U.S. patent application number 13/460646 was filed with the patent office on 2012-08-23 for system and method for battery charging.
This patent application is currently assigned to O2MICRO, INC.. Invention is credited to Guoxing LI.
Application Number | 20120212188 13/460646 |
Document ID | / |
Family ID | 40220908 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120212188 |
Kind Code |
A1 |
LI; Guoxing |
August 23, 2012 |
SYSTEM AND METHOD FOR BATTERY CHARGING
Abstract
A charging circuit includes an N-channel
metal-oxide-semiconductor field-effect transistor (NMOSFET) that
controls a charging current to a battery, a charge pump that
generates a driving signal based on a plurality of pulses, and a
resistor coupled to a gate of the NMOSFE. The resistor and a
capacitance of the gate of the NMOSFET form a low pass filter. The
driving signal is filtered by the low pass filter to control a gate
voltage of the NMOSFET. A variation of a gate-source voltage of the
NMOSFET is proportional to a pulse density of the plurality of
pulses. A variation of the charging current flowing through the
NMOSFET to the battery is proportional to the pulse density.
Inventors: |
LI; Guoxing; (Sunnyvale,
CA) |
Assignee: |
O2MICRO, INC.
Santa Clara
CA
|
Family ID: |
40220908 |
Appl. No.: |
13/460646 |
Filed: |
April 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11827144 |
Jul 5, 2007 |
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13460646 |
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Current U.S.
Class: |
320/139 |
Current CPC
Class: |
H02J 7/00711
20200101 |
Class at
Publication: |
320/139 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Claims
1. A charging circuit for charging a battery, said charging circuit
comprising: an N-channel metal-oxide-semiconductor field-effect
transistor (NMOSFET) that controls a charging current to a battery;
a charge pump that generates a driving signal based on a plurality
of pulses; and a resistor coupled to a gate of said NMOSFET,
wherein said resistor and a capacitance of said gate of said
NMOSFET form a low pass filter, wherein said driving signal is
filtered by said low pass filter to control a gate voltage of said
NMOSFET, wherein a variation of a gate-source voltage of said
NMOSFET is proportional to a pulse density of said plurality of
pulses, and wherein a variation of said charging current flowing
through said NMOSFET to said battery is proportional to said pulse
density.
2. The charging circuit of claim 1, further comprising: a pulse
generator that generates said plurality of pulses; and a
controller, coupled to said pulse generator, that controls said
pulse density of said plurality of pulses according to a status of
said battery.
3. The charging circuit as claimed in claim 2, wherein said pulse
density decreases when said charging current is greater than a
first predetermined threshold.
4. The charging circuit as claimed in claim 3, wherein said pulse
density increases when said charging current is less than a second
predetermined threshold that is less than said first predetermined
threshold.
5. The charging circuit as claimed in claim 2, wherein said
controller controls said pulse density when a battery voltage of
said battery charged by said charging current is less than a
predetermined voltage threshold.
6. The charging circuit as claimed in claim 2, wherein said
controller controls said pulse density when a cell voltage for each
cell of a plurality of cells charged by said charging current is
less than a predetermined voltage threshold.
7. The charging circuit as claimed in claim 2, further comprising:
an oscillator that generates a plurality of clock pulses, wherein
said charge pump receives said plurality of clock pulses and
generates said driving signal which turns on said NMOSFET.
8. The charging circuit of claim 7, wherein said charging circuit
powers off said oscillator and powers on said pulse generator when
a voltage of said battery is less than a threshold, and wherein
said charging circuit powers off said pulse generator and powers on
said oscillator when said voltage is greater than said
threshold.
