JP2001095170A - Charge circuit, charge method, and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charge circuit and a charge method which improve the accuracy in detection of a charge termination current at low cost, by suppressing the influence of the temperature property of a circuit and the dispersion of that temperature property to the utmost, and a storage medium. SOLUTION: The charge current in charging a battery cell 3 is detected, based on the voltage drop of a charge current detecting resistor R1, and when that detected current comes to a predetermined charge termination current, an FETQ1 is turned on by the control signal from a charge control circuit 20 so as to terminate the charge. What is more, CPU 10 stores beforehand the first detected current by the charge current detecting resistor R1 when the FETQ1 has been turned off under a given temperature, and gets the second detected current by the charge current detecting resistor R1 when the FETQ1 has been turned off in every fixed cycle at charge, and detects the temperature ripple of the charge circuit by the comparison between that second detected current and the first detected current, and compensates the specified charge termination current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit and a charging method applied to a battery-driven portable electronic device such as a cellular phone and a video camera, and a recording medium storing a program for executing the charging method. In particular, a charging circuit, a charging method, and a recording medium that can detect a low-cost and high-precision charging current and improve the detection accuracy of a charging termination current by minimizing the influence of temperature characteristics of a circuit and variations in the temperature characteristics as much as possible. About.

[0002]

2. Description of the Related Art Conventionally, in a battery-driven portable electronic device such as a cellular phone or a video camera, the battery cell is charged by applying charging energy supplied from an external charger to the battery cell. Charging circuit for charging. In such a charging circuit, an overcharge protection circuit that prevents overcharging in which a voltage is applied from the outside even after the charging is completely completed, and an overcharge protection circuit that prevents overdischarging in which the battery cell continues to discharge beyond the final voltage. Generally, a configuration having a discharge protection circuit is employed.

A general configuration of an overcharge protection circuit is as follows.
For example, a charging current detection resistor for detecting a charging current when charging a battery cell is provided in a charging current path, and when a charging current detected by a voltage drop of the charging current detection resistor becomes a predetermined charging termination current, There is a charge termination current detection circuit that turns off a switching element (for example, an FET) as a charge voltage control circuit to open a charge path and terminate charging.

In such a charge termination current detection circuit, a voltage of several [mV] must be detected because a current flowing through a very small resistor for detecting a charging current is detected in order to detect a charging current. In addition, there is a problem that accurate charging current cannot be detected due to the influence of temperature characteristics of the charging termination current detection circuit.

In order to deal with such a problem, conventionally, the influence of the temperature characteristic of the charge termination current detection circuit and the variation of the temperature characteristic are designed to be as small as possible.
Alternatively, the temperature characteristics are stored in a table, and the temperature of the charge termination current is corrected by a parameter calculation or the like.

[0006]

However, in a method of performing temperature correction by storing temperature characteristics in a table as in the above-described conventional charging circuit, variations in the temperature characteristics of the semiconductor integrated circuit are guaranteed within a certain range. There is a problem that it is necessary to affect the yield of the semiconductor integrated circuit, thereby increasing the cost of the semiconductor integrated circuit.

In particular, in recent years, the performance of battery cells has recently been improved, and the end-of-charge current has tended to decrease as the capacity of the battery cells has increased. Due to safety issues, the lower margin of the detected current has decreased, and the end of charge has been reduced. There is a demand for higher accuracy in current detection.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to detect a low-cost and highly accurate charging current by minimizing the influence of temperature characteristics of a circuit and variations in the temperature characteristics. It is another object of the present invention to provide a charging circuit, a charging method, and a recording medium with improved detection accuracy of a charge termination current.

[0009]

In order to solve the above-mentioned problems, a charging circuit according to a first aspect of the present invention includes a battery cell that is stored by a voltage supplied from an external charger. A charging circuit of an electronic device to be driven, wherein the current detecting unit detects a charging current when charging the battery cell, a switching unit that opens and closes a path of the charging current based on a control signal, and the current detecting unit. When the detected current becomes a predetermined charge termination current, the control signal causes the switching means to be in an open state to terminate charging, and a charge control means for previously setting the switching means to an open state at a predetermined temperature. The first detection current by the current detection means is stored, and the second detection current and the second detection current by the current detection means when the switching means is opened. By comparison with the first detected current to detect the temperature variation of the charging circuit is configured to and a temperature correction means for correcting the predetermined charging end current.

According to a second aspect of the present invention, in the charging circuit according to the first aspect, the temperature correction unit is configured to switch the second detection current and the first detection current at regular intervals during charging. , The temperature fluctuation of the charging circuit is detected, and the predetermined charge termination current is corrected.

