Note: Descriptions are shown in the official language in which they were submitted.
CA 02490402 2004-12-16
SPECIFICATION
Title of the Invention
CELLULAR TELEPHONE CHARGING CIRCUIT USING DRY BATTERY
Background of the Invention
1. Field of the Invention
The present invention relates to a cellular telephone
charging circuit for charging (normally quickly charging) a
battery built in the cellular telephone by using a dry battery.
More specifically, the present invention relate to a cellular
telephone charging circuit capable of displaying a charging
operation using a light-emitting diode (LED) only when a battery
built in the cellular telephone is actually charged.
2. Description of the Related Art
Many conventional cellular telephone charging circuits
using dry batteries are not provided with means (LED's) for
displaying respective charging operations. Some cellular
telephone chargers include LED's for displaying respective
charging operations and fully charged states.
Fig. 6 is a block diagram that depicts an example of a
conventional cellular telephone charger 5 using a dry battery
and including an LED for displaying a charging operation. In
the charger 5 shown in Fig. 6, a dry battery BC (at a power supply
voltage E ) is connected to input terminals al and a2 of a power
supply circuit (DC/DC converter) 51. A charging
current-limiting resistor R1 is connected between the power
supply circuit 51 and one output terminal b1 . A display circuit
constituted by an LED current-limiting resistor R2 and an LED
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D1 is connected between output terminals b1 and b2. A cellular
telephone built-in battery 52 is connected to the output terminals
b1 and b2 and the LED D1 is turned on during a charging operation.
Fig. 7 is a block diagram that depicts an example of a
cellular telephone charger 6 that charges a battery built in
a cellular telephone and that includes an LED for displaying
a charging operation. In the charger 6 shown in Fig. 7, a
commercial AC power supply is connected to input terminals al
and a2 of a power supply circuit (an AC/DC inverter) 61. A
charging current-limiting resistor R1 is connected between the
power supply circuit 61 and one output terminal b1 . A comparison
circuit 63 constituted by a comparator CMP, input-side resistors
R3, R4, R5, and R6, and a feedback resistor R7 is connected in
rear of the power supply circuit 61. A display circuit
constituted by an LED current-limiting resistor R2 and an LED
D1 is connected between one terminal of the power supply circuit
61, which terminal is connected to the charging current-limiting
resistor R1 and an output terminal of the comparator CMP. A
cellular telephone built-in battery 62 is connected to output
terminals b1 and b2 and the LED D1 is turned on during a charging
operation.
In the charger 5 shown in Fig. 6, when the power supply
circuit 51 is driven, a power is supplied to the cellular telephone
built-in battery 52 and the LED D1 is turned on by a charging
voltage between the output terminals b1 and b2. Due to this,
the LED D1 is turned on whenever the power supply circuit 51
is driven irrespectively of whether the cellular telephone
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built-in battery 52 is charged. A user, therefore, determines
that the charging operation is carried out even in a
non-chargeable state.
Specifically, the LED D1 is turned on even if ( 1 ) the cellular
telephone built-in battery 52 rejects being charged, (2) the
cellular telephone built-in battery 52 is fully charged, or ( 3 )
a capacity of the battery cell BC of the charger 5 is reduced,
the battery cell BC is incapable of charging the battery, but
the battery cell BC outputs a voltage sufficient to turn on the
LED D1.
An ordinary LED is turned on whenever a voltage equal to
or higher than a forward voltage Vf is applied between an anode
and a cathode. The forward voltage Vf for the LED depends on
an emission color, a current, a manufacturing method, an emission
material, or the like, and the forward voltage Vf for an ordinary
red LED is about 1.5 to 2.0 volts (V) . The LED is, therefore,
driven even if the capacity of the dry cell of the charger 5
is reduced (case (3) stated above).
In the charger 6 shown in Fig. 7, the LED can be turned
on when a current equal to or higher than a certain current is
carried to the cellular telephone built-in battery 62.
Namely, in the charger 6, if a voltage difference Vd of
the charging current-limiting resistor R1 is detected and the
voltage difference Vd is equal to or higher than a certain value
( R1 xi=Vd, where symbol i denotes a charging current ) , then the
comparator CMP is actuated, a current is applied to the LED D1,
and the LED D1 is thereby turned on.
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This conventional charger 6 has, however, many components
and each component is expensive. Due to this, although the
charger 6 can be used as a charger for charging a cellular telephone
built-in battery, it cannot be used as a cellular telephone
charger using a dry battery and sold at a low price.
Summary of the Invention
It is an object of the present invention to provide a cellular
telephone charging circuit using a dry battery and capable of
displaying a charging operation only when the charging operation
is actually carried out , with a simple circuit configuration .
According to the present invention, there is provided a
cellular telephone charging circuit using a dry battery as a
power supply and including a boost switching regulator that
supplies a predetermined charging power to a charging terminal
of a cellular telephone, comprising: a Light-emitting diode for
displaying a charging operation; a control circuit that generates
an ON and OFF control signal for driving a boost chopper included
in the boost switching regulator; a chopper ON-period detection
circuit that detects an ON-period of the boost chopper; and a
light-emitting diode lighting circuit that drives the
light-emitting device when the ON-period detected by the chopper
ON-period detection circuit reaches a predetermined value.