9. An electronic device comprising: a charger that charges a
battery; and a charging circuit, coupled to said battery and said
charger, that controls a charging current from said charger to said
battery, said charging circuit comprising: a pulse generator that
generates a plurality of pulses to control an N-channel
metal-oxide-semiconductor field-effect transistor (NMOSFET) coupled
between said charger and said battery; a charge pump, coupled to
said pulse generator, that receives said plurality of pulses and
generates a driving signal according to said pulses; and a low pass
filter coupled to said charge pump, wherein said driving signal is
filtered by said low pass filter to control a gate voltage of said
NMOSFET, wherein a variation of a gate-source voltage of said
NMOSFET is proportional to a pulse density of said plurality of
pulses, and wherein a variation of said charging current flowing
through said NMOSFET to said battery is proportional to said pulse
density.
10. The electronic device of claim 9, further comprising: a
controller, coupled to said pulse generator, that controls said
pulse density of said plurality of pulses according to a status of
said battery.
11. The electronic device of claim 9, wherein said low pass filter
is formed by a resistor coupled to a gate of said NMOSFET and a
capacitance of said gate of said NMOSFET.
12. The electronic device of claim 9, wherein said pulse density
decreases when said charging current is greater than a first
predetermined threshold.
13. The electronic device of claim 12, wherein said pulse density
increases when said charging current is less than a second
predetermined threshold that is less than said first predetermined
threshold.
14. The electronic device of claim 10, wherein said controller
controls said pulse density when a battery voltage of said battery
charged by said charging current is less than a predetermined
voltage threshold.
15. The electronic device of claim 10, wherein said controller
controls said pulse density when a cell voltage for each cell of a
plurality of cells charged by said charging current is less than a
predetermined voltage threshold.
16. The electronic device of claim 9, further comprising: an
oscillator that generates a plurality of clock pulses, wherein said
charge pump receives said plurality of clock pulses and generates
said driving signal which turns on said NMOSFET.
17. The electronic device of claim 16, wherein said charging
circuit powers off said oscillator and powers on said pulse
generator when a voltage of said battery is less than a threshold,
and wherein said charging circuit powers off said pulse generator
and powers on said oscillator when said voltage is greater than
said threshold.
Description
RELATED APPLICATION
[0001] This application is a continuation of the co-pending U.S.
application, Ser. No. 11/827,144, titled "System and Method for
Battery Charging," filed Jul. 5, 2007, which is hereby incorporated
by reference.
BACKGROUND
[0002] Battery pre-charging can be enabled when battery voltage is
low. A pre-charging current is relatively small compared to a
normal charging current during normal charging. Conventional
battery charging systems perform battery pre-charging by
controlling a switch coupled in series with a current limiting
resistor. Such battery charging systems are costly. In addition,
such battery charging systems have large power dissipation and low
efficiency during pre-charging.
SUMMARY
[0003] A charging circuit includes an N-channel
metal-oxide-semiconductor field-effect transistor (NMOSFET) that
controls a charging current to a battery, a charge pump that
generates a driving signal based on a plurality of pulses, and a
resistor coupled to a gate of the NMOSFE. The resistor and a
capacitance of the gate of the NMOSFET form a low pass filter. The
driving signal is filtered by the low pass filter to control a gate
voltage of the NMOSFET. A variation of a gate-source voltage of the
NMOSFET is proportional to a pulse density of the plurality of
pulses. A variation of the charging current flowing through the
NMOSFET to the battery is proportional to the pulse density.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Features and advantages of embodiments of the claimed
subject matter will become apparent as the following Detailed
Description proceeds, and upon reference to the drawings, wherein
like numerals depict like parts, and in which:
[0005] FIG. 1A shows a block diagram of a battery charging system,
in accordance with one embodiment of the present invention.
[0006] FIG. 1B shows a block diagram of a battery charging system,
in accordance with one embodiment of the present invention.
[0007] FIG. 2 shows a flowchart of operations performed by a
battery charging system, in accordance with one embodiment of the
present invention.
[0008] FIG. 3 shows a flowchart of operations performed by a
battery charging system, in accordance with one embodiment of the
present invention.
DETAILED DESCRIPTION
[0009] Reference will now be made in detail to the embodiments of
the present invention. While the invention will be described in
conjunction with these embodiments, it will be understood that they
are not intended to limit the invention to these embodiments. On
the contrary, the invention is intended to cover alternatives,
modifications and equivalents, which may be included within the
spirit and scope of the invention as defined by the appended
claims.
