U.S. patent application number 09/725833 was filed with the patent office on 2001-04-26 for battery recharging device and method and an automatic battery detection system and method therefor.
Invention is credited to Carkner, Steven, Fischer, Daniel.
Application Number | 20010000423 09/725833 |
Document ID | / |
Family ID | 46203972 |
Filed Date | 2001-04-26 |
United States Patent
Application |
20010000423 |
Kind Code |
A1 |
Fischer, Daniel ; et
al. |
April 26, 2001 |
Battery recharging device and method and an automatic battery
detection system and method therefor
Abstract
A system includes a recharging device to which an electronic
hand-held device powered by a battery can be connected. A
controller associated with the recharging device performs a method
of internal-device battery cell detection, i.e., distinguishing
between NiMH/NiCd and other types of cells in the battery, before
recharging the battery. A method determines the cell chemistry
without any modifications to the battery and/or without any user
input by performing tests on the battery. The tests include a
Battery Voltage Test, an Internal Resistance Test, and a Timed
Voltage Test. The testing is performed through a combination of
hardware and software in the charging cradle. By performing the
tests in a preferred order, detected alkaline, lithium,
rechargeable alkaline, and carbon-zinc cells, damaged NiMH and NiCd
cells, and close to fully charged NiMH and NiCd cells cause
termination of a recharging operation before damage to the device
or battery is sustained--without requiring input from a user.
Inventors: |
Fischer, Daniel; (Waterloo,
CA) ; Carkner, Steven; (Manotick, CA) |
Correspondence
Address: |
David B. Cochran, Esq.
Jones, Day, Reavis & Pogue
North Point
901 Lakeside Avenue
Cleveland
OH
44114
US
|
Family ID: |
46203972 |
Appl. No.: |
09/725833 |
Filed: |
November 29, 2000 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09725833 |
Nov 29, 2000 |
|
|
|
09343304 |
Jun 30, 1999 |
|
|
|
6191551 |
|
|
|
|
Current U.S.
Class: |
320/114 ;
320/116 |
Current CPC
Class: |
H02J 7/00041 20200101;
H02J 7/0031 20130101; H02J 7/00047 20200101 |
Class at
Publication: |
320/114 ;
320/116 |
International
Class: |
H02J 007/00 |
Claims
ave voltages above the specified threshold. Further, most fully
charged NiMH and NiCd cells have a terminal voltage in the
neighbourhood of the threshold voltage. Therefore, the Battery
Voltage Test 104 detects both fully charged NiMH and NiCd cells (to
prevent overcharging) and non-rechargeable cells. FIG. 6 sets forth
the preferred steps of the IR Test 106. The IR Test 106 determines
the internal resistance of the battery 28 inside the device 16 to
determine the cell-type. The NiMH and NiCd cells have a low
internal resistance (due to their construction) such that their
lower IRs allow them to be differentiated by this test. The values,
V.sub.AA1 and V.sub.AA2, are measured by determining the pulse
height voltage response to a 20 ms pulse of known current from the
constant current source. The voltages, V.sub.AA1 and V.sub.AA2, are
proportional to the internal resistance of the battery and are used
directly as a measure of the battery's internal resistance. The IR
Test 106 is performed by the controller 24 as follows. Once the
Battery Voltage Test 104 has passed, at step 302 the IR Test 106 is
started. A first voltage V.sub.AA1 of the battery 28 is read and
stored at step 304. Then, at step 306 the first voltage V.sub.AA1
is compared to a predetermined voltage value, preferably 1.1 V.
Based on this comparison, at step 308 a threshold voltage value
V.sub.T is determined and set so that it is used during testing.
