JP2003009407A - Information terminal equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information terminal equipment which can precisely indicate residual power of a battery by considering degradation of a secondary battery. SOLUTION: A resistance R19 and a switch SW 20 are arranged in parallel to a main battery 11, and the discharging current of the main battery 11 is switched either to a first mode applying the discharging current almost to the resistance R19 or to a second mode not applying it to the resistance R19, so that a battery voltage V1 with switch off and a battery voltage V2 with switch on can be measured. An AC adaptor 9 is then connected to the information terminal equipment, and when the main battery 11 is fully charged a battery's internal impedance Z is calculated with the battery voltages V1, V2 and the resistance R when the switch SW 20 is switched, based on a formula Z=R×(V1-V2)/V2. A temperature TH at the moment the V1 and V2 are measured is taken into consideration and a degradation condition of the battery is estimated. The residual power of the battery is, furthermore, displayed based on this estimated battery degradation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information terminal device in which a secondary battery is used as a main power source and an AC adapter can be connected as an external power source, and more particularly, to an error correction of a battery residual amount of the secondary battery. The present invention relates to a characteristic information terminal device.

[0002]

2. Description of the Related Art Recently, PDA (Personal Digital Assis)
A portable information terminal device called "tance" is in widespread use. This PDA is used by being connected to an AC adapter when a commercial power source is used as a power source, and a secondary battery is used as a power source when the commercial power source cannot be connected as in the case of portable use. On the other hand, the main storage device of the PDA has a DRAM (Dynamic Random Access Memory) along with the increase in the capacity of information.
Is used. The DRAM has the advantage of increasing the capacity as a storage device, but in order to retain the storage, the power must be supplied in order to constantly perform an operation of refreshing.

For example, in the case of a system in which user data is stored in a non-volatile memory such as a hard disk or a flash ROM such as a laptop computer, a video camera, a mobile phone, etc., in order to ask the user to estimate the usable battery time. Although it is necessary to accurately detect the remaining battery level, user data will not be lost even when the remaining battery level is exhausted. However, there are not a few devices in the PDA that incorporate only a volatile memory such as the aforementioned DRAM in order to differentiate the size and price from the notebook computer, and all stored information such as user data. The device that stores the data in the DRAM is required to have higher reliability for detecting the remaining battery level than the device in which the nonvolatile memory is incorporated.

FIG. 4 shows Li-i in a portable information terminal device.
FIG. 5 is a diagram showing an example of a battery discharge characteristic curve in an on-secondary battery and power management using this discharge characteristic curve. As can be seen from this discharge characteristic curve, in the operable area (A) where the remaining battery level is relatively high, the portable information terminal device can be activated and operated, and the user data backup area where the remaining battery level is low In (B), the portable information terminal device cannot be started or operated. This is because the information stored in the DRAM is lost as described above when the battery level is exhausted. That is, when the battery level becomes low, the power consumption of the battery is suppressed, and the storage time of the user data can be lengthened as much as possible until the user recharges the battery.

The method for detecting the remaining battery level is roughly classified into two methods, that is, a power integration method and the above-mentioned voltage detection method.

Power integration method The power integration method measures the charging voltage and the charging current to the secondary battery, integrates the charged power, and integrates the discharging voltage and the discharging current from the secondary battery. , A system that keeps track of the current battery level. This system requires a circuit for integrating voltage and current, which makes the system expensive. In addition, it is necessary to ensure the accuracy of current measurement. In particular, when measuring the discharge current, a current of several hundred mA during operation, several hundred μA to several mA for supplying power to a device that requires refreshing of DRAM or constant power supply when the terminal is powered off, which is called a suspend mode. Current also needs to be measured, and if an attempt is made to improve the current measurement accuracy, an expensive system will result.

Voltage detection system There is a fixed relationship between the remaining battery voltage and the voltage, and the relationship between the battery output open-circuit voltage (open circuit voltage) when the current is cut off from the battery and the remaining battery charge is highly accurate. The detecting circuit can be constructed relatively inexpensively. However, the problem with this method is the existence of factors that impede detection accuracy. Factors that impede accuracy include a decrease in capacity due to deterioration of the battery and an influence of internal impedance of the battery. That is, if a current is passed from the battery, the output terminal voltage of the battery will be measured as the output terminal voltage of the battery with a voltage drop corresponding to the internal impedance. The voltage will change. The factors that cause the internal impedance to fluctuate are temperature, output current, and
The deterioration of the battery may be mentioned.

