JPH07110109B2 - Charger - Google Patents

Description

The present invention relates to a charging device for charging a secondary battery such as a nickel-cadmium battery used in a rechargeable electric shaver or the like.

(B) Prior art As a conventional example of a charging device that detects the slope of a charging time-battery voltage characteristic curve of a secondary battery and terminates charging based on the change in the slope, Japanese Patent Laid-Open No. 53-103544 discloses a method. Kaisho 54-158641
JP-A-56-25340.

Japanese Patent Laid-Open No. 53-103544 discloses a charging device in which a constant current is supplied to a storage battery via a switch to charge the storage battery, and the terminal voltage of the storage battery is sampled at a predetermined cycle. Is held in the holding circuit, the output voltage of the holding circuit is compared with the terminal voltage of the storage battery, and it is detected that the terminal voltage is lower than the output voltage of the holding circuit, and the switch is turned off. The charging is terminated by the above-mentioned method, and JP-A-54-158
In 641 publication, electric energy is supplied to a battery for charging, the battery characteristics that change according to the state of charge of the battery are monitored, and the change in the characteristics with time is analyzed, and at least one inflection point during the change. Is confirmed and the energy supply to the battery is controlled based on the above-mentioned occurrence. Further, in JP-A-56-25340, a proportional high voltage of the charging voltage of the battery to be charged is detected and stored. A detection circuit, a storage circuit that stores a proportional low voltage of the maximum voltage of the charging voltage, and a predetermined difference voltage between the output voltage of the detection circuit that decreases after the maximum voltage and the storage voltage of the storage circuit. A control circuit for stopping the charging of the battery and a holding circuit for holding the output voltage and the storage voltage in a constant relationship after the charging of the battery is stopped are provided.

By the way, in JP-A-53-103544 and JP-A-54-158641, a change in battery voltage during a predetermined time is detected when detecting a peak point or an inflection point of a characteristic curve. However, it is impossible for a normal charging device to detect a minute voltage change, and the detection accuracy at the end of charging is limited.

Further, in JP-A-56-25340, the maximum value of the battery voltage is stored by a voltage storage element, and if the charging is stopped when the battery voltage drops by a certain value from the maximum value, a large current is supplied to the battery for charging. If the battery is terminated in a short time, the battery may be overcharged, causing deterioration and damage.

(C) Problems to be Solved by the Invention A problem to be solved by the present invention is that the charging end time of the battery can be accurately detected, and the charging time is always constant regardless of the magnitude of the charging current and the number of batteries to be charged. -To stop charging the battery near the maximum voltage of the battery voltage characteristic curve.

(D) Means for Solving Problems The charging device of the present invention detects the battery voltage of the secondary battery being charged at any time, and counts the time required to increase the predetermined voltage from the previously detected battery voltage by the number R calculated as _0, to count the number R ₁ to which this count number R ₀ is calculated before a specific time, R ₀
When the relation of ≧ KR ₁ (K is a constant) is satisfied, the charging of the secondary battery is controlled.

(E) Action The time from the previous detection time when the battery voltage rises to the time when the predetermined voltage rises is recorded in a count display such as a counter. By comparing these counts, the slope between any two points on the battery charging time-battery voltage characteristic curve can be obtained.

(F) Embodiment Hereinafter, the charging device of the present invention will be described in detail according to an embodiment of the drawings.

FIG. 2 shows a schematic diagram of the circuit. (1) is 8 bits
Microcomputer, (2) ladder resistor circuit,
(3) is a charging power source that outputs a direct current, (4) is a comparator that compares the output of the charging power source (3) with the output from the ladder resistor circuit (2), and (5) is the charging A nickel-cadmium battery that is charged by a power source (3). The ladder resistance circuit (2) comprises a plurality of resistors (2R) connected to the output terminals of each bit of 0 to 7 of the microcomputer (1) and a plurality of resistors (2R) bridging between the resistors (2R). It consists of resistance (R), and one resistance (2R) of each bit0 is grounded. In addition, the comparator (4)
Is connected to the input terminal (IN) of the microcomputer (1), and the output terminal (OUT) of the microcomputer (1) is connected to the charging power source (3).

The resistance circuit (2) is the microcomputer (1).
The analog voltage value corresponding to the digital value output from each output bit is output to the non-inverting input terminal of the comparator (4) with an accuracy of 256 (= 2 ⁸ ) steps. In this way, by configuring the A / D conversion circuit by the ladder resistance circuit (2) and the comparator (4), the voltage of the battery (5) can be detected as a digital value.

When the battery (5) is fully charged, the microcomputer (1) outputs a control signal from its output terminal (OUT) to control the charging power supply (3) to supply the charging current to the battery (5). Stop.

Next, the operation of the above circuit, especially the microcomputer (1)
Operation of the charging time of the flow chart of FIG. 1 and FIG.
An explanation will be given based on the battery voltage characteristic diagram.

It is assumed that charging of the battery (5) is started at time T ₀ in FIG. The microcomputer (1) first clears the register R ₀ that records the current count number, and sets the registers R ₁ and R ₂ that store the count values of the previous and second counts to the maximum possible count value. And set it to a sufficiently large number (not shown in the figure). Simultaneously with this initialization, the value E ₀ of the battery voltage at time T ₀ is recorded as E _n-1 .