[0010] Furthermore, in the following detailed description of the
present invention, numerous specific details are set forth in order
to provide a thorough understanding of the present invention.
However, it will be recognized by one of ordinary skill in the art
that the present invention may be practiced without these specific
details. In other instances, well known methods, procedures,
components, and circuits have not been described in detail as not
to unnecessarily obscure aspects of the present invention.
[0011] FIG. 1A shows a block diagram of a battery charging system
100, in accordance with one embodiment of the present invention. As
shown in FIG. 1 A, a charger 110 can be used to charge a battery
pack 102 having a plurality of cells 102_1-102.sub.--n. In one
embodiment, a charging circuit 170 coupled to the battery pack 102
and the charger 110 controls a charging current flowing from the
charger 110 to the battery pack 102 by controlling a charging
switch 130. A discharging switch 132 can be used to control a
discharging current during discharging. During charging, the
discharging switch 132 can be on or off. If the discharging switch
132 is off, a charging current can flow from the charger 110 to the
battery pack 102 through a body diode 134 of the discharging switch
132.
[0012] In one embodiment, the charging circuit 170 includes a pulse
generator 140 for generating a plurality of pulses 142 to control
the charging switch 130, and a controller 120 coupled to the pulse
generator 140 for controlling a pulse density of the plurality of
pulses 142. If N pulses are generated by the pulse generator 140
during a time period T, the pulse density D.sub.p is equal to the
number of pulses N divided by the time period T (D.sub.p=N/T).
Advantageously, a charging current flowing through the charging
switch 130 can be adjusted according to the pulse density of the
plurality of pulses 142, in one embodiment. In one embodiment, the
charging switch 130 can include, but is not limited to a
transistor, e.g., an n-type metal-oxide-semiconductor field-effect
transistor.
[0013] In one embodiment, the pulse generator 140 is a PDM (pulse
density modulation) pulse generator. The PDM pulse generator 140
can be used to generate a plurality of normally distributed pulses
142 over a time period. The PDM pulse generator 140 can have
numerous configurations. Advantageously, the controller 120
controls a pulse density of the plurality of PDM pulses 142
generated by the PDM pulse generator 140, in one embodiment.
[0014] A charge pump 150 coupled to the PDM pulse generator 140 can
be used to receive the plurality of PDM pulses 142 from the PDM
pulse generator 140 and to generate a driving signal 152 which
controls the charging switch 130. More specifically, the charge
pump 150 receives an input voltage Vcc and the plurality of PDM
pulses 142, and generates the driving signal 152 that controls a
gate voltage of the charging switch 130, thereby controlling a
conductance of the charging switch 130. In one embodiment, the
voltage of the driving signal 152 is higher than the voltage of the
input signal Vcc, and the voltage of the driving signal 152 is
sufficient to conduct the charging switch 130 during charging. The
charge pump 150 can be a single stage charge pump with numerous
configurations or a multi-stage charge pump with numerous
configurations, in one embodiment.
[0015] Advantageously, in one embodiment, the controller 120
monitors a battery voltage of the battery pack 102 (and/or cell
voltages of cells 102_1-102.sub.--n) and a charging current, and
controls the pulse density of the plurality of PDM pulses 142
generated by the PDM pulse generator 140. The charge pump 150
receives the plurality of PDM pulses 142 and generates a driving
signal 152 to control a conductance of the charging switch 130, in
one embodiment. Therefore, the conductance of the charging switch
130 can be controlled according to the pulse density of the PDM
pulses 142. Accordingly, the charging current flowing through the
charging switch 130 can be adjusted by controlling the pulse
density of the plurality of PDM pulses 142.
[0016] As show in FIG. 1A, the charging switch 130 has a gate 130g,
a source 130s, and a drain 130d. The charging current flowing
through the charging switch 130 is equal to the drain-source
current I.sub.DS of the charging switch 130, in one embodiment.
