Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Patent
1998-05-13
1999-08-31
Tso, Edward H.
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
320136, 320155, H01M 1046
Patent
active
059458100
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a battery protection circuit having a function for protecting rechargeable batteries such as lithium-ion cells against overcharge.
BACKGROUND ART
A lithium-ion power supply unit that employs lithium-ion cells as a power source (such a power supply unit is also called a "lithium-ion battery pack") usually incorporates a lithium-ion cell protection circuit for protecting the lithium-ion cells from overcurrent, overdischarge, and overcharge. A conventional lithium-ion power supply unit incorporating, for example, two serially connected lithium-ion cells and a lithium-ion cell protection circuit is constituted and operates as follows.
FIG. 4 is a block diagram of a conventional lithium-ion power supply unit having two lithium-ion cells connected in series. Numerals 101 and 102 represent lithium-ion cells. Numeral 103 represents a charge control FET (an n-channel field-effect transistor) for switching the state of the power supply unit between a state in which the lithium-ion cells 101 and 102 are charged and a state in which they are not charged. Specifially, when the FET 103 is on, the lithium-ion cells 101 and 102 are charged, and, when the FET 103 is off, they are not charged. Numeral 104 represents a charge control FET control circuit for turning on and off the charge control FET 103. Numerals 105 and 106 respectively represent a positive and a negative output terminal of the power supply unit. Numerals 107 and 108 represent resistors. Numeral 109 represents a chip capacitor provided as a capacitance element. Numeral 200 represents a lithium-ion cell protection circuit for protecting each of the lithium-ion cells 101 and 102 from overcharge. T1, T2, T3, T4, and T5 represent terminals of the lithium-ion cell protection circuit 200.
The higher-potential end of the series of the two lithium-ion cells 101 and 102 is connected to the positive terminal 105, and is also connected through the resistor 107 to the terminal T1. The node A between the two lithium-ion cells 101 and 102 is connected through the resistor 108 to the terminal T2. The lower-potential end of the series of the two lithium-ion cells 101 and 102 is connected through the FET 103 to the negative terminal 106, and is also connected to the terminal T3. Note that the terminal T3 is grounded within the lithium-ion cell protection circuit 200, and therefore the voltage at the lower-potential end of the series of the two lithium-ion cells 101 and 102 equals the ground level. The charge control FET control circuit 104 has its input connected to the terminal T4, and has its output connected to the gate of the charge control FET 103. The chip capacitor 109 has its one end connected to the terminal T5, and has its other end grounded.
The lithium-ion cell protection circuit 200 consists of an overcharge detection circuit 1 and a delay setting circuit 7. The overcharge detection circuit 1 is composed of two comparators 11 and 12, two constant voltage sources 13 and 14 whose output voltages are V.sub.ref1 and V.sub.ref2 respectively, and an OR circuit 15. The comparator 11 has its non-inverting input terminal (+) connected to the terminal T1, and has its inverting input terminal (-) connected to the higher-potential end of the constant voltage source 13, whose lower-potential end is connected to the terminal T2. The comparator 12 has its non-inverting input terminal (+) connected to the terminal T2, and has its inverting input terminal (-) connected to the higher-potential end of the constant voltage source 14, whose lower-potential end is grounded. The OR circuit 15 receives as its inputs the outputs of the comparators 11 and 12, and the output of the OR circuit 15 is used as the output of the overcharge detection circuit 1.
As a result of the above-described interconnection, the overcharge detection circuit 1 operates as follows. When the voltage across either of the lithium-ion cells 101 and 102 exceeds a predetermined voltage (the predetermined voltage is V.sub.ref1 for the lithium-ion cell 101 and V.su
Fujita Hiroyuki
Inoue Koichi
Rohm & Co., Ltd.
Tso Edward H.
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