Note: Descriptions are shown in the official language in which they were submitted.
CA 02796143 2016-11-29
SYSTEM AND METHOD FOR EXTERNALLY CONTROLLING THE CHARGING OF A
BATTERY POWERED DEVICE
RELATED APPLICATIONS
This application claims the benefit of priority from U.S. patent application,
publication
number 2011/0260685, filed April 23, 2010 and entitled "EXTERNAL BATTERY
CHARGING UNIT" and from U.S. patent application, publication number
2011/0260678
filed April 23, 2010 and entitled, "A SYSTEM AND METHOD FOR COMPENSATING
FOR IMPEDANCE LOSS ASSOCIATED WITH AN EXTERNAL CHARGING UNIT".
TECHNICAL FIELD
The present invention relates generally to systems and methods for charging
batteries.
More specifically, the present invention relates to a system and method for
charging a
battery, or batteries, in a device using an external charging unit.
BACKGROUND ART
The availability and widespread adoption of mobile computing devices, such as
smartphones, tablet computers, mobile data entry terminals etc. has increased
significantly recently and this trend appears poised to continue for many more
years.
Given the proliferation of mobile computing devices, the size and weight of
the mobile
computing device has become an important factor in enhancing their adoption,
usefulness and attractiveness for users. It is generally very desirable to be
able to
reduce the size and weight of mobile computing devices to increase their
appeal to
users. In addition to the expected issues of miniaturization, packaging and
design
necessary to reduce the size and weight of mobile computing devices, a related
issue
arises in that heat generated within the mobile computing device becomes a
serious
design issue due to the density of the components within the smaller
enclosures for the
computing devices and the higher operating speeds of processors within the
computing
devices, which results in additional heat generation, and the proliferation of
radios (WiFi,
Bluetooth, WAN, GPS, etc.) and other heat generating components with mobile
computing
devices.
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An additional issue facing the manufacturers of mobile computing devices is
the design
and provisioning of the rechargeable batteries used by such devices. Again, as
size and
weight are important design considerations, the selection and design of
batteries for
mobile computing devices typically focuses on the energy storage density of
the battery,
with higher densities desired to enable longer operating times for the
devices. Presently,
the majority of mobile computing devices employ batteries with a lithium ion
(Li-ion)
battery chemistry as these batteries provide a good energy storage density.
However Li-ion and most, if not all, other battery chemistries suitable for
use in mobile
computing devices require carefully managed charging regimes to be employed to
maximize the battery's energy storage and the potential operating lifetime
(number of
possible charge cycles, etc) of the battery and to reduce the possibility of
dangerous
conditions occurring during charging of the battery which could otherwise put
the
computing device and/or user at risk of harm.
Accordingly, mobile computing devices typically include charging control
circuitry and/or
mechanisms which operate to control the charging of their batteries and to
prevent
unsafe charging. While necessary for safe and appropriate operation of the
charging
functions of mobile computing devices, these control mechanisms add to the
weight of
the mobile computing device and also generate waste heat within the mobile
computing
device.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a system and method for
charging at
least one battery in a mobile computing device which obviates or mitigates at
least one
disadvantage of the prior art.
In accordance with an aspect of the present invention, there is provided an
external
charging unit for charging at least one rechargeable battery in a mobile
computing
device, the charging unit configured to be electrically coupled to the mobile
computer
device and being operable to provide a charge to the at least one rechargeable
battery in
accordance with a predefined charging profile; and the charging unit further
comprising
an offset compensator to apply an offset voltage to the charger to compensate
for
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impedance loss between the charger and the at least one battery thereby such
that the
charging proceeds in accordance with the predefined charging profile.
Preferably, the predefined charging profile comprises operating the charger in
a first
mode to provide a constant pre-defined charge current to the at least one
battery to be
charged based on an output voltage of the charger and a in a second mode to
provide a
constant pre-defined charge voltage to the at least one battery to be charged
and the
charger switches from the first mode to the second mode when the output
voltage of the
charger reaches a threshold voltage predefined in the charging profile. Also
preferably,
the charger further comprises a charging processor responsive to the
predefined
charging profile which is received as parameters associated with the at least
one battery
to be recharged, the charging processor determining an occurrence of a current
decrease
for the at least one battery to be charged prior to a measured battery voltage
of the at
least one battery to be charged being at the threshold voltage and providing a
trigger to
the offset compensator in response to the occurrence; wherein the offset
compensator is
configured for applying the offset voltage in response to the trigger to
adjust the output
voltage of the charger such as to maintain the charger in the first mode.
