JP2002010514A - Constant current, constant voltage, and constant current charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fully charge a lithium ion secondary battery in a short time by a simple circuit, without detecting its minute charging finish current. SOLUTION: When a portable telephone is connected to an external charger 11, constant-current charging is performed by a rated charging current Is. When the voltage of its battery 17 becomes a charging completion voltage Voff, the voltage is controlled by a charging voltage control circuit 12, and constant- voltage charging is performed by the completion voltage Voff. If the charging current decreases up to (charging completion current Ioff + error current Ierror), constant-current charging by the charging completion current Ioff is performed with a precise constant-current circuit 19. When the battery voltage becomes the completion voltage Voff, charging is finished. Since charging completion is decided by the charging completion voltage, detection of a minute charging completion current is unnecessary, and it becomes possible to perform full charging by a simple circuit safely certainly in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device using both constant current charging and constant current charging, and more particularly to a charging device built in a mobile communication terminal such as a portable telephone.

[0002]

2. Description of the Related Art In a mobile communication terminal such as a mobile phone, a secondary battery is used as a power source. Lithium-ion secondary batteries are suitable for mobile phones and the like, and are widely used these days. Before using a mobile phone, it is necessary to charge a secondary battery. When charging a secondary battery, if a charging voltage and a charging current higher than the rated values are applied to the secondary battery, the secondary battery may be damaged. The charging device includes a constant voltage circuit and a constant current circuit so as not to damage the secondary battery and to charge the battery in a short time. The charging voltage and charging current exceeding the rated value
The voltage is not applied to the secondary battery. The charging device is
A constant current circuit supplies a charging current of a rated value or less to the secondary battery, and a constant voltage circuit supplies a charging voltage of a rated value or less to the secondary battery.

A method of charging a conventional lithium ion secondary battery will be described. First, constant current charging is performed at the rated current. As the charging proceeds, the battery voltage rises and eventually reaches the rated voltage, so that the constant current charging ends. Subsequently, constant voltage charging is performed at the rated voltage. When the charging current gradually decreases and reaches a predetermined current value, charging is stopped.

In this charging method, the completion of charging is detected by detecting the charging current to the secondary battery during constant voltage charging. The method of detecting the charging current is a method in which the charging current is converted into a voltage by a minute resistor, the voltage is amplified by an amplifier, converted into a digital signal by an A / D converter, and the CPU determines the charging current. . Since a minute current is detected by a minute resistance, an error is increased due to the influence of the impedance of the substrate wiring, and variations occur due to the temperature characteristics of the amplifier, so that the resolution of the current measurement is low.

[0005] As the performance of the secondary battery is improved and more power can be charged, the charge termination current is reduced. In order to avoid overcharging and safely perform full charging, it is necessary to detect a minute charge termination current with high accuracy. In order to improve the current detection accuracy, a circuit is designed to minimize the temperature change of the amplifier, or the measured value is corrected using a temperature characteristic table to obtain a correct charging current.

[0006]

However, in the conventional charging method, it is necessary to provide an amplifier having a small temperature change and a temperature characteristic table in order to accurately detect a minute charge termination current, which leads to an increase in cost. There's a problem.
In addition, as a charging method that does not detect the charge termination current, there is a method of performing constant voltage charging for a fixed time or a method of measuring the temperature of a secondary battery. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the conventional problems and to provide a charging device which can eliminate the need to detect a minute charge termination current and can be fully charged in a short time with a simple circuit.

[0008]

In order to solve the above-mentioned problems, according to the present invention, a charging device includes a voltage detecting means for detecting a battery voltage, a current detecting means for detecting a charging current, and a first charging current. A constant current charging means for charging with a first charging voltage, a second constant current charging means for charging with a second charging current, and charge control means,
The charging control means detects that the mobile phone has been connected to the charger and starts charging by the first constant current charging means. Means for terminating charging by the first constant current charging means and starting charging by the constant voltage charging means in response to the voltage being reached;
Means for terminating charging by the constant voltage charging means and starting charging by the second constant current charging means in response to the charging current becoming the third charging current during charging by the constant voltage charging means; Means for stopping charging when the battery voltage reaches the first charging voltage during charging by the constant current charging means.