According to characteristics of the charging switch 130 (e.g., an
n-type metal-oxide-semiconductor field-effect transistor) during an
active (linear) region, an increment of the drain-source current
.DELTA.I.sub.DS during a time period T is given by:
.DELTA.I.sub.DS=2K(
V.sub.GS-V.sub.T).DELTA.V.sub.GS+K(.DELTA.V.sub.GS).sup.2.apprxeq.2K(
V.sub.GS-V.sub.T).DELTA.V.sub.GS, (1)
where V.sub.T represents a threshold voltage of the charging switch
130, .DELTA.V.sub.GS represents an increment of the gate-source
voltage of the charging switch 130 during the time period T,
V.sub.GS represents an average gate-source voltage of the charging
switch 130 during the time period T, and K represents a parameter
of the charging switch 130, which is related to the fabrication
process. As shown in equation (1), the increment of the
drain-source current .DELTA.I.sub.DS during the time period T is
proportional to the increment of the gate-source voltage
.DELTA.V.sub.GS during the time period T. Consequently, the
charging current can be adjusted by controlling the gate-source
voltage of the charging switch 130. In one embodiment, a resistor
126 coupled to the charging switch 130 is used as a low pass filter
to reduce fluctuation of the gate-source voltage of the charging
switch 130.
[0017] According to characteristics of the charge pump 150, a
voltage increase .DELTA.V.sub.1 at the gate 130g of the charging
switch 130 during the time period T can be given by:
.DELTA. V 1 = .eta. NC 150 V CC C 130 g , ( 2 ) ##EQU00001##
where N represents the number of PDM pulses 142 received by the
charge pump 142 during the time period T, C.sub.150 represents a
capacitance of a charge pump flying capacitor in the charge pump
150, Vcc represents an input voltage of the charge pump 150,
C.sub.130g represents a capacitance of a gate capacitor at gate
130g of the charging switch 130, and .eta. represents an efficiency
of the charge pump 150 (in one embodiment, for a single stage
charge pump, .eta.=1, for a multi-stage charge pump,
0<.eta.<1).
[0018] In one embodiment, a pull-down resistor 124 is coupled to
the gate 130g and the source 130s of the charging switch 130. As
such, during the time period T, a current will flow from the gate
capacitor (at gate 130g) to source 130s via the pull-down resistor
124. Therefore, there is a voltage decrease .DELTA.V.sub.2 at the
gate 130g of the charging switch 130 during time period T, which
can be given by:
.DELTA. V 2 = Q 130 g C 130 g = V GS _ R 124 T C 130 g , ( 3 )
##EQU00002##
where Q.sub.130g represents a total electric quantity decreased at
the gate capacitor during the time period T, and R.sub.124
represents a resistance of the pull-down resistor 124.
[0019] Accordingly, the total increment of the gate voltage (at
gate 130g) of the charging switch 130 during the time period T is
equal to .DELTA.V.sub.1-.DELTA.V.sub.2. In one embodiment, the
total increment of the gate-source voltage .DELTA.V.sub.GS of the
charging switch 130 during the time period T is equal to the total
increment of the gate voltage (at gate 130g) of the charging switch
130. Accordingly, the total increment of the gate-source voltage
.DELTA.V.sub.GS of the charging switch 130 during the time period T
can be given by:
.DELTA. V GS = .DELTA. V 1 - .DELTA. V 2 = NC 150 V CC - V GS _ R
124 T C 130 g . ( 4 ) ##EQU00003##
Since the pulse density D.sub.P of the PDM pulses 142 is equal to
the number of the PDM pulses N divided by the time period T,
equation (4) becomes:
.DELTA. V GS = .DELTA. V 1 - .DELTA. V 2 = NC 150 V CC - V GS _ R
124 T C 130 g = D P TC 150 V CC - V GS _ R 124 T C 130 g . ( 5 )
##EQU00004##
Therefore, the total increment of the gate-source voltage
.DELTA.V.sub.GS of the charging switch 130 during the time period T
is proportional to the pulse density D.sub.P of the PDM pulses 142
during the time period T. As described above, the increment of the
charging current during the time period T is proportional to the
increment of the gate-source voltage .DELTA.V.sub.GS during the
time period T. As a result, the increment of the charging current
of the charging switch 130 during the time period T is proportional
to the pulse density D.sub.P of the PDM pulses 142 during the time
period T.