In accordance with another aspect of the present invention, there is provided
a charging
unit for charging a rechargeable battery on a mobile computing device, the
charging unit
to be electrically coupled to the mobile computing device, the charging unit
comprising: a
charging circuit comprising a charger outputting a voltage and electrical
current to the
rechargeable battery, the charger operable to charge the battery in a first
mode wherein a
constant charge current is applied to the battery unit a predefined threshold
voltage is
obtained at the battery and to them operate in a second mode wherein a
constant charge
voltage is applied to the battery until the battery is charged; and an offset
compensator
configured for applying an offset voltage to a measurement of the output
voltage of the
charger to compensate for voltage drops in the charge path between the charger
and the
rechargeable battery thereby allowing the voltage of the rechargeable battery
voltage to
reach the threshold voltage before entering the second mode.
In accordance with yet another aspect of the present invention, the offset
compensator is
configured to apply the offset voltage to the output of the charger to
increase the pre-
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defined threshold voltage to compensate for the impedance loss between the
charger
and the battery. In accordance with yet another aspect of the present
invention, the offset
voltage is related to a difference between the measured battery voltage and
the pre-
defined threshold voltage.
In accordance with yet another aspect of the present invention, the offset
compensator is
configured to continually apply the offset voltage to maintain the charger in
the first mode
until the measured battery voltage is at least at the pre-defined threshold
voltage.
In accordance with yet another aspect of the present invention, there is
provided a
method for charging an external battery on a mobile device by a charging unit,
the
charging unit configured to be electrically coupled to the mobile device for
electrical
communication thereof, the method comprising: operating in a first mode to
provide a
constant pre-defined charge current to the external battery based on an output
voltage of
the charger; operating in a second mode to provide a constant pre-defined
charge
voltage to the external battery; switching from the first mode to the second
mode when
the output voltage of the charger reaches a predefined threshold voltage; and
applying an
offset voltage to the charger to maintain the charger in the first mode to
compensate for
impedance loss between the charger and the external battery thereby allowing
the
external battery voltage to reach the threshold voltage.
In accordance with yet another aspect of the present invention, there is
provided a
charging unit for communicating with a rechargeable battery located in a
mobile
computing device, the charging unit comprising: a connector port configured to
couple the
charging unit to the rechargeable battery in the mobile computing device; a
charging
circuit for monitoring a voltage reading of the rechargeable battery through
the connector
port, the charging unit configured to be coupled to an electrical power source
for
providing an electrical charge for charging the rechargeable battery in
dependence upon
the monitored voltage reading.
According to yet another aspect of the present invention, there is provided a
method for
charging a rechargeable battery in a mobile computing device from an external
charging
unit, the charging unit configured to be electrically coupled to the mobile
computing
device, the method comprising: operating in a first mode wherein a constant
predefined
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charge current is supplied to the rechargeable battery until the battery
voltage is at least
equal to a predefined threshold voltage for the battery; during operation in
the first mode,
measuring the output voltage of the charging unit to determine if the output
voltage of the
charger is at least equal to the predefined threshold voltage for the battery
and, if the
output voltage is at least equal to a predefined threshold voltage for the
battery,
determining if the charge current has decreased; if the charge current has
decreased,
obtaining from a power processor associated with the battery an indication of
the battery
voltage and, if the battery voltage is less than the predefined threshold
voltage, then
applying an offset voltage to the measurement of the charger output voltage to
compensate for voltage drops between the output of the charger and the
rechargeable
battery; if the charge current has decreased and the battery voltage is at
least equal to
the predefined threshold voltage, operating the charger in a second mode
wherein a
constant charge voltage is applied to the battery; and when in the second mode
the
charge current falls below a predefined minimum, deciding the battery is
charged.