Preferably, the threshold voltage V.sub.T is set at 137 mV if
V.sub.AA1 is equal to or greater than 1.1 v or V.sub.T is set at
200 mV if V.sub.AA1 is less than 1.1 V. Then, a sample-count value
and a pass-count value are both set to 0 at step 310. At step 312,
the controller 24 enables test charging of the battery 28,
preferably at a rate of 630 mA for 20 ms. During the test charging,
a second voltage value V.sub.AA2 is stored at step 314. This second
value V.sub.AA2 is then subtracted from the first value V.sub.AA1
to determined a difference value that is then compared to the
threshold voltage V.sub.T at step 316. If the difference
V.sub.AA1-V.sub.AA2 is less than the threshold voltage V.sub.T,
then (1) the pass-count value is incremented to pass-count+1 at
step 318, (2) the testing is delayed a predetermined time period at
step 320, which is preferably 1 ms, and (3) the sample-count value
is incremented to sample-count+1 at step 322. Otherwise, if the
difference V.sub.AA1 -V.sub.AA2 is equal to or above the threshold
voltage V.sub.T, then only steps 320 and 322 are performed and the
pass-count value step 318 is by-passed. At step 324, the controller
24 determines whether or not 20 voltage samples V.sub.AA2 have been
read, stored, and used to calculate the difference value for the
comparison to the threshold value. If it is determined that there
have been less than 20 samples, steps 314-324 are repeated until
the sample-count is equal to 20. Otherwise, if it is determined
that 20 samples have been taken, then the test charging is disabled
at step 326. After disabling the test charging at step 326, a
determination is made at step 328 if the pass-count value is
greater then or equal to 14, i.e., at least 14 times during the 20
samples the voltage difference V.sub.AA1-V.sub.AA2 was less than
the threshold voltage V.sub.T at step 316. If the pass-count value
is equal to or above 14, then the method 100 proceeds to the Timed
Charge Test 108 at step 330. Otherwise, if the pass-count value is
less than 14, then the user is alerted at step 332, via the
external interface 26, that the recharging operation is being
terminated. The threshold voltage V.sub.T of 137 mV was chosen
because most healthy NiMH and NiCd AA cells have a jump in their
terminal voltage, during the 20 ms charge, of less than 137 mV. The
NiMH and NiCd cells that do not fall below this value are usually
damaged cells. Also, the threshold voltage V.sub.T of 200 mV was
chosen because as cell voltage decreases, the internal resistance
of the AA cell rises and this must be taken into account. Further,
the predetermined pass-count value of 14 was used because a
non-insignificant noise floor is seen at the input pin to an A/D
converter (not shown) in the control circuit 84. Therefore, having
14 sample results (of the subtraction) is required to accurately
track the shape of the pulse created by charging for 20 ms. FIG. 7
sets forth the preferred steps of the Timed Charge Test 108. The
method 100 proceeds to the Timed Charge Test 108 at step 402 once
the battery 28 has passed the Battery Voltage Test 104 and the IR
Test 106. At step 404, a sample-count value is set to 0. Then, test
charging of the battery 28 is enabled at step 406. The controller
24 enables charging (at a rate of 630 mA) into the cells within the
battery 28 for a period of five seconds. During this period of
time, the controller 24 measures the voltage of battery 28 at node
30 in 17 equally time-spaced sets of 16 samples per set, which are
then averaged as V.sub.BAT at step 408. At step 410, it is
determined if V.sub.BAT is above a predetermined threshold value,
preferably 1.553 V. If V.sub.BAT is above this threshold value,
then the test charging is disabled at step 412. If this occurs, the
user is alerted at step 414, via the external user interface 26,
that the recharging operation is being terminated. Otherwise, if
the V.sub.BAT is below the threshold value, the Timed Charge Test
108 is delayed a predetermined time period, preferably 0.3 seconds,
at step 416, and then the sample-count value is increased by 1 to
sample-count+1 at step 418. Following the delay at step 416 and
increment at step 418, the sample-count value is compared to a
predetermined sample-count value at step 420, where the
predetermined sample-count value is preferably 17. If the
sample-count value is less than 17, then steps 408-418 are repeated
until the sample-count is equal to 17. Otherwise, the test charging
is disabled at step 422, and at step 424 the cell inside the
battery 28 is considered to be a NiMH or NiCd cell in need of
recharging. If this is determined at step 424, the controller 24
will bias the gate of the MOSFET 64 so that it is in an ON state
allowing electricity to flow through MOSFET 64 and the constant
current source 22 to the device 16 to begin recharging the battery
28. The value of 1.553 V as the threshold level for the V.sub.BAT
comparison is used because most NiCd and NiMH AA cells, when
charged for five seconds at a rate of 630 mA, have terminal
voltages that rise to less than 1.553 V. However, NiMH and NiCd
cells that are not ready to be recharged have terminal voltages
that are above 1.553 V. Thus this test 108, according to a
preferred embodiment of the present invention, detects and does not
recharge NiMH or NiCd cells that are close to fully charged. The
Timed Charge Test 108 detects and does not recharge any non-NiMH
and non-NiCd AA cells 28 that may have passed the previous two
tests 104 and 106. These three tests 104-108 in the preferred
combination accurately detect the presence of either a
non-NiCd/NiMH cell or a near fully charged NiCd/NiMH cell when the
electronic device 16 is positioned in the holder 14. Finally,
although some non-preferred cells may pass any of the three tests
104-108 individually, it is doubtful that the cells would not be
detected and pass all three of the battery detection tests 104-108
in the combination as taught in the preferred embodiment of the
present invention. The invention has been described with reference
to preferred embodiments. Those skilled in the art will perceive
improvements, changes, and modifications. Such improvements,
changes and modifications are intended to be covered by the
appended claims. We claim:
1. An apparatus comprising: a power source; an electronic hand-held
device powered by the power source; and recharging means including
a controller that is operative to determine, prior to beginning a
recharging operation, if the power source should not be recharged
when the electronic hand-held device is operatively connected to
the recharging means.
