JP2009290931A - Charging circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging circuit accurately detecting a fully charged state. <P>SOLUTION: At the start of charging, a charging current control circuit 23 performs a constant current and constant voltage charging into a battery 40, with a switch 110 kept turned on. A CPU 31 decides whether a value of the charging current flowing into the battery 40 is lower than a switching threshold value (100 mA, for example), based on the voltage across a resistor 50 measured with a voltage detection circuit 22, and when the value of the charging current is decided lower than the switching threshold value, the CPU 31 turns off the switch 110 and controls a constant current control circuit 122 so as to perform constant current charging into the battery 40 with a comparatively small current (50 mA, for example). The CPU 31 decides whether the voltage of the battery 40 reaches the voltage (4.2 V, for example) indicating a full charged state on the basis of the voltage of the battery detected by a voltage detection circuit 121, and when it is decided that the full charged state of the battery 40 is achieved, the CPU 31 controls the constant current control circuit 122 to stop charging into the battery 40. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charging circuit for a secondary battery that can be used in a mobile communication terminal such as a mobile phone.

As a charging method for a secondary battery such as a lithium ion battery that can be used in a mobile communication terminal such as a mobile phone, there is a constant current constant voltage charging method.
FIG. 4 is a diagram showing the relationship between the charging current flowing through the battery and the battery voltage when charging is performed by the constant current and constant voltage charging method. The constant current and constant voltage charging method will be briefly described with reference to FIG.

If charging is performed when the battery is in a discharged state, constant current charging is first started at T0 in FIG. The battery voltage, which was initially about 3.0V, becomes higher as constant current charging proceeds. When the battery voltage reaches 4.2V (T1), constant voltage charging is started.
As constant voltage charging progresses, the value of the charging current gradually decreases, and when the value of the charging current reaches a predetermined threshold (hereinafter referred to as “full charge detection threshold”) (T2), the fully charged state To stop charging.

That is, in the constant current / constant voltage charging method, the fully charged state of the battery is detected by detecting that the value of the charging current flowing through the battery is equal to or less than the full charge detection threshold.
FIG. 5 is a block diagram showing a conventional charging circuit that charges a battery of a mobile phone by a constant current constant voltage charging method.
In the figure, the voltage detection circuit 21 of the charge control circuit 20 indicates the voltage (potential from the ground) at the terminal connected to the battery 40 (lithium ion battery) of the resistor 50 (for example, 0.2Ω). The voltage detection circuit 22 measures the voltage at both ends of the resistor 50, outputs the voltage detection signal 1 indicating the measured voltage to the CPU 31 of the load circuit 30, and measures the voltage. The obtained voltage value is output to the charging current control circuit 23.

  The charging current control circuit 23 charges the battery 40 by a constant current / constant voltage charging method based on electric power (for example, 5.5 V, 600 mA) supplied from the charger 10 connected to a commercial AC power source. As described above, the circuit supplies power distributed to the load circuit 30 and the battery 40, and controls constant current and constant voltage based on the voltage values output from the voltage detection circuit 21 and the voltage detection circuit 22. I do.

Here, the load circuit 30 is a circuit that executes each function of the mobile phone (for example, a telephone call function, a mail function, etc.). It includes a CPU 31 that controls the peripheral circuit 32 and the charge control circuit 20 by executing the stored program.
The current supplied from the charging current control circuit 23 (hereinafter referred to as “supply current”) is distributed to the load circuit 30 and the battery 40, but the current to be supplied to the load circuit 30 (hereinafter referred to as “current consumption”). Is different depending on the function executed by the load circuit 30. Therefore, the value of the charging current flowing to the battery 40 also varies according to the value of the consumption current.

  Further, the CPU 31 calculates a supply current value based on the voltage detection signal 1 output from the voltage detection circuit 22, and is set in advance according to the function of the mobile phone executed in the load circuit 30 from this supply current value. The full charge state of the battery 40 is detected by determining whether the value of the charge current flowing through the battery 40 calculated by subtracting the current consumption value is equal to or less than the full charge detection threshold. When the fully charged state is detected, the CPU 31 stops charging the battery 40 by outputting the charge control signal 2 to the charge control circuit 20.