[0020] Advantageously, the charging current can be adjusted by
controlling the pulse density of the PDM pulses 142. More
specifically, the charging current increases when the pulse density
of the PDM pulses 142 increases and the charging current decreases
when the pulse density of the PDM pulses 142 decreases.
[0021] In one embodiment, the controller 120 can also enable an
oscillator 180 which generates a plurality of clock pulses (clock
signal) 144 having a constant frequency. As such, a pulse density
of the clock pulses 144 is constant. The charge pump 150 receives
the clock pulses 144 and generates a driving signal 152 which can
fully turn on the charging switch 130, in one embodiment.
[0022] The oscillator 180 enabled by the controller 120 can also
generate a plurality of clock pulses 146 to control a charge pump
160. In one embodiment, the charge pump 160 is used to receive the
plurality of clock pulses 146 and generate a driving signal 162 to
control the discharge switch 132.
[0023] FIG. 1B shows a block diagram of a battery charging system
100', in accordance with one embodiment of the present invention.
Elements that are labeled the same as in FIG. 1A have similar
functions and will not be repetitively described herein for
purposes of brevity and clarity.
[0024] As shown in the example of FIG. 1B, the controller 120
includes an A/D (analog-to-digital) converter 172, an A/D converter
174, and a processor 178. In one embodiment, the A/D converter 172
monitors all the cell voltages for cells 102_1-102.sub.--n during
each cycle (time period T). More specifically, the A/D converter
172 receives a voltage monitoring signal indicative of a cell
voltage for each cell of the plurality of cells 102_1-102.sub.--n
via a multiplexer 190 during each cycle. In one embodiment, the A/D
converter 174 monitors a charging current during each cycle (time
period T). More specifically, the A/D converter 174 receives a
current monitoring signal indicative of a battery charging current
via a sense resistor 180. In one embodiment, a processor 178 (e.g.,
a micro-processor) receives monitoring signals from the A/D
converter 172 and the A/D converter 174, and adjusts the pulse
density of PDM pulses during each cycle (time period T).
[0025] Advantageously, the controller 120 monitors a charging
current of the battery pack 102 and a cell voltage for each cell of
the plurality of cells 102_1-102.sub.--n, and controls the charging
current of the battery pack 102. In one embodiment, the processor
178 enables the PDM pulse generator 140 and controls the pulse
density of the PDM pulses during pre-charging (e.g., pre-charging
can be performed when a battery voltage for the battery pack 102 is
less than a predetermined voltage threshold V.sub.pre' or when a
cell voltage is less than a predetermined voltage threshold
V.sub.pre) such that a pre-charging current I.sub.pre
(I2<I.sub.pre<I1) flows to the battery pack 102. The charging
switch 130 is controlled linearly (that is, the charging switch 130
is operated in the active region) by the driving signal 152.
Advantageously, the processor 178 decreases the pulse density when
the charging current is greater than a first predetermined
threshold I1. The processor 178 increases the pulse density when
the charging current is less than a second predetermined threshold
I2 that is less than the first predetermined threshold I1. As such,
the battery charging system 100' is able to pre-charge the battery
pack 102 when the battery voltage is low or zero, in one
embodiment.
[0026] In one embodiment, the processor 178 disables the PDM pulse
generator 140 and enables the oscillator 180 during normal charging
(e.g., normal charging can be performed when all the cell voltages
of the plurality of cells 102_1-102.sub.--n are greater than the
predetermined threshold V.sub.pre) such that a normal charging
current I.sub.nor flows to the battery pack 102. In one embodiment,
the normal charging current I.sub.nor is greater than the
pre-charging current I.sub.pre. The charging switch 130 is fully
turned on during normal charging, in one embodiment.