According to yet another aspect of the present invention, there is provided
mobile
computing device comprising: a battery module configured to receive at least
two
different rechargeable batteries; a device circuitry module configured to
communicate
between the battery module and a charging circuit located on an external
charging unit;
and a connector port configured to couple the external charging unit to the
battery
module for providing an electrical charge to said at least one rechargeable
battery,
wherein each of said at least two different rechargeable batteries are
compatible for
being charged by a corresponding charging circuitry.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way of example only with
reference to the following drawings in which:
Figure 1 is a diagram of a mobile computer in accordance with the present
invention;
Figure 2 is a block diagram of the subsystems of the mobile computing device
of Figure
1;
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Figure 3 is a block diagram illustrating the communication between the mobile
computing
device of Figure 1 and an external charging unit in accordance with the
present invention;
and
Figure 4 is a flow chart of operations between the charging unit and the
mobile computing
device for charging the battery of the mobile computing device.
DETAILED DESCRIPTION OF INVENTION
A mobile computing device in accordance with the present invention is
indicated
generally at 100 in Figure 1. Mobile computing device 100 comprises a main
body 102, a
display 104, a keyboard module 106 and a battery compartment 108.
Additionally, in the
present embodiment, mobile computing device 100 has the capability of
wirelessly
communicating data and/or voice, to and from servers as well as data
acquisition sources
within a communication network. In one embodiment, the main body 102 comprises
a
top housing frame 205 and a bottom housing frame 206. In the embodiment shown,
the
top housing frame 205 may house the keyboard module 106 and the display screen
222.
The bottom housing frame 206 may house the battery compartment 108 for housing
a
rechargeable battery (210 in Figurer 2). The bottom housing frame 205 further
comprises
a circuitry module 207 (i.e. a circuit board) for providing the electronic
components
required to implement at least a portion of the functionality provided by
mobile computing
device 100.
Continuing with the embodiment depicted in exemplary manner in Figure 1, it is
noted
that by housing, it is meant that a module, including battery 210 and
circuitry module 207,
are substantially located or disposed within bottom housing frame 206.
Circuitry module
207 may include any combination of electronic components of mobile computing
device
100, such as any combination of wireless communication subsystem 211,
microprocessor 238, random access memory 226 and flash memory 224. However, it
will be appreciated by those of skill in the art that circuitry module 207 may
not
exclusively house all of the electronic components and interconnections
necessary for
mobile computing device 100 to function as intended.
Specifically, according to a preferred embodiment, the circuitry module 207 is
absent a
computing device charging circuitry for charging the battery 210 of mobile
computing
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device 100. Instead, the charging circuitry is provided on an external
charging unit (an
example of which is shown in Fig. 3). The external charging unit (i.e.
charging unit 300)
comprises an electrical power source 310 (or is configured to be coupled to an
electrical
power source 310) and the charging circuitry 312. As will be described below,
the
charging circuitry 312 monitors the voltage of the rechargeable battery 210
and the
electrical power source 310 provides the electrical charge for charging the
rechargeable
battery 210 in response to the monitored voltage reading of the rechargeable
battery 210.
It will be appreciated that prior mobile computing device architectures
included the
battery charging circuitry located internally on the mobile computing device
and the
mobile computing device would then be tethered to a power supply to charge the
battery.
In such cases, the mobile computing device must be sized to include the
charging
circuitry and thus is larger and/or heavier than would otherwise be required.
Further,
when operating, the charging circuitry typically produces significant amounts
of waste
heat which the mobile computing device must be designed to accommodate and
dissipate.
However, according to the preferred embodiment wherein the charging circuitry
312 is
provided on an external device (i.e. charging unit 300 shown in Figure 3), the
waste heat
from the charging circuitry 312 need not be dissipated by the mobile computing
device
100. Further, as the amount of waste heat produced by charging circuitry 312
is
proportional to the charging current, generally higher charging currents can
be employed
with the present invention than would be the case if charging circuitry 312 is
located
within mobile computing device 100.
As a result of charging circuitry 312 being located on charger 300, the
circuitry module
207 has additional space freed up for other processing circuitry to be added
for the
device or for circuitry module 207 to be reduced in size/weight, or both.
Further, since
the charging circuitry 312 is located on the charging unit 300, the battery
compartment
108 may accommodate different types of rechargeable batteries 210, as long as
the
charging unit 300 and the rechargeable battery 210 are compatible with each
other.
