JPH0831461A - Charger for lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide a charger for a lithium secondary battery having excellent properties of low cost and high precision which is capable of displaying charging quantity. CONSTITUTION:A charger is provided with fixed resistances 22, 23, 24 to separate a terminal voltage of a lithium secondary battery 21, switches 25, 26, an operation amplifier 27 to perform constant voltage control of the charger, a reference voltage source 28, and a changeable resistance 29 for fine adjustment of it. When the switches are switched in order in this constitution, two-stage constant voltage control is performed apparently, thereby by changing display at a point where a current starts decreasing, a high-precision charging quantity detection method without depending on fluctuation of the reference voltage can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charger used for charging a lithium secondary battery which has come to be used as a main power source of a VTR with a camera, and an AC adapter having a built-in charger. .

[0002]

2. Description of the Related Art In recent years, a rechargeable battery as a main power source of a VTR with a camera is shifting from a nickel-cadmium battery or a nickel-hydrogen battery to a lithium secondary battery because of a demand for smaller size and lighter weight.

A constant current / constant voltage system is used as a charge control system for a lithium secondary battery. Regarding constant voltage control, the control voltage value is closely related to the life of the lithium secondary battery. Therefore, it is controlled with high accuracy.

In a charger for a lithium secondary battery which performs such constant voltage control, a method for detecting and monitoring the charge amount is a lithium secondary battery in which the terminal voltage of the battery during charging / discharging changes substantially linearly. It uses the charging characteristics of.

A conventional lithium secondary battery charger having a charge amount display device will be described below.

FIG. 3 (a) is a circuit diagram of a conventional lithium secondary battery charger. In FIG. 3A, 1 is a lithium secondary battery, and 2 and 3 are fixed resistors for dividing the battery voltage. An A / D converter 4 detects a battery voltage. 5 is an operational amplifier for controlling the output of the charger at a constant voltage, 6
Is a reference voltage source for the constant voltage controller and the A / D converter. Reference numeral 7 is a variable resistor for finely adjusting the constant voltage control voltage value.

FIG. 3 (b) is a charging characteristic diagram of the lithium secondary battery having this structure. In FIG. 3B, 8
Is a charging current curve, and 9 is a charging voltage curve. 10 is a charge control current value, and 11 is a charge control voltage value. Reference numeral 12 is a threshold voltage for switching the charge amount display.

The operation of the lithium secondary battery charger with the charge amount display monitor constructed as described above will be described below.

The charging voltage of the lithium secondary battery is set to a resistance of 2 or 3
The voltage is divided by and the voltage at point a is input to the operational amplifier 5.

As the reference voltage input to the operational amplifier 5, the voltage at point a when the constant voltage control voltage value 11 is divided by the resistors 2 and 3 is input.

Since the accuracy of the voltage of the reference voltage source 6 usually has an error of about ± 5%, the input reference voltage is finely adjusted by the variable resistor 7 to obtain an accurate reference voltage.
The charging voltage of the lithium secondary battery is controlled to be constant (constant voltage control value 11) by taking the difference from the divided voltage value (point a) of the charging voltage.

In the conventional charger, the constant voltage control value is set to a constant value determined by the performance of the lithium secondary battery, and stable charging is performed without adversely affecting the durability of the rechargeable battery.

In a conventional lithium secondary battery charger, A
The voltage value at the point a obtained by dividing the charging voltage is input to the / D converter, the charge amount is detected by comparison with the voltage of the reference voltage source 6, and in FIG. When the voltage is reached, the indication of about 50% charging is displayed,
Further, when the charging voltage reaches the constant voltage control value 11, the charging amount is displayed so as to display that the charging is about 80% completed.

[0014]

However, in the above-mentioned conventional configuration, the accuracy of the charge amount display largely depends on the accuracy of the reference voltage source 6, so that if the voltage of the reference voltage source 6 has an error, accurate charging is performed. There was a problem that the quantity could not be displayed.

On the other hand, if the high-accuracy reference voltage source 6 is used to accurately display the charge amount, there is a problem that the charger with the charge amount display device becomes expensive.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an inexpensive and highly accurate lithium secondary battery charge amount display device.

[0017]

In order to achieve this object, a lithium secondary battery charger according to the present invention comprises a charging voltage control means for controlling the charging voltage of the lithium secondary battery to be constant, and the lithium secondary battery. And a charge amount display unit for switching the display of the charge amount of the lithium secondary battery based on the output of the detection unit.

The lithium secondary battery charger according to the present invention comprises voltage switching means for switching the charging voltage in multiple stages and charge amount display means for switching the display of the charge amount of the lithium secondary battery in multiple stages. Have.

[0019]

With the above structure, according to the present invention, lithium 2
Since the charge amount is displayed based on the decrease in the charge current when the charge voltage of the secondary battery becomes constant, the accurate charge amount can be displayed regardless of the accuracy of the reference voltage.

[0020]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 21 is a lithium secondary battery,
22 to 24 are fixed resistors, 25 and 26 are switches, 27 is an operational amplifier for constant voltage control of the charger output, 28 is a reference voltage source, and 29 is a variable resistor.

