U.S. patent application number 10/439257 was filed with the patent office on 2004-11-18 for circuit for regulating current to multiple batteries in a battery charger.
Invention is credited to Ramsden, Martin H., Riley, Marc B., Xiong, Seng P..
Application Number | 20040227487 10/439257 |
Document ID | / |
Family ID | 33417760 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040227487 |
Kind Code |
A1 |
Xiong, Seng P. ; et
al. |
November 18, 2004 |
CIRCUIT FOR REGULATING CURRENT TO MULTIPLE BATTERIES IN A BATTERY
CHARGER
Abstract
A charging circuit for regulating current to a plurality of
batteries is provided. The regulation is performed by a single
control signal that is optionally scaled by resistor dividers.
Switches coupled to the resistor dividers allow a microprocessor to
actuate a particular resistor divider, thereby scaling the current
flowing through a corresponding battery. As such, a single control
signal, like a pulse width modulated signal, may be used to cause
different currents to flow to different batteries, thereby leaving
other output pins of the microprocessor open for other
functions.
Inventors: |
Xiong, Seng P.; (Dacula,
GA) ; Ramsden, Martin H.; (Lawrenceville, GA)
; Riley, Marc B.; (Lawrenceville, GA) |
Correspondence
Address: |
Philip H. Burrus, IV
Motorola, Inc.
Law Department
1700 Belle Meade Court
Lawrenceville
GA
30043
US
|
Family ID: |
33417760 |
Appl. No.: |
10/439257 |
Filed: |
May 15, 2003 |
Current U.S.
Class: |
320/116 |
Current CPC
Class: |
H02J 7/00 20130101; H02J
7/0013 20130101 |
Class at
Publication: |
320/116 |
International
Class: |
H02J 007/00 |
Claims
What is claimed is:
1. A circuit for charging multiple batteries, the circuit
comprising: a. a means for generating an adjustable control signal;
b. a means for regulating current; c. a means for scaling the
adjustable control signal, the means for scaling the adjustable
control signal being coupled between the means for generating and
the means for regulating; and d. a means of actuating the means for
scaling; wherein when the means of actuating is actuated, the means
for scaling reduces the adjustable control signal by a factor
between 0 and 1.
2. The circuit of claim 1, wherein the means for scaling the
adjustable control signal comprises a resistor divider.
3. The circuit of claim 2, wherein the means for actuating the
means for scaling comprises a switch.
4. The circuit of claim 3, wherein the switch is selected from the
group consisting of transistors, relays, circuit breakers, positive
temperature coefficient devices, and fuses.
5. The circuit of claim 4, wherein the means for generating an
adjustable control signal comprises a microprocessor.
6. The circuit of claim 5, wherein the adjustable control signal
comprises a pulse width modulated signal.
7. The circuit of claim 6, wherein the means of actuating is
controllable by the microprocessor.
8. The circuit of claim 2, wherein the resistor divider comprises a
first resistor coupled serially between the means for generating
and the means for regulating, further comprising a second resistor
coupled serially between the first resistor and the means for
actuating.
9. The circuit of claim 8, wherein the means for actuating
comprises a transistor coupled serially between the second resistor
and a ground node.
10. A circuit for charging multiple batteries, the circuit
comprising: a. a means for generating an adjustable control signal;
b. at least two means for regulating current; c. at least two means
for scaling the adjustable control signal, the at least two means
for scaling the adjustable control signal being coupled between the
at least two means for generating and the at least two means for
regulating, respectively; and d. at least two means of actuating
the at least two means for scaling; wherein when the means of
actuating is actuated, the means for scaling reduces the adjustable
control signal by a factor between 0 and 1.
11. The circuit of claim 10, wherein when a first battery and a
second battery are coupled to the circuit, further wherein the
first battery has priority over the second battery, a first means
of actuating is actuated and a second means of actuating is not
actuated.
12. The circuit of claim 11, wherein the at least two means for
scaling the adjustable control signal comprise a first and a second
resistor divider.
13. The circuit of claim 12, wherein the at least two means for
actuating the means for scaling comprise a first and a second
switch.
14. The circuit of claim 13, wherein the first and second switches
are selected from the group consisting of transistors, relays,
circuit breakers, positive temperature coefficient devices, and
fuses.
15. The circuit of claim 14, wherein the means for generating an
adjustable control signal comprises a microprocessor.
16. The circuit of claim 15, wherein the adjustable control signal
comprises a pulse width modulated signal.
17. The circuit of claim 16, wherein the at least two means of
actuating are controllable by the microprocessor.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This invention relates generally to battery charging
devices, and more particularly to multiple battery charging devices
for electronic devices.
[0003] 2. Background Art
[0004] Portable computers, personal digital assistants (PDA's ),
cellular telephones, pagers, calculators, and other such electronic
devices are commonplace in today's mobile society. One of the
reasons these electronic devices are so popular is that they are
portable, i.e. they provide a user with virtual freedom regarding
the location of their use. Although these devices may be powered by
plugging them into a standard AC outlet, AC power is often not
convenient or accessible. Hence, batteries, by offering a portable
source of power, provide portability and added utility to these
electronic devices.
