U.S. patent application number 12/654355 was filed with the patent office on 2010-07-01 for charger for electronic device, electronic device, and charging method.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Takahiro Ikeda.
Application Number | 20100164440 12/654355 |
Document ID | / |
Family ID | 41796616 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100164440 |
Kind Code |
A1 |
Ikeda; Takahiro |
July 1, 2010 |
Charger for electronic device, electronic device, and charging
method
Abstract
A charger for an electronic device that charges a rechargeable
battery of the electronic device. The charger includes a detection
unit, which detects connection of another electronic device to the
electronic device through a communication cable including a power
supply line. A charging unit charges the rechargeable battery with
power supply voltage from the power supply line. A measurement unit
acquires a measurement value indicating a degree of a voltage drop
of the power supply voltage occurred when the charging unit
performs charging. A control unit instructs a charging current
value for charging the rechargeable battery with the charging unit.
When the detection unit detects connection of the other electronic
device, the control unit monitors the measurement value while
instructing the charging unit to increase the charging current
value from an initial current value and determines the charging
current value based on the monitored measurement value.
Inventors: |
Ikeda; Takahiro; (Tokyo,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NIKON CORPORATION
TOKYO
JP
|
Family ID: |
41796616 |
Appl. No.: |
12/654355 |
Filed: |
December 17, 2009 |
Current U.S.
Class: |
320/162 |
Current CPC
Class: |
H02J 7/342 20200101;
H02J 7/00 20130101 |
Class at
Publication: |
320/162 |
International
Class: |
H02J 7/04 20060101
H02J007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2008 |
JP |
2008-331509 |
Claims
1. A charger for an electronic device that charges a rechargeable
battery arranged in the electronic device, the charger comprising:
a detection unit which detects connection of another electronic
device to the electronic device through a communication cable
including a power supply line; a charging unit which charges the
rechargeable battery with power supply voltage from the power
supply line of the communication cable; a measurement unit which
acquires a measurement value indicating a degree of a voltage drop
of the power supply voltage occurred when the charging unit
performs charging; and a control unit which instructs a charging
current value for charging the rechargeable battery with the
charging unit; wherein when the detection unit detects connection
of the other electronic device, the control unit monitors the
measurement value obtained by the measurement unit while
instructing the charging unit to increase the charging current
value from an initial current value and determines the charging
current value based on the monitored measurement value.
2. The charger according to claim 1, wherein when the monitored
measurement value enters an unstable range in which the charging of
the charging unit is not guaranteed, the control unit determines
the charging current value to be in a range in which the
measurement value does not enter the unstable range and instructs
the charging unit to charge the rechargeable battery with the
determined charging current value.
3. The charger according to claim 1, wherein the measurement unit
acquires a dropped power supply voltage resulting from the charging
as the measurement value; and when the measurement value obtained
by the measurement unit is less than the threshold value, the
control unit determines the charging current value so that the
measurement value becomes greater than or equal to a threshold
value.
4. The charger according to claim 1, wherein the measurement unit
acquires a voltage drop amount as the measurement value, the
voltage drop amount being a difference between an initial power
supply voltage when the detection unit detects connection of the
other electronic device and a power supply voltage during charging;
and the control unit decreases the charging current value when the
voltage drop amount becomes greater than or equal to a set drop
amount.
5. The charger according to claim 1, wherein when the control unit
increases the charging current value from a previous value
I.sub.n-1 to a present value I.sub.n, the measurement unit
calculates, based on a previous power supply voltage V.sub.n-1 and
a present power supply voltage V.sub.n, a voltage drop rate
(V.sub.n-1-V.sub.n)/(I.sub.n-1-I.sub.n) as the measurement value;
and when the voltage drop rate exceeds a set threshold value, the
control unit determines the charging current value so that the
voltage drop rate does not exceed the set threshold value.
6. The charger according to claim 1, further comprising: a power
supply information acquiring unit which acquires specified power
supply information of the other electronic device by communicating
with the other electronic device through the communication cable;
and a determination unit which determines that the other electronic
device is an AC adapter when the power supply information acquiring
unit cannot perform communication with the other electronic
device.
7. The charger according to claim 6, wherein the control unit
determines the charging current value in accordance with specified
current value information contained in the specified power supply
information when the power supply information acquiring unit
performs communication with the other electronic device.
8. The charger according to claim 1 wherein: the measurement unit
measures the power supply voltage when the detection unit detects
connection of the other electronic device; and when the measured
power supply voltage is outside a specified voltage range that the
communication cable is capable of supplying and greater than or
equal to a full charge voltage of the rechargeable battery, the
control unit determines that the other electronic device is a
standard known AC adapter and instructs the charging unit for a
charging current value corresponding to known specified power
supply information of the standard known AC adapter.
9. The charger according to claim 1, wherein the control unit
continuously changes the charging current value as long as the
monitored measurement value guarantee the charging, and performs
test charging of the rechargeable battery with the changed charging
current value.
10. The charger according to claim 9, wherein when the monitored
measurement value does not guarantee the charging operation, the
control unit performs actual charging of the rechargeable battery
with the charging current value preceding the charging current
value changed last during the test charging.
11. The charger according to claim 9, wherein when the changed
charging current value exceeds a maximum current value that the
communication cable is capable of supplying, the control unit
performs actual charging of the rechargeable battery with the
charging current value preceding the charging current value changed
last during the test charging.
12. The charger according to claim 10, wherein the control unit
determines, based on a measurement value acquired first by the
measurement unit, whether the other electronic device has a known
specified current value, and determines whether to perform the test
charging based on the determination result.
13. The charger according to claim 1, wherein the control unit
increases the charging current value in predetermined increments,
and acquires the measurement value from the measurement unit
whenever charging the rechargeable battery with the newly increased
charging current value.
14. The charger according to claim 1, wherein the electronic device
includes: a main CPU which performs communication with the other
electronic device through the communication cable; and a sub-CPU
connected to the power supply line of the communication cable and
to the charging unit and the main CPU, wherein the sub-CPU
functions as the detection unit, the measurement unit, and the
control unit.
15. An electronic device capable of using a rechargeable battery,
the electronic device comprising: a charger which charges the
rechargeable battery that is arranged in the electronic device, the
charger including: a detection unit which detects connection of
another electronic device to the electronic device through a
communication cable including a power supply line; a charging unit
which charges the rechargeable battery with power supply voltage
from the power supply line of the communication cable; a
measurement unit which acquires a measurement value indicating a
degree of a voltage drop of the power supply voltage occurred when
the charging unit performs charging; and a control unit which
instructs a charging current value for charging the rechargeable
battery with the charging unit; wherein when the detection unit
detects connection of the other electronic device, the control unit
monitors the measurement value obtained by the measurement unit
while instructing the charging unit to increase the charging
current value from an initial current value and determines the
charging current value based on the monitored measurement
value.
16. A method for charging a rechargeable battery arranged in an
electronic device, the method comprising: detecting, by the
electronic device, connection of another electronic device to the
electronic device through a communication cable including a power
supply line; starting, by the electronic device, charging of the
rechargeable battery using a power supply voltage from the power
supply line of the communication cable; acquiring, by the
electronic device, a measurement value indicating a degree of a
voltage drop of the power supply voltage occurred during charging;
and determining, by the electronic device, a charging current value
of the rechargeable battery based on the measurement value; wherein
said determining includes: monitoring the measurement value during
the charging while increasing the charging current value from an
initial current value; and updating the charging current value
based on the monitored measurement value.
17. The method according to claim 16, wherein said updating the
charging current value includes: comparing the monitored
measurement value with a threshold value; increasing the charging
current value when the monitored measurement value is greater than
or equal to the threshold value; and decreasing the charging
current value when the monitored measurement value is less than the
threshold value.
18. The method according to claim 17, wherein said comparing
includes: acquiring the measurement value whenever the rechargeable
battery is charged with the newly increased charging current value;
and comparing the newly acquired measurement value with the
threshold value.
19. The method according to claim 17, wherein said updating the
charging current value includes returning the newly increased
charging current value to a preceding charging current value when
the newly increased charging current value exceeds a maximum
current value that the communication cable is capable of
supplying.
20. The method according to claim 16, further comprising:
determining whether the other electronic device is a device having
a known specified current value based on the measurement value that
is first acquired; setting the charging current value in accordance
with a known specified current value when the other electronic
device is a device having the known specified current value; and
setting the charging current value to the initial current value
when the other electronic device is not a device having the known
specified current value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2008-331509,
filed on Dec. 25, 2008, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a charger for an electronic
device that charges a rechargeable battery of the electronic
device, an electronic device, and a charging method.