However, in the conventional PDA, the voltage detection method is generally used for detecting the remaining battery amount because the remaining battery amount can be detected inexpensively even though there is a factor that hinders the accuracy as described above. Therefore, conventionally, in order to improve the accuracy of the fuel gauge, correction is made for the battery temperature, the battery output current value, the battery deterioration state, and the like. For example, JP-A-7-240235 and JP-A-2000-13332.
In Japanese Patent Laid-Open Publication No. 2 (1994), temperature detection and correction based on the output current value are performed. Therefore, the internal impedance of the battery is measured, the degree of progress of deterioration is estimated from the internal impedance value, and
A method of correcting for a table of battery voltages is disclosed. Further, as a method of measuring the internal impedance, Japanese Patent Laid-Open No. 7-240235 discloses a battery output open circuit voltage (open circuit voltage) V1 when the current is cut off, a charging current I1 when charging the battery, and a charging A method for obtaining the internal impedance R from the battery terminal voltage V2 at that time by R = (V1-V2) / I1 (1) is described.

As the method for measuring the internal impedance, the algorithm is the same as the above, but not the charging current but the discharging current I2 and the battery terminal voltage V at the time of discharging.
A method is also known in which the internal impedance R is calculated from R = (V1−V2) / I2 (2) from 2 and the open circuit voltage V1. This method is the most general method for measuring the internal impedance, and can be easily performed by a measuring instrument or the like.

[0010]

However, the battery output open circuit voltage (open circuit voltage) V1 when the former current is cut off, the charging current I1 when charging the battery, and the battery terminal portion voltage V2 at the time of charging. From equation (1), the internal impedance R
There is a problem when adopting the method of seeking
It is the influence of the error. That is, there is a problem that the internal impedance of the battery varies depending on the state of charge of the battery.
Therefore, in order to detect the deterioration with high accuracy, the battery remaining amount must be measured at a fixed time as the timing of measuring the internal impedance. An expensive circuit is apt to detect the current with high accuracy. There are problems such as.

Further, in the latter method of obtaining the internal impedance R from the discharge current I2, the battery terminal voltage V2 at the time of discharging and the open circuit voltage V1 by the formula (2), such a calculation process is applied to the information terminal device. If incorporated, it will be costly to set the timing for position measurement and detect the current accurately. The system becomes large in scale, which adversely affects miniaturization of the information terminal. If the configuration is inexpensive, the error factor in current detection will inevitably increase. However, it is difficult to correct deterioration in information terminal devices such as PDAs and mobile phones.

FIG. 5 is a characteristic diagram showing the relationship between the battery remaining amount and the battery voltage in the Li-ion secondary battery. Below, FIG.
The actual power management of the PDA will be described in detail with reference to FIG.

FIG. 5C is a characteristic curve showing the relationship between the remaining battery power and the battery voltage when the output current is cut off. In addition, the characteristic shown in FIG. 5 is that the backup time of user data can be backed up by the user for 5 days after the power supply of the portable information terminal does not start up (battery is exhausted) in the initial battery state at normal temperature. This is for the specifications. The current during suspension is mostly the refresh current of the DRAM in the portable information terminal using the DRAM as the main memory and the user data backup memory. 32 MB DRA as an example
Considering the efficiency of the DC / DC converter, the suspend current of the terminal equipped with M is 3.3V, 2m.
It is estimated to be about A. In this case, the amount of power that must be left for backup is 80
It will be about 0 mWh.

Further, the secondary battery is 3.7V, 1200mA
It is assumed that a Li-ion secondary battery of about h is adopted. This size is expected to be the main size of mobile information terminals such as PDAs. At this time, the ratio of the remaining battery level that must be left as a backup is about 800 / (3.7 × 1200) = 18%. FIG. 5C is the curve when the output voltage is cut off as described above, and it can be said that it is almost the same as the discharge curve when the secondary battery is discharged by the suspend current. Therefore, the power OFF voltage (H ) In the following cases, it is necessary to make the system so that it can only be forcibly suspended, that is, cannot be started.

