JPH11168841A - Secondary battery voltage monitor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery voltage monitor circuit which is capable of accurately checking the voltage of a lithium ion secondary battery for memory backup. SOLUTION: A memory backup circuit employs a lithium ion secondary battery 1 which is charged with a constant voltage. At that time, a voltage detection circuit 3 which cuts off a charging circuit by a switching circuit 2, when a reset signal /RES is generated immediately after a power supply is closed and detects the voltage of the lithium ion secondary battery only during the reset time is made to operate. The result of the voltage detection is held in a flip-flop FF4 at the time of the reset release as information for an alarm ALM.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for monitoring the state of charge of a lithium ion secondary battery used for memory backup of FA equipment and the like.

[0002]

2. Description of the Related Art Conventionally, lithium ion secondary batteries have been frequently used as power supplies for Vcc and DC / DC converters in small devices such as cellular phones, video cameras, and notebook personal computers. Since there are many cases where a lithium ion primary battery is used, there has been almost no record of a secondary battery. However, if such a rechargeable lithium ion secondary battery is used as a memory backup battery, a backup voltage generation circuit as shown in FIG. 3 can be assumed. In this case, what should be noted in the use of the lithium ion secondary battery is that overcharging and overdischarging of the battery must be avoided since the deterioration of the battery is accelerated. Therefore, constant voltage charging using a constant voltage diode or the like is performed. As a constant voltage charging circuit,
For example, in the circuit of FIG. 3 which is a conventional memory backup circuit, the power supply voltage Vcc of the device is supplied to the power supply Vmm of the memory performing battery backup through the diode D1 for preventing backflow, and at the same time, the charging input voltage Vref is Zener-controlled by Vcc. A constant voltage is generated by a diode ZD, and this constant voltage is passed through a current limiting resistor R and a diode D2 for preventing backflow.
To supply. In addition, the voltage of the lithium ion secondary battery E is supplied to a memory power supply Vmm by a diode D3 for preventing backflow.
Is supplied through. For battery voltage detection,
Although not shown, a configuration in which a battery voltage obtained by dividing a resistance is detected by a voltage detector is conventionally used.

[0003]

However, in the above-mentioned conventional example, the lithium ion secondary battery E is always charged at a constant charging input voltage Vref, and therefore, even if the battery voltage is detected after the power is turned on. Since the battery has already been charged and the battery voltage is constant and the battery voltage cannot be measured immediately before turning on the power, it cannot be clearly determined whether the memory was backed up normally.
There was a problem. Further, the voltage detection circuit of the battery has a problem that the consumption of the battery is expedited because the current flowing through the voltage dividing resistor for detection is considerably increased. Thus, the present invention provides a secondary battery capable of accurately detecting the battery voltage of a lithium ion secondary battery used for memory backup, reducing the consumption of the battery by detecting the battery voltage, and configuring a highly reliable memory backup. It is intended to provide a battery voltage monitoring circuit.