The register R ₀ to count up every time a lapse of a predetermined sampling time T _S (T or not _S elapsed) (R ₀ + 1 →
R ₀ ). Further, it is determined whether or not the value of the register R ₀ has become equal to twice the count value R ₁ one time before, and when R ₀ ≧ 2R ₁ , charging is stopped. If R ₀ ≧ 2R ₁ then 2 more
It is determined whether or not the value of the register R ₀ has become equal to twice the count value R ₂ before the count, and when R ₀ ≧ 2R ₂ , charging is stopped. When R ₀ ≥ 2 R ₂ is not satisfied Battery voltage recorded value E _n-1 and T
The voltage E _n after the passage of _S time is compared, and if the difference is not ΔE, the next sampling time T _S is executed. This operation is continued until the difference between the battery voltage stored value E _n-1 and the battery voltage E _n at each sampling satisfies E _n −E _n−1 ≧ ΔE. E ₁ -E ₀ = ΔE becomes at time T _1, to satisfy the _{E n -E n-1 ≧ ΔE} , the value of the register R ₀ at that time in R _1, the value of the register R ₁
The register R ₀ is rewritten to R ₂ to be cleared to 0, the battery voltage value E _n is recorded as E _n-1 , and sampling is started again. Then, the above series of operations is continued until the value of the register R ₀ is twice or more the value of the register R ₁ one time before or twice or more the value of the register R ₂ two times before.

In the characteristic diagram of FIG. 3, the battery voltages E _{0 to} E ₅ have an interval ΔE (V), and the charging times T _{0 to} T ₆ have a battery voltage ΔE.
(V) increments are shown, and the count numbers N _{0 to} N ₅ indicate the count numbers of the register R ₀ required to increment each by ΔE (V). For example, during the charging time T _{0 to} T ₁ , the fourth
As shown in the figure, sampling of the T _S time is performed N ₀ times, and N ₃ is set between each of T _{3 to} T ₄ , T _{4 to} T ₅ , T _{5 to} T ₆ as shown in FIG. , N ₄ , N ₅ times. Comparing the sizes of N _{1 to} N ₅ here, the slope of the battery voltage characteristic curve (6) gradually increases until time T ₅ (that is, the count number decreases).
Since the slope becomes smaller after T ₅ (that is, the count number increases), (a) N ₃ <2N ₂ , N ₃ <2N ₁ (b) N ₄ <2N ₃ , N ₄ <2N ₂ (c) The relations of N ₅ ≧ 2N ₄ and N ₅ <2N ₃ are satisfied. That is, at time T ₆ , the count number N ₅ at that time becomes twice the count number N ₄ one time before, and the charging is stopped.

This means that the slope of the battery voltage characteristic, which had been increasing up to a certain point, becomes smaller (the number of counts increases) after that point, which means that the number of counts required to increase the battery voltage by ΔEV It is suggested that the charging is terminated when the inclination is detected by the change and becomes sufficiently gentle after the maximum value of the battery voltage characteristic.

(G) Effect of the Invention As described above, the present invention detects the battery voltage of the rechargeable secondary battery at any time, and calculates the time required to increase the predetermined voltage from the previously detected battery voltage as the count number R _0. However, when the count number R ₀ satisfies the relationship of R ₀ ≧ KR ₁ (K is a constant) with respect to the count number R ₁ calculated before the specific number of times, charging is performed by controlling the charging of the secondary battery. It is possible to accurately detect the end-of-charge state regardless of the magnitude of the current or the number of rechargeable batteries to be charged, and moreover, the voltage rises by a certain amount as compared to the conventional method of obtaining the slope by increasing the battery voltage per predetermined time. The counting of the time required for can easily improve the accuracy of the tilt measurement by making the counting cycle as small as possible.

Further, by adopting R ₀ ≧ KR ₁ as a criterion for the charge control, if the value of K is appropriately set, it is possible to charge the battery as close to full charge as possible.

[Brief description of drawings]

FIG. 1 is a flow chart showing the operation of the charging device of the present invention, FIG. 2 is a circuit diagram of the same embodiment, FIG. 3 is a charging time-battery voltage characteristic diagram, and FIGS. 4 and 5 are the main parts of FIG. FIG. (5) …… Battery, (6) …… Charging time-battery voltage characteristic curve, (ΔE) …… Predetermined voltage, (R ₀ ) (R ₁ ) (R ₂ ) …… Count value.

Claims (2)

[Claims] 1. A battery voltage of a secondary battery which is being charged is detected at any time, and a time required for increasing a predetermined voltage from a previously detected battery voltage is calculated as a count number R _0.
R ₀ ≥ KR ₁ against the count R ₁ calculated before R ₀
A charging device which controls the charging of the secondary battery when a relationship (K is a constant) is satisfied. 2. The count number R ₀ is R ₀ ≧ K ₁ R ₁ with respect to the count number R ₁ calculated last time and the count number R ₂ calculated _two times before.
The charging according to claim 1, wherein the charging of the secondary battery is controlled when a relationship of (K ₁ is a constant) or R ₀ ≧ K ₂ R ₂ (K ₂ is a constant) is satisfied. apparatus.