  However, in recent years, it has become difficult to set current consumption values in advance for all the functions executed by the load circuit 30 as mobile phones and the like have become highly functional. In addition, since the current consumption value varies greatly depending on the function executed by the load circuit 30, if the current consumption value cannot be accurately specified, the accurate charge current value cannot be calculated, and the fully charged state can be accurately determined. It will not be detected.

As a charging circuit that solves this problem, a charging circuit is known in which a resistor is added in the path from the resistor 50 to the battery 40 in the conventional charging circuit shown in FIG. 5 (for example, Patent Document 1).
By measuring the current value flowing through the added resistor, the charging current value can be measured accurately, so that the fully charged state of the battery 40 can be accurately detected.
Japanese Patent No. 3321717

However, the charging circuit of Patent Document 1 has a problem in that the battery capacity that can be used by the load circuit 30 is reduced because a voltage drop due to the added resistor occurs when the battery 40 is discharged.
Therefore, the present invention has been made in view of the necessity, and an object of the present invention is to provide a charging circuit capable of accurately detecting a fully charged state by a method different from the conventional one.

  In order to solve the above problems, a charging circuit according to the present invention is a charging circuit that charges a secondary battery by power feeding from an external power source, and distributes the load circuit and the secondary battery based on the power feeding. A first current control circuit for supplying a current to be supplied, a second current control circuit for supplying a predetermined constant current to the secondary battery, based on the power supply, and the secondary battery Measures the current when a current is supplied to the load circuit and the secondary battery from a switch for switching from which current control circuit the current is supplied and from the first current control circuit The secondary battery includes switch switching means for switching the switch so as to supply current from the second current control circuit.

  With the above configuration, the charging circuit according to the present invention enables the power supply path to the load circuit and the power supply path to the secondary battery when the switch switching unit switches the switch so as to supply current to the secondary battery from the second current control circuit. If the battery fully charged state is detected after switching the switch, the fully charged state can be accurately detected without being affected by fluctuations in the current value consumed by the load circuit. Can do.

Hereinafter, as an embodiment of the charging circuit according to the present invention, an example of a charging circuit used in a mobile phone will be described.
<< Embodiment >>
<Overview>
The charging circuit according to the present embodiment is obtained by adding a switch, a constant current control circuit, and a voltage detection circuit to the conventional charging circuit shown in FIG.

  Although details will be described later, these will be briefly described. When the switch is on, power can be supplied from the charging current control circuit 23 to the load circuit 30 and the battery 40 as usual, and the CPU 31 of the load circuit 30 is turned off. Thus, the load circuit 30 can be continuously supplied with power from the charging current control circuit 23, and the battery 40 can be supplied with power from the constant current control circuit. In other words, the power supply path to the load circuit 30 and the power supply path to the battery 40 can be disconnected by turning off the switch.

The constant current control circuit and the voltage detection circuit described above are circuits that are controlled to operate by the CPU 31 when the switch is turned off. The constant current control circuit supplies power to the battery 40, and this voltage The detection circuit is a circuit that measures the voltage of the battery 40.
A charging method using this charging circuit will be briefly described.
FIG. 1 is a diagram showing the relationship between the charging current flowing through the battery 40 and the battery voltage when charging is performed by the charging circuit according to the present embodiment.

  Assuming that charging is performed when the battery 40 is in a discharged state, at the time T0 in the figure, the above-described switch is in an ON state, that is, without disconnecting the power supply path between the load circuit 30 and the battery 40. Similarly to the charging circuit, constant current charging (constant current charging (1) in the figure) is started from the charging current control circuit 23 to the battery 40. As this constant current charging proceeds, the battery voltage increases. When the battery voltage reaches 4.2 V (T1), constant voltage charging is started. Up to here, it is the same as the conventional one.

  As the constant voltage charging progresses, the value of the charging current gradually decreases, and when the value of the charging current reaches a predetermined threshold (for example, 100 mA. This threshold is hereinafter referred to as “switching threshold”) ( T2) The CPU 31 controls the above-described switch to OFF to disconnect the power supply path between the load circuit 30 and the battery 40, and the load circuit 30 is continuously supplied with power from the charging current control circuit 23 to the battery 40. Then, constant current charging (constant current charging (2) in the figure) with a relatively small current (for example, 50 mA) is started from the above-described constant current control circuit.