According to a third aspect of the present invention, in the charging circuit according to the first or second aspect, the current detecting means detects a current based on a voltage drop of the current detecting means. The switching unit is connected in series to a charging current path on the charging current supply side of the current detecting unit, and at a connection end of the current detecting unit with the battery cell,
A first circuit section through which a relatively large current flows during operation is connected, and a second circuit section through which a relatively small current flows during operation is connected to another connection end of the current detection means on the charging current supply side. .

According to a fourth aspect of the present invention, there is provided a method for charging a battery cell in an electronic device having the battery cell stored by a voltage supplied from an external charger.
A current detecting step of detecting a charging current when charging the battery cell; and, when the detected current of the current detecting step becomes a predetermined charge termination current, opening the path of the charging current to terminate charging. A charge control step, a first current detection step of storing a first detection current by the current detection step when the path of the charging current is opened at a predetermined temperature, and a path of the charging current. A temperature correction step of detecting a temperature change of the charging circuit by comparing the second detection current in the current detection step and the first detection current in the open state, and correcting the predetermined charge termination current. Things.

In the charging method according to a fifth aspect of the present invention, in the charging method according to the fourth aspect, the temperature correction step comprises the steps of: performing the second detection current and the first detection current at regular intervals during charging; , The temperature fluctuation of the charging circuit is detected and the predetermined charge termination current is corrected.

According to a sixth aspect of the present invention, there is provided a computer-readable recording medium recording a program for causing a computer to execute the charging method according to the fourth or fifth aspect.

In the charging circuit according to claims 1, 2 and 3 of the present invention, the charging method according to claims 4 and 5, and the recording medium according to claim 6, the battery cells are charged by the current detecting means (current detecting step). Switching means for detecting the charging current at the time of charging, and when the current detected by the current detecting means (current detecting step) becomes a predetermined end-of-charge current, the charging control means (charging control step) opens and closes the path of the charging current Is set to the open state by the control signal to terminate the charging, but the first detection current by the current detection means (current detection step) when the switching means is opened at a predetermined temperature (in the first current detection step) in advance. Is stored, and the temperature correction means (temperature correction step)
A temperature change of the charging circuit is detected by comparing the second detection current by the current detection means (current detection step) when the switching means is in the open state with the stored first detection current, and a predetermined charge termination current is detected. Is corrected.

As described above, the first detection current by the current detection means (current detection step) when charging is interrupted at a predetermined temperature, and the current detection means when charging is interrupted during charging (current detection step). By comparing with the second detection current, the charge termination current is corrected so as to cancel the temperature fluctuation of the charging circuit, so that the influence of the temperature characteristic of the circuit and the variation of the temperature characteristic can be suppressed as much as possible, and as in the conventional case. The charging current can be detected at low cost and with high accuracy without having a table for temperature characteristics, and the detection accuracy of the charging termination current can be improved.

In the charging circuit according to the second aspect, the charging method according to the fifth aspect, and the recording medium according to the sixth aspect, the temperature correction means (temperature correction step) includes: It is desirable to detect a temperature change of the charging circuit by comparing the second detection current with the first detection current, and correct a predetermined charge termination current. For example, when the charge termination current detection is performed by a control program executed on a CPU or the like, if a cycle for performing temperature correction according to an estimated charging time of a battery cell to be charged is determined, It is possible to more efficiently improve the detection accuracy of the charge termination current.

Further, in the charging circuit according to the third aspect, the current detecting means detects the current based on the voltage drop of the current detecting means, and the switching means is connected to the charging current on the charging current supply side of the current detecting means. Connected in series to the path of
A first circuit portion through which a relatively large current flows during operation is connected to the connection end of the current detection means to the battery cell, and a relatively small current flows during operation to another connection end of the current detection means on the charging current supply side. It is desirable to connect and configure the flowing second circuit units.

Thus, at the time of charging, only the charging current supplied to the battery cell flows through the current detecting means without flowing the current to the second circuit portion, and at the time of non-charging, the battery cell flows to the first circuit portion. Is supplied directly from the power supply.
Further, since the charge termination current is not detected during the operation of the first circuit portion, the current detection is performed when only the charging current to the battery cell flows to the current detection means. As a result, the accurate charge termination current is not detected. Detection is possible, and the detection accuracy of the charge termination current is improved. Further, when the battery is driven, the second circuit section can operate without being affected by a voltage fluctuation such as a voltage drop of the current detecting means.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a charging circuit, a charging method and a recording medium according to the present invention will be described below in detail with reference to the drawings. In the description of each embodiment, the charging circuit and the charging method according to the present invention will be described in detail. However, the recording medium according to the present invention is a recording medium that records a program for executing the charging method. Therefore, the description is included in the following description of the charging method.

