JPH04165928A - Detecting circuit for charging condition of secondary battery - Google Patents

Abstract

PURPOSE:To enable charging of a battery to be controlled fully even if an A/D conversion circuit with a low resolution and small number of bits is used by detecting time required for the A/D converted voltage data to be changed to a specified value and then by detecting charging state of a secondary battery according to increase and decrease of the time. CONSTITUTION:An A/D converter 2 converts a voltage of a secondary battery 7. A timer 3 measures time required for the voltage of the secondary battery to be changed by a specified amount under control of a CPU 1. A RAM 6 stores time required for the output data of the A/D converter 2 to be changed by a specified amount. The CPU 1 checks time required for the battery voltage to be increased by a specified amount instead of the amount of change of the battery voltage and then determines that the secondary battery 7 was fully charged when the obtained time becomes longer than a previously obtained time, thus enabling charging to be stopped without exceeding a complete full charging (point of voltage peak).

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a secondary battery charge state detection circuit suitable for use particularly in a battery-powered laptop personal computer.

(Prior Art) In the field of personal computers, laptops, which are small, lightweight, and convenient to carry, have become popular in place of conventional desktops, and are becoming mainstream as low-end machines. This type of personal computer can generally be driven by a secondary battery, and its power supply is controlled by a one-chip microcomputer installed independently of the main unit.

Conventionally, when controlling the charging of a secondary battery using a microprocessor, etc., the voltage of the secondary battery is measured at predetermined intervals.
When checking whether the secondary battery is fully charged, check that this amount of change is gradually decreasing. If the secondary battery is detected to be fully charged, processing such as stopping charging is performed.

(Problem to be Solved by the Invention) According to the conventional example described above, when the battery is near full charge, the amount of change in the battery voltage of the secondary battery is small, so high accuracy (ILS) is not achieved.
The disadvantage is that the voltage per B is small, and voltage changes cannot be detected without using an expensive A/D conversion circuit. For this reason, it has been difficult to employ this type of secondary battery control circuit in laptop-type personal computers that aim to be low-cost.

The present invention has been made in view of the above-mentioned circumstances, and provides a secondary battery that can control charging of the battery without any trouble even when using an A/D conversion circuit with relatively low accuracy and a small number of bits. The purpose of the present invention is to provide a charging state detection circuit.

"Structure of the Invention" (Means for Solving the Problems) In order to achieve the above object, a charging state detection circuit for a secondary battery according to the present invention includes a charging circuit for charging a secondary battery;
an A/D converter that detects the voltage of the secondary battery, converts the detected value from analog to digital, and outputs digital data;
A timer for measuring time and a time required for the output data of the A/D converter to change by a predetermined value are detected by the timer, and the state of charge of the secondary battery is detected by an increase or decrease in the detected time. A detection unit is provided.

(Function) In the above-described configuration, the detection section detects the state of charge of the battery by checking the A/D converted voltage, and stops charging by the charging circuit when the battery is fully charged, for example. The data used to detect the state of charge is not data directly indicating a change in battery voltage, but the time required for the output data of the A/D converter to rise by a predetermined value, for example, 1 LSB.

For example, depending on the charging characteristics of the battery, when the time required for the voltage value to rise by a predetermined amount becomes long, it is determined that the battery is almost fully charged, and charging is stopped.

This makes it possible to accurately control battery charging using hardware with relatively low precision (relatively high voltage value per 1, L S B).

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings. FIG. 1 is a block diagram showing a charging system according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 is a CPU, which starts charging by a constant current charging circuit 4 by controlling an A/D (anacotic/digital) converter 2 and other peripheral devices according to a program stored in a ROM 5. and control the stop. .

Reference numeral 2 is an A/D converter, which converts the voltage of the secondary battery 7 into A/D converter.
D-convert. η 3 is a timer that measures the time required for the voltage of the secondary battery to change by a predetermined amount under the control of the CPU. Reference numeral 4 denotes a constant current charging circuit, which receives power from the outside and charges the secondary battery 7. Reference numeral 5 denotes a ROM in which, for example, a charging control program whose control procedure is shown in FIG. 2 is stored. Reference numeral 6 is a RAM that stores data. In particular, in this embodiment, the RAM
6, the output data of the A/D converter 2 is a predetermined ffi (I
LSB (1 digit)) Stores the time required to change. Reference numeral 7 denotes a secondary battery, which is charged by the constant current charging circuit 4. The secondary battery 7 serves as a power source for supplying operating power and backup power to each block shown in FIG.

= 5- FIGS. 2 and 3 are diagrams for explaining the operation of the system shown in FIG. 1, and are a flowchart showing the operation of this embodiment and a graph showing the charging characteristics of the battery, respectively.

