Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells
Reexamination Certificate
2001-03-22
2002-05-28
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
C320S128000
Reexamination Certificate
active
06396243
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a power unit, a power source switching apparatus, and a computer, and more particularly to a power unit provided with a battery enabled to supply a power to an external device, a power source switching apparatus provided with a plurality of batteries and enabled to supply a power to a load, and a computer that employs the power source switching apparatus.
BACKGROUND OF THE INVENTION
In recent years, there have appeared portable personal computers (hereinafter “portable PCs”) developed in various sizes and provided with various functions so as to cope with the spread of mobile computing. For example, there are lap-top personal computers, more compact lap-top personal computers, palm-top personal computers and PDA (Personal Data Assistant) devices.
A portable PC generally has a removable battery mounted therein which allows the user to use the portable PC in an environment where no commercial power source is available, for example, in a train. Generally, a secondary battery that can be charged for repetitive use is employed as such a battery described above.
When a commercial power source is available, the user can connect an AC adapter (a device enabled to input a commercial AC voltage and output a DC voltage) to the portable PC. Consequently, the user can charge the secondary battery during operation of the portable PC.
However, because the capacity of one secondary battery is limited, the operating time of the portable PC is also limited. To extend the operating time of the portable PC, therefore, two secondary batteries are often built in the portable PC. Those two secondary batteries are referred to as the main battery and the second battery. A portable PC is started up with the power from the second battery. When the second battery is used up, the second battery is switched to the main battery, so that the portable PC can continue in operation.
Each of such portable PCs, home electric appliances, and other devices that use an AC adapter, a main battery, and a second battery as power sources is provided with a power source switching circuit for setting a charging path of the main or second battery via an AC adapter (hereinafter, referred to as the “charging path”), a discharging path used to supply a power from the main battery to an object computer (hereinafter, referred to as the “discharging path”), and another discharging path, etc. used to supply a power from the second battery to the object computer.
FIGS. 9 through 11
show block diagrams of such conventional power source switching circuits.
The block diagram of
FIG. 9
shows a power source switching circuit in which each of the main battery and the second battery is provided with a protective circuit for preventing excessive discharging and excessive charging.
As shown in
FIG. 9
, this power source switching circuit is provided with a first serial circuit
100
located between a power line L from an AC adapter
62
to a DC-DC converter
66
and a main battery
130
A and a second serial circuit
102
located between the power line L and a second battery
130
B.
The first serial circuit
100
is provided with field effect transistors (hereinafter, referred to as a “FET”) FET
1
and FET
2
. Just like the first serial circuit
100
, the second serial circuit
102
is also provided with field effect transistors FET
3
and FET
4
.
In FET
1
and FET
3
are formed internal diodes D
1
and D
3
in which the cathode is connected to the drain D and the anode is connected to the source S respectively. In FET
2
and FET
4
are formed internal diodes D
2
and D
4
in which the cathode is connected to the source S and the anode is connected to the drain D respectively. Those internal diodes are also sometimes referred to as parasitic diodes or body diodes.
A trickle charging circuit
140
A and a trickle charging circuit
140
B are provided between the power line L and the source S of FET
1
and between the power line L and the source S of FET
3
respectively. A quick charging circuit
142
is provided between the power line L and the drain D of FET
2
. The drains D of both FET
2
and FET
4
are connected to each other and FET
5
is provided between the junction point of those drains D and the power line L so as to prevent the quick charging circuit
142
from short-circuiting during a quick charging operation.
In the block diagram shown in
FIG. 9
, both of the main battery
130
A and the second battery
130
B are first charged by the trickle charging circuit until each battery voltage reaches a certain value, then charged rapidly by the quick charging circuit until they are fully charged. The expression ‘trickle charging’ means charging at a slow rate so as to avoid damage to the subject battery. The battery capacity is almost zero during such trickle charging and is therefore too low to supply the power required for system operation.
FET
5
is off while the quick charging circuit
142
charges the main battery
130
A or the second battery
130
B. FET
5
is turned on when the trickle charging circuit
140
A or
140
B charges the main battery
130
A or the second battery
130
B or when either the main battery
130
A or the second battery
130
B supplies the DC power to the DC-DC converter
66
.
Each of the main battery
130
A and the second battery
130
B is provided with a protective circuit
110
A/
110
B configured by two FETs connected serially. The two FETs (FET
6
, FET
7
) in the protective circuit
110
A are connected serially to the first serial circuit
100
in the same state of each FET in the first serial circuit. The two FETs (FET
8
, FET
9
) in the protective circuit
110
B are connected serially to the second serial circuit
102
in the same state of each FET in the second serial circuit
102
. Both FET
6
and FET
8
are used to protect the subject circuit from excessive charging and both FET
7
and FET
9
are used to protect the subject circuit from excessive discharging.
In the event that the power source switching circuit configured as described above is loaded with the AC adapter
62
, the main battery
130
A charged fully, and the second battery
130
B in the empty state during a system operation, the trickle charging circuit
140
B charges the second battery
130
B. At this time, FET
1
and FET
3
are turned off and FET
2
and FET
4
are turned on. FET
5
is also turned on.
Consequently, when the AC adapter
62
is disconnected from the system in that state and the power supply is thereby shut off, the DC-DC converter
66
receives DC power from the main battery
130
A via the internal diode D
1
in FET
1
, and also via FET
2
and FET
5
.
An alternative arrangement is shown in FIG.
10
. Serial circuits
100
and
102
are identical in configuration to those shown in
FIG. 9
; the first serial circuit
100
is formed in the power path from the main battery
132
A to the DC-DC converter
66
and the second serial circuit
102
is formed in the power path from the second battery
132
B to the DC-DC converter
66
. However, the configuration in
FIG. 10
differs from that shown in
FIG. 9
in that the power output line from the charging circuit
68
is branched into two lines wherein one line is connected between the first serial circuit
100
and the main battery
132
A via two FETs connected serially so that the cathodes of their internal diodes are connected to each other, and the other line is connected between the second serial circuit
102
and the second battery
132
B via two FETs connected serially so that cathodes of their internal diodes are connected to each other. In addition, the block diagram shown in
FIG. 10
is also different from the block diagram shown in
FIG. 9
in that neither the main battery
132
A nor the second battery
132
B is provided with a protective circuit and the charging circuit for charging each battery is configured as a single charging circuit
68
; it is not divided into a trickle charging circuit and a quick charging circuit. The control terminal (gate) of each FET is connected to a power path control IC
Schelkopf John B.
Tso Edward H.
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