[0009] With this configuration, full charge can be performed safely and reliably in a short time with a simple circuit without detecting a minute charge termination current.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS.

(Embodiment) An embodiment of the present invention relates to a charging apparatus which performs constant current charging up to a charging completion voltage, further performs constant voltage charging at a charging completion voltage, and further performs constant current charging at a charging completion current. is there.

FIG. 1 is a functional block diagram showing a configuration of a charging apparatus according to an embodiment of the present invention. In FIG. 1, a charger 11 is a device external to a mobile phone, and is a charging unit having a constant current circuit. Charge voltage control circuit 12
Is a means for keeping the charging voltage constant during constant voltage charging. The charging current detection resistor 13 is a minute resistor for detecting a charging current. The CPU 14 is an arithmetic unit that controls a charging operation by a program. The charge control circuit 15 includes a CP
This is a circuit for controlling the charging operation under the control of U14. The mobile phone main body circuit 16 is a circuit for a call other than the charge control. Battery 17 is a lithium ion secondary battery. The voltage detection circuit 18 is a circuit that detects the voltage of the battery 17. The constant current circuit 19 is a circuit that performs constant current charging with a charge completion current value.

FIG. 2 is a flowchart showing the operation of the charging apparatus according to the embodiment of the present invention. FIG. 3 is a diagram showing time-series changes in battery voltage and charging current of the charging device according to the embodiment of the present invention.

The operation of the charging apparatus according to the embodiment of the present invention configured as described above will be described with reference to FIGS. In the first constant current charging 1 shown in FIG. 3 of this example, the charging is performed with the rated charging current Is until the charging completion voltage Voff, which is the rated charging voltage, is reached. In the next constant voltage charging, constant voltage charging is performed at the charging completion voltage Voff. When the charging current becomes (charging completion current Ioff + detection error current Ierror), the constant voltage charging is completed. In the last constant current charging 2, constant current charging is performed with the charging completion current Ioff.
The charging is completed when the voltage reaches the charging completion voltage Voff.

In STEP 1 of FIG. 2, the fact that the portable telephone has been connected to the charger 11 is transmitted via the charge control circuit 15 to the CP.
U14 detects and starts the charging operation. In STEP 2, the charge control circuit 15 operates under the control of the CPU 14, and makes the charge voltage control circuit 12 conductive. The constant current charging 1 is started by the constant current circuit of the charger 11 at the rated charging current Is.

In STEP 3, the charge control circuit 15 monitors the battery voltage via the battery voltage detection circuit 18. The voltage of the battery 17 is compared with the charging completion voltage Voff, and the constant current charging 1 is continued until the voltage of the battery 17 exceeds the charging completion voltage Voff. When the voltage of the battery 17 exceeds the charging completion voltage Voff, S
Proceed to TEP4.

In STEP 4, the CPU 14 switches the charge voltage control circuit 12 from the conductive state to the constant voltage state via the charge control circuit 15, and terminates the constant current charging 1. The charge control circuit 15 and the charge voltage control circuit 12 control the charge voltage to a constant charge completion voltage Voff to start constant voltage charge. Up to this point, it is the same as the conventional charging method.

In STEP 5, the current charged in the battery 17 is detected by the charging current detecting resistor 13. The CPU 14 controls the charge interruption current value (charge completion current value Ioff +
The error current value Ierror) is compared with the detected current value. The error current value Ierror is the sum of errors in the charging current detection circuit and errors in the A / D converter. Since the charge interruption current value is not a very small current and does not need to be measured accurately, a simple measurement circuit is sufficient as a circuit for measuring the charge interruption current value. The charging current is the charging interruption current value (Ioff + Ierr
or) If it becomes smaller, go to STEP6. It is to be noted that the detection that the charging current has reached the charging interruption current value is as follows.
Hardware detection means may be used.