2. An apparatus according to claim 1, wherein the controller
determines if the power source is a non-rechargeable power source,
a damaged or abnormal rechargeable power source or a nearly fully
charged rechargeable power source to thereby determine that the
power source should not be recharged.
3. An apparatus according to claim 1, wherein the power source is
replaceable by a user of the hand-held electronic device.
4. An apparatus according to claim 1, wherein the power source is a
battery.
5. An apparatus according to claim 1, wherein the electronic
hand-held device is a wireless transceiver.
6. An apparatus according to claim 5, wherein the wireless
transceiver is a two-way paging computer.
7. An apparatus according to claim 5, wherein the wireless
transceiver is a portable electronic messaging device.
8. An apparatus according to claim 1, wherein the controller is
configured to measure predetermined characteristics of the power
source.
9. An apparatus according to claim 1, wherein the controller is
configured to perform a battery voltage test.
10. An apparatus according to claim 9, wherein when performing the
battery voltage test the controller is operative to determine if a
power source voltage value is below a threshold value.
11. An apparatus according to claim 1, wherein the controller is
configured to perform an internal resistance (IR) test.
12. An apparatus according to claim 11, wherein when performing the
IR test the controller is operative to determine if a difference
between a first power source voltage value and a second power
source voltage value is below a predetermined threshold value a
predetermined number of times.
13. An apparatus according to claim 1, wherein the controller is
configured to perform a timed charge test.
14. An apparatus according to claim 13, wherein when performing the
timed charge test the controller is operative to determine if a
power source voltage value is below a predetermined threshold
value.
15. An apparatus according to claim 1, wherein the controller is
configured to perform a battery voltage test and an IR test.
16. An apparatus according to claim 15, wherein: when performing
the battery voltage test the controller is operative to determine
if a first power source voltage value is below a first threshold
value; and when performing the IR test the controller is operative
to determine if a difference between a second power source voltage
value and a third power source voltage value is below a second
predetermined threshold value a predetermined number of times.
17. An apparatus according to claim 1, wherein the controller is
configured to perform a battery voltage test and a timed charge
test.
18. An apparatus according to claim 17, wherein: when performing
the battery voltage test the controller is operative to determine
if a first power source voltage value is below a first threshold
value; and when performing the timed charge test the controller is
operative to determine if a second power source voltage value is
below a second predetermined threshold value.
19. An apparatus according to claim 1, wherein the controller is
configured to perform an IR test and a timed charge test.
20. An apparatus according to claim 19, wherein: when performing
the IR test the controller is operative to determine if a
difference between a first power source voltage value and a second
power source voltage value is below a first predetermined threshold
value a predetermined number of times; and when performing the
timed charge test the controller is operative to determine if a
third power source voltage value is below a second predetermined
threshold value.
21. An apparatus according to claim 1, wherein the controller is
configured to perform a battery voltage test, an IR test, and a
timed charge test.
22. An apparatus according to claim 21, wherein: when performing
the battery voltage test the controller is operative to determine
if a first power source voltage value is below a first threshold
value; when performing the IR test the controller is operative to
determine if a difference between a second power source voltage
value and a third power source voltage value is below a second
predetermined threshold value a predetermined number of times; and
when performing the timed charge test the controller is operative
to determine if a fourth power source voltage value is below a
third predetermined threshold value.
23. An apparatus according to claim 1, wherein the controller is
configured to sequentially perform a battery voltage test, an IR
test, and a timed charge test.
24. An apparatus according to claim 23, wherein when performing the
battery voltage test the controller is operative to determine if a
first power source voltage value is below a first threshold value;
when performing the IR test the controller is operative to
determine if a difference between a second power source voltage
value and a third power source voltage value is below a second
predetermined threshold value a predetermined number of times; and
when performing the timed charge test the controller is operative
to determine if a fourth power source voltage value is below a
third predetermined threshold value.
25. An apparatus according to claim 4 further comprising: a user
interface coupled to the controller which is configured to provide
a user information regarding a status of testing performed on the
battery.
26. An apparatus according to claim 25, wherein the user interface
comprises a light-emitting diode.
27. An apparatus according to claim 25, wherein the user interface
comprises a graphical user interface.
28. A method comprising the steps of: powering an electronic
hand-held device with a power source; testing the power source when
the electronic hand-held device is operatively connected to a
recharging means, the testing being performed by a controller,
prior to beginning a recharging operation, to determine if the
power source should not be recharged; and controlling an operation
of the electronic hand-held device based on the testing step.