When the constant current charging advances and the voltage of the battery 40 measured by the voltage detection circuit reaches a voltage indicating full charge (in this example, 4.2 V) (T3), the charging is stopped.
As described above, the charging circuit according to the present embodiment detects the fully charged state of the battery 40 in a state where the power feeding path to the load circuit 30 and the power feeding path to the battery 40 are disconnected. The full charge state can be detected accurately without being affected by the increase or decrease in current, and a resistor is not used as in the charging circuit of Patent Document 1, so that no unnecessary voltage drop occurs when the battery 40 is discharged. .

  Further, if the battery 40 is to be charged with constant current by the above-described constant current control circuit from the beginning of charging (T0 in the figure), a relatively small current (for example, as described above) Therefore, the charging time may be extended as compared with the conventional charging circuit. However, since the charging circuit according to the present embodiment performs constant current and constant voltage charging by the charging current control circuit 23 as usual while the charging current is larger than the switching threshold, it is possible to suppress the extension of the charging time.

<Configuration>
FIG. 2 is a block diagram illustrating a charging circuit according to the embodiment.
This figure shows an example in which the charging circuit according to the embodiment is applied to a mobile phone, and the same reference numerals are given to the same circuits and signals as those in FIG.
Below, the structure of the charging circuit which concerns on this Embodiment is demonstrated centering on a different part from the conventional charging circuit shown in FIG.

In FIG. 2, the switch 110 is realized by a transistor or the like, and is normally turned on, and is turned off based on a control signal from the CPU 31.
In addition, the charging control circuit 120 is based on electric power (for example, 5.5 V, 600 mA) supplied from the charger 10 connected to a commercial AC power supply, like the charging control circuit 20 in the conventional charging circuit. 30 and a circuit for supplying power to the battery 40. As shown in FIG. 3, in addition to the voltage detection circuit 21, the voltage detection circuit 22, and the charging current control circuit 23, a voltage detection circuit 121 and a constant current control circuit 122 are provided. Is different from the charge control circuit 20 in that

The charging current control circuit 23 is a circuit similar to that included in the charging control circuit 20, but when the switch 110 is OFF, a necessary consumption current is supplied only to the load circuit 30.
Here, the voltage detection circuit 121 measures the voltage (potential from the ground) in the battery 40 by, for example, the potential difference method based on the charge control signal 3 output from the CPU 31 when the switch 110 is turned off. This circuit outputs the voltage detection signal 4 indicating the measured voltage to the CPU 31 of the load circuit 30 while outputting to the constant current control circuit 122.

The constant current control circuit 122 is a circuit that supplies a relatively small constant current (for example, 50 mA) to the battery 40 based on the charge control signal 3 output from the CPU 31 when the switch 110 is turned off. The constant current control circuit 122 performs constant current control based on the voltage value output from the voltage detection circuit 121.
<Operation>
FIG. 3 is a flowchart showing the operation of the charging circuit according to the present embodiment.

Hereinafter, the operation of the charging circuit will be described with reference to the flowchart shown in FIG. At the start of charging, the CPU 31 of the load circuit 30 does not output a control signal to the switch 110, so that the switch 110 is in an ON state.
When power is supplied from the charger 10, the charging current control circuit 23 of the charging control circuit 120 charges the battery 40 by a constant current / constant voltage method, similarly to the charging current control circuit 23 in the conventional charging circuit. Then, the electric power distributed to the load circuit 30 and the battery 40 is supplied (step S1). That is, the charging current control circuit 23 first performs constant current charging on the battery 40, and performs constant voltage charging when the voltage value output from the voltage detection circuit 21 reaches the battery voltage (for example, 4.2V). .

  The voltage detection circuit 22 measures the voltage across the resistor 50, and outputs a voltage detection signal 1 indicating the measured voltage to the CPU 31 (step S2). Based on the voltage detection signal 1, the CPU 31 detects, for example, a constant cycle. Thus, it is determined whether or not the value of the charging current flowing through the battery 40 is equal to or less than a switching threshold (for example, 100 mA) (step S3). The method for calculating the charging current value is the same as in the conventional method. Specifically, the voltage detection signal 1 output from the voltage detection circuit 22 is converted into a digital signal by an A / D converter (not shown), and the CPU 31 performs the above-described conversion based on the converted digital signal. Make a decision.