[0003] Nowadays, there are more electronic devices, such as an
electronic still camera, a mobile phone, a personal digital
assistant (PDA), and a portable game machine, that charge its
rechargeable battery with bus power, which is supplied from another
electronic device (e.g., personal computer), which serves as a
connection origin, through, for example, a USB or IEEE 1394
communication cable.
[0004] Japanese Laid-Open Patent Publication No. 2006-243863
describes technology for sending input current of bus power, which
is obtained from a USB bus, to a power supply line of an HDD block.
A charging circuit uses some of the input current to charge a
rechargeable battery. A step-up circuit increases the output
voltage of the rechargeable battery, and the output current of the
rechargeable battery is added to the current of the power supply
line and supplied to the HDD block. This ensures that the HDD block
is supplied with sufficient drive power while the value of the
current flowing to the USB remain in accordance with the
standardized specification.
[0005] The USB standard allows for two different currents to be
supplied, 100 mA and 500 mA.
[0006] For 100 mA, a problem occurs in that when there is not
enough power, a CPU of a charger in an electronic camera cannot be
activated. In such a case, communication cannot be performed with
an electronic device that is connected to the charger and serves as
the connection origin. Thus, information (specified voltage,
specified current, etc.) necessary for the charging cannot be
acquired from the connected electronic device.
[0007] An AC adapter incorporating a USB connector may be used to
charge a USB-applicable electronic device. In this case, the AC
adapter serves as the connection origin. Thus, the electronic
device cannot perform USB communication and therefore cannot
determine the specified current of the AC adapter.
[0008] In this manner, a rechargeable battery cannot be stably
charged when charging information, such as the specified current of
another electronic device serving as the connection origin cannot
be acquired. This problem does not occur only in electronic cameras
and also occurs in many types of electronic devices that charge its
rechargeable battery with bus power.
SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
provide a charger for an electronic device, an electronic device,
and a charging method that stably charge a rechargeable battery
even when charging information cannot be acquired from another
electronic device, which serves as a connection origin.
[0010] One aspect of the present invention is a charger for an
electronic device that charges a rechargeable battery arranged in
the electronic device. The charger includes a detection unit which
detects connection of another electronic device to the electronic
device through a communication cable including a power supply line.
A charging unit charges the rechargeable battery with power supply
voltage from the power supply line of the communication cable. A
measurement unit acquires a measurement value indicating a degree
of a voltage drop of the power supply voltage occurred when the
charging unit performs charging. A control unit instructs a
charging current value for charging the rechargeable battery with
the charging unit. When the detection unit detects connection of
the other electronic device, the control unit monitors the
measurement value obtained by the measurement unit while
instructing the charging unit to increase the charging current
value from an initial current value and determines the charging
current value based on the monitored measurement value.
[0011] A further aspect of the present invention is an electronic
device capable of using a rechargeable battery. The electronic
device includes a charger which charges the rechargeable battery
that is arranged in the electronic device. The charger includes a
detection unit which detects connection of another electronic
device to the electronic device through a communication cable
including a power supply line. A charging unit charges the
rechargeable battery with power supply voltage from the power
supply line of the communication cable. A measurement unit acquires
a measurement value indicating a degree of a voltage drop of the
power supply voltage occurred when the charging unit performs
charging. A control unit instructs a charging current value for
charging the rechargeable battery with the charging unit. When the
detection unit detects connection of the other electronic device,
the control unit monitors the measurement value obtained by the
measurement unit while instructing the charging unit to increase
the charging current value from an initial current value and
determines the charging current value based on the monitored
measurement value.
[0012] Another aspect of the present invention is a method for
charging a rechargeable battery arranged in an electronic device.
The method includes detecting, by the electronic device, connection
of another electronic device to the electronic device through a
communication cable including a power supply line; starting, by the
electronic device, charging of the rechargeable battery using a
power supply voltage from the power supply line of the
communication cable; acquiring, by the electronic device, a
measurement value indicating a degree of a voltage drop of the
power supply voltage occurred during charging; and determining, by
the electronic device, a charging current value of the rechargeable
battery based on the measurement value. The determining includes
monitoring the measurement value during the charging while
increasing the charging current value from an initial current
value, and updating the charging current value based on the
monitored measurement value.
[0013] Other aspects and advantages of the present invention will
become apparent from the following description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention, together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0015] FIG. 1 is a perspective view showing an electronic still
camera according to a first embodiment of the present
invention;
[0016] FIG. 2 is a perspective view showing a charging system in
which the electronic still camera of FIG. 1 is connected to another
electronic device;
[0017] FIG. 3 is a block diagram showing the electrical
configuration of the electronic still camera shown in FIG. 1;
[0018] FIG. 4 is a block diagram showing the electrical
configuration of a charger arranged in the electronic still camera
of FIG. 1;
[0019] FIG. 5 is a flowchart showing a charging process performed
by the charger of FIG. 4;
[0020] FIG. 6 is a flowchart showing a charging process according
to a second embodiment of the present invention that is performed
by the charger of FIG. 4;
[0021] FIG. 7 is a flowchart showing a charging process according
to a third embodiment of the present invention performed by the
charger of FIG. 4; and
[0022] FIG. 8 is a block diagram showing the electrical
configuration of a modified charger.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0023] An electronic device according to a first embodiment of the
present invention will now be discussed with reference to FIGS. 1
to 5. Here, the electronic device is an electronic still camera
11.
[0024] As shown in FIG. 1, the electronic still camera 11 (digital
still camera) of the present embodiment includes a camera body 12
having the shape of a rectangular cuboid. An image capturing lens
unit 13 is arranged in the front central part of the camera body
12. A flash 14 (strobe light emitting unit) and an emission window
15 are arranged on the camera body 12 at two locations above the
image capturing lens unit 13. The emission window 15 emits infrared
light, ultrasonic waves, or the like towards a subject to perform
focusing.
[0025] A release button 16, which a photographer pushes (i.e.,
activates) when initiating an image capturing operation with the
electronic still camera 11, is arranged at the left end on the
upper surface of the camera body 12 as viewed in FIG. 1. A power
switch 17, which the photographer pushes to switch on the power of
the electronic still camera 11, is arranged at the right side of
the release button 16. A monitor such as a liquid crystal display
(hereinafter referred to as "LCD 18") is arranged in the rear
surface of the camera body 12 (see FIG. 3).
[0026] A Universal Serial Bus (USB) connector 20 (female connector)
is arranged in an inner wall surface, which is exposed when a
opening a resin terminal cover 19 on one side (left side as viewed
in FIG. 1) of the camera body 12. A USB connector 21a (male
connector) of a USB cable 21, which serves as a communication
cable, is connectable to (insertable into) the USB connector
20.
[0027] As shown in FIG. 2, the electronic still camera 11 may be
USB-connected by the USB cable 21 to another electronic device,
which serves as a connection origin. The USB cable 21 has one USB
connector 21a, which is connected to the USB connector 20, and
another USB connector 21b, which is connected to another electronic
device. Examples of an electronic device that serves as the
connection origin includes a personal computer (hereinafter
referred to as "PC 22") and an AC adapter 23. It is only required
that the other electronic device serving as the connection origin
be applicable to USB communication and may be a Personal Digital
Assistant (PDA), a mobile phone, a portable game machine, a USB
hub, and the like.
[0028] When detecting a USB connection in a power OFF state
(standby mode), the electronic still camera 11 charges a
rechargeable battery 41 (shown in FIG. 3) with bus power supplied
through the USB cable 21.
[0029] As shown in FIG. 2, the AC adapter 23 includes a plug 24,
which is connectable to an outlet for commercial AC power (e.g., AC
100V), converts the AC power to DC power, and outputs direct
current with a predetermined voltage (e.g., 5V). The AC adapter 23
supplies the direct current with the predetermined voltage (e.g.,
5V) to the electronic still camera 11 through the USB cable 21,
which is connected to its USB connector (not shown). The AC adapter
23 may be a genuine AC adapter 23a, which is sold for exclusive use
to supply power to the electronic still camera 11, or a non-genuine
AC adapter 23b. The standard-specified information of the genuine
AC adapter 23a, such as the rated current, is known (e.g., the
known rated current is a predetermined value in the range of 500 mA
to 1000 mA). However, the standard-specified information of the
non-genuine AC adapter 23b, such as the rated current, is not
known.
[0030] When power supply voltage can be supplied as bus power from
an upper level device (e.g., USB host such as the PC 22 or a PDA)
to a lower level device (USB device) through the USB cable 21 with
the bus power method, USB is applicable to plug-and-play and also
to hot plugging, which allows for connection and disconnection of
the USB cable 21 in an active state. Further, in USB, two currents,
100 mA and 500 mA, are specified as the maximum current (specified
current) that can be supplied from an electronic device serving as
an upper level device (PC 22 etc.) to a lower level device (bus
power device). When the total current consumed by the connected
lower level device exceeds the specified current (100 mA or 500
mA), this may cause unstable operation or unstable charging due to
lack of power.