As described above, in the case of the voltage detection system, the output current value from the battery, the temperature of the battery, the state of deterioration of the battery, etc. are factors that impede the accuracy. Therefore, discharge curves when these conditions are changed are shown in FIGS. 5 (E), (F), and (G), respectively. That is, FIG. 5E shows the relationship between the battery remaining amount and the battery voltage when a certain constant output current is applied.
(F) shows the relationship between the battery remaining amount and the battery voltage when the temperature is lowered, and (G) shows the relationship between the battery remaining amount and the battery voltage in the battery deteriorated under the same low temperature condition as (F). From the characteristic diagram of FIG. 5, in the case of (G), if the power supply cannot be started with the power supply OFF voltage (H), it will be rotated 70% for backup, and the operation time will be extremely short. You can see that This indicates that when the voltage detection method is adopted, it is necessary to correct the above factors in order to accurately detect the remaining battery level.

The temperature can be accurately detected by using a temperature detecting element such as a thermistor. For output current, either measure the output current or
Since it is known in advance that a specific output current will be obtained in a specific operation mode, correction may be made in the specific operation mode. Since the current measurement detection accuracy here has a different application from the case of the power integration method, the detection accuracy as in the case of the power integration method is unnecessary. Therefore, when the voltage detection method is adopted, how to detect the deterioration of the battery becomes a problem. In particular, in a portable information terminal, a secondary battery is built in the main body for the purpose of downsizing, thinning, and cost reduction. Therefore, even if the secondary battery deteriorates, a general user must replace the secondary battery. It is not configured to be easy.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide an information terminal device capable of accurately presenting the remaining battery level in consideration of the deterioration of the secondary battery. To do.

[0018]

In order to achieve the above object, the present invention provides an information terminal device having display means for detecting the battery voltage of a secondary battery supplied from an AC adapter and displaying the remaining battery power. In the above, the means for measuring the internal impedance of the secondary battery, the means for determining deterioration of the secondary battery based on the measured internal impedance, and the battery according to the determined state of deterioration of the secondary battery A means for correcting an error in the remaining amount, wherein the means for measuring measures the internal impedance when the AC adapter is connected and power is supplied and the secondary battery is fully charged. Characterize.

In this case, when power is supplied from the AC adapter to the information terminal device, it is preferable to provide means for cutting off the discharge from the secondary battery.

The means for measuring the internal impedance of the secondary battery comprises a resistor and a switch arranged in parallel with the secondary battery, and a control means for connecting and disconnecting the switch, the control means comprising: If the AC adapter is connected, switch the switch
A first mode in which the discharge current of the secondary battery flows through the resistor and a second mode in which the discharge current does not flow through the resistor are set, and the internal impedance is detected from the terminal output voltage of the secondary battery in the first and second modes. You can also choose to do so. At this time, the secondary battery terminal output voltage is detected when a discharge current is passed through the resistor in the first mode after the secondary battery terminal output voltage is almost detected after switching to the first mode by the switch. It is desirable to perform at a fixed timing. The timing is usually several seconds to several tens of seconds after the switching to the first mode.

Further, means for detecting the temperature of the secondary battery,
When measuring the internal impedance, a means for detecting the temperature by the means for detecting the temperature, and means for estimating the deterioration of the battery from the internal impedance value of the secondary battery and the temperature information may be provided. it can. Further, there may be provided means for correcting a table for storing the relationship between the battery voltage and the remaining battery level, based on the state of battery deterioration estimated by the means for estimating battery deterioration.

When it is determined by the means for estimating the deterioration of the battery that the battery has deteriorated to a certain degree or more, it is preferable to display the fact on the display means to prompt the user to replace the battery. .

In the embodiments described later, the resistor R19, the switch SW20, and the MPU1 correspond to the means for measuring the internal impedance of the secondary battery, and the deterioration of the secondary battery is judged based on the measured internal impedance. Means, a means for correcting the error in the remaining battery level according to the determined state of deterioration of the secondary battery, a control means for connecting / disconnecting a switch, an internal impedance value of the secondary battery and the temperature information, The MPU 1 corresponds to the means for estimating the deterioration and the means for correcting the table that stores the relationship between the battery voltage and the battery level.

When the internal impedance is obtained by the means for measuring the internal impedance, in the present invention,
Instead of the charging current, the discharging current I2, the battery terminal portion voltage V2 at the time of discharging, and the open circuit voltage V1 are used to obtain by the above-mentioned equation (2).

The problem that the internal impedance of the battery changes depending on the remaining battery level is detected when the battery is fully charged. The detection of full charge may be performed even when a sufficient time elapses with respect to the time when it is normally fully charged.
-Ion rechargeable batteries are normally charged with constant current and constant voltage (CCC
Since V) is general, it may be set when the charging current is below a certain threshold value. In any case, it can be constructed with an inexpensive configuration.