[0005] Although battery technology has progressed greatly in recent
decades, a single battery is sometimes unable to meet a user's
demands. For example, many cellular telephone service providers are
offering plans with 3000 plus minutes of talk time or more per
month. Some business people talk on their cellular phones six or
more hours per day. Typical cellular telephone batteries provide
only three to four hours of talk time before needing to be
recharged. Consequently, some users carry two or more batteries
with them so that a spare is ready when the first battery dies. To
remain on the go, users now demand shorter charge times in addition
to extended battery life. They also want to be able to quickly
charge two or more batteries at the same time.
[0006] One solution to the problem of how to quickly recharge two
or more batteries is to charge the batteries serially. In other
words, when the two batteries are placed in the same charger, the
charger completely charges the first battery. The charger then
switches to the second battery and charges it. Total charging time
is the charging time of one cell multiplied by the number of cells.
Another solution to the problem with quickly recharging multiple
batteries was to charge each battery in a charging system with its
own power line or charging system.
[0007] Both prior art solutions, however, present problems. A
problem with the first solution is that it is not efficient, in
that it takes quite a long time to fully charge both batteries. The
second solution is prohibitive in terms of both cost and the amount
of space required for multiple charging circuits. For these
reasons, there is a need for an adaptive multiple battery charging
apparatus that allows simultaneous charging of multiple batteries
with a single battery charging system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 illustrates a prior art charger.
[0009] FIG. 2 illustrated a prior art charging circuit.
[0010] FIG. 3 illustrates a charging circuit in accordance with the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] A preferred embodiment of the invention is now described in
detail. Referring to the drawings, like numbers indicate like parts
throughout the views. As used in the description herein and
throughout the claims, the following terms take the meanings
explicitly associated herein, unless the context clearly dictates
otherwise: the meaning of "a," "an," and "the" includes plural
reference, the meaning of "in" includes "in" and "on."
[0012] Referring now to FIG. 1, illustrated therein is a prior art
charger 1 having a front pocket 2 and a rear pocket 3. Typically
the front pocket 2 is for receiving a portable electronic device
like a cellular telephone 6, and the rear pocket 3 is for receiving
just a spare battery module or pack 5. As such, the user may charge
the battery pack that is coupled to the phone 6 by inserting the
base of the phone 6 into the first pocket 2, while a spare battery
pack 5 is installed within the second slot 3. A connection 4 is
provided for coupling the charger 1 to a source of electric power.
Some phones are also known that contain a safety switch (SW) in
series with the battery, where the switch may be opened and closed
by the circuitry 7 within the phone. It is not required that both
slots 2 and 3 be used simultaneously, as one slot or the other
could be used at any given time.
[0013] The typical charging circuit for such a charger 1 is shown
in FIG. 2. A power source 10 with enough capacity to fully charge
two batteries 11, 12 is provided and coupled to the charging
circuit 13. A microprocessor 14 having at least two analog outputs
15, 16 drives a pair of corresponding current regulators 17, 18 to
simultaneously charge the pair of cells.
[0014] This prior art charging circuit 13 is less than optimum,
however, in that it is often difficult and expensive to dedicate
two analog outputs 15, 16 to current control. To begin, today's
chargers are being asked to provide more and more functionality. As
such, output pins for microprocessors are often required for fuel
gauging, driving displays, channeling data, and other high-end
functions. Thus, output pins are in high demand and are limited on
any one microprocessor.
[0015] Second, microprocessors with multiple, on-board Digital to
Analog (D/A) converters are expensive. While chargers are being
asked to do more, customers are simultaneously demanding lower and
lower prices. Thus, the addition of a microprocessor with multiple
D/As is not conducive to manufacturing high performance, low cost
chargers.
[0016] This invention solves this problem by providing a charging
circuit capable of regulating charging current in two pockets
simultaneously by using a single pulse width modulator (PWM). PWMs
are switching outputs with variable duty cycles that are less
expensive than analog outputs. For this reason, at least one PWM
output is routinely found on even the least expensive
microprocessors.
[0017] Referring now to FIG. 3, illustrated therein is one
preferred embodiment of a charging circuit in accordance with the
invention. The circuit includes a first and second current
regulators 20,21 that manage the current delivered to a pair of
rechargeable batteries 22,23. The current regulators 20,21 may be
as simple as a transistor operating in the ohmic, or linear,
region.
[0018] The amount of charge current flowing through the batteries
22,23 is determined by a pair of reference signals 24,25 coupled
through linear amplifiers 26,27 to the current regulators 20,21.