That is, by providing a charging unit 300 with a charging circuit 312 that is
compatible
with a selected rechargeable battery 210, the selected rechargeable battery
210 may be
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used within mobile computing device 100. In one aspect, the battery
compartment 108
may be sized and electrically configured to accommodate a number of different
rechargeable batteries 210 compatible with the charging unit 300. The number
of
different rechargeable batteries 210 being at least two different types. For
example, the
battery compartment 108 may be adjustably sized to receive different capacity
batteries
210, or batteries of different battery chemistries.
Bottom housing frame 206 may completely, or partially, house a connector slot
242
whereby an external charging unit (i.e. charging unit 300) may be electrically
coupled
(i.e. via a suitable connector) to the electrical contacts of the rechargeable
battery 210
of battery compartment 108.
Referring to Figure 2, a block diagram illustrating an example of the
functionality
provided by mobile computing device 100 is indicated generally at 200. The
circuitry
module 207 includes a microprocessor 238, which controls general operation of
mobile
computing device 100. The microprocessor 238 also interacts with functional
device
subsystems such as a communication subsystem 211 , the display module 222, a
flash
memory 224, random access memory (RAM) 226, auxiliary input/output (I/O)
subsystems 228, serial port 230, keyboard 332, speaker 234, microphone 236,
short-
range communications subsystem 240 such as a BluetoothTM transceiver for
example,
and a Universal Serial Bus (USB) expansion port 242 for peripherals. Mobile
computing
device 100 includes a power source, such as a rechargeable battery 210 which
may
also be removable and replaceable from mobile computing device 100. Mobile
computing device 100 may also include a positioning device 244, such as a =GPS
receiver for example, for receiving positioning information.
Operating system software used by the microprocessor 238 can be stored in a
persistent store such as the flash memory 224, which may alternatively be a
read-only
memory (ROM) or similar storage element (not shown). Those skilled in the art
will
appreciate that the operating system, specific device applications, or parts
thereof, may
be temporarily loaded into a volatile store such as RAM 226.
The microprocessor 238, in addition to its operating system functions, enables
execution of software applications on mobile computing device 100. A
predetermined
set
of
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applications, which control basic device operations, may be installed on
mobile
computing device 100 during its manufacture. These basic operations typically
include
data and voice communication applications, for example. Additionally,
applications may
also be subsequently loaded onto mobile computing device 100 through the
communication subsystem 211 , an auxiliary I/O subsystem 228, serial port 230,
USB
port 242, short-range communications subsystem 240, or any other suitable
subsystem,
and installed by a user in RAM 226, or the persistent store 224, for execution
by the
microprocessor 238. Such flexibility in application installation increases the
functionality
of mobile computing device 100 and may provide enhanced on-device features,
communication-related features, or both.
The radio frequency (RF) communication subsystem 211 , includes a receiver
112, a
transmitter 214, and associated components, such as one or more embedded or
internal antenna elements 216 and 218, local oscillators (L0s) 213, and a
processing
module such as a digital signal processor ([)SP) 220. As will be apparent to
those
skilled in field of communications, the particular design of the RF
communication
subsystem 211 depends on the communication network in which mobile computing
device 100 is intended to operate, but may include communication
functionalities such
as radio-frequency identification (RFID), Wi-F1 WLAN based on 802.1 standards,
and
the like. The display module 222 is used to visually present an application's
graphical
user interface (GUI) to the user via a display screen. The display screen
module 222
may employ a touch screen display, in which case the user can manipulate
application
data by.modifying information on the GUI using direct touches by a finger.
Depending
on the type of mobile computing device 100, the user may have access to
various types
of input devices, such as, for example, a scroll wheel, trackball, light pen
and/or a touch
sensitive screen.
In the present embodiment, the circuitry module 207 may be mounted onto a
metal
frame in order to be attached to the main body 102 of mobile computing device
100.
For many rechargeable batteries, a recommended charging profile is used for
safely
and effectively charging the battery. Typically, the charging profile
specifies charging by
delivering a specified constant current to the battery until a threshold
voltage is reached
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at the battery and this is referred to as constant current charging. In other
words, the
specified charge current is applied to the battery and, as it charges, the
voltage of the
battery increases and is monitored. Once the desired threshold voltage is
reached, the
charging profile specifies that the charging circuit complete the charge of
the battery by
providing a constant voltage and allowing the charge current to drop as the
battery is
charged. The constant voltage is provided to the battery until a current
decrease of a
selected amount is detected, indicating that the battery is properly charged.