[0031] The power supply voltage (rated voltage) that is suppliable
by the genuine AC adapter 23a is set to be outside the USB
specified voltage range (4.40 V to 5.25 V in the present example)
and greater than or equal to the rated voltage (fully charged
voltage) of the rechargeable battery 41 (4.2 V in the present
example). In the present example, a voltage exceeding 5.25 V cannot
be used. Specifically, the rated voltage of the genuine AC adapter
23a is set to be greater than the rated voltage (4.2 V) of the
rechargeable battery 41 and less than the lower limit of the USB
specified voltage (4.40 V). For example, the rated voltage of the
genuine AC adapter 23a is set at "4.3V".
[0032] The circuit configuration of the electronic still camera 11
will now be described with reference to the block diagram of FIG.
3.
[0033] As shown in FIG. 3, the electronic still camera 11 includes
an engine 35, which performs various types of processing such as
image processing. The electronic still camera 11 includes a main
CPU 25 and a sub-CPU 26. The main CPU 25 is arranged in the engine
35 and executes predetermined control programs to centrally control
various operations of the electronic still camera 11. The sub-CPU
26 serves as a control unit mainly responsible for power supply
control. The main CPU 25 and the sub-CPU 26 are communicable with
each other.
[0034] An operation unit 27 including the above-mentioned release
button 16 and the like, a motor control unit 28, a flash control
unit 29, a DRAM 31 (frame memory), a flash memory 32 (non-volatile
memory), a memory card 33 (e.g., SD card), the LCD 18, and the USB
connector 20 are connected to the main CPU 25.
[0035] The electronic still camera 11 includes a variable optical
system, which is formed by an optical lens group including the
image capturing lens unit 13 (only the image capturing lens 13 is
shown in FIG. 3), an aperture, a shutter, and the like. The motor
control unit 28 performs focusing, aperture adjustment, shutter
control, and the like in response to a command from the main CPU
25. The main CPU 25 performs a predetermined exposure calculation
in response to a photoelectric converted signal from a light
measurement element (not shown) to control the shutter and aperture
based on the exposure calculation result when the shutter is
released. Specifically, the motor control unit 28 includes a lens
drive motor, which is driven and controlled by a command from the
main CPU 25. The motor control unit 28 drives the motor to drive
the image capturing lens unit 13 (movable lens) with the motor and
change the zoom magnification (focal length) and perform focusing.
The motor control unit 28 drives an aperture motor to adjust the
opening diameter of the aperture to obtain the aperture value that
is obtained when the main CPU 25 performs a predetermined exposure
calculation using the luminance of the captured subject that is
detected from image data. The motor control unit 28 drives a
shutter motor to drive and control the shutter to obtain an
exposure time that is determined through the exposure calculation
performed by the main CPU 25.
[0036] The flash control unit 29 performs a light emission control
on the flash 14 in accordance with a command from the main CPU 25.
The main CPU 25 determines the color temperature of the necessary
emission light based on color information of the ambient light
acquired by the light measurement element. Then, the main CPU 25
transmits a light emission color control signal to the flash
control unit 29 so that the flash 14 emits light in correspondence
with the determined color temperature.
[0037] The electronic still camera 11 includes an image capturing
element 36. Light flux from an image-captured subject passes
through the variable optical system. The image capturing element 36
forms an image from the light of the captured subject at an image
side of the image capturing lens unit 13. The image capturing
element 36, which includes a complementary metal oxide
semiconductor (CMOS) image sensor or a charge coupled device (CCD)
image sensor, stores signal charges corresponding to the subject
image formed on an imaging plane and outputs the accumulated signal
charges as an analog signal, which is referred to as a pixel
signal.
[0038] The output side of the image capturing element 36 is
connected to a signal processing circuit 37. The signal processing
circuit 37 includes an analog front end (AFE) and an A/D converter.
The AFE, which is controlled by the main CPU 25, performs sampling
(correlation double sampling) on the pixel signal, which has
undergone photoelectric conversion by the image capturing element
36, at a predetermined timing and amplifies the sampled result to a
predetermined signal level based on, for example, ISO sensitivity.
The A/D converter converts the amplified image signal (analog
signal) output from the AFE portion to a digital signal and outputs
the digital-converted image data to the engine 35. The engine 35
generates a predetermined image signal by performing image
processing, such as contour compensation, gamma conversion, white
balance processing, and the like, on the digital image signal
output from the A/D converter. The image signal generated by the
engine 35 is temporarily stored in the DRAM 31, which functions as
a buffer memory.
[0039] Then, the main CPU 25 reads the image data from the DRAM 31,
performs JPEG data compression or on the data, and stores the
compressed image data in a memory card 33. The main CPU 25 reads
captured image data from the memory card 33, expands the image
data, and stores the image data in the DRAM 31. The main CPU 25
also displays an image of the image data on the LCD 18 via an LCD
drive circuit (not shown).
[0040] The engine 35 includes a USB controller 39, which is
connected to the USB connector 20. When the USB connector 21a is
connected to the USB connector 20 so that the electronic still
camera 11 is USB connected to another electronic device when the
power of the electronic still camera 11 is on, the USB controller
39 performs a communication complying with the USB communication
protocol with the other electronic device, which serves as a
connection origin. When the power of the electronic still camera 11
is off, the sub-CPU 26 is supplied with power supply voltage Vbus
so that the sub-CPU 26 detects connection of the USB connector 21a
(connection of another electronic device) to the USB connector 20.
That is, the sub-CPU 26 detects USB connection when the power of
the electronic still camera 11 is off.
[0041] The sub-CPU 26 is connected to the power switch 17 and a
power supply circuit 40. The power supply circuit 40 is connected
to the rechargeable battery 41. The sub-CPU 26 controls the power
supply circuit 40 based on an operation signal input from the power
switch 17 to switch on or off the power of the electronic still
camera 11. In a power on state, the power supply circuit 40 is
driven by a command from the sub-CPU 26, a plurality of
predetermined voltages are generated from the power supply voltage
of the rechargeable battery 41, and each section of the electronic
still camera 11 is supplied with the necessary power supply
voltage. When a predetermined time elapses in a power on state
without any image capturing operation or operation of the operation
unit 27 being performed with the electronic still camera 11, the
sub-CPU 26 controls the power supply circuit 40 to switch off the
power of the electronic still camera 11. In a power off state, the
power supply circuit 40 stops outputting power supply voltage
although it continues to supply voltage to some circuits such as
the sub-CPU 26 or a timing counter. In the present embodiment, a
lithium-ion battery or the like is used as the rechargeable battery
41. Other rechargeable batteries having a rated voltage that can be
charged with USB specified voltage may also be used. Furthermore,
in the present embodiment, the rechargeable battery 41 is removable
from a battery box of the electronic still camera 11 and thus
replaceable by the user. However, the rechargeable battery 41 may
be fixed in the electronic still camera 11 and irremovable by the
user.
[0042] The power supply circuit 40 shown in FIG. 3 includes a
charging circuit 42 for charging the rechargeable battery 41. In
the present embodiment, at least the sub-CPU 26 and the power
supply circuit 40 form a charger that charges the rechargeable
battery 41. The sub-CPU 26 includes a flash memory 26a, which
stores a charging control process routine illustrated in the
flowchart of FIG. 5. If a USB connection is detected when the power
of the electronic still camera 11 is off, the sub-CPU 26 executes
the program to perform the charging control on the rechargeable
battery 41.
[0043] FIG. 4 is a block diagram showing the engine 35, the sub-CPU
26, and the power supply circuit 40. The power supply circuit 40
includes a power supply IC 51, a reset IC 52, a charge control IC
53 serving as a charging unit, a first switch element S1, a second
switch element S2, and a third switch element S3.
[0044] The USB controller 39 in the engine 35 is connected to the
USB connector 20 by a power supply line 54 of the power supply
voltage Vbus, a D+ differential signal line 55, and a D-
differential signal line 56. The USB cable 21 includes a Vbus power
supply line and GND power supply line (both not shown) and a D+
differential signal line and D- differential signal line (both not
shown). The Vbus power supply line and GND power supply line are
respectively connected to a Vbus terminal and a GND terminal of the
USB connector 20 when the USB connectors 20 and 21a are connected.
The D+ differential signal line and D- differential signal line are
respectively connected to the D+ terminal and the D- terminal of
the USB connector 20 when the USB connectors 20 and 21a are
connected.
[0045] A wire 57 branched from the power supply line 54 is
connected to an interruption (INT) terminal of the sub-CPU 26. Node
A in the wire 57 is connected to the VDD terminal of the power
supply IC 51 via the first switch element S1 and a diode D1, which
are connected in series. The rechargeable battery 41 has a positive
electrode connected to the VDD terminal of the power supply IC 51
via the second switch element S2 and a grounded negative electrode.