The reference signals 24,25 derived from an adjustable control
signal 28. The control signal 28 preferably comprises PWM signal 28
generated by the microprocessor 30 and coupled through a D/A
converter 29. Note that while the D/A converter 29 may be any of a
number of types known in the art, in this preferred embodiment the
D/A converter comprises a series resistor and parallel capacitor.
This R-C filter converts the modulating output to a "ripply" DC
level. Once the control signal 28 has been converted to a DC
signal, it then becomes reference signals 24, 25 for use by the
current regulators 20,21.
[0019] Adjustment of the magnitude of the reference signal 24 is
achieved by way of a means for scaling the adjustable control
signal. In this preferred embodiment, the means for scaling
comprises a resistor divider 32 and a switch 34. The same is true
for reference signal 25 by way of resistor divider 33 and switch
35. In this preferred embodiment, the switch 34 (or corresponding
switch 35) comprises a transistor, although other applications may
find it more suitable to employ other devices known in the art,
like relays, circuit breakers, positive temperature coefficient
devices, fuses, etc. Field Effect Transistors (FETs) are preferable
due to their specified on impedance. If, for example, a bipolar
transistor were used, the microprocessor 30 would need to
compensate for any DC offset caused by current flowing through the
bipolar transistor.
[0020] By opening and closing the switches 34,35, the
microprocessor 30 may establish varying levels of current flowing
through the batteries 22,23 for any given PWM duty cycle. The
varying level is due to the scaling of the reference signal by way
of voltage division created by the resistor dividers 32,33. To see
how this is applied in practice, consider the following exemplary
scenarios:
[0021] The first scenario occurs where there is a single battery
present. When only one battery is present, all power supply current
may be directed to that battery. For instance, if battery 22 is
present and battery 23 is not, the PWM is set to a duty cycle that
corresponds to the full power supply current. If the power supply
can source 525 mA, for example, it is desirable for all 525 mA to
flow through current regulator 20. When switch 34 is open, the
output voltage 36 of the D/A converter 29 passes directly through
to amplifier 26 (due to its high input impedance) resulting in a
525 mA current flowing through battery 22.
[0022] Another scenario occurs when two batteries are present, each
with equal charging priority. (Some chargers may be programmed such
that the battery coupled to the phone has a higher priority, and
thus receives more charging current.) For instance, if battery 22
and battery 23 are both present with equal priority, these
batteries should share the charging current equally. Using the 525
mA supply from above, the PWM would be set to a duty cycle half of
that in the first scenario. Thus, by opening both switch 34 and
switch 35, each battery 22,23 would receive 262 mA of charging
current.
[0023] A third scenario occurs when two batteries are present and
one of the batteries takes priority over the other. For example,
assume that both battery 22 and battery 23 are present. Further
assume that battery 23, being coupled to a radio 37, takes
priority. (This can be the case because the radio 37 acts as a
load. Consequently, the charger must provide more current to
battery 23 to satisfy both charging requirements and radio
load.)
[0024] In this scenario, the resistor dividers 32,33 provide a
weighting factor that facilitates a higher level of current flowing
through battery 23. Staying with the 525 mA exemplary power supply
31, the microprocessor 30 may set PWM 28 so as to request a current
greater than half of the maximum. For discussion purposes assume
that this level is 350 mA. By turning on switch 34, and turning off
switch 35, more current will flow through battery 23 than battery
22. Battery 23 would receive the full 350 mA. Battery 22 would
receive a current scaled down by a factor set by the resistor
divider 32. This scaling factor may be any value between 0 and 1 of
the designer's choosing.
[0025] Yet another scenario occurs when either of the batteries is
in a state that requires a low current. One such example is known
as an undervoltage condition. The undervoltage condition occurs
when a battery has been discharged too deeply, such that the
voltage of the battery has fallen below the manufacturer's
recommended limits. In an undervoltage condition, a small current
is to be applied until the voltage across the battery reaches the
manufacturer's minimum limit. In such a scenario, the current in
that battery may be reduced by actuating its corresponding switch.
In so doing, the actuated switch causes the corresponding resistor
divider to scale the reference signal, thereby reducing the current
flowing through the corresponding battery. Meanwhile, the switch
that has not been actuated allows a current equal to that requested
by the control signal to flow through the corresponding
battery.
[0026] For example, assume that battery 22 is in an undervoltage
condition requiring no more than 100 mA. If all the resistors in
the resistor dividers 32,33 are of equal value, the PWM 28 may be
set to request a current of 200 mA. By closing switch 34 and
opening switch 35, 100 mA flow through battery 22 and 200 mA flow
through battery 23. Note that in each of the scenarios mentioned
above, the batteries are always charged in parallel, and not
sequentially. Note also that all current regulation is done by way
of a single control signal.
[0027] While the preferred embodiments of the invention have been
illustrated and described, it is clear that the invention is not so
limited. Numerous modifications, changes, variations,
substitutions, and equivalents will occur to those skilled in the
art without departing from the spirit and scope of the present
invention as defined by the following claims.
* * * * *