The specific
threshold voltage, constant current rates and other related charging
parameters can vary
depending upon the capacity of the battery, the battery chemistry and other
factors as will
be apparent to those of skill in the art.
As illustrated in Figure 3, external charging unit (element 300) provides
electrical
connection between the charging circuit (element 312) and mobile computing
device 100,
via mechanical connectors 318 (i.e. pogo pins, flex connectors, etc.). As will
be apparent
to those of skill in the art, electrical connections made with such mechanical
connectors
318 inherently include an impedance and across which a voltage drop occurs.
These
impedance losses result in the voltage measured at the output of charging unit
300 (i.e.
Vsensed 316) being higher than the voltage received (i.e. Vrcvd 319) at the
battery 210 as
the impedances of the connectors 318 along the charge path between the charger
314
and the battery 210 cause a voltage drop to occur a Vrcvd 319.
In addition, other impedances may be seen as a result of other connectors
(i.e. one or
more connectors between mobile computing device 100 and the charging unit 300)
and
other components in the charge path between the charging circuit 312 and
mobile
computing device 100. Due to these voltage drops, the voltage Vrcvd 319 at
mobile
computing device 100 (i.e. the battery 210) is less than the desired charging
profile
voltage (also referred to as a threshold voltage) for charging the battery 210
as sensed at
Vsensed 316.
Accordingly, in order for the desired threshold voltage to be provided to the
battery 210
such that the battery voltage 210 is charged according to the charging profile
at the
desired rate and threshold voltage, a compensation mechanism is provided by
the
charging unit 300.
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Accordingly, a power processor 250 measures the voltage Vsensed 319 at the
battery 210
as shown in Figure 3 and that measured parameter value is provided to the
charging
circuit 312 of the charging unit 300, over a digital communication path 320,
to allow for
the sensed voltage Vsensed 316 to be corrected such that the Vrcvd 319 is at
the desired
threshold value despite any voltage drops through the charge path.
Power processor 250 can be any of a wide variety of battery management devices
(often
referred to as "battery gas gauges") which are employed with batteries such as
Li-ion
batteries whose charging and operating parameters are controlled for safety
and
longevity issues. Such gas gauge devices typically output signals which are
available to
power management functions of the mobile computing device powered by the
battery, the
signals representing battery parameters to enable the mobile computing device
to
estimate expected remaining operating time, battery condition, etc. The
capabilities and
operation of such gas gauge devices is well known to those of skill in the art
and will not
be further discussed herein. The measured value communicated over path 320,
representing the voltage at the battery, is a value which is available from
such power
processors 250.
Referring now in detail to Figure 3, charging unit 300 comprises a charging
circuit 312,
and an electrical power source 310. The charging circuit 312 comprises a
charging
circuit processor 304, an offset compensator 308, and a charger 314. The
charging unit
300 is electrically coupled to mobile computing device 100 and the battery 210
via
mechanical connectors 318. The electrical connection through mechanical
connectors
318 may be via the connector port 242 which can be adapted to receive and/or
secure
connector 318 with connector port 242 for coupling the external charging unit
300 to the
electrical contacts of the rechargeable battery 210.
The charger 314 is thus configured for providing a constant charge current in
a first mode
of operation (i.e. to mobile computing device 100). In this first mode of
operation, the
charger 314 is configured for providing the constant charge current and
allowing Vrcvd
(and Vsensed) to increase as the battery is charged. Charger 314 operates in
this first
mode of operation until the Vsensed reaches the predetermined threshold
voltage that is
desired for charging the battery 210.
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However, if no compensation is applied, Vsensed is higher than Vrcvd, due to
the
impedances in the charge path, and thus charger 300 will incorrectly determine
that a
switch to the second charging mode (constant charge voltage) should be
performed.
Specifically, once the charger 314 determines that Vsensed is approximately
equivalent to,
or greater than, the desired threshold voltage, the charger 314 is configured
to operate in
a second mode of operation and provide a constant charge voltage until the
charge
current decreases, indicating that battery 210 is appropriately charged. As
will be
understood, a safety mechanism may be incorporated in the charger 314 such as
to allow
the threshold voltage to be limited to a maximum threshold voltage to prevent
overheating or other issues with the charger 300.
