Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2001-06-01
2003-11-11
Luk, Lawrence (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S136000
Reexamination Certificate
active
06646422
ABSTRACT:
RELATED APPLICATION DATA
This application claims priority to Japanese Patent Application JP 2000-170431, and the disclosure of that application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a battery pack and is applicable to a battery pack based on a lithium-ion secondary battery, for instance.
2. Description of the Related Art
Conventionally, a battery pack based on a lithium-ion secondary battery is adapted to prevent over-voltage charge and under-voltage discharge by use of a control IC for controlling operations of switching field effect transistors.
FIG. 6
is a connection diagram showing a battery pack. That is, a battery pack
1
has a secondary battery cell
2
and a protective circuit
3
respectively housed in a predetermined case. The battery pack
1
, when mounted to a charging device or a loading device, enables charge and discharge currents to be supplied and outputted between the charging device or the loading device and the secondary battery cell
2
through a positive external terminal
4
A and a negative external terminal
4
B.
In the battery pack
1
, a terminal voltage of the secondary battery cell
2
and terminal voltage between the positive external terminal
4
A and the negative external terminal
4
B or the like are monitored by use of the control IC
5
to permit switching field effect transistors
6
,
7
placed in a charge and discharge path to be on-off controlled according to the monitoring results. That is, the battery pack
1
is structured that discharge and charge-control N-channel field effect transistors
6
,
7
are placed in series in the charge and discharge path between the negative external terminal
4
B and a negative terminal of the secondary battery cell
2
. Incidentally, parasitic diode is existent between a source and a drain of each of the N-channel field effect transistors
6
,
7
for the structural reasons. Therefore, when the terminal voltage of the secondary battery cell
2
is reduced down to a predetermined value or less, the battery pack
1
switches over the discharge-control field effect transistor
6
to the Off-state to prevent under-voltage discharge. On the other hand, when the terminal voltage of the secondary battery cell
2
is increased up to a predetermined value or more, the battery pack switches over the charge-control field effect transistor
7
to the Off-state to prevent over-voltage charge.
Incidentally, the battery pack
1
applies P-channel field effect transistors
8
,
9
, instead of the N-channel field effect transistors
6
,
7
, to constitute the switching means in some cases as shown in FIG.
7
.
When high charge and discharge currents are required, the battery pack
31
is structured that the field effect transistors constituting the switching means are connected in parallel to control charge and discharge currents as shown in
FIG. 8
by contrast with FIG.
6
. That is, the battery pack
31
is provided to supply a control signal outputted from the control IC to gates of the field effect transistors
6
A,
6
B through a resistor
10
. Incidentally,
FIG. 8
shows only the discharge-control field effect transistors
6
A,
6
B without a description of the charge-control field effect transistors. It is to be understood that output impedance of a control signal output terminal in the control IC is considered to be ordinaryly 10 [K&OHgr;] or more, which corresponds to an equivalent circuit having the resistor
10
connected in series.
Incidentally, a user sometimes carries the battery pack of this kind in one's hand in use, and as a result, high voltage caused by static electricity is applied to the battery pack on such occasions. While the high voltage caused by the static electricity is limited to about 6 to 15 [kV], application of voltage of several [kV] or more is considered to be enough to cause breakdown of the field effect transistors. Accordingly, it is feared that breakdown of the field effect transistors might be caused by static electricity when the user frequently carries the battery pack in one hand in use.
With the breakdown of the field effect transistors caused by the static electricity or the like in the conventional battery pack, a source-to-drain resistance value of the field effect transistor is increased, resulting in difficulty in using the battery pack structured that each of the charge and discharge-control field effect transistors constituting the switching means is placed individually in the charge and discharge path as described in
FIGS. 6 and 7
. In this connection, while the source-to-drain resistance value is limited to 100 [m&OHgr;] or less in a ordinary condition, while being increased up to 1 [k&OHgr;] or more in consequence of the breakdown as described the above.
On the other hand, in the battery pack structured that the field effect transistors are connected in parallel as described in
FIG. 8
, the breakdown of only one of the parallel connected field effect transistors is supposed to be caused by static electricity. In this case, when a large number of field effect transistors are connected in parallel and so on, each field effect transistor makes sure of a capacity enough to permit the remaining field effect transistors to apply sufficient charge and discharge currents in some cases. The battery pack, if made available for such a case, is considered to be convenient. However, the conventional battery pack presents a problem in difficulty in making the battery pack available for such a case.
A description will now be given by taking the case of the battery pack having the structure shown in FIG.
8
. That is, the control IC is provided to set the discharge-control field effect transistors
6
A,
6
B to the On-state and the Off-state on the basis of the rise and fall of gate control voltage of the discharge-control field effect transistors
6
A,
6
B. The voltage required for setting the discharge-control field effect transistors to the On-state is set at a value approximately equal to the terminal voltage of the secondary battery cell
2
, for instance. On the other hand, there is a need for setting the gate control voltage at approximately 0 [V] to set the discharge-control field effect transistors to the Off-state. When the terminal voltage of the secondary battery cell is reduced down to 2 [V], the control IC for use in the lithium-ion secondary battery switches over the field effect transistors
6
A,
6
B from the On-state to the Off-state.
The resistor
10
in the battery pack is set to have a resistance value of about 100 [k&OHgr;] so that a gate-to-source resistance value in each of the field effect transistors
6
A,
6
B comes to about 1 to 200 [M&OHgr;] in a ordinary condition. Thus, the control IC
5
makes it possible to set the terminal voltage of the control terminals at 4 [V] and 0 [V] for setting the gate voltage of the field effect transistors
6
A,
6
B at 4 [V] and 0 [V] respectively.
The least gate-to-source voltage required for maintaining the source-to-drain resistance value of each of the field effect transistors
6
A,
6
B smaller is about 1.5 [V]. Accordingly, the battery pack makes it possible to set the terminal voltage of the control terminals at 4 [V] and 0 [V] for setting the field effect transistors
6
A,
6
B to the On-state and the Off-state.
On the other hand, when the breakdown of the field effect transistors is caused by static electricity or the like, the gate-to-source resistance of the field effect transistor is reduced down to about 1 [k&OHgr;]. Assuming that the breakdown of the field effect transistor
6
A is caused by static electricity, for instance, the gate-to-source voltage in the undamaged-side field effect transistor
6
B is also reduced down to about 0 [V], resulting in difficulty in setting the field effect transistor
6
B to the
Hogari Masaki
Maekawa Shuichiro
Luk Lawrence
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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