Here, the means and timing for flowing the discharge current from the battery will be described. As a charging method of the information terminal device, a battery is generally incorporated in the information terminal device, and an AC adapter is connected from the outside to charge the AC terminal as a power source. When the AC adapter is connected, the main power source of the information terminal device is AC.
Become an adapter. The problem is the timing of flowing the discharge current, but since the AC adapter is always inserted when the battery is fully charged, remove the AC adapter to flow the discharge current from the battery, and the battery is the information terminal. There is a method of detecting the current discharged from the battery when the information terminal device becomes the main power source of the device and is started.

In this method, since the current discharged from the battery is a current containing a plurality of frequency components, it is difficult to accurately detect the current value. Further, when the AC adapter is removed, whether the battery is fully charged or not becomes a problem. Li-i
In the case where an on-secondary battery or the like is constantly charged, safety problems due to overcharging and deterioration are promoted, so that charging is generally stopped by a timer or the like. At this time, if the AC adapter is connected for a long time due to self-consumption of the battery, etc.
The remaining battery level when the C adapter is removed cannot always be said to be fully charged.

Therefore, in the present invention, detection is always performed when the battery is fully charged. Therefore, as a configuration, a resistor and a switch are arranged in parallel with the secondary battery.
When the C adapter is connected, by switching the switch, it is possible to switch between the first mode in which the discharge current of the secondary battery almost flows through the resistor and the second mode in which it does not flow. Normally, set the mode to cut off the secondary battery discharge current to eliminate extra power consumption.
When the C adapter is connected and the secondary battery is fully charged, the first mode is set and the power consumption of the information terminal device main body is set to the circuit configuration supplied from the AC adapter. This allows most of the discharge current of the battery to flow through the main resistor. Further, the discharge voltage when the battery is fully charged is accurately determined, and by determining the resistance value of the resistor, it is not necessary to detect the discharge current value, and the voltage between the resistors can be detected. Only then, it is possible to estimate the internal impedance of the secondary battery.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a circuit configuration of a PDA (personal digital assistant) as an information terminal device according to an embodiment of the present invention. In the figure, a microprocessor (MPU1) is a main circuit element that controls the overall control of the present invention, and a ROM2 is a read-only nonvolatile memory that stores programs and control data necessary for the MPU1 to operate. RAM3 is the above M
It is a rewritable volatile memory for temporarily storing data handled by the PU 1 and storing user data. In this embodiment, a DRAM is used as the RAM3. The bus line 4 is a signal line including all data, address signals, and control signals from the MPU 1.

The display controller 5 is a controller for displaying on the display device 6, and the display device 6 comprises a liquid crystal panel. The display device 6 is provided with a portion for displaying the remaining battery capacity, and functions as a remaining battery meter. Therefore, in the present embodiment, the display device 6 functions as a display unit that displays the remaining battery level. Further, a backlight for liquid crystal brightness adjustment and the like are also included in the display device 6, and the brightness control of the backlight is also controlled by M.
This is performed by the display controller 5 according to a command from the PU 1. The display means for displaying the remaining amount of battery is a PDA as a remaining amount display device in addition to the display means for displaying data and the like.
It can also be provided at a desired location on the housing.

The input device 8 is a device for the user to input information, and includes a keyboard, a pointing device, and the like. The input controller 7 is a controller for transmitting information from the input device 8 to the MPU 1.

The AC adapter 9 is a commercial power source (A in Japan).
C100V, 50 / 60Hz) as a power source for PDA
This is an AC / DC converter for conversion, and becomes the main power source of the PDA when the AC adapter is used when working at a place where a commercial power outlet is provided. Buffer 10
Is for converting the input voltage from the AC adapter 9 into a voltage that can be handled by the MPU 1. The main battery 11 is a rechargeable secondary battery, and the PDA according to this embodiment uses a Li-ion secondary battery. Note that, for example, Ni-MH2 is used instead of the Li-ion secondary battery.
A secondary battery can also be used. This secondary battery supplies the main power source of the PDA when the AC adapter 9 is not inserted in the outlet of the commercial power source. The power from the AC adapter 9 or the main battery 11 is ORed by the diode D16 and the diode D17, and D
The C / DC converter 18 converts the level into a level to be supplied to the system power supply, and becomes the system power supply line 12. Here, the diode D16 has a function of preventing the main battery side power supply line 22 from going around to the AC adapter side power supply line 21 when the AC adapter 9 is not inserted into the outlet, and the diode D17 is an AC
It has a function of preventing backflow to the main battery 11 when the adapter 9 is inserted.