The gate terminal G of the second switch element S2 is connected to
the anode terminal of the diode D1. The diodes in each switch
element S1 and S2 are parasitic diodes.
[0046] The source terminal S and the gate terminal G of the first
switch element S1 are connected via a resistor R1. The source
terminal S of the third switch element S3 is connected to the
source terminal S of the first switch element S1, and the drain
terminal D of the third switch element S3 is connected to the gate
terminal G of the first switch element S1. The gate terminal G of
the first switch element S1 and the drain terminal D of the third
switch element S3 are both grounded via a resistor R2.
[0047] Node A and the gate terminal G of the third switch element
S3 are connected via a resistor R3. The gate terminal G of the
third switch element S3 is also connected to a Port 2 terminal
(open drain) of the sub-CPU 26. The gate terminal G of the second
switch element S2 is grounded via a resistor R4. In the present
embodiment, the first to the third switch elements S1 to S3 are
configured by a p-channel MOS field effect transistor (MOSFET).
[0048] The reset IC 52 has an IN terminal connected to the source
terminal S of the second switch element S2 and an OUT terminal
connected to a Reset terminal of the sub-CPU 26. The Port 1
terminal of the sub-CPU 26 is connected to an Enable terminal of
the power supply IC 51.
[0049] If the input voltage to the INT terminal of the sub-CPU 26
has an L level when the USB connectors 20 and 21a are unconnected,
the sub-CPU 26 opens the Port 2 terminal, which is connected to the
gate terminal G of the third switch element S3. Thus, in a USB
unconnected state (unconnected state of USB connectors 20 and 21a),
the first switch element S1 is deactivated and the voltage applied
to the gate terminal G of the second switch element S2 has an L
level. This deactivates the second switch element S2.
[0050] If the power switch 17 is turned on when the voltage input
to the INT terminal has an L level, the sub-CPU 26 determines
whether or not the power supply voltage Vbatt of the rechargeable
battery 41 input to the IN terminal of the reset IC 52 is greater
than or equal to a predetermined voltage. When the power supply
voltage Vbatt is greater than or equal to the predetermined
voltage, the sub-CPU 26 sends an enable signal from the Port 1
terminal to the Enable terminal of the power supply IC 51. When the
power supply voltage Vbatt is less than the predetermined voltage,
the sub-CPU 26 does not output the enable signal to the power
supply IC 51. Therefore, if the power switch 17 is turned on when
the electronic still camera 11 is in the USB unconnected state and
as long as the power supply voltage Vbatt is greater than or equal
to the predetermined voltage, the power supply IC 51 is driven
based on the enable signal input from the sub-CPU 26.
[0051] In other words, when the enable signal is input to the
Enable terminal, the power supply IC 51 generates a plurality of
power supply voltages VDD2, . . . , VDDn from the power supply
voltage Vbus or the power supply voltage Vbatt input from the VDD
terminal and outputs the power supply voltages from output
terminals OUT2, . . . OUTn. For instance, the voltage VDD2 is
supplied to the main CPU 25, the voltage VDD3 is output to the
motor control unit 28, and the voltage VDD4 is output to the flash
control unit 29. The power supply IC 51 constantly supplies the
power supply voltage VDD1 from the output terminal OUT1 to the
sub-CPU 26 even when the power is off. The sub-CPU 26 is thus
driven even when the power is turned off and is thereby capable of
detecting the connection and disconnection of the USB cable 21 to
and from the USB connector 20, detecting the operation of various
operation switches (operation buttons), and processing the time
measured by timing counter.
[0052] When the USB connector 21a is connected to the USB connector
20 and the power supply voltage Vbus (H level) is input to the INT
terminal of the sub-CPU 26, the sub-CPU 26 sends the enable signal
from the Port 1 terminal to the Enable terminal of the power supply
IC 51 to drive the power supply IC 51. The Port 2 terminal remains
open so that an H level voltage is applied to the gate terminal G
of the third switch element S3. This deactivates the third switch
element S3. As a result, the first switch element S1 is activated.
In this state, an H level voltage of H level is applied to the gate
terminal G of the second switch element S2. This deactivates the
second switch element S2. Thus, the power supply voltage supplied
to the VDD terminal of the power supply IC 51 switches from the
power supply voltage Vbatt of the rechargeable battery 41 to the
bus power of the USB cable 21, namely, the power supply voltage
Vbus.
[0053] If the voltage of the rechargeable battery 41 is less than a
predetermined voltage when the electronic still camera 11 is in an
USB unconnected state, the supply of power from the rechargeable
battery 41 to the sub-CPU 26 is also stopped. Thus, the sub-CPU 26
stops functioning and is deactivated. In this case, the output of
the Port 2 terminal becomes unstable (Hi-Z etc.). Even in such a
state, when the USB cable 21 is connected and the power supply
voltage Vbus is supplied, an H level voltage based on the power
supply voltage Vbus is applied to the gate terminal G of the third
switch element S3 via the resistor R3. This deactivates the third
switch element S3. As a result, the first switch element S1 is
activated and the second switch element S2 is deactivated.
[0054] The sub-CPU 26 includes an A/D converter circuit 60. The
rechargeable battery 41 incorporates a temperature sensor (not
shown) and includes a temperature terminal T, which outputs a
temperature detection signal of the temperature sensor. The A/D
converter circuit 60 digitally converts an analog detection signal
corresponding to the temperature of the rechargeable battery 41
output from the temperature terminal T to generate a digital
signal, which is input to the sub-CPU 26. Based on the detected
temperature represented by the digital value, the sub-CPU 26
determines the temperature of the rechargeable battery 41. In this
case, the sub-CPU 26 instructs the charge control IC 53 to charge
the rechargeable battery 41 when the temperature of the
rechargeable battery 41 is within a chargeable temperature range
(e.g., 40.degree. C. or less). The voltage at node C in the wire 57
(i.e., power supply voltage Vbus), which is connected to the power
supply line 54, is input to the A/D converter circuit 60 via a wire
58. The sub-CPU 26 receives a digital value corresponding to the
value of the power supply voltage Vbus as a measurement voltage Vm
via the A/D converter circuit 60. In the present embodiment, the
measurement voltage Vm corresponds to a measurement value. The
wires 57 and 58 and the A/D converter circuit 60 form a measurement
unit.
[0055] The charge control IC 53 is an integrated circuit that
controls the value of the charging current when charging the
rechargeable battery 41. The VDD terminal of the charge control IC
53 is connected to node B in the wire 57. The power supply voltage
Vbus is thus supplied to the VDD terminal of the charge control IC
53 when the USB connectors 20 and 21a are connected. An OUT
terminal of the charge control IC 53 is connected to the positive
electrode of the rechargeable battery 41. An SIO terminal of the
charge control IC 53 is connected to an SIO terminal of the sub-CPU
26. The sub-CPU 26 transmits in serial charging control command
data from the SIO terminal to the SIO terminal of the charge
control IC 53 to set a charging current value and instruct the
charge control IC 53 to perform charging at the set current value.
When receiving a charging initiation command, the charge control IC
53 charges the rechargeable battery 41 while controlling the value
of the charging current output from the OUT terminal so as to match
the set current value based on the power (bus power) of the power
supply voltage Vbus supplied to the VDD terminal.
[0056] The charging control process will now be discussed. The
charging control process is executed as shown in the flowchart of
FIG. 5. The charging control process of FIG. 5 is executed by the
sub-CPU 26 regardless of whether the power of the electronic still
camera 11 is on or off.
[0057] First, in step S10, the sub-CPU 26 determines whether or not
connection of a USB cable has been detected. The sub-CPU 26
proceeds to step S20 when connection of a USB cable has been
detected and waits until a connection is detected when the
connection of a USB cable is not detected. In the present
embodiment, the wire 57 and the sub-CPU 26 performing the
determination of step S10 form a detection unit.
[0058] In step S20, the sub-CPU 26 determines whether or not the
temperature of the rechargeable battery 41 is within the chargeable
range. The sub-CPU 26 proceeds to step S30 when the temperature of
the rechargeable battery 41 is within the chargeable range and
terminates the charging control process routine when the
temperature is not within the chargeable range (i.e., outside the
chargeable range).
[0059] In step S30, the sub-CPU 26 acquires the measurement voltage
Vm.
[0060] In step S40, the sub-CPU 26 determines whether or not the
measurement voltage Vm is the rated voltage of the genuine AC
adapter 23a (i.e., whether Vg1.ltoreq.Vm.ltoreq.Vg2 is satisfied).
