Note: Descriptions are shown in the official language in which they were submitted.
CA 02523091 1999-06-29
System for Optimizing the Life of a Battery
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to extending the life of batteries. In particular,
extending the life of a primary power source in a multiple power source
electronic
device.
Description of the Prior Art
In the art where an electronic device has two power sources (or
energy storage devices), namely a removable primary power source/cell (such as
a single use AA alkaline-type battery) and a fixed secondary power source,
traditionally the power supply system would be optimized to achieve the
maximum
efficiency of the dc-do converter between the two energy storage devices.
Figs. 1
and 2 illustrates a typical power supply system for the current state of the
art.
These approaches have several disadvantages. First, the time required to
charge
the secondary energy storage device is fixed. Unfortunately, this time could
be too
fast or too slow and, as a result, could degrade the user's perception of the
portable
device. For instance, in traditional systems, when a fresh AA battery is
inserted into
the electronic device, the device is not operational right away - instead a
relatively
undesirable period of time elapses for the secondary power source to charge.
The
prior art also teaches to optimize the efficiency of the dc-do converter while
the
current from the primary cell is fixed. This is not suitable for optimizing or
extending
the life of the primary cell. In addition, in the prior art, a separate dc-do
converter
CL 408472v1
Optimizing Battery Life-RIM
1
CA 02523091 1999-06-29
is used for each voltage rail, but this undesirably impacts the product size
and cost of
the electronic device that encapsulates such a power supply system. Moreover
the dc-
do converter is undesirably always on.
The present invention is directed to an application wherein the electronic
device requires a high duty cycle between sleep mode versus active mode time.
Such
an application would be in wireless two-way communications devices such as an
integrated email device or a personal digital assistant (PDA). In such an
application, a
removable and disposable AA alkaline battery may be the primary source and an
internally fixed all, such as rechargeable lithium-ion battery would act as
the secondary
source.
SUMMARY OF THE INVENTION
It is an object of an aspect of the invention to overcome some of the
drawbacks of traditional power supply systems.
It is another object of an aspect of the invention to extend the life of a
primary power source in a multiple-power source power supply system.
It is another object of an aspect of the invention to make available
sufficient power to operate the device employing the present invention in any
operating
condition.
In the invention there is provided a system to optimize energy transfer
from a primary power source to a secondary power source. In another aspect of
the
present invention, there is provided the ability to switch from the optimized
energy
transfer mode to a fast charge mode.
In the invention, an electronic device includes a primary power source
that is configured to perform a charging operation on a secondary power source
in a
plurality of energy transfer modes, which are selected by a controller, to
optimize the life
2
CA 02523091 1999-06-29
of the primary power source. Powering of the electronic device, such as a two-
way
messaging device, is performed by the secondary power source. In one
embodiment,
during an idle state of the electronic device, the secondary power source is
charged in
an optimized energy transfer mode. In another state, such as during an
information
transfer state, the controller switches the charging operation from an optimal
charge
mode to a fast charge mode to quickly charge the secondary power source such
that
multiple messages can be sent and received without delays. In still another
preferred
embodiment, the controller switches between an off state, a slow charge mode,
and a
fast charge mode.
Therefore, according to one aspect of the present invention there is
provided a mobile device, comprising:
a non-rechargeable power source;
a rechargeable power source;
current limiting circuitry configured to supply power from the non-
rechargeable power source to charge the rechargeable power source, the current
limiting circuitry being controllable to limit a rate of energy transfer
between the non-
rechargeable power source and the rechargeable power source; and
charge control circuitry configured to control the rate of energy transfer in
the current limiting circuitry and to discontinue energy transfer when an
output voltage
of the rechargeable power source reaches a predetermined level,
the charge control circuitry only being responsive to software instructions
for enabling or disabling charging operations, and otherwise operating
independent of
any software such that a software malfunction in the mobile device cannot
result in
overcharging the rechargeable power source.
According to another aspect of the present invention there is provided a
mobile device, comprising:
3
CA 02523091 1999-06-29
a first power source;
a second power source;
means for supplying power from the first power source to charge the
second power source;
means for controlling a rate of energy transfer between the first power
source and the second power source;
means for discontinuing energy transfer between the first power source
and the second power source when an output voltage of the second power source
reaches a predetermined level, the means for discontinuing energy transfer
being
responsive to software instructions for enabling or disabling charging
operations, and
otherwise operating independent of any software such that a software
malfunction in the
mobile device cannot result in overcharging the second power source.
Further features of the invention will be described or will become apparent
in the course of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more clearly understood, the preferred
embodiment thereof will now be described in detail by way of example,
3a
CA 02523091 1999-06-29
with reference to the accompanying drawings, in which:
Fig. 1 is a power supply system illustrative of the prior art;
Fig. 2 is another power supply system illustrative of the prior art;
Fig. 3 illustrates a graph of the efficiency of a typical dc-do switcher
and a graph of the primary cell capacity based on a duty cycle;
FIG. 4 is a block diagram of a two-way, full-text, messaging device
incorporating the. invention;
Fig. 5 is a block diagram illustrating a power supply system
incorporating a preferred embodiment of the invention;
Fig. 6 is a block diagram illustrating a power supply system
incorporating an alternative embodiment of the invention suitable for
applications
with super capacitors;
Fig. 7 is a circuit diagram of Fig. 5;
Fig. 7a is an alternative circuit diagram of the system of Fig. 5; and,
Fig. 8 is a circuit diagram of Fig. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The description of a preferred embodiment of the invention will be
described with reference to Figures 1-8.
