Electricity: battery or capacitor charging or discharging – Battery or cell charging
Reexamination Certificate
2000-03-22
2002-09-17
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell charging
C320S138000
Reexamination Certificate
active
06452364
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a battery charge control circuit, a battery charging device, and a battery charge control method.
Charging a lithium-ion secondary battery is performed by a constant voltage/current control circuit, and the completion of the charging operation is normally determined when the charging current for the battery becomes smaller than a predetermined reference value.
In the case where completion of the charging operation is determined when the charging current value becomes smaller than the predetermined reference value, a charging device is expected to constantly supply a charging current larger than the predetermined reference value. However, when the battery is charged by a charger contained in an electronic device such as a notebook computer, only the difference between the power supply capacity of an AC adapter and the power consumption of the notebook computer is available to supply the charging current. In such a case, the charging current required by the battery is not always supplied to the battery.
When the charging current for the secondary battery becomes extremely small due to high power consumption by the notebook computer, a wrong determination that the charging operation has been completed is made. To avoid such an error, a charging constant voltage/current control circuit outputs a signal to determine whether the charging current is limited because the load of the electronic device is heavy or because the battery is actually fully charged.
In a portable electronic device such as a notebook computer, a battery is mounted as a power source for the electronic device. Generally, such a battery is a lithium battery in consideration of operating costs and instantaneously dischargeable current capacity. Also, a charger circuit is often contained in a portable electronic device, so that a secondary battery in the electronic device can be readily charged simply by connecting an AC adapter to the electronic device. For its portability, a portable electronic device normally has an internal secondary battery as a power source. However, when used on a desk, it might be supplied with power from an external power source such as an AC adapter.
A lithium secondary battery often used in notebook computers is charged at a constant voltage and/or a constant current. And the completion of the charging operation is normally determined when the charging current value becomes smaller than a predetermined reference value.
There are various techniques for charging a secondary battery by a charger contained in an electronic device such as a notebook computer. For example, the secondary battery is charged with power supplied from an external device such as an AC adapter, and the charging operation is performed whether or not the electronic device is in operation.
2. Description of the Related Art
FIG. 1
is a block diagram showing the structure of a conventional power supply unit for notebook (or lap-top, portable) computers.
An AC adapter
1
is connected to an AC power supply
2
, and converts alternating current supplied from the AC power supply
2
into direct current. The AC adapter
1
is also connected to a power supply connector
3
. The power supply connector
3
is in turn connected to a DC/DC converter
4
via a resistor R
1
and a diode D
1
. The DC/DC converter
4
is connected to a secondary battery
5
via a diode D
2
, and converts DC power supplied from the AC adapter
1
or the secondary battery
5
into a predetermined DC voltage to be supplied to a load
6
.
The secondary battery
5
is connected to a charger circuit
24
which comprises a voltage/current regulator
8
, a differential amplifier
9
, a voltage comparator
10
, reference voltage supplies
12
to
14
, and a microcomputer (or microprocessor)
11
.
The voltage/current regulator
8
is a switching regulator-type DC/DC converter that operates in a PWM control system. The voltage/current regulator
8
comprises a switching transistor Tr
1
, a choke coil L
1
, a flywheel diode D
3
, a smoothing capacitor C
1
, a charging current detecting resistor R
0
, and a control unit
7
.
The switching transistor Tr
1
is formed by an FET, and is switched on and off by the control unit
7
. The charging current detecting resistor R
0
is a sense resistor which measures the value of current for charging the battery
5
. A voltage drop caused by the current flowing through the sense resistor is inputted into the control unit
7
. The switching transistor Tr
1
is switched on and off to control current flowing through the choke coil L
1
. Thus, the voltage/current regulator
8
can perform DC/DC control.
Both ends of the charging current detecting resistor R
0
are connected to the differential amplifier
9
.
The non-inverting input terminal of the differential amplifier
9
is connected to the connection point between the charging current detecting resistor R
0
and the battery
5
, while the inserting input terminal of the differential amplifier
9
is connected to the connection point between the charging current detecting resistor R
0
and the choke coil L
1
. The differential amplifier
9
amplifies voltages at both ends of the charging current detecting resistor R
0
. The output of the differential amplifier
9
is a voltage corresponding to the current supplied to the battery
5
. The output of the differential amplifier
9
is supplied to the microcomputer
11
.
The non-inverting input terminal of the voltage comparator
10
is connected to the AC adapter
1
, and the inverting input terminal of the voltage comparator
10
is connected to the reference voltage supply
12
. The voltage comparator
10
outputs a high-level signal or a low-level signal depending on the voltage of the AC adapter
1
. More specifically, when the voltage generated from the AC adapter
1
is higher than a reference voltage supplied from the reference voltage supply
12
, the voltage comparator
10
outputs a high-level signal. When the voltage generated from the AC adapter
1
is lower than the reference voltage supplied from the reference voltage supply
12
, the voltage comparator
10
outputs a low-level signal. When the AC adapter
1
is connected to the charger circuit
24
, the voltage comparator
10
outputs the high-level signal. When the AC adapter
1
is not connected, the voltage comparator
10
outputs the low-level signal. The output signals of the voltage comparator
10
are supplied to the microcomputer
11
.
The microcomputer
11
controls the operation of the control unit
7
in accordance with the output signals of the differential amplifier
9
and the voltage comparator
10
. When the output of the differential amplifier
9
is higher than a predetermined voltage, i.e., when the charging current is flowing, the microcomputer
11
determines that the battery
5
is not fully charged. When the output signal of the voltage comparator
10
is high, the microcomputer
11
determines that the AC adapter
1
is connected to the charger circuit
24
.
After determining that the battery
5
and the AC adapter
1
are connected from the outputs of the differential amplifier
9
and the voltage comparator
10
, the microcomputer
11
determines that the battery
5
can be charged, and supplies a control signal to the control unit
7
to switch on the control unit
7
. When the output of the differential amplifier
9
is lower than the predetermined voltage, i.e., when the battery
5
is in a fully charged state, or when the output signal from the voltage comparator
10
is low, i.e., when the AC adapter
1
is not connected to the charger circuit
24
, the microcomputer
11
determines that the battery
5
cannot be charged any more, and supplies a control signal to the control unit
7
to switch off the control unit
7
.
Besides the control signals from the microcomputer
11
, the control unit
7
receives the voltages from both ends of the resistor R
1
, the voltages from both ends of the charging current detecting resistor R
0
, and refere
Kitagawa Seiya
Matsuyama Toshiyuki
Ozawa Hidekiyo
Saeki Mitsuo
Fujitsu Limited
Luk Lawrence
Staas & Halsey , LLP
Tso Edward H.
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