  When it is determined that the charging current value is greater than the switching threshold (step S3: N), the processing of steps S2 and S3 is performed to determine again whether the charging current value is equal to or lower than the switching threshold, and the charging current When it is determined that the value is equal to or less than the switching threshold (step S3: Y), the CPU 31 starts outputting a control signal to the switch 110 and turns off the switch 110 (step S4).

  Further, the CPU 31 outputs a charge control signal 3 indicating that constant current charging is started from the constant current control circuit 122 to the charge control circuit 120, and based on the charge control signal 3, the constant current control circuit 122 The supply of a constant current (for example, 50 mA) to 40 is started (step S5). That is, since the switch 110 is turned off in step S4, the current is continuously supplied from the charging current control circuit 23 to the load circuit 30 and the current is supplied from the constant current control circuit 122 to the battery 40.

The voltage detection circuit 121 starts measuring the voltage in the battery 40 based on the charge control signal 3 output from the CPU 31 in step S5, and outputs a voltage detection signal 4 indicating the measured voltage to the CPU 31 (step S5). S6).
Based on the voltage detection signal 4, the CPU 31 determines whether or not the voltage of the battery 40 has reached a voltage indicating full charge (for example, 4.2V), for example, at a constant cycle (step S7). When it is determined that the battery has not reached the voltage indicating full charge (step S7: N), the voltage of the battery 40 indicates full charge (for example, 4.2 V) by performing the processes of steps S6 and S7. It is determined again whether or not.

  If it is determined in step S7 that the voltage of the battery 40 has reached a voltage indicating full charge (step S7: Y), the CPU 31 stops outputting the control signal to the switch 110 and switches to the switch 110. And a charge control signal 3 indicating the end of charging is output to the charge control circuit 120. Based on the charge control signal 3, the charge current control circuit 23 and the constant current control circuit 122 are connected to the load circuit 30, respectively. The supply of current to the battery 40 is stopped (step S8), and the charging process is terminated.

<Supplement>
The charging circuit according to the present invention has been described above based on the embodiment. However, the charging circuit can be modified as follows, and the present invention is not limited to the charging circuit as described in the above-described embodiment. Of course.
(1) A charging circuit according to the present invention is a charging circuit that charges a secondary battery by power feeding from an external power source, and based on the power feeding, a current distributed to the load circuit and the secondary battery. A first current control circuit for supplying, a second current control circuit for supplying a predetermined constant current to the secondary battery based on the power supply, and a current supply to the secondary battery. , When a current is supplied to the load circuit and the secondary battery from the first current control circuit and a switch for switching from which current control circuit to perform, the current is measured, and the 2 The secondary battery includes switch switching means for switching the switch so as to supply current from the second current control circuit.

  With the above configuration, the charging circuit according to the present invention enables the power supply path to the load circuit and the power supply path to the secondary battery when the switch switching unit switches the switch so as to supply current to the secondary battery from the second current control circuit. If the battery fully charged state is detected after switching the switch, the fully charged state can be accurately detected without being affected by fluctuations in the current value consumed by the load circuit. Can do.

Further, the switch switching means, when the current from the first current control circuit is supplied to the load circuit and also distributed to the secondary battery, the secondary battery includes: The switch can be configured to switch the current to be supplied from the second current control circuit.
(2) The charging circuit measures a voltage of the secondary battery when current is supplied from the second current control circuit to the secondary battery, and the measured voltage indicates a full charge. When the voltage reaches the voltage, supply stop means for stopping the supply of current from the second current control circuit may be provided.

As a result, the supply stopping means can detect the full charge state of the battery in a state where the power supply path to the load circuit and the power supply path to the secondary battery are disconnected, and therefore, the fluctuation of the current value consumed by the load circuit It is possible to accurately detect the fully charged state without being affected by.
(3) The switch switching unit may switch the switch so as to supply current from the second current control circuit to the secondary battery according to the measured current.

  Thereby, for example, when the measured current becomes a predetermined threshold value or less, the power supply path to the load circuit is thereafter switched by switching the switch to supply the current from the second current control circuit to the secondary battery. In addition, the fully charged state of the battery can be detected with the power supply path to the secondary battery disconnected, so the fully charged state can be accurately detected without being affected by fluctuations in the current value consumed by the load circuit. can do.

