Protection method, control circuit, and battery unit

Details Protection method, control circuit, and battery unit Protection method, control circuit, and battery unit

2000-03-17

2002-12-10

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

Regulated discharging

C320S118000, C320S134000, C320S136000, C324S433000

Reexamination Certificate

active

06492791

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a protection method, a control circuit, and a battery unit. More particularly, the present invention relates to a protection method for preventing batteries from over-discharging and being overcharged, and a control circuit and a battery unit both employed in said protection method.
In recent years, lithium ion (Li+) batteries have been replacing nickel-cadmium (NiCd) batteries and nickel-metal-hydrogen (NiMH) batteries in portable electronic devices such as notebook-type personal computers. Compared with the NiCd batteries and NiMH batteries, the Li+ batteries are lighter but have a larger capacity per unit volume. For this reason, the Li+ batteries are suitable for a device which is preferably light and required to endure continuous use for a long time.
In an over-discharged state, however, the Li+ batteries deteriorate rapidly. Therefore, the Li+ batteries need to be prevented from over-discharging.
2. Description of the Related Art
A battery unit used in a portable electronic device has a plurality of battery cells connected in series. The maximum number of battery cells connected in series in one battery unit is determined by the relationship between the output voltage of the battery unit and a power source voltage supplied from outside at the time of charging. For instance, the output voltage of one NiCd battery cell or one NiMH battery cell is 1.2 V, and the power source voltage supplied at the time of charging is approximately 1.7 V. Since a 16-V output voltage of a battery unit is the most suitable for a general purpose electronic device, the maximum number of NiCd or NiMH battery cells connected in series in the battery unit is 9. On the other hand, the highest possible output voltage of one Li+ battery cell is approximately 4.2 V. Accordingly, the maximum number of Li+ battery cells connected in series in one battery unit is 3.
Unlike a NiCd battery unit and a NiMH battery unit, the Li+ battery unit has a function to protect against short-circuiting inside and outside the Li+ battery unit. This prevents the Li+ battery unit from deteriorating and shortening its life. For instance, if short-circuiting occurs inside or outside the Li+ battery unit, a fuse cuts off an over-discharging current or overcharging current when the discharging current or charging current becomes larger than a predetermined current value. Thus, the LI+ battery unit is prevented from deteriorating and shortening its life.
FIG. 1
is a block diagram of an example battery unit of the prior art, and
FIG. 2
is a circuit diagram of a voltage monitor circuit of the example battery unit of the prior art.
In
FIGS. 1 and 2
, a battery unit
100
comprises battery cells E
1
, E
2
, and E
3
connected as shown in the figures, a voltage monitor circuit
101
, a fuse
102
, p-channel FETs
103
and
104
, and power supply terminals
105
and
106
.
The battery cells E
1
, E
2
, and E
3
are connected in series. The FET
103
is a charge control FET which functions as a charge control switch. The FET
104
is a discharge control FET which functions as a discharge control switch. The voltage monitor circuit
101
monitors the voltages of the battery cells E
1
, E
2
, and E
3
. In accordance with the respective voltages of the battery cells E
1
, E
2
, and E
3
, the voltage monitor circuit
101
switches on and off the FETs
103
and
104
.
As shown in
FIG. 2
, the voltage monitor circuit
101
comprises an overcharge monitor circuit
101
a
and an over-discharge monitor circuit
101
b
. The overcharge monitor circuit
101
a
monitors whether the battery cells E
1
, E
2
, and E
3
are in an overcharged state, and switches off the FET
103
when the battery cells are in an overcharged state. The over-discharge monitor circuit
101
b
monitors whether the battery cells E
1
, E
2
, and E
3
are in an over-discharged state, and switches off the FET
104
when the battery cells E
1
, E
2
, and E
3
are in an over-discharged state.
The overcharge monitor circuit
101
a
comprises comparators
121
,
122
, and
123
, reference power sources e
1
a
, e
1
b
, and e
1
c
, and an OR gate
124
.
The comparator
121
compares the voltage of the battery cell E
1
with a reference voltage Vref
1
generated by the reference power source ela. If the voltage of the battery cell E
1
is higher than the reference voltage Vref
1
, the comparator
121
outputs “1”. If the voltage of the battery cell E
1
is lower than the reference voltage Vref
1
, the comparator
121
outputs “1”. Here, “1” indicates that the output of a comparator is at the high logic level, and “0” indicates that the output of a comparator is at the low logic level. The comparator
122
compares the voltage of the battery cell E
2
with a reference voltage Vref
1
generated by the reference power source elb. If the voltage of the battery cell E
2
is higher than the reference voltage Vref
1
, the comparator
122
outputs “1”. If the voltage of the battery cell E
2
is lower than the reference voltage Vref
1
, the comparator
122
outputs “0”. The comparator
123
compares the voltage of the battery cell E
3
with a reference voltage Vref
1
generated by the reference power source e
1
c
. If the voltage of the battery cell E
3
is higher than the reference voltage Vref
1
, the comparator
123
outputs “1”. If the voltage of the battery cell E
3
is lower than the reference voltage Vref
1
, the comparator outputs “0”.
The outputs of the comparators
121
,
122
, and
123
are supplied to the OR gate
124
. The OR gate
124
performs an OR operation on the outputs of the comparators
121
,
122
, and
123
, and supplies a result of the OR operation to the gate of the FET
103
. If any of the outputs of the comparators
121
,
122
, and
123
is “1”, i.e., if any of the battery cells E
1
, E
2
, and E
3
is in an overcharged state and the signal supplied from the OR gate
124
to the gate of the FET
103
is “1”, the FET
103
is switched off so as to prevent overcharge.
The over-discharge monitor circuit
101
b
comprises comparators
111
,
112
, and
113
, reference power sources e
2
a
, e
2
b
, and e
2
c
, and an OR gate
114
.
The comparator
111
compares the voltage of the battery cell E
1
with a reference voltage Vref
2
generated by the reference power source e
2
a
. If the voltage of the battery cell E
1
is higher than the reference voltage Vref
2
, the comparator
111
outputs “0”. If the voltage of the battery cell E
1
is lower than the reference voltage Vref
2
, the comparator
111
outputs “1”. The comparator
112
compares the voltage of the battery cell E
2
with a reference voltage Vref
2
generated by the reference power source e
2
b
. If the voltage of the battery cell E
2
is higher than the reference voltage Vref
2
, the comparator
112
outputs “0”. If the voltage of the battery cell E
2
is lower than the reference voltage Vref
2
, the comparator
112
outputs “1”. The comparator
113
compares the voltage of the battery cell E
3
with a reference voltage Vref
2
generated by the reference power source e
2
c
. If the voltage of the battery cell E
3
is higher than the reference voltage Vref
2
, the comparator
113
outputs “0”. If the voltage of the battery cell E
3
is lower than the reference voltage Vref
2
, the comparator
113
outputs “1”.
The outputs of the comparators
111
,
112
, and
113
are supplied to the OR gate
114
. The OR gate
114
performs an OR operation on the outputs of the comparators
111
,
112
, and
113
, and supplies a result of the OR operation to the gate of the FET
104
. If any of the outputs of the comparators
111
,
112
, and
113
is “1”, i.e., if any of the battery cells E
1
, E
2
, and E
3
is in an over-discharged state and the signal supplied from the OR gate
114
to the gate of the FET
104
is “1”, the FET
104
is switched off so as to prevent over-discharge.
When a current larger than a certain current value flows, the fuse
102
fuses a

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