Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1999-09-10
2001-10-02
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C307S010700
Reexamination Certificate
active
06297619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a secondary battery cell protection circuit, and more particularly, to a lithium-ion battery cell protection circuit capable of shutting down a charge circuit when a charge voltage in excess of a predetermined voltage is applied.
2. Description of the Related Art
Compared to the conventional nickel-cadmium battery cell or nickel-hydrogen battery, the light, compact lithium-ion battery that is one type of secondary battery cell delivers approximately three times as much operating voltage, approximately twice as much power per unit of weight and substantially greater power per unit of volume as well. The power, lightness and compactness of the lithium-ion battery cell has led to its widespread use in video cameras, portable telephones, PHS, notebook-type personal computers and a wide array of other portable electronic products.
In order to ensure the safety and enhance the performance of these light, compact but powerful battery cells, protection circuits are used.
FIG. 1
shows the circuit conventionally used to protect secondary battery cells such as the lithium-ion battery cell. This circuit has a battery cell protection circuit
20
, resistors R
1
-R
3
, capacitors C
1
-C
3
, discharge control field-effect transistor (hereinafter FET) Q
1
and charge control FET Q
2
. Either a charger or a load is connected between terminal +B and terminal −B.
The battery cell protection circuit
20
has an over-current detection circuit
10
, an over-discharge detection circuit
11
, a discharge control unit dead time circuit
12
, a charge/load detection circuit
13
, an over-charge detection circuit
14
, a dead time setting circuit and a charge control FET drive transistor TR
1
.
The VCC terminal of the battery cell protection circuit
20
is connected to the positive terminal of the secondary battery cell
1
via resistor R
1
and capacitor C
1
.
The GND terminal is the terminal connected to the negative terminal of the secondary battery cell
1
and is also the battery cell protection circuit
20
ground terminal (standard power terminal).
The DO terminal is the discharge control FET Q
1
drive output terminal. When there is an over-discharge the output appearing at the DO terminal turns the discharge control FET Q
1
OFF, the charge/discharge path
30
is cut and the discharge stopped.
The VM terminal is an over-current detection terminal, and is connected to the −B terminal via resistor R
3
.
The TD terminal is the charge control dead time setting terminal. This TD terminal is grounded via capacitor C
2
. This capacitor C
2
is connected to the dead time setting circuit
15
and determines the dead time of the over-charge detection circuit
14
.
The CO terminal is the drive output terminal for the charge control FET Q
2
. When the over-charge detection circuit
14
detects an overcharge, transistor TR
1
is shut OFF, a LOW-level signal is applied to the CO terminal, that LOW-level signal is applied to the gate of the charge control FET Q
2
and the charge control FET Q
2
turns OFF. When the charge control FET Q
2
turns OFF, one charge-discharge path consisting of the negative terminal of the secondary battery and the −B terminal discharge path
30
is cut and charging stops.
The over-discharge detection circuit
11
detects the voltage at the VCC terminal and, if the voltage detected at the VCC terminal meets or exceeds an over-discharge detection voltage V
s
of, for example, 2.3 V, maintains a state of operation. If the VCC terminal voltage is less than an over-discharge voltage V
s
the over-discharge detection circuit
11
outputs an over-discharge detection signal to the DO terminal, turns the discharge control FET Q
1
OFF and stops the discharge.
In order to prevent repeated starting and stopping of the discharge, the over-discharge detection circuit
11
is set so that a shift to a normal mode, that is, a state in which there is no over-discharge, is carried out at a voltage exceeding the over-discharge voltage V
s
. That is, the over-discharge detection circuit
11
has a hysteresis characteristic, in that the stopping of the discharge is carried out at the over-discharge voltage V
s
and the shift to a normal mode is carried out at a voltage larger than the over-discharge voltage V
s
.
In addition, although the over-discharge detection circuit
11
determines whether or not an over-discharge exists based on the VCC terminal voltage, in fact such a determination does not necessarily match the relation between the voltage of the secondary battery cell
1
and the residual capacity of the secondary battery cell
1
. In order therefore to derive maximum usage from the secondary battery cell
1
a discharge control unit dead time circuit
12
is provided so as to continue discharging for that time set by the discharge control unit dead time circuit
12
beginning with that point in time at which over-discharge detection was carried out, after which the discharge control FET Q
1
is shut OFF.
Over-current detection circuit
10
is provided mainly as short-circuit protection for the power charge/discharge path
30
.
A charger or a load is connected to the +B and −B terminals. The charger/load detection circuit
13
detects whether a charger or a load is connected to the +B and −B terminals.
The over-charge detection circuit
14
detects the voltage at the VCC terminal and, if the voltage detected at the VCC terminal is less than or equal to an over-charge detection voltage V
ALM
off, for example, 4.2 V, maintains a state of operation. If the VCC terminal voltage exceeds an over-charge voltage V
ALM
the over-charge detection circuit
14
outputs an over-charge detection signal to the base of transistor TR
1
. As a result, the charge control FET Q
2
turns OFF, stopping the charging of the secondary battery cell
1
.
In order to prevent repeated starting and stopping of the charge, the over-charge detection circuit
14
is set so that a release to a normal mode, that is, a state in which there is no over-charge, is carried out at a release voltage (V
P
: V
ALM
−&Dgr;V) less than the overcharge detection voltage V
ALM
. That is, the over-charge detection circuit
14
has a hysteresis characteristic, in that the stopping of the charging is carried out at the over-charge detection voltage V
ALM
and the release to a normal mode is carried out at a release voltage (V
P
: V
ALM
−&Dgr;V) less than the overcharge detection voltage V
ALM
.
However, it is known that although the over-charge detection circuit
14
determines whether or not an over-charge exists based on the VCC terminal voltage, in fact such a determination does not necessarily match the relation between the voltage of the secondary battery cell
1
and the amount by which the secondary battery cell
1
has been charged. In order therefore to charge the secondary battery cell
1
fully before cutting the charge circuit a dead time setting circuit
15
is provided so as to continue charging for that time set by the dead time setting circuit
15
, beginning with the point in time at which over-charge detection was carried out. The dead time of the dead time setting circuit
15
can be set to a desired time by changing the capacitor C
2
connected to the TD terminal.
FIG. 2
is a diagram showing a time chart of the operation of the conventional secondary battery cell protection circuit shown in FIG.
3
. The chart depicts an example in which charging of the secondary battery cell begins at a time t1 and terminates thereafter at a time t10 at which an over-discharge is detected and the discharge circuit cut off. T1-t5 represent a charge mode, during which an overcharge (V
ALM
) is detected at t3 and the charge control FET is turned OFF at t4. The interval t3-t4 is over-charge dead time. T5-t8 represent a discharge mode, with a load connected at t5 and an over-current detected at t6. After a dead time at t6-t7 the discharge control FET is turned OFF. Further, t8-t9 represent
Ladas & Parry
Mitsumi Electric Co. Ltd.
Tibbits Pia
Wong Peter S.
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