Electricity: battery or capacitor charging or discharging – Battery or cell discharging – Regulated discharging
Reexamination Certificate
2001-09-19
2002-12-31
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
Regulated discharging
Reexamination Certificate
active
06501248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charge/discharge protection apparatus provided in a battery pack that supplies power to a mobile electronic system, the charge/discharge protection circuit protecting a secondary battery, such as a lithium-ion battery, from being damaged when the battery is placed in an overcharge condition, an over-discharge condition, a discharge-state overcurrent condition or a charge-state overcurrent condition. Further, the present invention relates to a battery pack in which the secondary battery and the charge/discharge protection circuit are provided.
2. Description of the Related Art
In recent mobile electronic systems, a battery pack containing a secondary or rechargeable battery, such as a lithium-ion battery, is often used as the power supply that supplies power to the mobile electronic system. When the time the lithium-ion battery continues to be in overcharge condition is excessively long, the deposition of lithium metal will occur, which damages the battery pack or the mobile electronic system. On the other hand, when the time the lithium-ion battery continues to be in an over-discharge condition is excessively long, the repetitive charge/discharge operational life of the battery pack will deteriorate.
Conventionally, in order to eliminate the problems, a protection switch is provided on the charge/discharge current line between the secondary battery and the electronic system body. The protection switch is turned off when the overcharge condition or the over-discharge condition of the battery is detected, so as to disconnect the secondary battery from the charge/discharge current line. By using the protection switch, it is possible to avoid the continuation of the overcharge condition or the over-discharge condition of the secondary battery.
For example, Japanese Laid-Open Patent Application No. 11-103528 discloses a charge/discharge protection circuit for protecting a secondary battery from damage, which detects an overcharge condition, an over-discharge condition or a discharge-state overcurrent condition of the battery. In the protection circuit of the above document, the terminal to which the voltage of the battery is applied is constructed in a low voltage-resistance structure, and only the terminal to which the voltage of the charger (part of the semiconductor device) is applied is constructed in a high voltage-resistance structure. Such configuration allows the high voltage-resistance structure of the entire protection circuit, and it is possible to safely prevent the damaging of the protection circuit even when an improper charger is erroneously attached to supply a high voltage to the secondary battery.
The conventional protection circuit of the above document is capable of detecting the discharge-state overcurrent condition only. However, the conventional protection circuit of the type is not provided with a function of detecting a charge-state overcurrent condition of the battery. In order to protect the damaging of the secondary battery in the charge state after an improper charger (a defective or broken charger) is attached to the battery pack, the conventional protection circuit requires an externally attached fuse or the like. For this purpose, the conventional protection circuit including a mounting portion for the externally attached fuse has to be large in size, and the manufacturing cost will be raised.
Further, Japanese Laid-Open Patent Application No. 9-182283 discloses a charge/discharge protection circuit which detects any of an overcharge condition, an over-discharge condition and a discharge-state overcurrent condition of a lithium-ion battery.
FIG. 7
shows a conventional charge/discharge protection circuit which is disclosed in the above document.
Generally, when the battery voltage is nearly equal to an operation stop voltage at which the discharging operation should be stopped, the voltage margin becomes small and a malfunction in the protection circuit due to a rapid change of the loading voltage is likely to occur. The setting of the protection switch in OFF state immediately after the battery voltage is equal to the operation stop voltage is avoided. It is desirable to set the protection switch in OFF state only when it is determined that the time the secondary battery is continuously set in any of the overcharge condition, the over-discharge condition and the discharge-state overcurrent condition exceeds a given reference period. To detect any of the overcharge condition, the over-discharge condition and the discharge-state overcurrent condition of the secondary battery, the conventional charge/discharge protection circuit in
FIG. 7
utilizes a timer including an internal oscillator and a frequency-division counter.
As shown in
FIG. 7
, the conventional charge/discharge protection circuit is formed on an integrated circuit (IC) chip, and it generally includes an internal oscillator (OSC)
501
, a frequency-division counter (FDC)
502
, an OR gate
503
, a voltage comparator (COMP)
504
, a decoder (DEC)
505
, an inverter
506
, a protection switch
507
, and a latch (LTC)
508
.
In the conventional charge/discharge protection circuit of
FIG. 7
, the voltage comparator
504
compares a divided battery voltage VCC/N with a given reference voltage V
4
. When the battery voltage VCC is detected as being less than the operation stop voltage, the voltage comparator
504
outputs a low-level detection signal to the counter
502
. At this time, the resetting of the counter
502
to zero is canceled by the low-level detection signal, so that the counter
502
starts counting. When the count value obtained at the counter
502
reaches a predetermined value that is set to the decoder
505
, the decoder
505
sets the latch
508
so as to set the protection switch
507
in OFF state. The protection switch
507
is constructed by a MOS (metal-oxide semiconductor) transistor.
However, when the battery voltage is raised to a level higher than the operation stop voltage before the count value reaches the predetermined value, the voltage comparator
504
outputs a high-level detection signal (reset signal) to the counter
502
. At this time, the counting of the counter
502
is canceled by the reset signal, so that the count value thereof is reset to zero. If the predetermined value that is set to the decoder
505
is made to a comparatively large value, it is possible to prevent the erroneous operation of the protection switch
507
even when the battery voltage VCC is temporarily changed to the level below the operation stop voltage due to a change of the loading voltage.
The above operation of the conventional protection circuit is given for explaining the detection of the over-discharge condition. Similar to the detection of the over-discharge condition, the delay time upon detection of the overcharge condition or the discharge-state overcurrent condition can be controlled by using the internal oscillator
501
and the counter
502
in the conventional protection circuit. Conventionally, in order to determine the delay times upon detection of these conditions, an externally attached capacitor has been needed on the protection circuit IC. According to the above-described conventional protection circuit of
FIG. 7
, the externally attached capacitor is no longer needed, and it is possible to reduce the total number of circuit components needed for the protection circuit.
The conventional protection circuit of
FIG. 7
is not provided with a function of detecting a charge-state overcurrent condition of the battery. In order to protect the damaging of the battery in the charge state after an improper charger is attached to the battery pack, the conventional protection circuit requires an externally attached fuse or the like.
Further, the delay time upon detection of the over-discharge condition or the discharge-state overcurrent condition of the battery is usually set to a time on the order of 10 to 10
2
ms. However, the delay time when detecting the overcharge conditi
Dickstein , Shapiro, Morin & Oshinsky, LLP
Ricoh & Company, Ltd.
Tso Edward H.
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