When the measurement voltage Vm is within the range of Vg1 to Vg2,
the sub-CPU 26 determines that the electronic device serving as the
connection origin is the genuine AC adapter 23a. In this example,
Vg1 is the rated voltage 4.2 V of the rechargeable battery 41, and
Vg2 is 4.39 V, which is less than the lower limit 4.40 V of the USB
specified voltage. Further, in this example, the rated voltage of
the genuine AC adapter 23a is set to 4.3 V and thereby sets
Vg1.ltoreq.Vm.ltoreq.Vg2. The sub-CPU 26 proceeds to step S50 when
Vg1.ltoreq.Vm.ltoreq.Vg2 is satisfied, and proceeds to step S60
when Vg1.ltoreq.Vm.ltoreq.Vg2 is not satisfied. If
Vg1.ltoreq.Vm.ltoreq.Vg2 is not satisfied, the sub-CPU 26 executes
following steps S60 to 5120 to determine the appropriate charging
current value Ib for charging the rechargeable battery 41.
[0061] First, in step S60, the sub-CPU 26 calculates an initial
charging current Io. The initial charging current Io is calculated
as a value obtained by subtracting the current consumed during
charging operation from the minimum value of the USB standard,
which is 100 mA. For instance, if the consumption current of the
sub-CPU 26, the charge control IC 53, and the like that are driven
during the charging is 20 mA (known consumption current), the
sub-CPU 26 sets 100-20=80 mA as the initial charging current Io.
The rechargeable battery 41 is charged even when the electronic
still camera 11 is turned on as long as there is enough bus power.
In such a case, for example, when the LCD 18 is driven, the initial
charging current Io is calculated by further subtracting the
consumption current of the display systet including the LCD 18.
[0062] In step S70, the sub-CPU 26 sets the charging current I and
instructs the charge control IC 53 to start charging. In this
specification, the charging performed with the charging current I
is referred to as "test charging". Since the test charging is
performed for the first time, the sub-CPU 26 sets the initial
charging current Io as the charging current I. When the sub-CPU 26
instructs test charging with the initial charging current Io for
the first time, the charge control IC 53 charges the rechargeable
battery 41 with the initial charging current Io.
[0063] In following step S80, the sub-CPU 26 acquires the present
measurement voltage Vm.
[0064] In step S90, the sub-CPU 26 determines whether or not the
measurement voltage Vm is greater than or equal to a threshold
value Vo (threshold voltage) (i.e., whether Vm.gtoreq.Vo is
satisfied). The threshold value Vo is a value corresponding to the
lowest voltage value of the measurement voltage Vm that guarantees
the charging of the charge control IC 53 (charging unit). The
threshold value Vo is set to include a slight margin so that the
charging may be reliably guaranteed even if a slight voltage
fluctuation or the like occurs. Thus, when Vm.gtoreq.Vo cannot be
satisfied, the sub-CPU 26 determines that the monitored measurement
voltage Vm is in an unstable range that cannot guarantee the
charging of the charge control IC 53. When Vm.gtoreq.Vo is
satisfied, the sub-CPU 26 determines that the monitored measurement
voltage Vm is a value in a stable range that can guarantee the
charging of the charge control IC 53. If determined that
Vm.gtoreq.Vo is satisfied, the sub-CPU 26 proceeds to step
S100.
[0065] In step S100, the sub-CPU 26 increases the charging current
I by .DELTA.I. That is, the sub-CPU 26 increases the charging
current I by one step from the initial charging current Io in step
S100 to monitor the measurement voltage Vm while increasing the
charging current I in steps by .DELTA.I (e.g. 50 mA) during the
test charging. The current value increment .DELTA.I may be any
value that allows for test charging to be performed for a number of
times until the charging current I, which starts from the initial
charging current Io, reaches the maximum current value 500 mA of
the USB standard. However, the current value increment .DELTA.I is
preferably set to a predetermined value within a range of 10 to 100
mA.
[0066] In step S110, the sub-CPU 26 determines whether or not the
charging current I is less than or equal to 500 mA (i.e., whether
or not I.ltoreq.500 mA is satisfied). That is, the sub-CPU 26
determines whether or not the charging current I has not reached
the maximum current value "500 mA" of the USB standard. This is
because the charging current I cannot be further increased when it
exceeds the USB standard maximum current value of "500 mA" (when
I.ltoreq.500 mA is not satisfied). Therefore, the sub-CPU 26
determines whether or not the charging current I during test
charging exceeds the upper limit.
[0067] When I.ltoreq.500 mA is satisfied, the charging current I
has not yet exceeded the upper limit. Thus, the sub-CPU 26 returns
to step S70.
[0068] In step S70, the sub-CPU 26 sets the charging current I
instructs the charge control IC 53 to start charging. This time,
the charging start command is performed with the current value
(Io+.DELTA.I), which is set as the charging current I that has been
incremented by the current value increment .DELTA.I from the
initial charging current Io. The charge control IC 53 charges the
rechargeable battery 41 with the charging current
I=Io+.DELTA.I.
[0069] The sub-CPU 26 then acquires the present measurement voltage
Vm (S80) and determines whether or not Vm.gtoreq.Vo is satisfied
(S90). When Vm.gtoreq.Vo is satisfied, the sub-CPU 26 again
increases the charging current I by the current value increment
.DELTA.I (I=Io+2.DELTA.I) (S100). When I.ltoreq.500 mA is satisfied
(S110), the sub-CPU 26 sets the charging current I(=Io+2.DELTA.I)
and instructs the charge control IC 53 to start charging.
[0070] Subsequently, in the same manner, the sub-CPU 26 repeats
steps S70 to S110 until one of either the measurement voltage Vm
becomes smaller than the threshold value Vo (Vm.gtoreq.Vo is not
satisfied in S90) or the charging current I exceeds 500 mA
(I.ltoreq.500 mA is not satisfied) is satisfied while repetitively
increasing the charging current I by the current value increment
.DELTA.I.
[0071] Test charging is performed an n number of times while
increasing the charging current I by .DELTA.I from Io to
Io+.DELTA.I, Io+2.DELTA.I, Io+3.DELTA.I, . . . , and
Io+(n-1).DELTA.I (where "n" indicates nth time). If either one of
Vm.gtoreq.Vo (S90) and I.ltoreq.500 mA (S110) is not satisfied at
the nth time, the sub-CPU 26 proceeds to step S120. That is, when
Vm.gtoreq.Vo (S90) is not satisfied and the charging current value
I is in an unstable range in which charging is unstable or when
reaching the maximum current value 500 mA of the USB standard, the
sub-CPU 26 proceeds to step S120.
[0072] In step S120, the sub-CPU 26 calculates In=I-.DELTA.I. When
the charging current value I is in the unstable range win which
charging may be unstable, the sub-CPU 26 returns the charging
current value I to the preceding value and uses Ib=I-.DELTA.I at
which charging is stable. That is, if the monitored measurement
voltage is in the unstable range in which the charging operation of
the charge control IC 53 (charging unit) cannot be guaranteed, the
sub-CPU 26 uses the charging current I used in the preceding test
charging as the charging current value Ib. The charging current
value Ib is the maximum value of the charging currents I that were
used until the preceding test charging was performed and is a value
that maintains the power supply voltage Vbus (measurement voltage
Vm) in the range that guarantees stable charging. When the charging
current value I exceeds the maximum current value 500 mA of the USB
standard, the sub-CPU 26 also uses Ib=I-.DELTA.I (.ltoreq.500 mA),
which is the preceding charging current value I (>500), as the
charging current value Ib.
[0073] After the charging current value Ib is determined through
the above test charging (S60 to S120), the sub-CPU 26 sets the
charging current Ib and instructs the charge control IC 53 to start
charging in step S130. The charging (actual charging) of the
rechargeable battery 41 is performed with the determined charging
current Ib by the charge control IC 53. As a result, the
rechargeable battery 41 is stably charged.
[0074] If the suppliable current of another electronic device
serving as a connection origin is 100 mA, Vm.gtoreq.Vo becomes
unsatisfied when the charging current value I has a relatively low
current during the test charging, and the rechargeable battery 41
is either charged by a small charging current or not charged at
all. If the suppliable current of another electronic device serving
as the connection origin is 500 mA, Vm.gtoreq.Vo is not satisfied
or I.ltoreq.500 mA is not satisfied when the charging current value
I is a relatively high current during the test charging, and the
rechargeable battery 41 is charged with the relatively high
preceding charging current Ib (Ib<500).
[0075] When the non-genuine AC adapter 23b is used, the condition
of Vg1.ltoreq.Vm.ltoreq.Vg2, which is for the genuine AC adapter
23a, is not satisfied. Thus, the appropriate charging current value
Ib corresponding to the unknown specified current of the
non-genuine AC adapter 23b is determined by performing the test
charging (S60 to S120). As a result, the rechargeable battery 41 is
stably charged even when the other electronic device serving as a
connection origin is the non-genuine AC adapter 23b.