In STEP 6, the CPU 14 turns off the charging voltage control circuit 12 and terminates the constant voltage charging. Thereafter, the constant current circuit 19 is activated, and constant current charging 2 is started. The battery 17 is charged at a constant current with the charge completion current Ioff. The constant current circuit 19 is a constant current circuit that accurately outputs a small charge completion current Ioff, but can be realized by a relatively simple circuit. In STEP 7, the CPU 14 obtains the battery voltage by the battery voltage detection circuit 18 and the charge control circuit 15, and compares the battery voltage with the charge completion voltage Voff. Since this circuit can use the same circuit as the constant current charging 1, the circuit configuration is simplified. The constant current charging 2 is continued until the battery voltage exceeds the charging completion voltage Voff. When the battery voltage exceeds the charging completion voltage Voff, the process proceeds to STEP8. In STEP 8, the constant current circuit 19
Is stopped to complete the charging operation.

As described above, in the embodiment of the present invention,
The charging device is configured to perform constant current charging up to the charging completion voltage, perform constant voltage charging at the charging completion voltage, and perform constant current charging at the charging completion current. .

[0021]

As is apparent from the above description, according to the present invention, the battery charger is charged by the voltage detecting means for detecting the battery voltage, the current detecting means for detecting the charging current, and the first charging current. A constant current charging means, a constant voltage charging means for charging with a first charging voltage, a second constant current charging means for charging with a second charging current, and a charge control means, wherein the charge control means is a mobile phone Means for detecting that the battery has been connected to the charger and starting charging with the first constant current charging means, and responding to the fact that the battery voltage has reached the first charging voltage during charging with the first constant current charging means. Means for terminating the charging by the first constant current charging means and starting charging by the constant voltage charging means, and determining whether the charging current becomes the third charging current during charging by the constant voltage charging means. End charging by voltage charging means and start charging by second constant current charging means And a means for stopping charging when the battery voltage reaches the first charging voltage during charging by the second constant current charging means, so that a minute charging termination current is detected. The effect of being able to fully charge in a short time with a simple circuit is obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a charging device according to an embodiment of the present invention;

FIG. 2 is a flowchart showing the operation of the charging device according to the embodiment of the present invention;

FIG. 3 is a diagram showing a relationship between a battery voltage, a charging current, and time of the charging device according to the embodiment of the present invention.

[Explanation of symbols]

 11 Charger 12 Charge voltage control circuit 13 Charge current detection resistor 14 CPU 15 Charge control circuit 16 Mobile phone body circuit 17 Battery 18 Battery voltage detection circuit 19 Constant current circuit of charge completion current value

Claims (3)

[Claims] 1. A voltage detecting means for detecting a voltage of a secondary battery to be charged, a current detecting means for detecting a charging current, a first constant current charging means for performing a constant current charging with a first charging current, and a first constant current charging means. Constant voltage charging means for performing constant voltage charging with a charging voltage; second constant current charging means for performing constant current charging with a second charging current; and charging control means. Means for detecting connection and starting charging by the first constant current charging means; and responding to the fact that the battery voltage has reached the first charging voltage during charging by the first constant current charging means. Means for terminating the charging by the first constant current charging means and starting charging by the constant voltage charging means, and responding to the fact that the charging current has become the third charging current during the charging by the constant voltage charging means. To terminate the charging by the constant voltage charging means and Charging means for initiating charging at a stage and means for stopping charging in response to the battery voltage reaching the first charging voltage during charging by the second constant current charging means. apparatus. 2. The secondary battery is a lithium ion secondary battery, the first charging current is a rated charging current of the lithium ion secondary battery, and the first charging voltage is a lithium ion secondary battery. And the rated charging voltage of the second
The charging current is a charging completion current value of the lithium ion secondary battery, and the third charging current is a sum of the second charging current and a maximum value of an error current caused by a device error. The charging device according to claim 1. 3. A constant current charge is started at the maximum allowable charging current by detecting that the mobile phone is connected to the charger, and the constant current charging is terminated when the battery voltage is detected to be the maximum allowable charging voltage. The constant voltage charging is started at the maximum allowable charging voltage, and when it is detected that the charging current has reached the sum of the charging completion current value and the error current value, the constant voltage charging is terminated and the charging completion is completed. A method of charging a lithium ion secondary battery, comprising: starting constant current charging at a current value; and stopping constant current charging when detecting that the battery voltage has reached the maximum allowable charging voltage.