29. A method according to claim 28, wherein the controller
determines if the power source is a non-rechargeable power source,
a damaged or abnormal rechargeable power source or a nearly fully
charged rechargeable power source to thereby determine that the
power source should not be recharged.
30. A method according to claim 28, wherein the testing step
comprises performing a power source voltage test.
31. A method according to claim 28, wherein the testing step
comprises performing an IR test.
32. A method according to claim 28, wherein the testing step
comprises performing a timed charge test.
33. A method according to claim 28, wherein the testing step
comprises: performing a power source voltage test; and performing
an IR test.
34. A method according to claim 28, wherein the testing step
comprises: performing a power source voltage test; and performing a
timed charge test.
35. A method according to claim 28, wherein the testing step
comprises: performing an IR test; and performing a timed charge
test.
36. An apparatus for testing a battery, the apparatus comprising:
an electronic device powered by the battery; recharging means that
comprises a controller that is operative to perform tests on the
battery when the electronic device is operatively connected to the
recharging means, the tests being operative to determine, prior to
beginning a recharging operation, if the battery should not be
recharged.
37. An apparatus according to claim 36, wherein the controller
determines if the battery is a non-rechargeable battery, a damaged
or abnormal rechargeable battery or a nearly fully charged
rechargeable battery to thereby determine that the battery should
not be recharged.
38. An apparatus according to claim 36, wherein the electronic
device is a hand-held two-way paging computer.
39. An apparatus according to claim 36, wherein the electronic
device is a portable electronic messaging device.
40. An apparatus according to claim 36, wherein the electronic
device is a hand-held email client.
41. A method for determining if a battery powering an electronic
device should not be recharged the method comprising the steps of:
performing a battery voltage test on the battery; performing a IR
test on the battery; and performing a timed charge test on the
battery; the testing of the battery being performed by a controller
in a recharging means when the electronic device is operatively
connected to the recharging means, prior to beginning a recharging
operation.
42. A method according to claim 41, wherein the IR test is only
performed if the power source voltage test passes, and the timed
charge test is only performed if the IR test passes and all the
tests must pass for a recharging operation to begin for the
battery.
Description
REFERENCE TO RELATED APPLICATION
1. This application is a continuation-in-part of the copending U.S.
Utility application Ser. No. 09/343,304, entitled "Automatic
Battery Detection System and Method for Detecting a Rechargeable
Battery with Low Remaining Charge", filed on Jun. 30, 1999 and
assigned to the assignee of the instant invention.
BACKGROUND OF THE INVENTION
2. The present invention relates to a battery recharging device and
method which tests a battery to determine if it should not be
recharged. More specifically, the present invention relates to an
automatic battery detection system and method for use with an
electronic device, such as wireless two-way communication devices,
pagers, integrated email devices and cellular phones, powered by a
battery. The electronic device is electrically connected to an
associated recharging device to test the battery. This testing is
performed by a controller that determines if the device includes a
battery that should not be recharged. If the testing does not
indicate that the battery should not be recharged, then a
recharging operation is performed.
3. Generally, wireless transceivers, such as those used in radios,
cell phones, pagers, etc., are powered by rechargeable batteries.
Most commercially available rechargeable cells, such as Nickel
Metal Hydride (NiMH) or Nickel-Cadmium (NiCd) cells, are recharged
by an external charger (i.e., the user removes the batteries from
the device and recharges them in the external charger). However,
some devices recharge the batteries without removing them from the
device.
4. To recharge the battery without removing it from the device, the
type of cell within the battery must first be determined by the
recharging device. Usually, the rechargeable batteries are modified
to facilitate cell-type detection. This modification of the battery
typically is done by adding a third terminal to the battery where
detection is performed by a detector that measures the batteries
characteristics through an electrical contact with the third
terminal.
5. Another method of in-unit cell detection is performed through
some form of user input such as a mechanical switch with an arrow
that is lined up with one or more markings on the device. These
markings represent chemical symbols or words that indicate the
cell-type of the battery to the device charging the cell.
6. When recharging a battery though a charging cradle it is
necessary to first test the battery to reduce the possibility of
damaging either the device or the battery. If a device having a
non-rechargeable battery is placed in the charging cradle during a
recharging operation both the battery and the device could be
damaged. Further, if a rechargeable battery is recharged when it is
already almost fully charged, the number of charging cycles is
lowered and the lifetime of the battery is drastically reduced.