[0027] Alternatively, the processor 178 can also enable the PDM
pulse generator 140 instead of oscillator 180 and controls the
pulse density of the PDM pulses during normal charging, in one
embodiment. More specifically, the processor 178 increases the
pulse density of the PDM pulses 142, such that the voltage of the
driving signal 152 is sufficient to fully turn on the charging
switch 130. Therefore, a normal charging current I.sub.nor can be
provided to the battery pack 102.
[0028] In one embodiment, the controller 120 also performs battery
protection which includes, but is not limited to, over-voltage
protection, over-current protection, under-voltage protection,
over-temperature protection.
[0029] FIG. 2 shows a flowchart 200 of operations performed by a
battery charging system, in accordance with one embodiment of the
present invention. FIG. 2 is described in combination with FIG. 1A
and FIG. 1B.
[0030] In block 202, the charger 110 is plugged in, such that the
battery pack 102 is coupled to the charger 110. In block 204, the
battery charging system monitors a cell voltage V.sub.cell for each
cell 102_1-102.sub.--n. More specifically, the A/D converter 172
converts a voltage monitoring signal indicative of the cell voltage
V.sub.cell for each cell 102_1-102.sub.--n to a digital signal, and
sends the converted digital signal to the processor 178.
[0031] In block 206, the cell voltage V.sub.cell for each cell
102_1-102.sub.--n is compared with a predetermined voltage
threshold V.sub.pre. If any cell has a cell voltage V.sub.cell
which is less than the predetermined voltage threshold V.sub.pre,
the flowchart 200 goes to block 210 to perform pre-charging.
Otherwise, the flowchart 200 goes to block 206 to perform normal
charging. The detailed operation of the normal charging is omitted
herein for purposes of brevity and clarity.
[0032] During pre-charging, the PDM pulse generator 140 is enabled
by the controller 120 and the oscillator 180 is disabled. The
battery 102 can be charged by a constant power (that is, the
charging power for the battery pack 102 is constant) or it can be
charged by a constant current (that is, the charging current for
the battery pack is constant), either of which can be selected by a
user before charging, in one embodiment. In block 210, if constant
power charging is selected, the flowchart 200 goes to block 212 to
perform a constant power charging. In block 212, a predetermined
pre-charging current flowing to the battery pack 102 can be given
by:
I pre = P pre V pre - V cell_min , ( 6 ) ##EQU00005##
where P.sub.pre represents a constant preset power level for
charging the battery pack 102, which can be defined and programmed
by the user before charging, and V.sub.cell.sub.--.sub.min
represents the lowest cell voltage among all the cell voltages for
cells 102_1-102.sub.--n.
[0033] In block 210, if constant power charging is not selected,
the flowchart 200 goes to block 214 to perform constant current
charging. In block 214, a predetermined pre-charging current
flowing to the battery pack 102 can be given by:
I.sub.pre=I.sub.pre.sub.--.sub.set, (7)
where I.sub.pre.sub.--.sub.set is a preset constant current level
which can be defined and programmed by the user before
charging.
[0034] In block 216, a charging current I.sub.sen monitored from
the sense resistor 180 is compared with a first predetermined
threshold I1 and a second predetermined threshold I2. More
specifically, the processor 178 receives a current monitoring
signal indicative of the charging current from the sense resistor
180, and compares the current monitoring signal with the first
predetermined threshold I1 and the second predetermined threshold
I2. In one embodiment, the first predetermined threshold I1 and the
second predetermined threshold I2 are given by:
I1=I.sub.pre+I.sub.hys,I2=I.sub.pre-I.sub.hys, (8)
where I.sub.hys represents a hysteresis value which can be used to
reduce oscillation of the charging current.
[0035] In block 216, if the monitored charging current I.sub.sen is
greater than the second predetermined threshold I2 and less than
the first predetermined threshold I1 (I2<I.sub.sen<I1), the
flowchart 200 goes to block 222. In block 222, the pulse density is
unchanged. More specifically, the processor 178 maintains the pulse
density of the PDM pulses generated by the PDM pulse generator 140
in order to keep the charging current.