Further, in the circuit configuration of this embodiment,
The output voltage from the AC adapter 9 is higher than the maximum voltage of the main battery 11. As a result, when charging is stopped and the AC adapter 9 is inserted, power can be supplied to the system from the AC adapter 9. The charger 14 is for charging the main battery 11, and can switch ON / OFF of charging according to a command from the MPU 1. When a Li-ion secondary battery is used as the main battery 11, a charge control IC for constant current and constant voltage (CCCV) or the like is applicable. The timer 15 is a timer provided to prevent continuous charging for the sake of safety and not to accelerate deterioration of the battery, and is longer than a time for fully charging the main battery. The time is set, a certain specific time is detected, and a signal is output to the MPU 1.

The A / D converter 13 is the main battery 11
Of the main battery 11 is transmitted to the MPU 1 according to the input analog voltage value. The resistors R28 and R29 convert the main battery voltage Vmain23 to the A / D converter 1
Although it is a resistor that divides the voltage into a voltage that can be input to 3, it can be removed if unnecessary. When used, it is desirable that the resistance value is large in order to reduce the power consumption, and that the resistance value is high in order to improve the detection accuracy of the main battery voltage. A
In the MP30, when a resistor having a large resistance value is used as the resistor R28, the input voltage to the A / D converter 13 may change due to a minute current value flowing into the input gate of the A / D converter 13. , To reduce the effect. Also in this case, it can be removed if unnecessary.

The thermistor TH25 is a main battery 11
A variable resistance element for monitoring the temperature of the
High precision can be achieved by using a configuration in which the voltage is divided by 26 and the Vtemp 24 that is further regulated from the system power supply line 12 is pulled up. Similarly to the above, the AMP 27 is the A / D converter 1 that uses the resistor R26 and a minute current input to the A / D converter 13.
To reduce the change in the input voltage value to 3
Can be removed if not needed.

The resistor R19 is a resistor for measuring the internal impedance of the main battery 11 in the present invention. It is necessary to select a resistance value of the resistor R19 that allows a current such that the voltage drop of the main battery 11 can be read by the A / D converter 13 when a current is supplied from the main battery 11, and is a power resistance. Switch 20 is MPU1
An element that can be turned on and off by a command from
It is desirable that the ON resistance is sufficiently low. Where resistance R
With respect to the resistance value of 19 and the ON resistance value of the switch SW20, it is necessary to use a highly accurate one in order to suppress variations due to individual differences as much as possible. Further, with this circuit configuration, when the switch SW20 is turned on when the AC adapter 9 is inserted in the outlet and charging is stopped, almost all the discharge current from the main battery 11 is discharged. It can flow to the resistor R19.

A flowchart of FIG. 2 shows a procedure of detecting deterioration of the main battery 11 in the PDA circuit thus constructed, that is, a procedure of measuring internal impedance. The process corresponding to this flowchart is ROM2
The MPU 1 executes the program according to the program stored in. In a PDA using a secondary battery, the AC adapter 9 is used by being plugged into the outlet when charging the secondary battery or because the battery does not want to be consumed at a place where there is a commercial power outlet, the timing is used. . First, when the AC adapter 9 is inserted into the outlet (step S1), the MPU1 is notified via the buffer 10 and the MPU1 instructs the charger 14 to charge the battery, and the charging is started (step S1). S2),
At the same time, the timer 15 starts counting (step S
3). The set value of the timer 15 is set based on the charging rate of the charger 14 so that the main battery 11 can be fully charged even when the main battery 11 is fully discharged. Timer 15
When the time is up (step S4), charging is stopped by the MPU 1 (step S5). At this time, the battery is fully charged, and steps S1 to S5 are the charging process.