Figs. 1 and 2 are illustrative of the prior art.
As can be seen in Fig. 3, as the current is decreased, the efficiency
of the dc-do converter 28 (see Figures 7-7a) decreases and the available
energy
from a primary cell 12 (see Figure 5) increases. This phenomena is utilized in
the
CL 408472v1
Optimizing Battery Life-RIM
4
CA 02523091 1999-06-29
present invention. To make the maximum power available to the messaging device
10
(see Figure 4) from the primary battery 12 it is therefore desirable to
operate the energy
extraction circuitry 300 (see Fig 4) at the optimal range where the dc-do
converter 28
efficiency is high and the energy available for extraction from the primary
battery 12 is
also high. This range occurs in the preferred embodiment of the present
invention 10
from about 15 to 50mA range. In alternative configurations, other systems with
other
dc-do converters or primary batteries will result in a different optimized
range. At high
energy extraction rates the efficiency of the dc-do converter 28 remains
nearly constant
while the energy available from the primary battery 12 decreases, therefore
the total
system power will decrease. However, this decrease in total power can be
partially
recovered if the system 10 is only operated in high-extraction rate mode for
short
periods of time. The graph in Figure 3 shows the improvement by comparing the
Total
System Power with a continuous load and with a 15:1 duty cycle load. The end-
of-life
for the primary cell 12 is determined by the no load voltage minus the voltage
drop due
to the equivalent series resistance (ESR). By adjusting the energy extraction
rate, the
voltage drop due to the ESR can be minimized thereby extending the battery
life.
Fig. 4 is a block diagram of the major subsystems and elements
comprising a palm-sized, mobile, two-way messaging device that preferably
incorporates the invention. In its broadest terms, the messaging device 10
includes
a transmitter/receiver subsystem 100 connected to a digital signal processor
(DSP)
200 for digital signal processing of the incoming and outgoing data
transmissions,
power supply and management subsystem 300, which supplies and manages
5
CA 02523091 1999-06-29
power to the overall messaging device components, microprocessor 400, which is
preferably an X86 architecture processor, that controls the operation of the
messaging device, display 500, which is preferably a full graphic LCD, FLASH
memory 600, RAM 700, serial output and output 800, keyboard 900, thumbwheel
1000 and thumbwheel control logic 1010. In its intended use, a message comes
via a wireless data network, such as the Mobitex network, into subsystem 100,
where it is demodulated via DSP 200 and decoded and presented to
microprocessor 400 for display on display 500. To access the display of the
message, the user may choose from functions listed under a menu presented as a
result of user interaction with thumbwheel 1000. If the message is an email
message, the user may chose to respond to the email by selecting "Reply" from
a
menu presented on the display through interaction via thumbwheel 1000 or via
menu selection from keyboard 900. When the microprocessor 400 receives an
indication that the message is to be sent, it processes the message for
transport
and, by directing and communicating with transmitter/receiver subsystem 100,
enables the reply message to be sent via the wireless communications data
network
to the intended recipient. Similar interaction through I/O devices keyboard
900 and
thumbwheel 1000 can be used to initiate full-text messages or to forward
messages
to another party. The present invention is directed to the power supply
management subsystem 300.
In Fig. 5, there is shown a power supply system 300 whereby
two power sources (or energy storage devices), a primary power source 12 and a
secondary power source 34, are utilized. In one aspect of the present
invention,
CL 408472v1
Optimizing Battery Life-RIM
6
CA 02523091 1999-06-29
there is provided a system to optimize energy transfer from a primary power
source
to a secondary power source. In another aspect of the present invention, there
is
provided the ability to switch from the optimized energy transfer mode to a
fast
charge mode. This latter aspect addresses the concern of a user undesirably
waiting too long for the secondary cell to recharge. The invention is
preferably
implemented into a portable device as described in Fig. 4 having the following
characteristics: a high ratio of sleep current versus active current mode (the
"pulsed
load ratio") and the nominal voltage level of the secondary power source is
marginally greater than the regulated voltage source. With reference to Fig.
