Secondary battery protection circuit

Details Secondary battery protection circuit Secondary battery protection circuit

1999-08-30

2001-09-04

Wong, Peter S. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

With charging

Reexamination Certificate

active

06285165

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a secondary battery protection circuit, and more particularly, to a secondary battery protection circuit that permits charging of a secondary battery even when the secondary battery has fully discharged.
2. Description of the Related Art
Compared to the conventional nickel-cadmium storage battery or nickel-hydrogen storage battery, the light, compact lithium-ion battery that is one type of secondary battery delivers approximately three times as much operating voltage. The power, lightness and compactness of the lithium-ion battery has led to its widespread use in video cameras, portable telephones, PHS, lap-top personal computers and a wide array of other portable electronic equipments.
In order to ensure the safety and enhance the performance of these light but powerful batteries, protection circuits have been used.
FIG. 3
shows a circuit for driving a charge control circuit in a conventional lithium battery protection circuit. Between a terminal {circle around (
1
)} and a terminal {circle around (
2
)} a lithium-ion battery
1
to be charged is connected. Between a terminal {circle around (
3
)} and a terminal {circle around (
5
)} a battery charger
2
for charging a lithium-ion battery
1
is connected and charges the lithium-ion battery
1
. The actual charging of the lithium-ion battery
1
is carried out under the control of the charge control circuit
9
.
The circuit that drives the charge control circuit
9
includes a transistor
3
, a transistor
4
, a resistor
5
and a controller
6
. The transistor
3
is provided for charge control drive, and is connected in parallel to a power line
7
that connects the lithium-ion battery
1
and the battery charger
2
. The emitter of the transistor
3
is connected to the power line
7
, and the base of the transistor
3
is connected to the power line
7
via the resistor
5
. The collector of the transistor
4
is connected to a node which connects the base of transistor
3
and the resistor
5
. The emitter of transistor
4
is grounded. To the base of transistor
4
the controller
6
is connected, and to the controller
6
the charging terminal {circle around (
5
)} is connected.
A description will now be given of the charging operation. The negative potential of the battery charger
2
is applied to the base of transistor
4
as a positive potential via the controller
6
. As a result, when the transistor
4
is turned ON a current I
0
flows. A voltage drop is generated across both ends of the resistor
5
by the current I
0
and the base of transistor
3
is forward biased, turning ON the transistor
3
. When the transistor
3
is turned ON a positive gate signal is output from the collector of the transistor
3
. This gate signal is applied to the charge control circuit
9
to drive the charge control circuit
9
and begin charging the lithium-ion battery
1
.
However, the conventional circuit as depicted in
FIG. 3
requires the transistor
3
to be turned ON in order to drive the charge control circuit
9
. Further, in order to drive this transistor
3
it is necessary to turn ON the transistor
4
. Moreover, in order to turn ON the transistor
4
the collector-emitter voltage required to turn ON the transistor
4
must be applied between the collector and the emitter.
In order to achieve the activations described above, the lithium-ion battery
1
must retain the collector-emitter voltage necessary to turn ON the transistor
4
. However, if the lithium-ion battery
1
is almost completely discharged then the residual voltage of the battery is not enough to turn ON the transistor
4
. In that case the transistor
4
cannot be turned ON and, accordingly, the transistor
3
also cannot be turned ON. As a result, no drive signal can be output from the collector of the transistor
3
to the charge control circuit
9
.
It is possible to charge the lithium-ion battery
1
even when the residual voltage of the battery is 0 V if a circuit configuration like that shown in
FIG. 4
is used. In that case, connecting a battery charger
2
between a terminal {circle around (
3
)} and a terminal {circle around (
5
)} causes a current I
1
to flow, a transistor
3
is turned ON by a voltage drop across the resistor
5
, a positive drive signal is obtained from the collector of the transistor
3
and a drive signal can be applied to the charge control circuit
9
.
However, the circuit described above consumes power. When the battery charger
2
is connected between the terminals {circle around (
3
)} and {circle around (
5
)}, the current I
1
, flows through resistors
5
and
8
such that a power described by formula (1) is consumed, where R
5
is the resistance of resistor
5
and R
8
is the resistance of resistor
8
.
I
1
2
(
R
5
+R
8
)  (1)
It should be noted that the circuit shown in
FIG. 4
can still operate even if the resistor
5
is removed, although the same problem of power consumption remains due to the operation of resistor
8
.
It is possible to externally connect a logic circuit on the protection circuit so as to obtain a positive drive signal from the collector of the transistor
3
even when the residual voltage of the lithium-ion battery
1
to be charged is 0 V. However, in that case the scale of the circuit increases substantially.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a secondary battery protection circuit in which the problems described above are solved.
In particular, it is an object of the present invention to provide a secondary battery protection circuit comprising a limited number of structural elements and consuming a reduced amount of power, and which is capable of charging a battery such as a lithium-ion battery even when the residual voltage of the battery is 0 V.
The above-described object of the present invention is achieved by a secondary battery protection circuit for controlling charging of a secondary battery, comprising[: ] a first transistor having either an emitter or a collector thereof coupled in parallel to a power line coupling a secondary battery which is to be charged and a battery charger. Further, a base of the first transistor being coupled to the power line via either a resistor or a leak absorption circuit. A second transistor having either a collector or an emitter thereof coupled to the base of the first transistor. Further, a clamping circuit having a node coupled to either the emitter or the collector of the second transistor, the clamping circuit normally clamping the node at or above ground level. Finally, the second transistor and the first transistor being turned ON when a residual voltage of the secondary battery is near 0 V and the clamping circuit does not operate.
According to the invention described above, it is possible to provide a secondary battery protection circuit comprising a limited number of structural elements and consuming a reduced amount of power, and which is capable of charging a battery such as a lithium-ion battery even when the residual voltage of the battery is 0 V.
Additionally, the above-described object of the present invention is also achieved by the secondary battery protection circuit as described above, further comprising an overcharge protection circuit, the overcharge protection circuit being controlled depending on a potential at a node connecting the base of the first transistor and the resistor or leak absorption circuit.
According to the invention described above, charging of the battery can be halted when overcharged.
Further, the above-described object of the present invention is also achieved by the secondary battery protection circuit as described above, wherein the clamping circuit commences operation when the potential of the secondary battery is at or above a predetermined potential.
According to the invention described above, the amount of power consumed can be drastically reduced.
Additionally, the above-described object of the present invention is a

Affiliated with

Also associated with

Rating

Secondary battery protection circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Secondary battery protection circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Secondary battery protection circuit will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2493315