In the deterioration detecting step, it is confirmed that the AC adapter 9 is inserted, and the voltage of the main battery 11 is set to A /
It is detected by the D converter 13 (step S6).
The main battery voltage value at this time is V1. Further, at this time, since there is almost no discharge current from the main battery 11, the influence of the internal impedance 31 of the main battery 11 hardly occurs. Next, SW20 is turned on, and a constant current is passed through the resistor R19 for measuring internal impedance (step S7). Accordingly, the voltage Vma of the main battery 11
The voltage of in23 drops in the internal impedance R31. The main battery voltage value after the voltage drop is set to V2, and this is detected (step S8). Also, turn on SW20
The battery voltage curve at that time is shown in FIG. 3, and the ON time is set to several tens of seconds in order to stabilize the voltage. Tens of seconds O
The main battery 11 is discharged in N hours, but the amount of discharge causes almost no problem. If the battery is discharged for a maximum of 30 seconds, the rated current amount of the battery is set to 1C, and the resistance R
Even if a current of 0.5 C is passed through 19, it is about 0.4% of the battery energy amount when fully charged.

If the AC adapter 9 continues to be inserted after the charging is stopped until the battery voltage V2 is detected, the process proceeds to the next process. If it is detected that is removed, this process is immediately interrupted and the current deterioration detection is not performed (step S20). Then, without updating the battery deterioration table (correction table) (step S2
1) and returns to step S1. It should be noted that the battery deterioration is several months
Although there is a change in units of several years, the frequency of inserting the AC adapter 9 and charging the secondary battery is in units of several days to several weeks, so even if the deterioration of the battery cannot be detected several times in particular, No problem.

After detecting the main battery voltage V2, the internal impedance R31 of the main battery 11 is calculated (step S9). This internal impedance R31 is calculated from the values detected so far by R31 = R19 × (V1−V2) / V2. Further, since the internal impedance 31 of the battery is greatly affected by temperature, Vtemp24, R2
6, the temperature when the above process is performed is detected from the TH25 and the A / D converter 13 (step S10),
The internal impedance of the main battery, that is, the state of deterioration of the main battery can be estimated by converting the temperature into the room temperature using the correction table prepared in advance (step S11). Then, the correction table is updated based on this result (step S12).

As for the deterioration information of the main battery 11, the accuracy of the fuel gauge can be improved by correcting the error of the remaining capacity with respect to the battery fuel gauge. If the battery deteriorates as the battery usage time becomes shorter, the warning is displayed on the display device 6 indicating that the battery has deteriorated and is at the end of its life, and the user is informed of the new battery. The user is prompted to replace the battery, and if the user can replace it, the user replaces it by himself.

Next, a method of specifically improving the accuracy of the fuel gauge will be described. As a method for detecting the remaining battery level, the present invention adopts a voltage detection method that can be configured at low cost. When this system is adopted, factors that impede the accuracy of the fuel gauge include the influence of temperature, the influence of battery output current change during system startup, and the influence of battery deterioration as described above. Detection of temperature and deterioration may be performed as described above. Therefore, the effect of the change in the battery output current will be supplemented.

As a breakdown of the battery output current in a device such as a portable information terminal, the display controller 5 including the backlight and the display device 6 occupy a very large proportion. Therefore, in a device equipped with a backlight or the like, the battery output current is estimated by the brightness setting value of the backlight. This is actually a cheap and fairly accurate configuration. To further improve the accuracy, the output current may be measured, and in the case of a system in which another unit with large power consumption is attached, the battery output current due to the influence of the unit may be considered. Then, a correction table is created for the above three obstruction factors, and correction is performed from the main battery voltage when the fuel gauge display is actually operated, temperature information, backlight brightness setting value information, and latest deterioration information. Then, the fuel gauge of the main battery has a low-cost and highly accurate system configuration.

[0045]

As described above, according to the present invention, the means for measuring the internal impedance of the secondary battery and the means for judging the deterioration of the secondary battery based on the measured internal impedance are determined. And a means for correcting an error in the remaining battery level according to the state of deterioration of the secondary battery, the means for measuring is connected to an AC adapter and supplied with power, and
Since the internal impedance is measured when the secondary battery is fully charged, the deterioration of the secondary battery can be accurately detected at low cost. Further, this makes it possible to accurately correct the remaining battery charge at low cost. In addition, it is possible to improve the reliability of the battery management system by providing accurate battery level correction, to provide the user with appropriate battery usage time, and to improve the reliability of user data protection. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a PDA as an information terminal device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of battery deterioration detection processing according to the embodiment of the present invention.

[Fig. 3] 2 during energization during internal impedance measurement
It is a figure which shows the secondary battery voltage characteristic.

