Electrical transmission or interconnection systems – Plural supply circuits or sources – Substitute or emergency source
Reexamination Certificate
1998-09-23
2002-07-02
Leja, Ronald W. (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
Substitute or emergency source
C323S224000, C320S127000
Reexamination Certificate
active
06414403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power unit having a built-in battery and which is suitable for use with small electronic instruments. More particularly, the present invention relates to a power unit to supply electric power to a load and having a built-in battery, wherein the power unit charges the battery even when electric power is being supplied to the load from an external power source at an external power source voltage lower than the battery voltage.
2. Description of the Related Art
Conventional power units used in personal computers and other small electronic instruments have built-in batteries and supply electric power to a load by connecting an AC adapter that converts commercial alternating current power into a specified direct current voltage. When the power unit is not connected to the AC adapter, the power unit supplies electric power to the load from the built-in battery. The conventional power units include a battery charger that uses external electric power to charge the built-in battery when connected to an external power source.
FIGS. 9A-9C
illustrate a conventional type of power unit and its operation. More specifically,
FIG. 9A
illustrates a conventional power circuit;
FIG. 9B
is a timing diagram illustrating the switching action of a transistor Q
1
of the power circuit shown in
FIG. 9A
; and
FIG. 9C
is a diagram illustrating the operation of the circuit shown in FIG.
9
A.
As shown in
FIG. 9A
, an AC adapter connecting member
110
is connected to an AC adapter and receives a supply of electric power. A load
111
is supplied electric power from a battery
112
when electric power is not being supplied to the AC adapter connecting member
110
from an external power source. A charge/discharge control circuit
113
controls the charging of the battery
112
by switching the transistor Q
1
. A charge/discharge monitor circuit
114
monitors whether the battery
112
is charging or discharging, and, if the battery
112
is charging, the charge/discharge monitor circuit
114
monitors the state of the charge and controls switching of the transistor Q
1
. A battery protection switch
115
connected to the battery
112
shuts off when the battery
112
reaches a discharge final voltage (Vdead) so that the battery
112
does not discharge.
The power circuit includes capacitors C
1
, C
2
, an inductor L
1
, and a diode D
1
. During the time that the transistor Q
1
is off, the diode D
1
sends a flywheel electric current to the circuit L
1
-C
1
-D
1
. A diode D
2
prevents electric current from flowing from the battery
112
to the AC adapter connecting member
110
. A diode D
3
is connected across the switching transistor Q
1
, and is a parasitic diode for the switching transistor Q
1
.
The switching action of the transistor Q
1
controls the voltage applied to the battery
112
.
FIG. 9B
illustrates the switching cycle of the transistor Q
1
. As shown in
FIG. 9B
, the switching period of the transistor Q
1
is Ts; the on period of the transistor Q
1
is Ton; and the off period of the transistor Q
1
is Toff.
FIG. 9C
illustrates a relation between an external power source voltage Vin, a battery voltage Vbat, a discharge final voltage Vdead, a range of voltage Vop that operates the load
111
, and a minimum voltage which operates the load Vop (min) (i.e., the minimum operating voltage) for the operation of the circuit shown in FIG.
9
A.
The circuit shown in
FIG. 9A
operates as described below. The battery protection switch
115
remains on while the battery
112
has not yet reached the discharge final voltage Vdead. When the power unit is connected to the AC adapter, the external power source voltage Vin is greater than the battery voltage Vbat, and the power unit reduces the external power source voltage Vin and charges the battery
112
. When the AC adapter connecting member
110
is connected to the AC adapter, the electric power input to the AC adapter connecting member
110
is supplied to the load
111
via the diode D
2
. The charge/discharge monitor circuit
114
monitors the condition of the AC adapter connecting member
110
connection and the status of the charge on the battery
112
. The charge/discharge monitor circuit
114
relays the status of the charge on the battery
112
to the charge/discharge control circuit
113
. If the battery
112
is fully charged, the charge/discharge control circuit
113
turns off the transistor Q
1
and, in general, adjusts the period of time the transistor Q
1
is switched on depending on the status of the charge on the battery
112
. At this time, the relation between the voltage Vbat of the battery
112
, the externally input voltage Vin, the switching time Ts of the transistor Q
1
, and the on time Ton of transistor Q
1
is given by the following equation:
Vbat=Ton×Vin/Ts.
Therefore, by adjusting the length of time Ton depending on the status of the charge on the battery
112
, the reduction of the external power source voltage Vin is adjusted and the charging of the battery
112
can be controlled.
The charge/discharge monitor circuit
114
detects when no electric power is being supplied from an external source because of various causes, such as the AC adapter connecting member
110
not being connected to the AC adapter, and relays the detected information to the charge/discharge control circuit
113
. The charge/discharge control circuit
113
turns transistor Q
1
on and supplies electric power from the battery
112
to the load
111
. At this time, electric current is prevented from flowing from the battery
112
to the AC adapter connecting member
110
by the diode D
2
, thus preventing unnecessary consumption of the battery
112
.
FIG. 9C
illustrates a relation between the charge/discharge of the battery
112
and the load voltage both when electric power is being supplied from an external power source and when electric power is not being supplied from an external power source. More particularly,
FIG. 9C
illustrates a relationship between the externally supplied voltage Vin; the terminal voltage Vbat of the battery
112
; the operating voltage of the load Vop, which is the voltage range that operates the load
111
; the minimum operating voltage Vop (min) of the load
111
; and the discharge final voltage Vdead, which is the minimum battery voltage permitted by the battery
112
.
As shown in
FIG. 9C
, the period AB is the length of time spent charging the battery
112
(Tchg). The period BC is the length of time the battery
112
is fully charged. The time at which the external power source (AC adapter) is disconnected is represented by C. The period AC is the length of time the battery
112
is connected to an external power source. The time at which the battery voltage Vbat reaches the minimum load operating voltage Vop is represented by D. The period CD is the length of battery
112
discharge time (Tdis). The time at which the battery voltage Vbat reaches the discharge final voltage (Vdead) is represented by E.
During the time period AB, the transistor switch Q
1
is adjusted and the battery
112
is charged. During the time period BC, the battery
112
is fully charged and transistor Q
1
is switched off. At time C, the external power source (AC adapter) is disconnected and transistor switch Q
1
is switched on to supply electric power from the battery
112
to the load
111
. During the time period CD, the battery
112
discharges. The battery protection switch
115
is turned off and voltage supply to the load
111
is halted when the battery voltage Vbat reaches the minimum operating voltage of the load Vop (min) at time D. At this time however, even when the supply of electric power to the load
111
from the battery
112
is halted at the point in time D, there still remains some power left in the battery
112
before it reaches the discharge final voltage Vdead. Therefore, use of the battery
112
is halted before the battery
112
is completely drained.
In the above-described manner, the conventional
Kitagawa Seiya
Ozawa Hidekiyo
Saeki Mitsuo
Leja Ronald W.
Rios Roberto
Staas & Halsey , LLP
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