[0076] Since Vg1.ltoreq.Vm.ltoreq.Vg2 is satisfied when the genuine
AC adapter 23a is used, the charging current Ib is obtained through
calculations based on the known suppliable current Ig (specified
current value) of the genuine AC adapter 23a (S50). Thus, the
rechargeable battery 41 is stably charged with the genuine AC
adapter 23a.
[0077] When one part of the electronic still camera 11 is driven
during the actual charging and additional power is thereby
consumed, a command for changing the charging current value in
accordance with the monitoring result of the measurement voltage is
output. Therefore, the rechargeable battery 41 is stably charged
and subtly affected by the driving of another part of the
electronic still camera 11.
[0078] As described above in detail, the first embodiment has the
advantages described below.
[0079] (1) The sub-CPU 26 monitors the measurement voltage Vm while
increasing the charging current value by .DELTA.I from the initial
charging current Io. When the monitored measurement voltage Vm
enters the unstable range in which the charging of the charge
control IC 53 (charging unit) cannot be guaranteed, the sub-CPU 26
determines the charging current value Ib so that the measurement
voltage Vm would not be in the unstable range. This stably charges
the rechargeable battery 41.
[0080] (2) The sub-CPU 26 determines a charging current Ib that is
appropriate regardless of whether the other electronic device
serving as the connection origin uses the USB specified current of
100 mA or 500 mA.
[0081] (3) If the charging current I reaches a value greater than
or equal to the USB specified maximum current of 500 mA during the
test charging, the sub-CPU 26 uses the preceding charging current
value Ib (=I-.DELTA.I) for the actual charging and determines the
charging current Ib to be less than the upper limit (smaller than
500 mA) of the USB standard. This stably charges the rechargeable
battery 41 and avoids unstable charging with excessive charging
current.
[0082] (4) Test charging is performed to determine the appropriate
charging current value Ib. Thus, even during connection of the
non-genuine AC adapter 23b, of which suppliable current value
(specified current value) is not known, the rechargeable battery 41
is stably charged.
[0083] (5) The suppliable voltage (specified current value Vg) of
the genuine AC adapter 23a is set as a value that is in the voltage
range in which the rechargeable battery 41 is charged and in a
range (Vg1.ltoreq.Vg.ltoreq.Vg2) that differs from the USB
specified voltage (=5V). The sub-CPU 26 determines that the other
electronic device serving as the connection origin is the genuine
AC adapter 23a when the initial measurement voltage Vm, which is
obtained before starting the test charging, satisfies the condition
of Vg1.ltoreq.Vm.ltoreq.Vg2. That is, connection of the genuine AC
adapter 23a is determined from the value of the measurement voltage
Vm without performing the test charging. Therefore, the sub-CPU 26
determines the charging current Ib based on the known suppliable
current Ig of the genuine AC adapter 23a. This stably charges the
rechargeable battery 41.
[0084] (6) The sub-CPU 26 monitors whether or not the measurement
voltage Vm is greater than or equal to the threshold value Vo by
directly using the detection value of the power supply voltage Vbus
as the measurement value (measurement voltage Vm). This eliminates
the need to perform unnecessary calculations of the measurement
value and allows for simple monitoring.
[0085] (7) The sub-CPU 26 does not need to know the specified
current of another electronic device that serves as a connection
origin. Thus, the main CPU 25 does not need to be activated even
when the USB connection is detected while the power is off.
Second Embodiment
[0086] A second embodiment will now be discussed with reference to
FIG. 6. The second embodiment differs from the first embodiment in
that the main CPU 25 is activated to acquire the standard-specified
current information (specified power supply information) of another
electronic device serving as the connection origin with the USB
communication. Otherwise, the structure of the electronic still
camera 11 is the same as the first embodiment. Thus, only the
contents of the charging control process will be described below in
detail. In the present embodiment, at least the main CPU 25, the
sub-CPU 26, and the power supply circuit 40 form the charger for
charging the rechargeable battery 41.
[0087] Referring to FIG. 6, when the sub-CPU 26 detects connection
of the USB cable 21 (affirmative determination in step S210) and
determines that the temperature of the rechargeable battery 41 is
in a chargeable range (affirmative determination in step S220), the
sub-CPU 26 proceeds to step S230 and activates the main CPU 25.
When the main CPU 25 is activated (affirmative determination in
step S240), the main CPU 25 performs USB communication in step
S250. In this case, if the other electronic device serving as the
connection origin is a USB host (or upper level USB device) such as
the PC 22, the main CPU 25 performs USB communication through the
USB controller 39 with the other electronic device serving as the
connection origin to acquire the suppliable current Iusb (specified
current) from that other electronic device. The USB communication
connection cannot be established if the other electronic device
serving as the connection origin is an AC adapter 23. The main CPU
25 that performs USB communication in step S250 and acquires the
standard-specified power supply information (information on
specified current etc.) forms a power supply information acquiring
unit.
[0088] In step S260, the sub-CPU 26 determines whether or not USB
communication has been established. If USB communication has not
been successful (affirmative determination in step S260), the
sub-CPU 26 calculates the charging current Ib based on the
suppliable current Iusb acquired through the USB communication by
the main CPU 25 in step S270. In step S280, the sub-CPU 26
deactivates the main CPU 25. Then, the sub-CPU 26 sets the charging
current Ib and instructs the charge control IC 53 to start charging
in step S400. As a result, the rechargeable battery 41 is stably
charged with the appropriate charging current Ib corresponding to
the suppliable current Iusb acquired from the other electronic
device serving as the connection origin. In the present embodiment,
the suppliable current Iusb (e.g., information on whether 100 mA or
500 mA) acquired through USB communication in step S270 corresponds
to specified current value information (specified power supply
information).
[0089] If USB communication is not established in step S260
(negative determination in S260), the other electronic device
serving as the connection origin is not a USB device and is an
electronic device that cannot perform USB communication. Thus, the
sub-CPU 26 determines that the other electronic device serving as
the connection origin is an AC adapter. In the present embodiment,
the sub-CPU 26 performing the determination process of step S260
forms a determination unit for determining that the other
electronic device is an AC adapter when the power supply
information acquiring unit cannot perform communication with the
other electronic device. The main CPU 25 may function as a
determination unit that notifies its determination result to the
sub-CPU 26.
[0090] If USB communication is not established, the sub-CPU 26
deactivates the main CPU 25 in step S290 and acquires the
measurement voltage Vm in step S300. Then, in step S310, the
sub-CPU 26 determines whether or not the measurement voltage Vm is
in the specified voltage range of the genuine AC adapter 23a (i.e.,
whether or not Vg1.ltoreq.Vm.ltoreq.Vg2 is satisfied). The sub-CPU
26 proceeds to step S320 if Vg1.ltoreq.Vm.ltoreq.Vg2 is satisfied
and proceeds to step S330 if Vg1.ltoreq.Vm.ltoreq.Vg2 is not
satisfied. If Vg1.ltoreq.Vm.ltoreq.Vg2 is not satisfied in step
S310, the sub-CPU 26 determines the appropriate charging current
value with which the rechargeable battery 41 is to be charged
through the processes of steps S330 to S390. The processes of S330
to S390 are similar to the processes of S60 to S120 in the first
embodiment.
[0091] During test charging, when the measurement voltage Vm enters
an unstable range in which it cannot be greater than or equal to
the threshold value Vo (Vm.gtoreq.Vo) (negative determination in
step S360), the sub-CPU 26 sets the charging current Ib preceding
the present charging current I (=I-Ib) as the actual charging in
step S390. When determining that the charging current I exceeds the
maximum current 500 mA of the USB standard (I.ltoreq.500 mA is not
satisfied) in step S380, the sub-CPU 26 sets the charging current
Ib preceding the present charging current I (=I-Ib) as the actual
charging in step S390. In the second embodiment as well, Thus, the
charging current Ib is appropriately determined, and the
rechargeable battery 41 is stably charged.
[0092] (8) In the second embodiment, the main CPU 25 acquires the
suppliable current Iusb from the other electronic device serving as
the connection origin when USB communication can be performed.
Thus, the charge control IC 53 stably charges the rechargeable
battery 41 with the charging current Ib based on the acquired
suppliable current Iusb. The sub-CPU 26 performs test charging and
determines the charging current Ib when USB communication is not
established. Therefore, the sub-CPU 26 determines the appropriate
charging current Ib, and the rechargeable battery 41 is stably
charged by the charge control IC 53 even when the non-genuine AC
adapter 23b is connected. When the genuine AC adapter 23a is
connected, the sub-CPU 26 identifies the electronic device as the
genuine AC adapter 23a from the value of the measurement voltage Vm
and determines the charging current Ib based on the known
suppliable current Ig. Thus, the rechargeable battery 41 is more
stably charged compared to the charging current determined in the
test charging.