The cellular telephone charging circuit using the dry
battery according to the present invention is mainly applied
to a cellular telephone quick charger.
The cellular telephone charging circuit using the dry
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battery according to the present invention can be constitute
so that the chopper ON-period detection circuit is a CR
integrating circuit that inputs the ON and OFF control signal,
and so that the light-emitting diode lighting circuit drives
the light-emitting diode when a voltage of the CR integrating
circuit reaches a predetermined voltage. In this case, the
light-emitting diode lighting circuit includes a resistor and
a transistor switch between a positive terminal and a negative
terminal of the battery, the light-emitting device is connected
between the transistor switch and a ground, and the voltage output
from the CR integrating circuit is input to a control terminal
of the transistor switch.
The present invention can provide the cellular telephone
charging circuit using the dry battery, and capable of displaying
a charging operation only when the charging operation is actually
carried out, with a simple circuit configuration, or low
production cost.
Brief Description of the Drawings
Fig. 1 is a functional block diagram of a cellular telephone
charging circuit using a dry battery according to the present
invention;
Fig. 2 is a specific circuit diagram of the cellular
telephone charging circuit using the dry battery shown in Fig.
1;
Fig. 3 is a circuit diagram that depicts a chopper ON-period
detection circuit, an LED lighting circuit, and an LED extracted
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from the circuit shown in Fig. 2;
Fig. 4 is a time chart that depicts a control signal, a
terminal voltage of a capacitor, and transistor ON and OFF states
in the circuit shown in Figs. 2 and 3;
Fig. 5 is a front view of a cellular telephone charger
mounting therein the cellular telephone charging circuit using
the dry battery according to the present invention;
Fig. 6 is a block diagram that depicts one example of a
conventional cellular telephone charger using a dry battery and
including an LED for displaying a charging operation; and
Fig. 7 is a block diagram that depicts one example of a
conventional cellular telephone built-in battery charger and
including an LED for displaying a charging operation.
Detailed Description of the Preferred Embodiment
Fig. 1 is a functional block diagram of a cellular telephone
charging circuit 100 using a dry battery according to the present
invention. In Fig. 1, the cellular telephone charging circuit
100 using a dry battery includes a boost chopper 101, a control
circuit 102, a chopper ON-period detection circuit 103, an LED
lighting circuit 104, and a charging operation display LED 105.
The boost chopper 101 is constituted by an inductor and a
transistor switch, as will be described later.
In an actual charging circuit, the boost chopper 101 and
an output circuit 106 constitute a boost switching regulator
as shown in Fig. 2.
The control circuit 102 can generate an on and off control
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signal, e.g. , a pulse width modulation (PWM) control signal or
a pulse frequency modulation (PFM) control signal, for driving
the boost chopper 101. The chopper ON-period detection circuit
103 can detect an ON period of the boost chopper 101. The LED
lighting circuit 104 can drive the LED 105 when the ON period
detected by the chopper ON-period detection circuit 103 reaches
a predetermined value. The LED 105 is, for example, red
light-emitting diode (red LED).
In the cellular telephone charging circuit 100 using the
dry battery 200 shown in Fig. 1, when a power S1 is supplied
(from the dry battery 200), the control circuit 102 controls
the boost chopper 101 by a predetermined signal S3 . Under control
of the control circuit 102 , the power S1 from the dry battery
200 is supplied to the boost chopper 101, and the boost chopper
101 charges a cellular telephone built-in battery 300 at a
predetermined charging voltage and a predetermined charging
current denoted by reference symbol S2.
The control signal S3 from the control circuit 102 is also
input to the chopper ON-period detection circuit 103, and the
copper ON-period detection circuit 103 can thereby detect an
ON period of the boost chopper 101. Specifically, the chopper
ON-period detection circuit 103 can be constituted by a CR
integrating circuit, as will be described later. If the chopper
ON-period detection circuit 103 is the CR integrating circuit,
for example, the LED lighting circuit 104 turns on the LED 105
when an output voltage (a charging voltage of a capacitor
constitutingthe CR integrating circuit)reachesa predetermined
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voltage ( in response to a detection signal S4 transmitted from
the LED lighting circuit 104 ) . In addition, the LED 105 is turned
on by a power S5 from the dry battery 200.
A lithium-ion battery is normally used as the cellular
telephone built-in battery 300. A rated output voltage of the
lithium-ion battery is normally about 3.6 to 3.7 V. It is
necessary to charge the lithium-ion battery at a voltage equal
to or higher than the rated output voltage and a current equal
to or higher than 80 milliamperes (mA). Normally, the
lithium-ion battery is charged at a voltage equal to or higher
than 4.5 V and lower than 5.7 V and a current of 300 to 600 mA.