Hereinafter, the operation of the charging system shown in FIG. 1 will be described in detail with reference to the drawings.

First, the CPU instructs the constant current charging circuit 4 to charge, starts charging the secondary battery 7, and starts the timer 3 (step S]-).

The A/D converter 2 A/D converts the voltage of the secondary battery 7, and converts the voltage of the secondary battery 7 into C
Supply to PUI. The CPUI reads the output data of the A/D converter 2 (step S2).

The CPU reads the previous output data of the A/D converter 2 stored in the RAM 6 (which is saved in the RAM 6 in step S4, which will be described later, but is the initial setting data immediately after the start of charging), and outputs the current A/D converter 2. Compared with the output data of the D converter 2, the output data of the A/D converter 2 is L S 8
It is checked whether the amount has increased by the amount (step S3).

If there is no change in the output data of the A/D converter 2, the flow returns to step S2. - On the other hand, if the output data of the A/D converter 2 is higher than the previous output data by ILSB, the flow advances to step S4.

In step S4: - The CPUI stops timer 3. The time indicated by the timer 3 indicates the time required for the output data of the A/D converter 2 to rise by 1, LSB.

The CPUI stores the time indicated by the timer 3 and the output data of the A/D converter 2 in the RAM 6, resets the timer 3, and restarts the timer 3.

The charging characteristics of the secondary battery 7 are as shown in the graph shown in FIG. 3, for example. It can be determined that charging is almost complete. For this reason, C
In step S5, the PUI stores the current water-filled time and the time previously determined and stored in the RAM 6 in step S4.
Compare with. If the current immersion time is shorter than the previously determined time, the flow returns to step S2 and repeats the process described above. On the other hand, if the current immersion time is longer than the previously determined time, the flow advances to step S6.

In step S6, the CPUI stops the charging operation of the constant current charging circuit 4.

As explained above, the CPU checks not the amount of change in battery voltage (but the time tl, t2, etc. required for the battery voltage to rise by a predetermined amount), and checks the time required for the battery voltage to rise by a predetermined amount. It is determined that the secondary battery 7 is almost fully charged at the time when the time becomes longer than the time required for charging.Thereby, charging can be stopped without exceeding a completely full charge (voltage peak point).

In the above embodiment, the ILS of the output data of the A/D converter 2
I calculated the time required for the voltage of B to rise, but A/
The time required for the output data of the D converter 2 to change by 2LSB or more may be determined.

In the embodiment described above, it is detected that charging of the secondary battery 7 is almost completed when the calculated time becomes longer than the previously calculated time. The present invention is not limited thereto, and full charge can be detected by various methods depending on the charging characteristics of the secondary battery 7. For example, multiple times required for the voltage of the secondary battery to rise by 1, LSB are determined, and the determined times are expressed in a predetermined relationship (for example, tn-
2:tn-1:tn-1,+2:3), it is also possible to determine that the battery is fully charged. Also,
It is possible to arbitrarily change the charging of the secondary battery 7, for example, instead of stopping the charging of the secondary battery 7 immediately after a full charge is detected, the charging of the secondary battery 7 is stopped after a predetermined period of time has elapsed even after a full charge has been detected.

The CPU in FIG. 1 does not need to constantly execute the process shown in FIG. 2. For example, the CPU in FIG. 1 may perform the process shown in FIG. good. Moreover, C P'U 1 shown in FIG.
may be used exclusively for charge control or power supply control, and a separate CPU may be provided to perform main data processing.

In this embodiment, the case of detecting full charge of a secondary battery has been described as an example, but the present invention is not limited to this.
The present invention can be applied to any device that uses an A/D converter to detect changes in the voltage of a secondary battery or detects the inflection point of voltage changes.

[Effects of the Invention] According to the present invention, changes in battery voltage can be detected using hardware such as a relatively low-precision A/D converter, and battery charging and the like can be accurately controlled.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a flowchart for explaining the operation of the circuit shown in FIG. 1, and FIG. 3 is a diagram showing charging characteristics of a battery. 1... CPU, 2... A/D converter, 3... timer, 4... constant current charging circuit, 5... ROM, 6...
・Secondary battery, 7...RAM0 Applicant's agent Patent attorney Takeshi Suzuki 13 Figures 2 and 3

Claims (1)

[Claims] A charging circuit that charges a secondary battery, an A/D converter that detects the voltage of the secondary battery, converts the detected value from analog to digital, and outputs digital data; a timer that measures time; The battery is characterized by comprising a detection unit that detects the time required for the output data of the D converter to change by a predetermined value using the timer, and detects the state of charge of the secondary battery based on an increase or decrease in the detected time. A charging state detection circuit for a secondary battery.