SUMMARY OF THE INVENTION
7. According to the present invention, a recharging device, which
may for example be a charging cradle, is electrically connected to
an electronic device powered by a battery. A controller performs a
method of internal-device battery cell detection, i.e.,
distinguishing between NiMH/NiCd and other types of cells in the
battery, before recharging the battery. A method determines the
cell chemistry without any modifications to the battery and/or
without any user input by performing a plurality of tests. The
tests may include a Battery Voltage Test, an Internal Resistance
(IR) Test, and a Timed Voltage Test. The tests are preferably
executed in a predetermined order. The testing is performed through
a combination of hardware and software which may be in the charging
cradle.
8. One advantage of the present invention is that alkaline,
lithium, rechargeable alkaline, and carbon-zinc cells are detected
and not recharged while the battery remains in the device without
modifying the battery, which protects the device from being
damaged.
9. Another advantage of the present invention is that damaged NiMH
and NiCd cells are detected and not recharged while the battery
remains in the device without modifying the battery, which protects
the device from being damaged.
10. Still another advantage of the present invention is that close
to fully charged NiMH and NiCd cells are detected and not recharged
while the battery remains in the device without modifying the
battery, which extends the life of the battery and prevents
overcharging of the battery.
11. Another advantage of the present invention is that the
detection process may be conducted without requiring input from a
user.
12. These are just a few of the many advantages of the invention,
which is described in more detail below in terms of a preferred
embodiment. As will be appreciated, the invention is capable of
other and different embodiments, and its several details are
capable of modifications in various respects, all without departing
from the invention. Accordingly, the drawings and description of
the preferred embodiments are to be regarded as illustrative in
nature and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
13. The present invention will be apparent to those skilled in the
art upon reading the following description in view of the
accompanying drawings, wherein:
14. FIG. 1 is a high-level block diagram of a system according to a
preferred embodiment of the present invention;
15. FIG. 2 is a detailed circuit architecture of the system of FIG.
1 according to a preferred embodiment of the present invention;
16. FIG. 3 is a detailed circuit architecture of a section of the
system of FIG. 1 according to a preferred embodiment of the present
invention;
17. FIG. 4 is a flow chart of the overall battery detection method
according to a preferred embodiment of the present invention;
18. FIG. 5 is a flow chart of a Battery Voltage Test according to a
preferred embodiment of the present invention;
19. FIG. 6 is a flow chart of an IR Test according to the preferred
embodiment of the present invention; and
20. FIG. 7 is a flow chart of a Timed Charge Test according to a
preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
21. An apparatus 10 comprising a preferred embodiment of the
present invention is shown in FIG. 1. The apparatus 10 includes an
external power source adapter 12, preferably an AC adapter, a
recharging device 14 and an electronic device 16. The device 16 is
preferably a hand-held electronic device such as those disclosed in
copending U.S. patent application Ser. No. 09/106,585, entitled
"Hand-Held Electronic Device With a Keyboard Optimized for Use With
The Thumbs", filed on Jun. 29, 1998, assigned to the assignee of
the instant invention and incorporated into this disclosure by
reference. The recharging device 14 is preferably a charging cradle
or recharging device adapted for use with the electronic device 16.
It is to be appreciated that although these are the preferred
devices, other devices for use with the present invention that
operate in a similar manner could also be used. For example, the AC
adapter 12 could be integrated with the recharging device 14 into a
single recharging unit.
22. With continuing reference to FIG. 1, the recharging device 14
preferably includes a DC-DC converter 18, a switch block 20, a
constant current source 22, a controller 24, and an external user
interface 26. The converter 18 is preferably a 12 V to 5 V
converter, which converts voltage received from the adapter 12 and
sends the converted voltage to the switch block 20. Electricity
flowing through the switch block 20 to the constant current source
22 is controlled by the controller 24.
23. The device 16 preferably includes a battery 28, a Schottky
diode 30, a device circuit 32, and a temperature detection circuit
34. Through use of the Schottky diode 30, the constant current
source 22 in the recharging device 14 is protected from reverse
current since the diode 30 only permits current flow into the
electronic device 16. The controller 24 performs tests on the
battery 28 by reading the voltage at node 36 of the device 16 to
determine if the battery 28 contains rechargeable NiMH or NiCd
cells that need to be recharged. This determination is actually
made by determining that the battery does not contain cells that
should not be recharged, as will become apparent from the
description below. The battery 28 is recharged by the constant
current source 22 when the controller 24 determines that the
battery 28 is a rechargeable battery that is in need of recharging.
Also, the controller 24 monitors other parameters of the electronic
device 16, such as temperature, through a temperature detection
circuit 34.
24. The device circuit 32 is preferably configured to operate as a
wireless transceiver, such as a two-way paging computer, a portable
electronic messaging device, or a hand held e-mail client. An
example of such a device is set forth in the U.S. patent
application Ser. No. 09/106,585 referenced above. Although this is
the preferred device circuit 32, other types of circuits could be
utilized in the present invention.
