter 38 is lower than 2.2V, the process proceeds to step S1420, otherwise to step S1421.

In step S1420, the process turns off the microcontroller 30 itself.

In step S1421, the process reads information indicating whether the charger is on and whether the charging voltage is applied from the AD converter 38. If charging is started, the process proceeds to step S1422, otherwise the subroutine is terminated.

In step S1422, the process turns on the protection switch SW 1.

In step S1423, the process rewrites the secure mode in the RAM34, thereby indicating normal operation and terminating the subroutine.

The above process performs the charge and discharge control corresponding to the present cell voltage and recovers from the overcurrent state under the software control of the microcontroller 30. When the secure mode is rewritten, it is preferable to record the state change in the EEPROM 35.

Fig. 18 is a flowchart showing the remaining battery capacity calculation processing (corresponding to steps S1305 and S1308 in fig. 16) by the microcontroller 30.

In step S1501, the process reads the temperature of the battery unit 1 according to the output signal from the AD converter 38.

In step S1502, the process reads the voltage of the battery cell 1 in accordance with the output signal from the AD converter 38.

In step S1503, the process reads the accumulated value of the charge and discharge current from the fuel gauge 39.

In step S1504, the process determines the presence or absence of a charging operation of the charger from the output signal from the AD converter 38.

In step S1505, the process calculates information required for the remaining battery capacity in the display device from the information obtained in steps S1501 to S1504. In this step, for example, the process calculates the accumulated remaining discharge current amount and the power consumption from the accumulated current value obtained from the fuel gauge 39.

In step S1506, the process stores the calculated value in the EEPROM 35. For example, the process also stores the detected voltage and temperature of the battery cell 1.

In step S1507, the process clears the count values in the charge counter 39d and the discharge counter 39e, and then terminates the subroutine.

The above-described processing in fig. 18 is performed for a given period of time, thereby monitoring the remaining battery capacity very accurately.

[ Circuit Structure of series-connected Battery cells ]

The use of a single battery cell has been described. In practice, a plurality of series-connected battery cells may be used according to the degree of load on the connection device. In this case, it is necessary to determine an overcharge or overdischarge state for each battery cell. In view of this, the following provides additional explanation regarding circuit structure and operation.

Fig. 19 shows an example of the internal structure of a battery pack using a plurality of battery cells connected in series. Elements corresponding to each other in fig. 19 and 4 are denoted by the same reference numerals, and detailed description thereof is omitted for the sake of simplicity.

It is necessary to detect the cell voltage for each of the series-connected battery cells, respectively. For this reason, it is necessary to provide the AD converter with an input path corresponding to the number of battery cells. Fig. 19 shows an example of two battery packs 1a and 1b connected in series. Two input terminals ADCin1 and ADCin2 are provided to detect the voltages on the respective positive electrodes of the battery packs 1a and 1b, respectively. The AD converter in the microcontroller has differential inputs (differential inputs) configured to detect the difference between the input terminals adin 1 and adin 2 and the difference between the input terminal adin 2 and the installation potential (installation potential). In this manner, the CPU of the microcontroller can obtain the cell voltages of the battery cells 1a and 1b, respectively.

Referring to fig. 16, the battery protection process at the time of steps S1304 and S1307 only needs to be performed for each of the battery cells connected in series. However, in view of safety, it is necessary to cut off the charging current even if a single battery cell indicates an overdischarge state during a normal operation state. For example, if the cell voltage of at least one battery cell becomes lower than 2.6V in step S1408 in fig. 17, the process needs to proceed to step S1409 to change the state to the overdischarge state. In step S1404, the state cannot be restored to the normal operation state until the cell voltages of all the battery cells become higher than 2.65V.

Also, it is necessary to cut off the discharge current even when a single battery cell indicates an overcharged state. For example, if the cell voltage of at least one battery cell becomes higher than 4.25V in step S1412 in fig. 17, the process needs to proceed to step S1413 to change the state to the overcharged state. In step S1416, the state cannot be restored to the normal operation state until the cell voltages of all the battery cells become lower than 4.15V.

As described above, the overcharge or overdischarge state is determined under software control of the microcontroller. This embodiment can be used for a plurality of series-connected battery cells by easily modifying the software according to the loop portion of the program module. This makes it possible to compress the design cost and the circuit size without conventionally providing additional wiring according to the number of battery cells.

On the other hand, it is preferable to initially install software adapted to the battery cells connected in series. Then, the protection process for all battery packs can be performed using the same software up to a specified number of battery cells. For example, software applicable to two series connected cells as shown in fig. 19 may be used for a single cell, by assuming that the voltages at input terminals ADCin1 and ADCin2 are the same. The protection process may be performed without changing software.

