Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1999-08-23
2001-01-09
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S136000
Reexamination Certificate
active
06172482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a battery protection circuit for preventing at least overcharging of a secondary battery and an electronic device having the battery protection circuit.
2. Description of the Related Art
Among electronic devices loaded with battery packs for power supply, also referred to as a battery package, and adapted for being fed from the battery pack with the power for driving the devices, there are, for example, a portable so-called note-book type personal computer, occasionally abbreviated to note-book personal computer, an information terminal, a video tape recorder, a sound recorder, and a portable telephone. Among non-portable type electronic devices of this type, there is, for example, an electric car having, for example, a motor for assisting the motive power.
The battery packs used in these electronic devices are frequently provided with secondary battery cells that can be charged/discharged repeatedly. As such secondary battery cells, so-called lithium ion secondary batteries, having a high volumetric energy density, are frequently used.
However, the lithium ion secondary batteries are narrow in tolerance values for over-charging or over-discharging. Thus, the battery packs are usually provided with a battery protection circuit for preventing over-charging or over-discharging of the lithium ion secondary batteries.
FIG. 1
shows an illustrative structure of a conventional battery protection circuit provided in a battery pack
200
having a lithium ion secondary battery cell
202
.
Referring to
FIG. 1
, terminals
211
,
212
are charging/discharging terminals of the battery pack, with the terminal
211
being a battery plus terminal and with the terminal
212
being a battery minus terminal (GND side terminal). The battery pack
200
furnishes the current via these plus terminal
211
and minus terminal
212
from the battery cell
202
to a main body portion of the electronic device, by way of charging. On the other hand, the battery pack
202
is charged by the charging current furnished from an external charger, not shown, via these plus terminal
211
and minus terminal
212
.
A field effect transistor (FET)
206
and another field effect transistor (FET)
205
are connected in series between a plus terminal
211
of the battery pack
200
and the positive terminal of the battery cell
202
. The FETs
206
,
205
are provided as a charging on/off controlling switching device and as a discharging on/off controlling switching device, respectively. These FETs
205
,
206
are provided with parasitic diodes.
A control IC circuit
203
has its terminal
235
fed with a voltage value of the plus terminal
211
, while having its terminals
231
and
232
fed with the positive terminal side voltage value and with the negative terminal side voltage value of the battery cell
202
, respectively. The control IC circuit
203
outputs a driving signal for the switching operation (on/off operation) of the FET
206
and a driving signal for the switching operation (on/off operation) of the FET
205
from its terminals
233
,
234
, respectively. That is, the control IC circuit
203
monitors a voltage value of the plus terminal
211
and the voltage values of the positive and negative terminal sides of the battery cell
202
to control the switching operation (on/off operation) of the FETs
205
,
206
.
Meanwhile, in the battery pack employing the FET for charging/discharging control, as shown in
FIG. 1
, the two FETs
205
,
206
are provided for charging/discharging control, these FETs
205
,
206
being connected in series between the plus terminal
211
and the positive terminal side of the battery cell
202
, thus undesirably raising the internal resistance. Although there is such a battery protection circuit having FETs connected in parallel to realize a low internal resistance, the number of component parts is increased in this case to raise the cost.
There are occasions wherein it is necessary to provide a spare protection circuit in addition to the inherent protection circuit, that is two protection circuits, thus further increasing the number of components and increased cost.
If, with the use of a dual FET with the outer shape TSSOP and an N channel, with a drain-to-source withstand voltage of 20 V, a gate withstand voltage of 12 V and with an on-resistance of 35 m&OHgr;, with gate voltage being 2.5 V, two such parallel-connected FETs are used for charging/discharging, the element resistance is 70 m&OHgr;, that is the resistance per FET is 35 m&OHgr;. On the other hand, if these FETs are connected in series with each other, the element resistance is 35 m&OHgr;, that is the resistance per FET is 17.5 m&OHgr;.
FIG. 1
shows an example of a P-channel FET, which has a higher internal resistance than the N-channel FET, so that it is more undesirable.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an inexpensive battery protection circuit made up of a smaller number of components and an electronic device provided with a battery pack having the battery protection circuit.
In one aspect, the present invention provides a battery protection circuit including over-charging detection means for detecting at least the over-charging state of a secondary battery, fuse means fitted with the heater and which is connected to a current path of the secondary battery, and heater driving means for driving the heater of the fuse means. The heater driving means drives the heater of the fuse means to blow off the fuse when the over-charging detection is established.
In another aspect, the present invention provides an electronic device operated by the current supplied from a secondary battery and adapted to charge the secondary battery, including a battery pack having over-charging detection means for detecting at least the over-charging state of a secondary battery, fuse means fitted with a heater, and which is connected to a current path of the secondary battery; and heater driving means for driving the heater of the fuse means. The heater driving means drives the heater of the fuse means to blow off the fuse when the over-charging detection is established.
According to the battery protection circuit and the electronic device, according to the present invention, the fuse of the heater connected to the current path of the secondary battery is blown off on detection of at least the over-charging state of the secondary battery. Thus, the secondary battery is protected by an inexpensive structure with a smaller number of component parts.
REFERENCES:
patent: 5703463 (1997-12-01), Smith
Frommer William S.
Frommer Lawrence & Haug LLP.
Sony Corporation
Tso Edward H.
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