Electricity: battery or capacitor charging or discharging – Battery or cell charging – With detection of current or voltage amplitude
Reexamination Certificate
2001-05-11
2003-01-07
Toatley, Jr., Gregory J. (Department: 2831)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
With detection of current or voltage amplitude
C320S134000
Reexamination Certificate
active
06504345
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charge/discharge control circuit which is capable of controlling the charge/discharge of a secondary battery by the on/off operation of a switching circuit and a charging type power supply circuit using the circuit.
2. Description of the Related Art
As a conventional charging type power supply device formed of a secondary battery, there has been known a power supply device shown by a circuit block diagram of FIG.
2
. This structure is disclosed in, for example, “charging type power supply device” of Japanese Patent Application Laid-Open No. Hei 4-75430. That is, a secondary battery
101
is connected to an external terminal −V
0
105
or +V
0
104
through a switching circuit
103
. A charge/discharge control circuit
102
is also connected in parallel with the secondary battery
101
.
The charge/discharge control circuit
102
has a function of detecting a voltage across a secondary battery
101
. In the case where the secondary battery
101
is in an overcharged state (a state where the battery voltage is higher than a given voltage value; hereinafter referred to as “overcharge protecting state”) or in an overdischarged state (a state where the battery voltage is lower than the given voltage value; hereinafter referred to as “overdischarge protecting state”), a signal is outputted from the charge/discharge control circuit
102
so that the switching circuit
103
turns off. Also, if discharging operation stops when the external terminal +V
0
104
reaches a certain voltage, it is possible to limit a current that flows in the switching circuit
103
. That is, the discharging operation can stop (over-current control) when an excessive current flows in the switching circuit
103
. Hereinafter, this state is referred to as “over-current protecting state”.
As another example of the conventional charging type power supply device formed of a secondary battery, there has been also known a power supply device shown by a circuit block diagram of FIG.
3
. This circuit is designed such that the switching circuit
103
shown in
FIG. 2
is connected in series to a negative pole
111
of the secondary battery.
FIG. 4
shows a conventional example of a circuit block diagram of a specific charge/discharge control circuit. A secondary battery
101
is connected to an external terminal −V
0
105
through a switching circuit
103
. The switching circuit
103
is made up of two n-channel FETS. A voltage across the secondary battery
101
is detected by a charge/discharge control circuit
102
. The charge/discharge control circuit
102
is made up of an overcharge detection comparator
119
, an overdischarge detection comparator
118
, an over-current detection comparator
117
, a reference voltage circuit A
116
, a reference voltage circuit B
114
, a voltage divider circuit A
120
, a voltage divider circuit B
121
, an output logic control circuit
124
, etc. The charge/discharge control circuit
102
is connected to the switching circuit
103
by signal lines
107
A and
107
B to send out an on/off signal of the switching circuit
1039
A charger
108
for charging the secondary battery
101
and a device (a load viewed from the secondary battery) drivable by the secondary battery
101
are connected between the external terminal +V
0
104
and −V
0
105
. An FET-A
112
and an FET-B
113
are connected in series to the external terminal −V
0
105
or +V
0
104
.
The overcharge detection comparator
119
and the overdischarge detection comparator
118
have a function of comparing the voltage across the secondary battery
101
with the voltage across the reference voltage circuit A
116
. Since the output logic control circuit
124
sends out a signal to the terminals
125
A and
1258
in accordance with the outputs of the respective comparators
119
and
118
, the gate voltages of the respective FETs vary in accordance with the respective states so as to turn on/off the charging and discharging operation with respect to the secondary battery. For example, in the overcharge state, the plus input terminal voltage of the overcharge detection comparator
119
becomes higher than the reference voltage A
116
, and the output of the comparator
119
is inverted from low to high. When the output signal is inputted to the output logic control circuit
124
, the gate voltage of the FET-B
113
in the switching circuit changes from high to low. As a result, the discharge current does not flow in the secondary battery
101
, to thereby stop the charging operation.
The over-current detection comparator
117
compares the external terminal −V
0
105
with the voltage across the reference voltage circuit B
114
and outputs a signal in accordance with respective states to the output logic control circuit
124
. In the over-current protecting state, the output logic control circuit
124
sends out a signal to the FET-A
112
so as to stop the discharging operation while sending out a signal to the FET-C
126
s
, to thereby pull down the external terminal −V
0
105
by a resistor
127
. when the load
109
is out of the over-current protecting state after the detection of the over-current, the pull down becomes necessary to stabilize the external terminal −V
0
105
to the voltage of the reference voltage B
114
or lower and return the state to a normal state.
Although it is possible to realize a switch using one FET instead of the above switching circuit, it is necessary to change the gate potential of the FET as well as the substrate potential in order to achieve the above. If the above change is not made, because the source potential of the FET can be made higher than the drain potential, the charge/discharge control described above is impossible. At present, it is general to control the charge/discharge by two FETS.
However, in the charge/discharge control circuit thus structured, when the load is out of the over-current protecting state and the charge/discharge control circuit returns to the normal state, there arise the following drawbacks which will be described with reference to FIG.
4
.
In order that the charge/discharge control circuit is automatically restored when the load
109
is out of the over-current protecting state, it is necessary that the external terminal −V
0
105
becomes a voltage Va of the reference voltage B
114
or lower. To achieve this, an open-circuit impedance when the load is out of the over-current protecting state must be a constant value (Ra) or more with respect to the resistor
127
(Rb). If the secondary battery
101
is Vb, Ra can be represented by the following expression.
Ra>Rb
(
Vb/Va
−1) (1)
There is known that Vb is generally set to about 3.5 V during the normal operation. In the case where the charge/discharge control device is formed of a semiconductor integrated circuit, since the potential of the external terminal −V
0
105
becomes lower than the potential of the negative pole
111
of the secondary battery when the charger
108
is connected to the charge/discharge control device, and a current flows through the resistor
127
(Rb) from the drain of the FET-C
126
, Rb is generally set to about 100 K&OHgr; in order to limit that current. Va is generally set to about 0.1 V which is set on the basis of the on resistances of the FET-A
112
and the FET-B
113
and currents flowing therein.
If the above-mentioned values are inputted to the expression (1), Ra is represented as follows:
Ra
>100 K&OHgr;(3.5 V/0.1−1)=3.4 M&OHgr;
There is the possibility that the actual open-circuit impedance becomes 1 M&OHgr; or less according to the characteristics of such as the mounted substrate, and the charge/discharge control circuit may not return to the normal state merely when the load is out of the over-current protecting state.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to solve the above problem.
In order to achieve the above object, according to t
Sakurai Atsushi
Yamasaki Koichi
Adams & Wilks
Seiko Instruments Inc.
Toatley , Jr. Gregory J.
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