[0004]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a memory backup circuit using a lithium ion secondary battery for performing constant voltage charging, wherein a reset signal is generated immediately after power is turned on. The charging circuit is occasionally shut off, and the voltage detection circuit for detecting the voltage of the lithium ion secondary battery is operated only during the reset time, and the result of the voltage detection is retained when the reset is released. According to the above configuration, the charging is stopped by the signal for resetting the system at the time of turning on the power, the battery voltage is detected by operating the voltage detection circuit during this time, and the charging is restarted by holding the detected voltage value. Thus, only the battery voltage value can be accurately detected. Then, the battery consumption due to the detection occurs only at the moment when the reset period voltage detection circuit is operating.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a secondary battery voltage monitoring circuit according to an embodiment of the present invention. FIG. 2 is an operation explanatory diagram of the voltage detection circuit shown in FIG. In FIG. 1, when the circuit constitutes a charging system for the lithium ion secondary battery 1, a charging input voltage Vref is supplied to the lithium ion secondary battery from the backflow prevention diodes D1 and Vcc which supply Vcc to the memory power supply Vmm. Current limiting resistor R, Zener diode ZD, backflow prevention diode D2, and backflow prevention diode D3 for supplying the output of lithium ion secondary battery to memory power supply Vmm are the same as those of the conventional circuit shown in FIG. Configuration. In the present embodiment, as the battery voltage monitoring system, a switch circuit 2 that cuts off the charge input voltage Vref to the lithium ion secondary battery 1 by the reset input / RES is provided. This switch circuit 2 includes a transistor, an FET,
It is composed of a switch such as a semiconductor switch such as a thyristor or an optical switch. Further, in conjunction with the switching operation of the switch circuit 2, a voltage detection circuit 3 which operates when charging of the lithium ion secondary battery is cut off is connected to one end of the switch circuit 2. Although the details of the voltage detection circuit 3 are not shown, the voltage detection circuit 3 includes a voltage dividing resistor, a voltage detector, a comparator, and the like as in the conventional example. The lithium ion secondary battery 1 detected by the voltage detection circuit 3
And a flip-flop FF4 for holding the battery voltage value of. Next, the operation will be described. When the main power is turned on and Vcc is applied, the backup system is reset by the reset signal / RES. The switch circuit 2 is operated by the reset signal / RES, and the charge input voltage Vref and the lithium ion secondary battery 1 are cut off.
The lithium ion secondary battery is switched to the voltage detection circuit 3 side. The detection value obtained by dividing the voltage by the voltage dividing resistor of the voltage detection circuit 3 is used as the capacity voltage of the lithium ion secondary battery 1 and compared with a reference voltage value created by a zener diode or the like by a comparator (not shown). The value is lower than the reference value, that is, the lithium ion secondary battery 1
If the remaining capacity voltage is lower than the charging set voltage, an alarm signal ALM is issued. The alarm signal ALM is stored in the flip-flop FF4 and used for an alarm or an alarm display. If the remaining capacity voltage is equal to or higher than the reference voltage value, it is stored as a normal value in the flip-flop FF4 and used as a reference value. In this case, the switch circuit 2 is actuated by the system reset signal / RES to shut off the charging circuit, and the voltage is detected in the state where the diode D3 prevents backflow to the memory power supply Vmm. The battery voltage of the secondary battery 1 can be detected. The battery voltage detection operation described above is performed during the short period of the reset pulse / RES, and when / RES returns, the switch circuit 2 again switches the lithium ion secondary battery 1
Side, and the system returns to the normal constant voltage charging system. That is, “the main power supply of the device is OFF → main power supply O
The sequence of “N, system reset / RES → main power ON” is the sequence of the secondary battery voltage monitoring system.
Therefore, the detection current of the battery consumed by the voltage detection circuit 3 is limited to a short period and is greatly reduced. Note that the voltage detection circuit 3 is only required to be able to detect the battery voltage in any configuration other than that shown in FIG. Thus, the configuration may be such that the battery voltage is converted and calculated by A / D converting and counting the divided voltage value. FIG. 3 is a time chart showing the voltage monitoring operation of the lithium ion secondary battery 1 described with reference to FIG. 2, and the time t0 on the horizontal axis represents the reset point of the reset pulse / RES shown in FIG. ing. The voltage detecting operation of the lithium ion secondary battery 1 by the voltage detecting circuit 3 is performed before the time t0, and the detection result is that the flip-flop FF4 is activated at the time t0, that is, at the rising edge of the arrow at which the reset pulse / RES returns. And hold. Also, after time t0, the switch circuit 2 is switched to the charging side, and charging of the lithium ion secondary battery 1 by the charging input voltage Vref is started. In the above, the present invention has been more effectively implemented using the reset pulse / RES. However, the present invention is not limited to this, and may be implemented using, for example, a power-on signal. Further, the holding operation of the flip-flop FF4 is set at the rising point of the reset pulse / RES, but may be performed at any time after the voltage detecting operation is completed. Furthermore, so far,
The voltage monitoring circuit in which a single battery such as the lithium ion secondary battery 1 is applied to the memory backup has been described. However, a plurality of such lithium ion secondary batteries are connected in series or in parallel, so-called In the case of a battery pack, the invention can be applied to each individual battery. For example, when two lithium ion secondary batteries having a nominal voltage of 3.6 V are connected in series with two batteries A and B to obtain a voltage of 7.2 V, a voltage monitoring circuit of 3.6 V is arranged for each of the batteries A and B. Check individually, plus a total of 7.
In this configuration, a 2V voltage monitoring circuit is added. This method also incorporates nearly 100 nominally 3.6V lithium-ion secondary batteries and charges a lithium-ion secondary battery for electric vehicles that constitutes a large assembled battery of several hundred volts in total to drive the motor. There is a possibility that the range of use can be expanded to systems and the like.

[0006]

As described above, according to the present invention,
In a memory backup circuit using a lithium ion secondary battery that performs constant voltage charging, the charging circuit is shut off when a reset signal is generated immediately after power-on, and voltage detection that detects the voltage of the lithium ion secondary battery only during the reset time Since the circuit is operated to hold the result of voltage detection when the reset is released, charging can be stopped when the power is turned on. During this time, the voltage detection circuit is operated to measure the voltage of only the lithium ion secondary battery. After that, charging can be restarted, accurate battery voltage of the lithium ion secondary battery can be detected, and unnecessary consumption of the lithium ion secondary battery at the time of voltage detection can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a secondary battery voltage monitoring circuit according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the voltage detection circuit shown in FIG. 1;

FIG. 3 is a configuration diagram of a conventional memory backup circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Lithium ion secondary battery 2 Switch circuit 3 Voltage detection circuit 4 Flip-flop FF Vcc Main power supply Vmm Memory power supply D1, D2, D3 Backflow prevention diode R Current limiting resistor ZD Zener diode / RES Reset input Vref Charge input voltage ALM alarm signal

Claims (1)

[Claims] In a memory backup circuit using a lithium-ion secondary battery that performs constant-voltage charging, the charging circuit is shut off when a reset signal is generated immediately after power-on, and the voltage of the lithium-ion secondary battery is maintained during the reset time. A secondary battery voltage monitoring circuit characterized by operating a voltage detection circuit for detecting a voltage, and holding a result of the voltage detection when the reset is released.