Third Embodiment
[0093] A third embodiment will now be discussed with reference to
FIG. 7. In the third embodiment, the measurement value differs from
each of the above-described embodiments. More specifically, in each
of the embodiments described above, the sub-CPU 26 controls the
charging current amount Ib by directly using the measurement value
(measurement voltage Vm). In the third embodiment, the sub-CPU 26
determines the voltage drop amount and the voltage drop rate based
on the measurement (measurement voltages Vm and Vp) of the power
supply voltage Vbus to control the charging current amount Ib using
at least one of the voltage drop amount and the voltage drop rate
as the measurement value. Otherwise, the structure of the
electronic still camera 11 is the same as the first embodiment.
Thus, only the contents of the charging control process will be
discussed below in detail.
[0094] As shown in FIG. 7, the processes of steps S510 to S550 and
S660 are similar to the processes of steps S10 to S50 and S130 of
FIG. 5. Hence, when the temperature of the rechargeable battery 41
is in the chargeable range (affirmative determination in S520)
after detection of a USB cable connection (affirmative
determination in S510), the sub-CPU 26 acquires the measurement
voltage Vm (S530). If the measurement voltage satisfies the
condition of Vg1.ltoreq.Vg.ltoreq.Vg2 (affirmative determination in
S540), the sub-CPU 26 calculates the charging current Ib based on
the suppliable current Ig of the genuine AC adapter 23a (S550), and
performs the setting of the charging current Ib and instructs the
charge control IC 53 to start charging (S660) to charge the
rechargeable battery with the supply voltage from the genuine AC
adapter 23a.
[0095] When the other electronic device that serves as the
connection origin is an electronic device that is not the genuine
AC adapter 23a, the sub-CPU 26 determines the appropriate charging
current Ib by performing the processes of steps S560 to S650.
First, in step S560, the sub-CPU 26 calculates the initial charging
current Io (I=Io). In step S570, the sub-CPU 26 sets the charging
current I and instructs the charge control IC 53 to start charging
(test charging). The sub-CPU 26 then acquires the measurement
voltage Vp obtained in the test charging under the present charging
current I (=Io). The measurement voltage Vp is the same as the
measurement voltage Vm in step S80 of FIG. 5. However, in the
present embodiment, the measurement voltage during test charging is
denoted as "Vp" to distinguish it from the measurement voltage Vm
measured in step S530 before starting charging.
[0096] In step S590, the sub-CPU 26 calculates the voltage drop
amount .DELTA.V from the equation .DELTA.V=Vm-Vp. The voltage drop
amount .DELTA.V indicates the voltage drop amount represented by
the difference between the measurement voltage Vm obtained before
charging is started and the measurement voltage Vp obtained in the
present test charging. In the present embodiment, the measurement
voltage Vm in step S530 corresponds to the "initial power supply
voltage". The voltage drop amount .DELTA.V of step S590 corresponds
to the "voltage drop amount or the difference between the initial
power supply voltage and the power supply voltage during
charging".
[0097] In step S600, the sub-CPU 26 determines whether or not the
voltage drop amount .DELTA.V is greater than or equal to a
threshold value .DELTA.Vo. If the voltage drop amount .DELTA.V is
greater than or equal to the threshold value .DELTA.Vo (set drop
amount), this indicates that the power supply voltage Vbus has been
lowered to an extent in which the charging of the rechargeable
battery 41 becomes unstable. The sub-CPU 26 proceeds to step S610
if .DELTA.V.gtoreq..DELTA.Vb is not satisfied and proceeds to step
S650 if .DELTA.V.gtoreq..DELTA.Vo is satisfied.
[0098] In step S610, the sub-CPU 26 calculates the voltage drop
rate Rv from the equation Rv=(Vpold-Vpnew)/.DELTA.I. Here, Vpold is
the previous measurement voltage Vp, Vpnew is the present
measurement voltage Vp, and .DELTA.I is the incremented amount of
the present charging current I from the preceding charging current
I. In general terms, when the charging current is raised from the
preceding value I.sub.n-1 to the present value I.sub.n, the voltage
drop rate Rv is expressed by the equation
Rv=(V.sub.n-1-V.sub.n)/(I.sub.n-1-I.sub.n) using the previous
measurement voltage V.sub.n-1 and the present measurement voltage
V.sub.n. Here, n is the number of times test charging is performed.
In the present example in which the charging current is increased
by .DELTA.I, the expression of I.sub.n-1-I.sub.n=.DELTA.I is
obtained. Thus, the .DELTA.I is a constant in the test charging in
which the charging current is increased by .DELTA.I. The previous
measurement voltage V.sub.n-1 is the power supply voltage Vbus
measured when performing charging with charging current I.sub.n-1.
The present measurement voltage V.sub.n is the power supply voltage
Vbus measured when performing charging with the charging current
I.sub.n. When test charging is performed for the first time at the
initial charging current Io, the first voltage drop rate Rv may be
calculated using .DELTA.I=Io. First, the determination by the
voltage drop rate Rv may be omitted as long as test charging is
performed for the first time.
[0099] As apparent from the above equation, the voltage drop rate
Rv is a value indicating the proportion (ratio) of the voltage
change amount between the previous measurement voltage V.sub.n-1
and the present measurement voltage V.sub.n for the change amount
(incremented current value) .DELTA.I of the previous charging
current I.sub.n-1 and the present charging current I.sub.n. When
the charging current is raised by .DELTA.I and the measurement
voltage Vp (measurement value of power supply voltage Vbus) thereby
suddenly falls for a large amount, this may indicate that the
consumption current of the electronic still camera 11 has exceeded
the USB specified current and the power supply voltage Vbus has
become unstable. Therefore, in the present embodiment, the sub-CPU
26 determines that the charging current I has entered the unstable
range in which stable charging cannot be performed when the voltage
drop rate Rv becomes greater than or equal to the threshold value
Rvo (set threshold value).
[0100] In step S620, the sub-CPU 26 determines whether or not the
voltage drop rate Rv is greater than or equal to the threshold
value Rvo. The sub-CPU 26 proceeds to step S630 when Rv.gtoreq.Rvo
is not satisfied and proceeds to step S650 when Rv.gtoreq.Rvo is
satisfied.
[0101] In step S630, the sub-CPU 26 increases the charging current
I by the current value increment .DELTA.I (I=I+.DELTA.I) and
repeats the processes of steps S570 to S640 until
.DELTA.V.gtoreq..DELTA.Vo is satisfied in S600, Rv.gtoreq.Rvo is
satisfied in S620, or I.ltoreq.500 mA is not satisfied in S640.
When raising the charging current I by .DELTA.I during test
charging, if the consumption current in the electronic still camera
11 exceeds the USB specified current and the power supply voltage
Vbus becomes unstable, at least one of .DELTA.V.gtoreq..DELTA.Vo or
Rv.gtoreq.Rvo is satisfied. Thus, the sub-CPU 26 proceeds to step
S650. The sub-CPU 26 returns the charging current I to the
preceding value and sets this value as the charging current Ib
(=I-.DELTA.I) for actual charging (S650). Then, the sub-CPU 26 sets
the charging current Ib and instructs the charge control IC 53 to
start charging (S660). The rechargeable battery 41 is stably
charged with the charging current Ib that is determined in this
manner.
[0102] In the present embodiment, an affirmative determination in
step S600 corresponds to a state in which "the voltage drop amount
is greater than or equal to the set drop amount". The expression of
Ib=I-.DELTA.I in step S650 corresponds to a state for "reducing the
charging current value". Furthermore, in the present embodiment,
the wires 57 and 58, the A/D converter circuit 60, and the sub-CPU
26 form a measurement unit for acquiring the voltage drop amount
.DELTA.V and the voltage drop rate Rv, which serve as measurement
values.
[0103] It should be apparent to those skilled in the art that the
present invention may be embodied in many other specific forms
without departing from the spirit or scope of the invention.
Particularly, it should be understood that the present invention
may be embodied in the following forms.
[Modification 1]
[0104] As shown in FIG. 8, a structure using only one CPU 70 may be
employed. As shown in FIG. 8, the CPU 70 includes the USB
controller 39, the A/D converter circuit 60, the Reset terminal,
the Port 1 terminal, the Port 2 terminal, the SID terminal, the IN
terminal, and the like. The CPU 70 implements the functions of both
the main CPU 25 and the sub-CPU 26 of the first to third
embodiments. The power supply voltage VDD1 (standby voltage) is
supplied from the power supply circuit 40 to the CPU 70 in a power
off state so that the CPU 70 performs the detection of a USB
connector connection, the detection of a switch operation, the
counting process of the timing counter, and the like. In a power on
state, the power supply voltages VDD2 to VDDn are generated by the
power supply IC 51 based on the enable signal from the Port 1
terminal and output to the corresponding power supplying
destinations. The voltage (power supply voltage Vbus) at node C in
the wire 57, which is capable of supplying the power supply voltage
Vbus, is input to the A/D converter circuit 60 through the wire 58.