Further, the charging circuit, the charging method and the recording medium of the present invention are intended for charging a battery cell such as a nickel cadmium storage battery, a nickel hydride storage battery or a lithium ion secondary battery.
It is used for battery-powered portable electronic devices such as video cameras and notebook computers.

FIG. 1 is a circuit diagram showing a charging circuit according to an embodiment of the present invention. In the figure, the charging circuit of the present embodiment constitutes a part of a mobile electronic device, and here, a mobile phone is exemplified as the mobile electronic device.

In FIG. 1, the charging circuit according to the present embodiment comprises:
A terminal T connected to the external charger 1 during charging, a battery cell 3, a diode D1 for preventing backflow, and a field-effect transistor (hereinafter abbreviated as FET) as a charging voltage control circuit.
Q1, charging current detection resistor R1, charging control circuit 20, CP
U10, regulators 21 and 22, reception amplification circuit 23,
An analog / digital processing circuit 24, a backlight driving circuit 25, and a transmission power unit 27 are provided.
In addition, the charging circuit includes, in addition to the above components, a thermistor that detects whether or not charging is performed within a predetermined temperature range and controls charging, a charging temperature detection circuit, an overdischarge protection circuit, and the like. However, since it is not directly related to the present invention, the description of the configuration and operation is omitted.

In FIG. 1, some of the components of the portable electronic device are separately shown in a first circuit section 11 and a second circuit section 12. Here, the first circuit portion 11 is a circuit portion connected to the connection end of the charging current detection resistor R1 with the battery cell 3, and through which a relatively large current flows during operation. The second circuit section 12 is connected to another connection end of the charging current detection resistor R1 on the charging current supply side (terminal T side), and a relatively small current flows during operation. In FIG. 1, the charge control circuit 20, the regulators 21 and 22, the reception amplification circuit 23, and the analog / digital processing circuit 24 are provided in one IC package 29 called a power supply IC.

The first circuit section 11 includes a circuit related to power amplification during transmission and reception, that is, a transmission power section 27 and a reception amplification circuit 23, and is a circuit section through which a large current flows during transmission and reception during a call. The first circuit unit 11 is supplied with power from the battery cell 3 and also supplied with a stabilized power supply voltage from the regulator 22.

The second circuit section 12 includes an on / off drive of the FET Q1 in conjunction with the CPU 10 to perform a charge start / stop control based on a voltage from the terminal T and thermistor information (not shown). Charge control circuit 2 that performs
0, a regulator 21 for supplying stabilized power to a control system and the like, a regulator 22 for supplying stabilized power to a communication system and the like, and an analog / digital processing circuit 24 for performing signal processing for modulation and demodulation. And a backlight drive circuit 25 connected to the LCD light and outputting a drive signal.

A battery cell (unit cell) 3
Is a unit battery configured to include a negative electrode, a positive electrode, an electrolyte, a current collector, and the like as its structure. In the case of a lithium-ion battery, since it is not strong against extreme overcharging, the internal structure of the
It has an element, a safety valve, a low melting point separator and the like.

Next, the charging current detecting resistor R1 corresponds to the current detecting means described in the claims, and detects a charging current when charging the battery cell 3. The FET Q1 corresponds to a switching unit, and opens and closes a path of a charging current based on a control signal from the charging control circuit 20. Further, the charge control circuit 20 corresponds to a charge control means, detects a current based on a voltage drop across the charging current detection resistor R1, and, when the detected current becomes a predetermined charge termination current, turns off the FET Q1 by a control signal. The charging is terminated by turning off (charging path is opened).

The source-drain of the FET Q1 is connected in series to the charging current path on the charging current supply side of the charging current detection resistor R1, and the first circuit portion 11 is connected to the connection end of the charging current detection resistor R1 with the battery cell 3. Is connected to the other connection terminal of the charging current detection resistor R1 on the charging current supply side.
Are connected.