Fig. 2 is a specific circuit diagram of the cellular
telephone charging circuit 100 using the dry battery 200 shown
in Fig. 1. In the cellular telephone charging circuit 100 using
the dry battery 200 shown in Fig . 2 , the dry battery 200 is connected
to input terminals al and a2. It is assumed herein that the
dry battery 200 is two battery cells each at a voltage of 1.5
V, connected in series, and having a voltage of 3 V in all.
The boost chopper 101 is constituted by an inductor L, a
transistor switch (a field effect transistor (FET) in this
embodiment ) Q1, and a diode ( a Schottky barrier diode ) SBD . The
control circuit 102 is constituted by an integrated circuit ( IC )
capable of outputting the PWM or PFM control signal to an output
terminal of the transistor switch Q1.
The chopper ON-period detection circuit103is constituted
by an integrating circuit composed by a resistor R2 and a capacitor
C2. The LED lighting circuit 104 is constituted by an LED
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current-limiting resistor R3 and a transistor switch (a bipolar
transistor in this embodiment) Q2. The LED 105 is a red LED.
Fig. 2 also shows that the output circuit 106 composed by
an output current-limiting resistor R1 and a smoothing capacitor
C1 is connected to an output stage (between the output terminals
b1 and b2 ) of the cellular telephone charging circuit 100 using
the dry battery 200.
In Fig. 2, the boost chopper 101 and the output circuit
106 constitute the boost switching regulator.
In the cellular telephone charging circuit 100 using the
dry battery 200 shown in Fig. 2, when the transistor switch Q1
is turned on, energy is accumulated in the inductor L. When
the transistor switch Q1 is turned off , the energy accumulated
in the inductor L is supplied to the output circuit 106 through
the Schottky barrier diode SBD and a charging current i is supplied
to the cellular telephone built-in battery 300.
Therefore, if the ON period of the transistor switch Q1
( a period for energizing the inductor L ) is longer, the energy
accumulated in the inductor L is higher and the charging current
i is higher.
In this embodiment, if the charging current i exceeds a
predetermined value, the ON period of the transistor switch Q1
is equal to or longer than a certain time and the LED 105 is
turned on, accordingly.
Fig. 3 is a circuit diagram that depicts the chopper
ON-period detection circuit 103, the LED lighting circuit 104,
and the LED 105 extracted from the circuit shown in Fig. 2.
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Referring to Fig. 3, a control signal CTRL (appearing at a point
A) of the transistor switch Q1 is integrated by the chopper
ON-period (integrating circuit) 103 composed by the resistor
R2 and the capacitor C2 . When a voltage at a point B ( a voltage
of the capacitor C2 ) reaches a predetermined voltage Vsh ( =Vbe+Vf ) ,
the transistor switch Q2 is turned on to carry a current to the
LED 105, thereby turning on the LED 105.
The voltage Vbe is an emitter-base voltage of the transistor
switch Q2, and the voltage Vf is a forward voltage of the LED
105.
Fig. 4 is a time chart that depicts the control signal CTRL,
a terminal voltage VC2 of the capacitor C2 , and ON and OFF states
of the transistor switch Q2.
In this embodiment , the LED 105 is connected to an emitter
side of the transistor switch Q2. It is thereby possible to
increasethe predetermined voltage,i.e.,threshold voltage Vsh,
at which the transistor switch Q2 is turned on, by as much as
the forward voltage Vf (e.g., about 1.7 V).
Further, when a waveform at the point A is at an L level,
charges accumulated in the capacitor C2 can be promptly emitted
(that is, a difference between the Vsh and an L-level potential
can be set large). It is thereby possible to ensure turning
off the LED 105 when an H-level time of the waveform at the point
A is short and the charging current i is not carried to the cellular
telephone built-in battery 300.
When the dry battery 200 is consumed and the battery voltage
E is lower, the H-level time at the point A is longer even at
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the equal charging current i . In this embodiment , the LED 105
is connected to the emitter of the transistor switch Q2 and
directly driven by the battery voltage E.
Therefore, to turn on the LED 105, the following condition
needs to be satisfied.
Vf<E-Vcc-IfxR3, that is,
E>Vf+Vce-IfxR3, where symbol Vce denotes an
emitter-collector voltage of the transistor switch Q2 and If
denotes the current carried to the LED 105.
If it is assumed that Vf is 1.7 V, Vce is 0.2 V, and IfxR3
is 0.1 V, the condition is represented by:
E>1.7+0.2+0.1=2.0 [V]
According to this embodiment, therefore, the LED 105 is
turned off in a battery consumed state ( the battery voltage lower
than 2.0 V).
Fig. 5 is a front view of a cellular telephone charger 400
mounting therein the cellular telephone charging circuit 100
using the dry battery 200. In the cellular telephone charger
400 mounting therein the cellular telephone charging circuit
100 using the dry battery 200 shown in Fig. 5, when a terminal
portion 401 (corresponding to the output terminals b1 and b2)
is connected to a charging terminal of a cellular telephone ( not
shown), the charging current is carried from the dry battery
200. In addition, the LED 105 is turned on only when an
appropriate charging operation is carried out.
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