Electricity: battery or capacitor charging or discharging – Capacitor charging or discharging
Reexamination Certificate
2001-10-15
2002-11-05
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Capacitor charging or discharging
Reexamination Certificate
active
06476587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power circuit using a chemical cell and more particularly to the power circuit that can be suitably used when power is supplied to a load whose power consumption changes intermittently, for example, to a power source of a power amplifier for transmission of a radio wave embedded in a portable cellular phone and to a method for controlling the power circuit and an electronic device using the above power circuit.
The present application claims priority of Japanese Patent Application No.2000-318310 filed on Oct. 18,2000, which is hereby incorporated by reference.
2. Description of the Related Art
When a power circuit using a chemical cell is connected to a load whose power consumption changes intermittently, since an internal impedance of the chemical cell is comparatively large, a phenomenon occurs in which a voltage of the chemical cell drops instantaneously at a same time when a load current increases instantaneously. To solve this problem, conventionally, a capacitor having a comparatively low internal impedance is connected to the chemical cell in parallel. This allows a combined impedance whose level is lower than that of the internal impedance of the chemical cell to be formed and therefore even when the load whose power consumption changes intermittently is connected, an instantaneous voltage drop rate in voltage decreases compared with a case in which the chemical cell is singly used.
The conventional power circuit of this type, as shown in
FIG. 5
, includes a chemical cell
1
and a capacitor
2
connected to the chemical cell
1
in parallel and a load L connected to the chemical cell
1
and the capacitor
2
. The chemical cell
1
is made up of, for example, a secondary cell such as a nickel-cadmium cell, nickel-hydrogen cell, or lithium ion cell, or an alkaline primary cell. Such the chemical cell
1
stores a predetermined amount of energy, produces electromotive force (that is, voltage V
1
) based on the stored energy and supplies it to the load L. The chemical cell
1
has an internal impedance
1
a
. The capacitor
2
is made up of, for example, an electrical double layer capacitor and is charged by the voltage V
1
of the chemical cell
1
, thus accumulating electric power, and then feeds the accumulated power to the load L. The capacitor
2
has an internal impedance
2
a.
The load L is, for example, a power amplifier for transmission of radio waves embedded in portable cellular phone or a like, whose power consumption changes intermittently and through which a pulse-like load current IL flows.
FIG. 6
is a timing chart explaining operations of the conventional power circuit of
FIG. 5
, in which a current or voltage is plotted as ordinate and time is plotted as abscissa. Operations of the power circuit of
FIG. 5
will be described by referring to FIG.
6
.
At a time t
1
, the load current IL increases instantaneously and the voltage V
1
of the chemical cell
1
drops from a voltage level Va to a voltage level Vb. At this point, an internal impedance Z of the power circuit is given by:
Z=R
1×
R
2/(
R
1+
R
2)
where R
1
denotes a value of the internal impedance
1
a
and R
2
denotes a value of the internal impedance
2
a.
The internal impedance Z is smaller than the value R
1
of the internal impedance
1
a.
Therefore, a drop rate of the voltage Vb is lower than that of a voltage Vc occurring when the power circuit is made up of only the chemical cell
1
. At a time t
2
, the pulse-like load current IL decreases instantaneously and the voltage V
1
returns from the voltage level Vb to the voltage level Va. A voltage V
2
of the capacitor
2
changes in the same manner as in the voltage V
1
.
Thus, when the capacitor
2
is connected to the chemical cell
1
in parallel, since the drop rate of the voltage Vb is lower than that of the voltage Vc, time during which the chemical cell
1
can be used per one time charging is made longer compared with the case in which the power circuit is made up of only the chemical cell
1
. Moreover, when the chemical cell
1
is constructed of the alkaline primary cell having a comparatively high internal impedance, a life of the chemical cell
1
is made longer when compared with the case in which the power circuit is made up of only the chemical cell
1
.
However, the above conventional power circuit has a following problem.
That is, in an electronic device having the power circuit shown in
FIG. 5
, since judgement on a residual capacity of the chemical cell
1
is made based on the drop in the voltage V
1
, the chemical cell
1
is judged to have no residual capacity even by the instantaneous drop in the voltage V
1
in some cases. However, when the chemical cell
1
is constructed of, for example, the alkaline primary cell, even if the chemical cell
1
is judged to have no residual capacity in an electronic device, in some cases, the chemical cell
1
can be used in another electronic device. This phenomenon shows that the chemical cell
1
has not run out of its capacity completely. As a result, the chemical cell
1
is judged to have gotten to an end of its life in a state where a depth of discharge (a ratio of discharged capacity to a rated capacity) of the chemical cell
1
is still shallow, thus causing a decrease in use efficiency of the energy of the chemical cell
1
.
On the other hand, when the chemical cell
1
is made up of, for example, the secondary cell such as the nickel-cadmium cell, nickel-hydrogen cell, lithium ion cell, or a like, there is a problem that, if the chemical cell
1
has not run out of the capacity completely, time during which the chemical cell
1
can be used per one time charging becomes extremely shorter than the usable time that the capacity of the original chemical cell
1
can provide. Moreover, when the capacitor
2
is connected to the chemical cell
1
in parallel, if the capacitor
2
has not been charged, since a large inrush current flows from the chemical cell
1
into the capacitor
2
, burning of a wiring pattern used to connect the chemical cell
1
to the capacitor
2
and/or degradation of the chemical cell
1
and the capacitor
2
occur in some cases. In particular, when the chemical cell
1
is made up of the lithium ion secondary cell in which a current control circuit is embedded, a failure occurs in the current control circuit.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a power circuit capable of improving use efficiency of energy in a chemical cell and of preventing an inrush current from flowing from the chemical cell into a capacitor even when the capacitor having not yet been charged is connected to the chemical cell in parallel and a method for controlling the above power circuit and an electronic device using the power circuit.
According to a first aspect of the present invention, there is provided a power circuit including:
a chemical cell used to store a predetermined amount of energy, to produce electromotive force based on the energy and to feed the electromotive force to a load;
a capacitor which is charged by the electromotive force produced by the chemical cell and accumulates electric power and applies the accumulated electric power to the load;
a control section; and
wherein the control section, when a voltage of the capacitor is higher than a first reference value and when a load current flowing through the load is smaller than a second reference value, applies a voltage produced by the chemical cell to the capacitor from the chemical cell to charge the capacitor and, at a same time, feeds the electromotive force produced by the chemical cell and the accumulated electric power in the capacitor to the load and, when the load current is larger than the second reference value, feeds only the accumulated electric power in the capacitor to the load and, when a voltage of the capacitor is lower than the first reference value and the load current flowing through the load is smaller than th
Hayes & Soloway P.C.
NEC Tokin Corporation
Tso Edward H.
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