Instead, as will be further described with respect to Figure 3, the charging
processor 304
and the offset compensator 308 are configured for cooperatively causing the
charger 314
to remain in the first mode of operation for a longer period of time (i.e.
even after Vsensed
316 reaches the threshold voltage) such as to allow the Vrcvd at battery 210
reach the
desired threshold voltage value, thereby compensating for any impedance losses
across
the charge path.
Continuing with the embodiment depicted in Figure 3, the power processor 250
on mobile
computing device 100 is configured to measure battery 210 parameters
comprising at
least one of the voltage value and the current value of the battery 210 and
provide at
least one of the detected battery voltage value and the current value to the
charging
circuit processor 304. Power processor 250 may further be configured to
measure other
battery 210 parameters comprising any one of the battery voltage, battery
charge current,
capacitance, temperature and other charge parameters for monitoring the
charging
activity of the battery 210.
The power processor 250 is further configured to provide the battery
parameters to the
charging circuit processor 304 across a digital communication path 320. In one
aspect,
the charging circuit processor 304 may be configured to poll the power
processor 250 for
receiving the battery parameters thereafter. In another aspect, the power
processor 250
may be configured to provide the battery 210 parameters at certain intervals
and/or upon
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detection of pre-determined criteria that may trigger the battery 210
parameters to be
provided to the charging processor 304.
The charging circuit processor 304 is configured to monitor the current drop
of the battery
210 as determined and reported by the power processor 250. If a current drop
of greater
than a predefined minimum drop value is detected, this indicates that the
charger 314
has completed the first mode of operation (i.e. - constant current charging)
and should
switch to the second mode (constant voltage) of operation. However, if the
current drop
is realized before Vrcvd attains the desired threshold voltage value (i.e. the
measured
battery voltage value as provided by the power processor 250 is less than the
desired
threshold voltage value), then the charging circuit processor 304 is
configured to provide
a control signal or a trigger to the offset compensator 308 to compensate for
the
impedance losses through the charge path. Specifically, the offset compensator
308
applies a negative offset to the voltage value charger 314 senses at Vsensed
316 and thus
charger 314 allows the voltage sensed by the charger 314 at Vsensed 316 to
continue to
rise so that Vrcvd 319 at battery 210 can reach the threshold voltage despite
impedance
losses in the charge path. Thus, charger 314 will remain in, or revert to, the
first mode of
operation until Vrcvd reaches the threshold value.
In this manner the charging processor 304 continually monitors the battery
voltage and
battery current to determine when the battery 210 has reached the desired
threshold
value.
Accordingly, the charger 314 is configured to continue providing a constant
current (first
mode of operation) to the battery 210 until the battery 210 reaches the
predefined
threshold voltage value (as detected by the power processor 250 and
communicated to
the charging processor 304). The charging unit 300 is configured to compensate
for the
difference between the measured voltage at Vsensed 316 detected by the
charging circuitry
312 and the voltage (Vrcvd) of battery 210. Once the threshold voltage is
reached at the
battery 210 (as determined by the power processor 250), the charging circuit
processor
304 is configured (second mode of operation) to deliver a constant voltage to
the battery
210 until the battery 210 charge current decreases. In this way, the desired
threshold
voltage is provided and reached at the battery 210.
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Referring again to Figure 3, placing the charging circuit 312 external to
mobile computing
device 100 allows flexibility with mobile computing device 100 such as to
allow a variety
of batteries 210 (i.e. of different types and/or charging capacities) to be
used in mobile
computing device 100 as long as they are compatible with the charging circuit
312. For
example, it is contemplated that different batteries (or different capacities
of batteries
and/or batteries from different manufacturers and/or batteries with different
battery
chemistries) can be employed in portable computer device 100 and charged with
charger
300, provided that their respective power processor 250 provides the relevant
battery
charging parameters (threshold voltage, amount of current drop, etc.) to
charger 300.
Accordingly, this enhances the practicality and economics of replacing the
battery 210.
Referring now to Figure 4 a flow chart of a method of operation 400 for a
charger in
accordance with the present invention is shown. At step 400, the charger 314
commences, in the first mode of operation, to provide a constant charge
current to
battery 210 based on the charge profile for battery 210, as can be obtained
from power
processor 250 or via any other suitable means.