[0036] Otherwise, if the monitored charging current I.sub.sen is
greater than the first predetermined threshold I1
(I.sub.sen>I1), the flowchart 200 goes to block 220. In block
220, the pulse density is decreased. More specifically, the
processor 178 decreases the pulse density of the PDM pulses 142
generated by the PDM pulse generator 140 in order to reduce the
charging current.
[0037] Otherwise, if the monitored charging current I.sub.sen is
less than the second predetermined threshold I2 (I.sub.sen<I2),
the flowchart 200 goes to block 218. In block 218, the pulse
density is increased. More specifically, the processor 178
increases the pulse density of the PDM pulses 142 generated by the
PDM pulse generator 140 in order to increase the charging
current.
[0038] Advantageously, by adjusting the pulse density of the PDM
pulses 142, the charging current can be controlled within a
predetermined range. More specifically, the charging current can be
controlled such that the charging current is less than a first
predetermined threshold I1 (I1=I.sub.pre+I.sub.hys) and is greater
than a second predetermined threshold I2 (I2=I.sub.pre-I.sub.hys).
The hysteresis value I.sub.hys is used to reduce oscillation of the
charging current, in one embodiment.
[0039] In block 224, if a cycle (time period T) is finished, the
flowchart 200 returns to block 204. Any repetitive description
following block 204 that has been described above will be omitted
herein for purposes of clarity and brevity. Otherwise, the
flowchart 200 returns to block 224. Accordingly, the processor 178
adjusts the pulse density during each cycle (time period T).
[0040] FIG. 3 shows a flowchart 300 of operations performed by a
battery charging system, in accordance with one embodiment of the
present invention. FIG. 3 is described in combination with FIG. 1A
and FIG. 1B.
[0041] In block 302, the battery charging system generates a
plurality of pulses 142 by a pulse generator 140 (e.g., a PDM pulse
generator). In block 304, the battery charging system monitors a
charging current flowing to the battery pack 102. The battery
charging system can also monitor a battery voltage and/or
individual cell voltages for the plurality of cells
102_1-102.sub.--n in the battery pack 102.
[0042] In block 306, the battery charging system controls a pulse
density of the plurality of pulses. More specifically, the battery
charging system decreases the pulse density when the charging
current is greater than a first predetermined threshold I1. The
battery charging system increases the pulse density when the
charging current is less than a second predetermined threshold I2
that is less than the first predetermined threshold I1.
[0043] In block 308, the battery charging system controls a
conductance of a charging switch 130 according to the pulse
density. Accordingly, the charging current flowing through the
charging switch 130 to the battery pack 102 can be adjusted
according to the pulse density of the pulses 142 as shown in block
310. Advantageously, the battery charging current can be controlled
such that the battery charging current is less than the first
predetermined threshold I1 and greater than the second
predetermined threshold I2.
[0044] Accordingly, a battery charging system is provided. In one
embodiment, the battery charging system adjusts a charging current
by controlling a pulse density of a plurality of pulses.
Advantageously, in one embodiment, an n-channel metal oxide field
effect transistor can be used as a charging switch, which saves
costs and reduces power dissipation. Furthermore, the battery
charging system is able to charge the battery when a battery
voltage is low or zero, in one embodiment.
[0045] While the foregoing description and drawings represent
embodiments of the present invention, it will be understood that
various additions, modifications and substitutions may be made
therein without departing from the spirit and scope of the
principles of the present invention as defined in the accompanying
claims. One skilled in the art will appreciate that the invention
may be used with many modifications of form, structure,
arrangement, proportions, materials, elements, and components and
otherwise, used in the practice of the invention, which are
particularly adapted to specific environments and operative
requirements without departing from the principles of the present
invention. The presently disclosed embodiments are therefore to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims and
their legal equivalents, and not limited to the foregoing
description.
* * * * *