  (4) Further, the secondary battery is a lithium ion battery, the first current control circuit charges the secondary battery by a constant current constant voltage charging method, and the switch switching means includes: The current distributed to the secondary battery is calculated based on the measured current, and when the current value is equal to or less than a predetermined threshold, the current is supplied from the second current control circuit to the secondary battery. A constant current supplied by the second current control circuit may be equal to or less than the threshold value, including a processor that switches the switch to supply.

  As a result, until the current distributed to the secondary battery becomes equal to or lower than a predetermined threshold, the secondary battery is charged with a constant current and constant voltage by the first current control circuit. In order to charge the secondary battery with a relatively small constant current supplied from the second current control circuit below the threshold, charging is performed in comparison with the case where the secondary battery is charged only by the second current control circuit. The time extension can be suppressed.

  The first current control circuit in the present invention corresponds to the voltage detection circuit 21, the voltage detection circuit 22, and the charging current control circuit 23 in the embodiment, and the second current control circuit in the present invention is the same as in the embodiment. It corresponds to the voltage detection circuit 121 and the constant current control circuit 122. Further, the switch switching means in the present invention corresponds to the voltage detection circuit 22 and the CPU 31 in the embodiment, and the supply stop means in the present invention corresponds to the voltage detection circuit 121 and the CPU 31 in the embodiment.

(5) In the embodiment, the switching threshold has been described as 100 mA. However, this is an example, and for example, a switching threshold that shortens the charging time from the discharged state to the fully charged state as much as possible is obtained through experiments. The obtained switching threshold value may be used.
(6) In the embodiment, the CPU 31 is described as controlling the switch 110 and the charging control circuit 120 by executing a program stored in the ROM. However, this control is performed by providing a dedicated circuit. It may be realized.

  The charging circuit according to the present invention is used for charging a secondary battery that can be used in a mobile communication terminal such as a mobile phone.

It is a figure which shows the relationship between the charging current which flows into the battery at the time of charging with the charging circuit which concerns on embodiment, and a battery voltage. It is a block diagram which shows the charging circuit which concerns on embodiment. It is a flowchart which shows operation | movement of the charging circuit which concerns on embodiment. It is a figure which shows the relationship between the charging current which flows into the battery at the time of charging with the conventional constant current constant voltage charging system, and a battery voltage. It is a block diagram which shows the conventional charging circuit.

Explanation of symbols

1, 4 Voltage detection signal 2, 3 Charge control signal 10 Charger 20, 120 Charge control circuit 21, 22, 121 Voltage detection circuit 23 Charge current control circuit 30 Load circuit 31 CPU
32 Peripheral circuit 40 Battery 50 Resistor 110 Switch 122 Constant current control circuit

Claims (4)

A charging circuit that charges a secondary battery by supplying power from an external power source,
A first current control circuit for supplying a current distributed to the load circuit and the secondary battery based on the power supply;
A second current control circuit for supplying a predetermined constant current to the secondary battery based on the power supply;
A switch for switching from which current control circuit the current is supplied to the secondary battery;
When current is supplied from the first current control circuit to the load circuit and the secondary battery, the current is measured, and current is supplied from the second current control circuit to the secondary battery. A switch switching means for switching the switch as described above. The charging circuit is
When a current is supplied to the secondary battery from the second current control circuit, the voltage of the secondary battery is measured, and when the measured voltage reaches a predetermined voltage indicating full charge, the second battery The charging circuit according to claim 1, further comprising supply stopping means for stopping supply of current from the two-current control circuit. The switch switching means is
The charging circuit according to claim 2, wherein the switch is switched so as to supply a current from the second current control circuit to the secondary battery according to the measured current. The secondary battery is a lithium ion battery,
The first current control circuit charges the secondary battery by a constant current constant voltage charging method,
The switch switching means is
Based on the measured current, the current distributed to the secondary battery is calculated, and when the current value is equal to or less than a predetermined threshold, the current is supplied from the second current control circuit to the secondary battery. Including a processor to switch the switch to
The charging circuit according to claim 3, wherein the magnitude of the constant current supplied by the second current control circuit is equal to or less than the threshold value.

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