25. The external interface 26 of the recharging device 14 is
preferably either a light-emitting diode (LED) or a graphical user
interface (GUI) that alerts a user of the device 16 the status of
the testing being performed. For example, an LED illuminates
continuously during the detecting. Then, if the controller 24
determines the battery 28 contains NiCd or NiMH cells that need to
be recharged, the LED blinks until a recharging cycle is completed
at which time the LED is illuminated continuously again. In the
alternative embodiment with the GUI, the external interface 26 may
be located on the recharging device 14 or may be a computer monitor
(not shown) that is coupled to the recharging device 14. Further,
the information can alternatively be displayed on a GUI 38 of the
pager 16.
26. Turning to FIG. 2, a preferred circuit architecture of the
components in the recharging device 14 are shown in more detail.
The switching block 20 controls the flow of current from the
converter 18 to the constant current source 22 by only allowing
current to pass through it when it is turned ON by the controller
24. This occurs when the controller 24 determines the battery 28
needs to be recharged. Further, when current flows through switch
block 20 it acts as a level shifting switch. The switch block 20
includes a low pass filter 50, a NP load switch circuit 52, and a
filtering capacitor 54. The low pass filter 50, which includes
resistor 56 and capacitor 58, filters the power from the converter
18. Preferably, the low pass filter 50 includes a 100 k .OMEGA.
resistor 56 and a 1000 pF capacitor 58, and the value of the
filtering capacitor 54 is 1 uF capacitor.
27. As seen in FIG. 3, a preferable circuit for the NP load switch
circuit 52 is shown, which is a FCD6363L connection circuit
manufactured by Fairchild Semiconductor Corporation. This
connection circuit 52 includes a p-channel, high current MOSFET 60
with a diode 62 connected drain to source across the FET 60 and an
n-channel, low current MOSFET 64 with a diode 66 connected source
to drain across the FET 64. By connecting the low pass filter 50 to
the MOSFET 60 in this configuration, the MOSFET 60 acts as a
switch. Further, the MOSFET 64 is configured as a level shifting
switch that is switched to an ON state by the controller 24 by
biasing the gate of the MOSFET 64. This allows a 5 volt processor
to control a 12 volt signal. Then, based on the ON state of MOSFET
64, the gate of MOSFET 60 is biased, switching it to an ON state.
In the ON state, the MOSFET 60 allows electricity to flow through
the switch block 20 to the constant current source 22 via the
filtering capacitor 54.
28. With continuing reference to FIGS. 2-3, the constant current
source 22 includes a constant voltage circuit 70 and a low pass
filter 72. A capacitor 74 and a resistor 76 make up the low pass
filter 72. The constant current source 22 further includes a
resistor 78 across which there is a constant voltage from the
constant voltage circuit 70 such that the constant voltage is
converted into the constant current. This constant current flows
into the electronic device 16. Further, the constant current source
22 only conducts when switch block 20 is turned on by the
controller 24 during a recharging operation of battery 28.
Preferably, the constant voltage circuit 70 is a EZ1117CM circuit
manufactured by Semtech Corporation. Also, preferably the value of
capacitor 74 is 0.1 uF, the value of resistor 76 is 383 .OMEGA.,
the value of resistor 78 is 2 .OMEGA., and the value of capacitor
74 is 10 uF.
29. As also seen in FIGS. 2-3, the controller 24 includes a control
circuit 84 and a low pass filter 86. The low pass filter 86, which
includes a resistor 88 and a capacitor 90, filters signals flowing
through a coupling element 92 between the node 36 and the control
circuit 84. Preferably, the control circuit 84 is a PIC16C711
control chip manufactured by Microchip Technology, Inc., the value
of resistor 88 is 10 k .OMEGA., and the value of capacitor 90 is
6800 pF.
30. In this configuration, through the method 100 described in
detail below, the controller 24 determines what type of cells are
contained in the battery 28 without any previous knowledge of the
cell-type. The determination is made when the device 16 is
electrically connected to the recharging device 14. Where the
device 14 is a cradle or holder as described above, the cell type
determination operations are executed when device 16 is properly
inserted into the holder 14. Once proper connection or insertion is
detected, the controller 24 starts testing of the battery 28. If
the testing is successful, i.e., the battery 28 is rechargeable and
in need of recharging, the controller 24 turns ON the FET 64 by
biasing its gate. Then, once the FET 64 is turned ON, the
amplifying PET 60 is turned ON, which permits current flow from the
converter 18 to the constant current source 22. The current then
passes through the constant current source 22 into the device 16 to
recharge the battery 28.