The CPU 70 acquires the measurement voltage Vm. Thus, the CPU 70
performs the charging control-process in accordance with the
flowchart shown in FIG. 5 of the first embodiment or the flowchart
shown in FIG. 6 of the second embodiment. Furthermore, the CPU 70
may calculate the voltage drop amount .DELTA.V and the voltage drop
rate Rv from the measurement voltage Vm and perform the charge
control through the flowchart shown in FIG. 7 of the third
embodiment. The power supply circuit 40 shown in FIG. 8 has a
structure similar to that shown in FIG. 4. In this modification,
the CPU 70 forms the detection unit, the measurement unit, the
control unit, the power supply information acquiring unit, and the
determination unit.
[Modification 2]
[0105] In each of the embodiments described above, when the
measurement value of the charging current I enters an unstable
range, the sub-CPU 26 sets Ib=I-.DELTA.I as the charging current
value Ib for actual charging. The sub-CPU 26 may also further
finely add .DELTA.i (<.DELTA.I) in the range of
I-.DELTA.I.ltoreq.Ib<I (I=I-.DELTA.I+.DELTA.i, . . . ,
I-.DELTA.I+m.DELTA.i) and determines the maximum charging current
that guarantees that the present measurement value obtained from
the monitoring result of the measurement value is in a stable
range. Further, the expressions of Ib=I-.DELTA.In (where
.DELTA.In>.DELTA.I) may be used.
[Modification 3]
[0106] In the third embodiment, the sub-CPU 26 may activate the
main CPU 25 when detecting a USB connection to perform USB
communication with the other electronic device that serves as the
connection origin and determine the charging current Ib based on
the suppliable current (specified current) of that electronic
device in the same manner as the second embodiment. That is, the
processes of S230 to S290 shown in FIG. 6 may be added between S520
and S530 in FIG. 7.
[Modification 4]
[0107] In the third embodiment, only either one of the voltage drop
amount .DELTA.V and the voltage drop rate Rv may be used as the
measurement value. Furthermore, when the voltage drop amount
.DELTA.V and the voltage drop rate Rv are both greater than or
equal to their threshold values .DELTA.Vo and Rvo, it may be
determined that the charging current is in the unstable range, and
the charging current Ib(=I-.DELTA.I) preceding the present charging
current I may be used for the actual charging.
[Modification 5]
[0108] The measurement voltage Vm in the first and the second
embodiments may be further added as a measurement value in the
third embodiment. For instance, when one of the measurement voltage
Vm, the voltage drop amount .DELTA.V, and the voltage drop rate Rv
is in the unstable side of the corresponding threshold value, the
charging current that was in the stable range preceding the present
charging current I may be used for the actual charging. When two or
more of the three measurement values, which are the measurement
voltage Vm, the voltage drop amount .DELTA.V, and the voltage drop
rate Rv, is at the unstable side of the corresponding threshold
value, the preceding charging current may be used for the actual
charging. Further, when all three of the measurement values are at
the unstable side of the corresponding threshold values, the
preceding charging current may be used for the actual charging.
[Modification 6]
[0109] The communication cable is not limited to a USB cable. For
instance, an IEEE 1394 cable may be used.
[Modification 7]
[0110] The electronic device including the charger of the present
invention is not limited to the electronic still camera (digital
still camera), and may be an electronic device such as a mobile
phone, a PDA, a portable game machine, and the like.
[0111] The present examples and embodiments are to be considered as
illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the
scope and equivalence of the appended claims.
[0112] Aspects of the present invention that can be understood from
the disclosure of this specification will now be discussed.
[First Aspect]
[0113] A first aspect is a charger for an electronic device that
charges a rechargeable battery arranged in the electronic device.
The charger includes a detection unit which detects connection of
another electronic device to the electronic device through a
communication cable including a power supply line. A charging unit
charges the rechargeable battery with power supply voltage from the
power supply line of the communication cable. A measurement unit
acquires a measurement value indicating a degree of a voltage drop
of the power supply voltage occurred when the charging unit
performs charging. A control unit instructs a charging current
value for charging the rechargeable battery with the charging unit.
When the detection unit detects connection of the other electronic
device, the control unit monitors the measurement value obtained by
the measurement unit while instructing the charging unit to
increase the charging current value from an initial current value
and determines the charging current value based on the monitored
measurement value.
[0114] In the first aspect, when the detection unit detects
connection of another electronic device, the control unit monitors
the measurement value of the measurement unit, while instructing
the charging unit to increase the charging current value from the
initial current value, and determines the charging current value
based on the monitoring result of the measurement value. Further,
the control unit instructs the charging unit to charge the
rechargeable battery with the determined charging current value.
Therefore, the charging unit stably charges the rechargeable
battery with the charging current value determined from the
monitoring result even when the control unit cannot acquire the
necessary charging information, such as the specified current, from
the other electronic device that serves as the connection
origin.
[Second Aspect]
[0115] In the charger according to the first aspect, when the
monitored measurement value enters an unstable range in which the
charging of the charging unit is not guaranteed, the control unit
preferably determines the charging current value to be in a range
in which the measurement value does not enter the unstable range
and instructs the charging unit to charge the rechargeable battery
with the determined charging current value.
[Third Aspect]
[0116] In the charger according to the first or second aspect, the
measurement unit preferably acquires a dropped power supply voltage
resulting from the charging as the measurement value. When the
measurement value obtained by the measurement unit is less than the
threshold value, the control unit preferably determines the
charging current value so that the measurement value becomes
greater than or equal to a threshold value.
[Fourth Aspect]
[0117] In the charger according to any one of the first to third
aspects, the measurement unit preferably acquires a voltage drop
amount, which is a difference between an initial power supply
voltage when the detection unit detects connection of the other
electronic device and a power supply voltage during charging, as
the measurement value. The control unit preferably decreases the
charging current value when the voltage drop amount becomes greater
than or equal to a set drop amount.
[Fifth Aspect]
[0118] In the charger according to any one of the first to fourth
aspects, when the control unit increases the charging current value
from a previous value I.sub.n-1 to a present value I.sub.n, the
measurement unit preferably calculates, based on a previous power
supply voltage V.sub.n-1 and a present power supply voltage
V.sub.n, a voltage drop rate
(V.sub.n-1-V.sub.n)/(I.sub.n-1-I.sub.n) as the measurement value.
When the voltage drop rate exceeds a set threshold value, the
control unit preferably determines the charging current value so
that the voltage drop rate does not exceed the set threshold
value.
[Sixth Aspect]
[0119] The charger according to any one the first to fifth aspects,
further comprising a power supply information acquiring unit which
acquires specified power supply information of the other electronic
device by communicating with the other electronic device through
the communication cable. A determination unit determines that the
other electronic device is an AC adapter when the power supply
information acquiring unit cannot perform communication with the
other electronic device.
[Seventh Aspect]
[0120] In the charger according to the sixth aspect, the control
unit preferably determines the charging current value in accordance
with specified current value information contained in the specified
power supply information when the power supply information
acquiring unit performs communication with the other electronic
device.
[Eighth Aspect]
[0121] In the charger according to any one of the first to seventh
aspects, the measurement unit preferably measures the power supply
voltage when the detection unit detects connection of the other
electronic device. When the measured power supply voltage is
outside a specified voltage range that the communication cable is
capable of supplying and greater than or equal to a full charge
voltage of the rechargeable battery, the control unit preferably
determines that the other electronic device is a standard known AC
adapter and instructs the charging unit for a charging current
value corresponding to known specified power supply information of
the standard known AC adapter.
[Ninth Aspect]
[0122] An electronic device including the charger according to any
one of the first to the eighth aspects.
[Tenth Aspect]
[0123] A method for charging a rechargeable battery arranged in an
electronic device. The method includes detecting, by the electronic
device, connection of another electronic device to the electronic
device through a communication cable including a power supply line;
starting, by the electronic device, charging of the rechargeable
battery using a power supply voltage from the power supply line of
the communication cable; acquiring, by the electronic device, a
measurement value indicating a degree of a voltage drop of the
power supply voltage occurred during charging; and determining, by
the electronic device, a charging current value of the rechargeable
battery based on the measurement value. The determining step
includes monitoring the measurement value during the charging while
increasing the charging current value from an initial current
value, and updating the charging current value based on the
monitored measurement value. The method of the tenth aspect has the
same advantages as the first embodiment.
* * * * *