Therefore, during charging, only the charging current supplied to the battery cell 3 flows through the charging current detecting resistor R1 without flowing the current to the second circuit section 12, and during non-charging, the first circuit section 11 , Power is supplied directly from the battery cell 3. In addition, since the end-of-charge current is not detected during the operation of the first circuit unit 11, current detection is performed when only the charging current to the battery cell 3 flows through the charging current detection resistor R1, and as a result, accurate detection is performed. The end-of-charge current can be detected, and the detection accuracy of the end-of-charge current is improved. In addition, when the battery is driven, the second circuit section 12 can operate without being affected by a voltage change such as a voltage drop of the current detection resistor R1.

Further, the CPU 10 controls the operation of each component in the mobile phone and corresponds to a temperature correcting means described in the claims.
The first detection current by the charging current detection resistor R1 when the TQ1 is turned off (the charging path is opened) is stored, and the charging current detection resistor when the FET Q1 is turned off (the charging path is opened) is stored. A second detection current is determined by R1, a temperature change of the charging circuit is detected by comparing the second detection current with the first detection current, and a predetermined charge termination current is corrected.

Next, the operation of the charging circuit of this embodiment having the above configuration will be described. When not charging, battery cell 3
Power is supplied directly to the first circuit unit 11 from the
Power is supplied from the battery cell 3 to the second circuit unit 12 via the charging current detection resistor R1, and normal operation as a mobile phone is performed. At this time, since a large current does not flow through the second circuit section 12, large power consumption does not occur in the charging current detection resistor R1. Also, the second circuit unit 1
2 operates irrespective of slight voltage fluctuation, the voltage drop in the charging current detection resistor R1 does not adversely affect the operation of the device.

Next, at the time of charging when the external charger 1 is connected to the mobile phone via the terminal T, the connection of this terminal T is made by, for example, connection of another terminal (not shown) or application from the external charger 1. The voltage is recognized by the CPU 10 or the charge control circuit 20, and an ON drive signal is output to the gate of the FET Q1 to turn the FET Q1 ON (the charging path is closed) to conduct, and to the battery cell 3 through the charging current detection resistor R1. A charging current is supplied. Note that the charging current via the charging current detection resistor R1 is supplied to the reception amplification circuit 23 of the first circuit unit 11.
And the transmission power unit 27. The charging current is also supplied to the regulators 21 and 22 and the backlight drive circuit 25 inside the power supply IC 29,
The supply of the communication and control system stabilizing power from the communication systems 1 and 22 drives all functional circuits and drives the CD write. The voltage drop due to the charging current detection resistor R1 does not affect the talk time and the like regardless of the reception amplifier circuit 23 and the transmission power unit 27 of the first circuit unit 11.

At this time, the charging control circuit 20 in the power supply IC 29 takes in the voltage drop across the charging current detecting resistor R 1, amplifies it, and outputs it to the CPU 10. CPU1
At 0, the charging current is constantly monitored based on the voltage drop,
When the charging current has reached a predetermined charging termination current, the control signal from the charging control circuit 20 turns off the FET Q1 (opens the charging path) and terminates charging. In this case, it is common for the CPU 10 to notify the user of the charging or the end of the charging by lighting in a different emission color using a light emitting diode (LED) (not shown) or the like. It should be noted that the charge termination current is detected only at the timing excluding the time of a mobile phone call, and therefore, the charging current does not include the current flowing into the reception amplifier circuit 23 and the transmission power unit 27 of the first circuit unit 11. That is, the charging current detection resistor R
The current detection is performed when only the charging current to the battery cell 3 flows into the battery cell 1. As a result, it is possible to accurately detect the charging end current, and to improve the detection accuracy of the charging end current.

Here, the CPU 10 previously turns off the FET Q1 at normal temperature, for example (turns off the charging path), and detects the charging current based on the voltage drop across the charging current detecting resistor R1 at that time. This is stored as the first detection current. Next, at the time of charging, the FET Q1 is turned off (the charging path is opened) at regular intervals,
A charging current is detected based on a voltage drop across the charging current detection resistor R1 at that time, and the detected charging current is used as a second detection current. The temperature fluctuation of the charging circuit is determined by comparing the second detection current with the first detection current. And the temperature of the charge termination current is corrected.

More specifically, the detection of the charge termination current is as follows:
The charge control circuit 20 captures and amplifies the voltage drop across the charging current detection resistor R1 and outputs it to the CPU 10,
Since the CPU 10 determines whether the amplified voltage has become equal to or lower than the voltage corresponding to the charge termination current, the second detection current (the voltage corresponding to the second detection current) is used for the temperature correction in order to correct the temperature. It is taken as an offset voltage including the temperature characteristics of the detection resistor R1 and the charge control circuit 20, and a difference between the offset voltage and a previously stored offset voltage at normal temperature (a voltage corresponding to the first detection current) is taken to terminate charging. The difference may be subtracted from the voltage corresponding to the current. As a result, the temperature change of the charging current detection resistor R1 and the charging control circuit 20 can be canceled, and the detection accuracy of the charging termination current can be improved.