31. FIG. 4 sets forth a preferred method 100 of cell detection
performed by the controller 24, which allows for differentiation
between NiMH/NiCd cells and other cells. By applying this method of
testing, the controller 24 detects and does not recharge an
alkaline, lithium, rechargeable alkaline, and carbon-zinc cells,
damaged NiMH and NiCd cells, and close to fully charged NiMH and
NiCd cells.
32. With continuing reference to FIG. 4, once it has been
determined that the device 16 is properly connected to the
recharging device 14, the testing is started at step 102. A
plurality of tests is preferably performed by the controller 24 to
determine the presence of a "good" NiMH or NiCd cell in the battery
28. Three of the plurality of tests include a Battery Voltage Test
104, an Internal Resistance (IR) Test 106, and a Timed Charge Test
108. As shown in step 110, for a successful detection of a NiMH or
NiCd cell, these tests 104-108 should be passed in a predetermined
order, although alternatively they could be configured to operate
in a different order. If any of the three tests 104-108 fail, then
at step 112 a user is alerted, via the external interface 26, that
the recharging operation is being terminated. These tests 104-108
are described in more detail below with reference to FIGS. 5-7.
33. FIG. 5 sets forth the preferred Battery Voltage Test method
104. The Battery Voltage Test 104 is started at step 200. At step
202 the controller 24 reads the voltage V.sub.BAT of the battery 28
at node 36 through the coupling element 92. Then, at step 204, the
controller 24 determines if the voltage V.sub.BAT is below a
certain threshold value, preferably 1.396 V. If the voltage
V.sub.BAT is below the threshold value, then the Battery Voltage
Test 104 test was successful and the method 100 proceeds to the IR
Test 106 at step 206. If the voltage V.sub.BAT is equal to or above
the threshold value, then the user is alerted, via the external
interface 26, that the recharging operation is being terminated to
ensure there is no damage to the battery 28 or the device 16.
34. In the preferred embodiment of the present invention, the
controller 84 reads the battery voltage 16 times. The purpose of
sampling the voltage 16 times is to remove any random (or white)
noise that could be seen on the coupling element 92. The 16 samples
are then averaged as V.sub.BAT and compared to the threshold
voltage of 1.396 V. The reason for performing the Battery Voltage
Test 104 is because most fully charged alkaline and lithium AA
cells have voltages above the specified threshold. Further, most
fully charged NiMH and NiCd cells have a terminal voltage in the
neighbourhood of the threshold voltage. Therefore, the Battery
Voltage Test 104 detects both fully charged NiMH and NiCd cells (to
prevent overcharging) and non-rechargeable cells.
35. FIG. 6 sets forth the preferred steps of the IR Test 106. The
IR Test 106 determines the internal resistance of the battery 28
inside the device 16 to determine the cell-type. The NiMH and NiCd
cells have a low internal resistance (due to their construction)
such that their lower IRs allow them to be differentiated by this
test. The values, V.sub.AA1 and V.sub.AA2, are measured by
determining the pulse height voltage response to a 20 ms pulse of
known current from the constant current source. The voltages,
V.sub.AA1 and V.sub.AA2, are proportional to the internal
resistance of the battery and are used directly as a measure of the
battery's internal resistance.
36. The IR Test 106 is performed by the controller 24 as follows.
Once the Battery Voltage Test 104 has passed, at step 302 the IR
Test 106 is started. A first voltage V.sub.AA1 of the battery 28 is
read and stored at step 304. Then, at step 306 the first voltage
V.sub.AA1 is compared to a predetermined voltage value, preferably
1.1 V. Based on this comparison, at step 308 a threshold voltage
value V.sub.T is determined and set so that it is used during
testing. Preferably, the threshold voltage V.sub.T is set at 137 mV
if V.sub.AA1 is equal to or greater than 1.1 v or V.sub.T is set at
200 mV if V.sub.AA1 is less than 1.1 V. Then, a sample-count value
and a pass-count value are both set to 0 at step 310. At step 312,
the controller 24 enables test charging of the battery 28,
preferably at a rate of 630 mA for 20 ms. During the test charging,
a second voltage value V.sub.AA2 is stored at step 314. This second
value V.sub.AA2 is then subtracted from the first value V.sub.AA1
to determined a difference value that is then compared to the
threshold voltage V.sub.T at step 316. If the difference
V.sub.AA1-V.sub.AA2 is less than the threshold voltage V.sub.T,
then (1) the pass-count value is incremented to pass-count+1 at
step 318, (2) the testing is delayed a predetermined time period at
step 320, which is preferably 1 ms, and (3) the sample-count value
is incremented to sample-count+1 at step 322. Otherwise, if the
difference V.sub.AA1 -V.sub.AA2 is equal to or above the threshold
voltage V.sub.T, then only steps 320 and 322 are performed and the
pass-count value step 318 is by-passed.