At step 404, charger 300 determines if the charge current to battery 210 has
dropped. If
the current has not decreased, the methid returns to step 400. If at step 404
the charge
current has dropped, this has occurred because charger 300 has determined that
Vsensed
316 has reached the threshold value for battery 210, and charger 300 operates
to
prevent further increases to the voltage at 316, thus resulting in a decrease
in the charge
current applied to battery 210.
Accordingly, if a drop in the charge current has been detected at step 404, at
step 408
charger 300 determines if battery 210 has actually reached the threshold
voltage. As
described above, this can be achieved be examining the information provided
from power
processor 250 over digital connection 320, including the provided measure of
Vrcvd
provided by power processor 250.
If, at step 408, it is determined that battery 210 is not at the threshold
voltage, offset
compensator 308 will compensate (decrease) the sensed value of the voltage
Vsensed 316
to compensate for the difference between the sensed value of Vsensed 316 and
the
reported value of Vrcvd 319 and the method returns to step 400.
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As the voltage drop due to the impedances of the connectors in the charge path
is
dependent upon the charge current, the method will continue to perform steps
400, 404,
408 and 412 until, at step 408, it is determined that the battery voltage
Vrcvd is equal to, or
above, the threshold voltage. When this determination is made, the method
continues at
step 416 wherein charger 300 commences charging in the second mode (constant
voltage) of operation.
At step 420, the method checks the charge current to determine if it has
fallen below a
predefined minimum (provided as part of the charge profile). If the charge
current is
above the predefined minimum, the method returns to step 416 and the battery
continues
to be charged in the second mode.
If, at step 420, it is determined that the charge current supplied to the
battery is at, or is
below, the predefined minimum current level, the battery is assumed to be
properly
charged and the method completes at step 424.
As described above, the charger 314 is configured to operate in two modes of
operation.
That is, in a first mode the charger 314 provides a constant pre-defined
charge current to
the external battery 210 based on an output voltage 316 of the charger 314;
and in a
second mode provide a constant pre-defined charge voltage to the external
battery 210.
In one embodiment, the charger 314 is configured to switch from the first mode
to the
second mode when the output voltage of the charger 314 reaches a predefined
threshold
voltage. Preferably, the offset compensator 308 is configured for applying an
offset
voltage to the charger 314 to maintain the charger in the first mode to
compensate for
voltage drops resulting from impedances between the charger 314 and the
external
battery 210 thereby allowing the external battery voltage 210 to reach the
threshold
voltage. As described above, the offset voltage applied by the charger 314 may
be in
dependence upon the charging circuit processor 304, and the power processor
250
determining that the battery 210 has not reached the desired threshold voltage
but the
current of the battery 210 is dropping (indicative of the charger 314
operating in the
second mode). Accordingly, the charging circuit processor 304 communicates
with the
offset compensator 308 to cause the applying of an offset voltage to the
output voltage
316 of the charger 314. In another embodiment, once the charging circuit
processor 304
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determines that the charger 314 is operating in the second mode of operation
but that the
battery 210 has not reached the threshold voltage (based on the battery
parameters), the
offset compensator 308 applies an offset to the threshold voltage of the
charger 314 (i.e.
to increase the threshold voltage of the charger by a pre-defined amount such
as to
compensate for the impedance loss across the communication path between the
charger
314 and the battery 210). In this way, the charger 314 does not switch to the
second
mode of operation until the increased threshold voltage is reached such as to
allow the
external battery 210 to reach the desired threshold voltage at the battery.
Although the specific implementations of the invention are described above, a
person of
ordinary skill in the art will appreciate that various modifications can be
made without
detracting from the spirit of the invention.
Although a mobile or handheld computer has been used to establish a context
for
disclosure herein, it is contemplated as having much wider applicability
within the field of
handheld devices. Furthermore, the disclosure herein has been described with
reference
to specific exemplary embodiments; however, varying modifications thereof will
be
apparent to those skilled in the art without departing from the scope of the
invention as
defined by the appended claims.
Therefore, although the invention has been described with reference to certain
specific
embodiments, various modifications thereof will be apparent to those skilled
in the art
without departing from the scope of the invention as defined by the appended
claims.
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