Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Patent
1999-07-22
2000-11-28
Wong, Peter S.
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
320164, 320166, 307 107, 324433, H02J 700, H02J 724, H02H 718, G01N 27416
Patent
active
061540099
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a power supply monitoring integrated circuit device (hereafter a "power supply monitoring IC") for monitoring the voltage of a lithium-ion cell or the like, and to a battery pack incorporating such a power supply monitoring IC.
BACKGROUND ART
A power supply monitoring IC monitors the voltage of a cell such as a lithium-ion cell and performs control operations necessary to prevent the cell from being brought into an overcharged or overdischarged state. For example, when the voltage of the cell becomes higher than an overcharge voltage, the power supply monitoring IC outputs a control signal to turn off a switching device connected in series with the cell, and thereby inhibits the charging of the cell. With a lithium-ion cell, the overcharge voltage is, for example, 4.2 V.
However, the voltage (i.e. the detected voltage) of the cell, when the cell is charged to close to the overcharge voltage, may temporarily exceed the overcharge voltage because of noise or the like. In such a case, if the power supply monitoring IC in response thereto immediately outputs the control signal, erroneous detection results. This makes it impossible to charge the cell so fully as to have a voltage close enough to the overcharge voltage, and thus causes the cell to last for an accordingly shorter length of time than it should. For this reason, as shown in FIG. 3, the power supply monitoring IC is provided with a non-responsive interval setting circuit for setting a non-responsive interval in which it does not respond to noise (i.e. the interval in which it does not output the control signal in response to noise). Thus, only when the detected voltage remains higher than the overcharge voltage for a longer period of time than the non-responsive interval, does the power supply monitoring IC output the control signal. In this way, erroneous detection is prevented.
In FIG. 3, a constant current source 1, which outputs a current 11, is connected through a switching device 2 to the base of a transistor 3c. When the voltage of the cell exceeds the overcharge voltage, a high-level signal S1 is applied to the switching device. When this signal S1 is applied to the switching device 2, the switching device 2 is turned off. As the switching device 2, a switching transistor or the like is used. The transistor 3c has its emitter connected to ground, and has its collector connected to the constant current source 4.
Between the collector of the transistor 3c and ground, a capacitor 5 for setting the non-responsive interval is connected. To detect the voltage across the capacitor 5, the non-inverting input terminal (+) of a comparator 6 is connected to the collector of the transistor 3c, and to the inverting input terminal (-) of the comparator 6 is fed a voltage higher than the ground level by a non-responsive interval setting voltage Vref.
According to this circuit configuration, when the voltage of the cell becomes higher than the overdischarge voltage, the signal S1 is fed. Then, the switching device 2 is turned off, and thus the transistor 3c is turned off. Then, the current I2 from the constant current source 4 is fed to the capacitor 5 to charge it. This causes the voltage Vc across the capacitor 5 to increase linearly. The comparator 6 compares this voltage Vc with a predetermined non-responsive interval setting voltage Vref, and outputs a high level if the voltage Vc is higher than Vref or a low level if the voltage Vc is lower than Vref.
Now, consider a case where noise happens to generate the signal S1. Then, the switching device 2 is turned off, and thus the transistor 3c is turned off. As a result, the capacitor 5 starts being charged. However, since noise usually lasts for a short period of time (i.e. is narrow in width), the signal S1 disappears in a moment, turning the switching device 2 and the transistor 3c on. Thus, the voltage Vc across the capacitor 5 does not become higher than the voltage Vref. This case is illustrated in FIG. 4. In FIG. 4, VH represents the overcharge vol
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patent: 5742148 (1998-04-01), Sudo et al.
Fujita Hiroyuki
Inoue Koichi
Rohm & Co., Ltd.
Toatley, Jr. Gregory S.
Wong Peter S.
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