37. At step 324, the controller 24 determines whether or not 20
voltage samples V.sub.AA2 have been read, stored, and used to
calculate the difference value for the comparison to the threshold
value. If it is determined that there have been less than 20
samples, steps 314-324 are repeated until the sample-count is equal
to 20. Otherwise, if it is determined that 20 samples have been
taken, then the test charging is disabled at step 326. After
disabling the test charging at step 326, a determination is made at
step 328 if the pass-count value is greater then or equal to 14,
i.e., at least 14 times during the 20 samples the voltage
difference V.sub.AA1-V.sub.AA2 was less than the threshold voltage
V.sub.T at step 316. If the pass-count value is equal to or above
14, then the method 100 proceeds to the Timed Charge Test 108 at
step 330. Otherwise, if the pass-count value is less than 14, then
the user is alerted at step 332, via the external interface 26,
that the recharging operation is being terminated.
38. The threshold voltage V.sub.T of 137 mV was chosen because most
healthy NiMH and NiCd AA cells have a jump in their terminal
voltage, during the 20 ms charge, of less than 137 mV. The NiMH and
NiCd cells that do not fall below this value are usually damaged
cells. Also, the threshold voltage V.sub.T of 200 mV was chosen
because as cell voltage decreases, the internal resistance of the
AA cell rises and this must be taken into account. Further, the
predetermined pass-count value of 14 was used because a
non-insignificant noise floor is seen at the input pin to an A/D
converter (not shown) in the control circuit 84. Therefore, having
14 sample results (of the subtraction) is required to accurately
track the shape of the pulse created by charging for 20 ms.
39. FIG. 7 sets forth the preferred steps of the Timed Charge Test
108. The method 100 proceeds to the Timed Charge Test 108 at step
402 once the battery 28 has passed the Battery Voltage Test 104 and
the IR Test 106. At step 404, a sample-count value is set to 0.
Then, test charging of the battery 28 is enabled at step 406. The
controller 24 enables charging (at a rate of 630 mA) into the cells
within the battery 28 for a period of five seconds. During this
period of time, the controller 24 measures the voltage of battery
28 at node 30 in 17 equally time-spaced sets of 16 samples per set,
which are then averaged as V.sub.BAT at step 408. At step 410, it
is determined if V.sub.BAT is above a predetermined threshold
value, preferably 1.553 V. If V.sub.BAT is above this threshold
value, then the test charging is disabled at step 412. If this
occurs, the user is alerted at step 414, via the external user
interface 26, that the recharging operation is being terminated.
Otherwise, if the V.sub.BAT is below the threshold value, the Timed
Charge Test 108 is delayed a predetermined time period, preferably
0.3 seconds, at step 416, and then the sample-count value is
increased by 1 to sample-count+1 at step 418.
40. Following the delay at step 416 and increment at step 418, the
sample-count value is compared to a predetermined sample-count
value at step 420, where the predetermined sample-count value is
preferably 17. If the sample-count value is less than 17, then
steps 408-418 are repeated until the sample-count is equal to 17.
Otherwise, the test charging is disabled at step 422, and at step
424 the cell inside the battery 28 is considered to be a NiMH or
NiCd cell in need of recharging. If this is determined at step 424,
the controller 24 will bias the gate of the MOSFET 64 so that it is
in an ON state allowing electricity to flow through MOSFET 64 and
the constant current source 22 to the device 16 to begin recharging
the battery 28.
41. The value of 1.553 V as the threshold level for the V.sub.BAT
comparison is used because most NiCd and NiMH AA cells, when
charged for five seconds at a rate of 630 mA, have terminal
voltages that rise to less than 1.553 V. However, NiMH and NiCd
cells that are not ready to be recharged have terminal voltages
that are above 1.553 V. Thus this test 108, according to a
preferred embodiment of the present invention, detects and does not
recharge NiMH or NiCd cells that are close to fully charged. The
Timed Charge Test 108 detects and does not recharge any non-NiMH
and non-NiCd AA cells 28 that may have passed the previous two
tests 104 and 106. These three tests 104-108 in the preferred
combination accurately detect the presence of either a
non-NiCd/NiMH cell or a near fully charged NiCd/NiMH cell when the
electronic device 16 is positioned in the holder 14. Finally,
although some non-preferred cells may pass any of the three tests
104-108 individually, it is doubtful that the cells would not be
detected and pass all three of the battery detection tests 104-108
in the combination as taught in the preferred embodiment of the
present invention.
42. The invention has been described with reference to preferred
embodiments. Those skilled in the art will perceive improvements,
changes, and modifications. Such improvements, changes and
modifications are intended to be covered by the appended
claims.
* * * * *