Claims (8)

1. A battery pack including a secondary battery integrated with a processing circuit that performs processing including prevention of occurrence of a failure in the secondary battery, the battery pack comprising:

discharge current cutoff means for selectively cutting off a discharge current in the secondary battery;

a charging current cut-off device for selectively cutting off a charging current in the secondary battery;

protection processing means for controlling operations of the discharge current cutoff means and the charge current cutoff means in accordance with at least an interelectrode voltage between a positive electrode and a negative electrode of the secondary battery; and

start enable voltage detection means for generating a detection signal when a power supply voltage supplied to the protection processing means reaches a minimum voltage for starting the protection processing means,

wherein the protection processing means performs an initialization process according to the detected detection signal from the start enable voltage detecting means,

the battery pack further includes: a stable driving voltage detection means for generating a detection signal when the power supply voltage reaches a minimum voltage of a stable driving protection processing means higher than the minimum voltage,

wherein the protection processing means starts the protection processing in accordance with the detected detection signal from the stable driving voltage detecting means.

2. The battery pack of claim 1, the processing circuit further comprising:

an unstable operation avoiding means for monitoring the operation of the protection processing means using the monitoring timer and allowing the protection processing means to execute the initialization processing when an unstable state of the protection processing means is detected,

wherein the protection processing means initializes the configuration value for the monitoring timer of the unstable operation avoiding means based on the detected signal from the stable driving voltage detecting means.

3. The battery pack according to claim 1, wherein the battery pack,

wherein the protection processing means receives the detection signal from the stable driving voltage detecting means after the initialization processing is performed, and the protection processing means starts the protection processing after a time sufficiently longer than an instruction clock period of the protection processing means has elapsed in order to stably operate the protection processing means.

4. The battery pack of claim 1, the processing circuit further comprising:

read-only storage means for storing an initialization value in advance for the operation of the protection processing means;

a non-volatile storage device for rewritably storing configuration values for protecting the operation of the processing device,

wherein after the initialization processing is performed, the protection processing means controls the operations of the discharge current cutoff means and the charge current cutoff means using the initialization value stored in the read-only memory means, and reads the configuration value stored in the nonvolatile memory means when the inter-electrode voltage of the secondary battery rises to a minimum voltage at which the protection processing means is stably driven.

5. The battery pack according to claim 1, wherein when the initialization process is performed, the power supply voltage supplied to the protection processing means is generated in accordance with a voltage between charging terminals for connecting a charger to charge the secondary battery.

6. The battery pack of claim 1, the processing circuit further comprising:

a boosting means for boosting one of a voltage between electrodes of the secondary battery and a voltage supplied from the charger,

wherein the power supply voltage is supplied to the protection processing means through the boosting means.

7. A battery protection processing apparatus for performing processing for preventing occurrence of abnormality of a secondary battery, the apparatus comprising:

discharge current cutoff means for selectively cutting off a discharge current in the secondary battery;

a charging current cut-off device for selectively cutting off a charging current in the secondary battery;

protection processing means for controlling operations of the discharge current cutoff means and the charge current cutoff means in accordance with at least an interelectrode voltage between a positive electrode and a negative electrode of the secondary battery; and

start enable voltage detection means for generating a detection signal when a power supply voltage supplied to the protection processing means reaches a minimum voltage for starting the protection processing means,

wherein the protection processing means performs an initialization process according to the detected detection signal from the start enable voltage detecting means,

the battery protection processing apparatus further includes: a stable driving voltage detection means for generating a detection signal when the power supply voltage reaches a minimum voltage of a stable driving protection processing means higher than the minimum voltage,

wherein the protection processing means starts the protection processing in accordance with the detected detection signal from the stable driving voltage detecting means.

8. A start-up control method for a battery protection processing device that performs processing for protecting a secondary battery against occurrence of an abnormality by operations of controlling a discharge current cutoff circuit to selectively cut off a discharge current of the secondary battery and controlling a charge current cutoff circuit to selectively cut off a charge current of the secondary battery, according to a voltage between a positive electrode and a negative electrode of the secondary battery, the method comprising:

when the power supply voltage supplied to the battery protection processing means reaches a minimum voltage for starting the battery protection processing means, the initialization processing of the battery protection processing means is executed,

the method further comprises the following steps:

after the initialization process, a protection process is started when the power supply voltage reaches a minimum voltage higher than the minimum voltage at which the battery protection process apparatus is stably driven.