As described above, in the charging circuit and the charging method according to the present embodiment, the first detection current detected when charging is interrupted at a predetermined temperature and the second detection current detected when charging is interrupted during charging. By comparing with the detected current, the charge termination current is corrected so as to cancel the temperature fluctuation of the charging circuit (the charging current detection resistor R1 and the charging control circuit 20), so that the influence of the temperature characteristic of the circuit and the variation of the temperature characteristic is reduced. It is possible to detect the charging current at a low cost and with high accuracy without suppressing the temperature characteristic as much as possible and without having a table for the temperature characteristic as in the related art, thereby improving the detection accuracy of the charging termination current.

[0038]

As described above, according to the charging circuit, the charging method, and the recording medium of the present invention, the current detecting means (current detecting step) detects the charging current when charging the battery cell, and detects the current. Means (current detection step)
When the current detected by the control circuit becomes a predetermined charge termination current, the charging control means (charging control step) sets switching means for opening and closing the path of the charging current to an open state by a control signal to terminate charging. Current detecting means (current detecting step) when the switching means is opened at a predetermined temperature (by the first current detecting step)
Is stored, and the temperature correction means (temperature correction step) compares the second detection current and the first detection current by the current detection means (current detection step) when the switching means is opened. By detecting the temperature fluctuation of the charging circuit by comparison and correcting the predetermined charge termination current, the influence of the temperature characteristics of the circuit and the variation of the temperature characteristics is suppressed as much as possible, and the charging current with low cost and high accuracy is obtained. Can be detected, and the detection accuracy of the charge termination current can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a charging circuit according to an embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 external charger T terminal 3 battery cell D1 backflow preventing diode Q1 field effect transistor (FET; charging voltage control circuit) R1 charging current detection resistor 10 CPU 11 first circuit unit 12 second circuit unit 20 charge control circuit 21, 22 Regulator 23 Receive amplifier circuit 24 Analog / digital processing circuit 25 Backlight drive circuit 27 Transmission power unit 29 Power supply IC

Claims (6)

[Claims] 1. A charging circuit for an electronic device driven by a battery cell, wherein the battery cell is charged by a voltage supplied from an external charger, wherein a charging current for charging the battery cell is detected. A switching means for opening and closing the path of the charging current based on a control signal; and when the detection current of the current detection means has reached a predetermined end-of-charge current, the control signal opens the switching means. Charge control means for terminating charging, and a first detection current by the current detection means when the switching means is opened at a predetermined temperature is stored in advance, and the switching means is opened. The temperature fluctuation of the charging circuit is detected by comparing the second detection current and the first detection current by the current detection means at the time, and the predetermined charge is detected. Charging circuit and having a temperature correction means for correcting the end current. 2. The temperature correction means detects a temperature change of the charging circuit by comparing the second detection current and the first detection current at regular intervals during charging, and detects the predetermined charge termination current. 2. The charging circuit according to claim 1, wherein 3. The current detecting means detects current based on a voltage drop of the current detecting means. The switching means is connected in series with a charging current path on a charging current supply side of the current detecting means. A first circuit portion through which a relatively large current flows during operation is connected to a connection end of the current detection means with the battery cell, and an operation is connected to another connection end of the current detection means on a charging current supply side. 3. The charging circuit according to claim 1, wherein a second circuit section through which a relatively small current flows sometimes is connected. 4. A method of charging a battery cell in an electronic device having a battery cell stored by a voltage supplied from an external charger, wherein the current detection detects a charging current when the battery cell is charged. And a charging control step of, when the detection current of the current detection step becomes a predetermined charging termination current, terminating the charging by opening the path of the charging current, A first current detection step of storing a first detection current in the current detection step when the path is opened, and a second detection current in the current detection step when the charging current path is opened. And a temperature correction step of detecting a temperature change of the charging circuit by comparing with the first detection current, and correcting the predetermined charge termination current. Charging method that. 5. The temperature correction step comprises: detecting a temperature change of a charging circuit by comparing the second detection current and the first detection current at regular intervals during charging, and detecting the predetermined charging termination current. The charging circuit according to claim 4, wherein the correction is performed. 6. A computer-readable recording medium recorded as a program for causing a computer to execute the charging method according to claim 4.