Numeral 40 is a detecting means for detecting a decrease in charging current. The operation of the lithium secondary battery charger with the charge amount display monitor configured as described above will be described with reference to FIG.

In FIG. 2, 30 is a charging current curve, and 31 is
Is the charging voltage curve. 32 is a charge control current value, and 33 is a charge control voltage value. Reference numeral 34 is a threshold voltage for switching the charge amount display.

First, the switch 25 is closed and the terminal voltage of the lithium secondary battery 21 is divided by the resistors 22 and 23, and the divided value is input to the constant voltage control operational amplifier 27. As the reference voltage of the operational amplifier 27, the charger output is lithium 2
Reference voltage source 2 so that the charge control voltage value of the secondary battery becomes 33
8 is finely adjusted by the variable resistor 29 and input.

The switch 25 is opened and the switch 26
The resistance value of the resistor 24 is set so that the constant voltage control value when the switch is closed becomes the threshold voltage 34 for switching the charge amount display.

The switch 26 is closed and the switch 25 is opened to start charging. When the terminal voltage of the lithium secondary battery rises to the threshold voltage 34 after the start of charging, the constant current charging is switched to the constant voltage charging, and the charging current starts to decrease.

When the detection means 40 detects that the charging current has begun to decrease, the charge amount display means (not shown) switches the charge amount of the lithium secondary battery.

When the detecting means 40 detects the decrease of the charging current and at the same time the switch 26 is opened and the switch 25 is closed, constant current charging is performed again, and when the terminal voltage of the lithium secondary battery 21 reaches the charge control voltage 33, The charging voltage becomes constant, the charging current begins to drop again, and charging is performed until the lithium secondary battery is fully charged.

In the case of the present embodiment, when the charging voltage reaches the threshold voltage 34 and the charging current decreases, the charging amount display means displays the charging amount of 50% and reaches the constant voltage control value 33. Sometimes it shows about 80% charge.

Further, it is possible to display the charge amount in three stages by displaying the charge amount of 100% at the time when an arbitrary fixed time has elapsed after reaching the constant voltage control value 33.

The characteristics of the charge amount detection method according to the present embodiment (voltage detection accuracy) and the characteristics of the conventional charge amount detection method (voltage detection accuracy) are shown in comparison with (Table 1). (Table 1) shows that when the charge control voltage is 8.4 V, the charge amount display switching threshold voltage is 8.0 V, and the reference voltage is 5 V, the resistance tolerance is ± 2% and the reference voltage tolerance is ± 2%. The variation of the threshold voltage (8.0 V) in the case of 5% is calculated by the root mean square method.

[0032]

[Table 1]

As is clear from (Table 1), the charge amount detecting method according to this embodiment has an excellent effect in that the voltage can be detected with high accuracy.

As described above, according to this embodiment, the charge amount of the lithium secondary battery can be detected and displayed with high accuracy without using an expensive reference voltage source.

[0035]

As described above, according to the present embodiment, since the charge amount is displayed based on the decrease of the charge current when the charge voltage of the lithium secondary battery becomes constant, the charge amount can be displayed with high accuracy. Can be displayed.

Since the detection of the charge amount does not depend on the comparison with the reference voltage, it is not necessary to use a highly accurate reference voltage,
A charge amount display device for a lithium secondary battery, which accurately displays the charge amount, can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a charger for a lithium secondary battery that is an embodiment of the present invention.

FIG. 2 is a charging characteristic diagram of the same embodiment.

3A is a circuit diagram of a charger for a conventional lithium secondary battery, and FIG. 3B is a charging characteristic diagram of a conventional lithium secondary battery.

[Explanation of symbols]

 1 Lithium secondary battery 2 Fixed resistance 3 Fixed resistance 4 A / D converter 5 Operational amplifier 6 Reference voltage source 7 Variable resistance 8 Charging current curve 9 Charging voltage curve 10 Constant current control current value 11 Constant voltage control voltage value 12 Charge amount display switching Threshold voltage 21 lithium secondary battery 22 fixed resistance 23 fixed resistance 24 fixed resistance 25 switch 26 switch 27 operational amplifier 28 reference voltage source 29 variable resistance 30 charging current curve 31 charging voltage curve 32 constant current control current value 33 constant voltage control Voltage value 34 Charge amount display switching threshold voltage 40 Charge current detection means

Claims (2)

[Claims] 1. A charging voltage control means for controlling the charging voltage of a lithium secondary battery to be constant, and a detecting means for detecting a decrease in charging current when the charging voltage of the lithium secondary battery is constant, A charger for a lithium secondary battery, comprising: a charge amount display unit for switching the display of the charge amount of the lithium secondary battery based on the output of the detection unit. 2. A charging voltage control means for controlling a charging voltage of a lithium secondary battery to be constant, a voltage switching means for switching the charging voltage in multiple stages, and a charging voltage of the lithium secondary battery being constant. Detecting means for detecting a decrease in the charging current of the lithium, and the lithium 2 based on the output of the detecting means.
A charger for a lithium secondary battery, comprising a charge amount display means for switching the display of the charge amount of the secondary battery in multiple stages.