FIG. 4 is a diagram showing an example of a discharge characteristic curve of a battery in a Li-ion secondary battery in a portable information terminal device and an example of power management using this discharge characteristic curve.

FIG. 5 is a characteristic diagram showing a relationship between a battery remaining amount and a battery voltage in a Li-ion secondary battery.

[Explanation of symbols]

1 MPU 2 ROM 3 RAM 4 Bus line 5 Display controller 6 Display device 7 Input controller 8 Input device 9 AC adapter 10 Buffer 11 Main battery 12 System power supply line 13 A / D converter 14 Charger 15 Charging timer 16 To AC adapter power supply line Diode 17 for preventing sneak-in from the backside 18 Diode for preventing backflow to the battery side power supply line 18 DC / DC converter 19 Battery deterioration detection resistor 20 Battery deterioration detection resistor ON / OFF switch 21 AC adapter side power supply line 22 Battery side power supply line 23 Battery voltage 24 High-accuracy power supply voltage for temperature detection 25 Temperature detection thermistor 26 Temperature detection resistance 27 Temperature detection voltage stabilization AMP 28 Battery voltage detection voltage dividing resistor 29 Battery voltage detection voltage dividing resistor 30 Battery voltage stabilization AMP 31 Battery internal impedance Nsu

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04Q 7/38 H04B 7/26 L (72) Inventor Yoshio Miyamoto 1410 Inada, Hitachinaka City, Ibaraki Hitachi, Ltd. Factory Digital Media Products Division (72) Inventor Hitoshi Yoneaga 1410 Inada, Hitachinaka City, Ibaraki Prefecture Stock Company Hitachi Ltd. Digital Media Products Division (72) Inventor Akihiko Emori 7-1-1, Mikamachi, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Kazufumi Takagishi 1410 Inada, Hitachinaka City, Ibaraki Prefecture F-Term (Reference) 2G016 CB06 CB11 CB12 CB13 CB21 CC03 CC04 CC05 CC06 Hitachi Digital Media Products Division CC07 CC10 CC12 CC16 CC23 CC27 CC28 CD09 CD14 CE03 CF06 5G003 AA01 BA01 DA07 EA 05 EA08 GC05 5H030 AA06 AS11 BB01 BB21 FF22 FF43 FF44 FF52 5K067 AA33 EE02 FF19 FF23 HH21 KK05

Claims (8)

[Claims] 1. An information terminal device having display means for detecting a battery voltage of a secondary battery supplied with power from an AC adapter and displaying the remaining battery level, and means for measuring an internal impedance of the secondary battery, And a means for judging deterioration of the secondary battery based on the measured internal impedance; and a means for correcting an error of the battery remaining amount according to the judged deterioration state of the secondary battery, Means for supplying power when the AC adapter is connected and the secondary battery is fully charged,
An information terminal device characterized by measuring the internal impedance. 2. The information terminal device according to claim 1, further comprising means for cutting off the discharge from the secondary battery when power is supplied to the information terminal device from the AC adapter. . 3. The means for measuring the internal impedance of the secondary battery comprises a resistor and a switch arranged in parallel with the secondary battery, and control means for connecting and disconnecting the switch, the control means comprising: When an AC adapter is connected, the switch is switched to set a first mode in which the discharge current of the secondary battery flows through the resistor and a second mode in which the discharge current does not flow through the resistor, and the first and the second modes are set. The information terminal device according to claim 1, wherein the internal impedance is detected from a terminal output voltage of a secondary battery in a mode of 2. 4. The secondary battery terminal output voltage when a discharge current is passed through the resistor in the first mode is detected after switching to the first mode by the switch. The information terminal device according to claim 3, wherein is performed at a timing at which is substantially constant. 5. The information terminal device according to claim 4, wherein the timing is several seconds to several tens of seconds after the switching to the first mode. 6. A means for detecting the temperature of a secondary battery, and a temperature at that time is detected by the means for detecting the internal impedance when measuring the internal impedance, and the internal impedance value of the secondary battery and the temperature are measured. The information terminal device according to any one of claims 1 to 5, further comprising means for estimating deterioration of a battery from information. 7. A means for correcting a table for storing the relationship between the battery voltage and the remaining battery level based on the state of battery deterioration estimated by the means for estimating battery deterioration. The information terminal device according to claim 6. 8. The information according to claim 6, wherein when the means for estimating the deterioration of the battery determines that the battery has deteriorated to a certain degree or more, the fact is displayed on the display means. Terminal device.