5, the
power supply system 300 includes a primary power source 12, an on/off switch
16,
a step-up switcher 14 coupled to a current limit 15, which in turn is
controlled by a
high/low controller 18. The power supply system 300 also includes a secondary
power source 34 and a voltage regulator 31. The first energy storage device 12
is
preferably a single use AA battery and the secondary cell 34 is a rechargeable
or
renewable energy storage device such as a lithium-ion battery. In the first
aspect
of the invention, the rate that the energy is extracted from the primary cell
12 is
minimized so as to increase the available capacity from the primary cell. The
extracted energy from the primary cell is transferred and stored in the
secondary
cell 34. The energy stored in the secondary cell 34 is then used to power the
device 10. In another aspect of the invention, three energy extraction rate
modes,
namely: high, low and off. In other alternative configurations, there can be
any
number of extraction rates. Indeed, over a selected range of energy extraction
rates, there can be a continuous range of extraction rates. The "off'
extraction rate
CL 408472v9
Optimizing Battery Life-RIM
7
CA 02523091 1999-06-29
mode is utilized in the system when the secondary cell is either fully charged
or
when the primary cell is depleted. The "low" extraction rate mode, which is
related
to the optimized extraction rate region of Fig. 3, is utilized when the
present
invention is using the optimizing energy transfer from the primary cell 12 to
the
secondary power source 34. The "high" extraction rate mode is utilized when it
is
desired to charge the secondary cell 34 rapidly as would be the case when the
device 10 continuously transmits a communication over the wireless network and
the secondary cell 34 has depleted its energy store. In this manner, the
secondary
cell 34 is quickly ready for another data information transmission or
communication.
The "high" extraction rate is particularly useful when the user inserts into
the device
a fresh primary cell 12 and the secondary power source 34 is depleted in
power.
The "high" extraction rate allows the secondary power source 34 to be rapidly
charged in this case.
Fig. 7 is a preferred circuit diagram of the system disclosed in
Fig. 5 in a two-way wireless communications device. This circuit includes the
primary power source 12, integrated circuit 30, current mirror 32, and
secondary
power source 34 delivering power to voltage regulators 31 and power amplifier
39.
In this circuit, the efficiency of the dc-do converter 28 (similar to the step-
up-switch
14 in Fig. 5) is optimized concurrently with the energy extraction rate of the
primary
cell 12. The output voltage of integrated circuit 30 is selected to match the
technology of the secondary cell 34. In this embodiment the secondary cell 34
is
preferably a rechargeable lithium-ion cell battery 34. The output voltage of
the
integrated circuit 30 is preferably set to 4.2 V. The lithium-ion cell 34
provides
CL 408472v1
Optimizing Battery Life-R!M
8
CA 02523091 1999-06-29
power to an voltage regulators 31 and a power amplifier 39. Power is supplied
to
the voltage regulators 31 and the power amplifier 39 and this power can be up
to
2 A of current from the lithium-ion cell 34 while the current from the primary
power
source 12 can be limited to optimal energy extraction rate. The peak current
drain
from the lithium-ion cell 34 does not effect the life of the primary power
source 12.
The integrated circuit 30 includes a step-up switcher, which increases the
input
voltage from the primary battery 12 up to a predetermined output voltage,
preferably
4.2 V. The voltage output is then used to charge the lithium-ion cell 34
battery. In
the current mirror 32, 1150'" of the current through resistor 35 is mirrored
through
resistor 36. Current minor 32 generates a voltage across resistor 37. The
voltage
across resistor 37 is then used to increase the voltage on the feed back pin
of
integrated circuit 30. As the voltage rises at the feedback pin 29, the output
from
the integrated circuit 30 is reduced thereby limiting the output current. By
defining
the value of resistor 37 using ohm law also sets the output current (measured
via
resistor 35). The current through resistor 37 is 1/50'" of the limit and the
voltage
across resistor 37 is the feedback voltage of integrated circuit 30 plus the
forward
voltage drop across diode 38. Resistor 33 is used to reduce the effective
resistance
of resistor 37, providing a second current limit. If resistor 33 is 0 ohms (as
an
indirect result of a FET located in the integrated circuit 30 and resistor
37), then the
effective resistance of resistor 37 is limited by the maximum output current
of
integrated circuit 30. Resistor 33 is shorted to ground via the FET. This FET
is
turned on and off via the CHARGE_HIGH N signal connected to pin 1 of
integrated
circuit 30.
CL 408472v1
Optimizing Battery Life-RIM
9
CA 02523091 1999-06-29
Fig. 7a is similar to Fig. 7 with the exception of additional circuitry 41
that provides a very accurate secondary power source 34 charge termination. In
this
alternative embodiment, the switcher 28 output voltage is set to a higher
voltage,
preferably 4.5 V. When the operational amplifier 42 detects that voltage on
the
lithium-ion cell 34 battery is a predetermined value, preferably 4.2 V, the
charger is
turned off. The internal reference of 42 and the precision resistors 43 and 44
provide an accurate voltage termination for the charge cycle. This embodiment
also
prevents the switcher 28 from consuming a high quiescent current while
delivering
a relatively small charge current to the lithium-ion cell 34. In this
embodiment, if
enabled by the software, the charging process is preferably under hardware
control,
so that a software malfunction cannot result in a overcharged lithium-ion cell
34. In
this embodiment, software only has the ability to disable the charging
process.
Fig. 6 is a block diagram illustrating a power supply system
incorporating an alternative embodiment of the invention suitable for device
applications with super capacitors as a secondary power source. This
alternative
embodiment of the invention is particularly suitable when the nominal voltage
of the
secondary cell is significantly higher than the regulating voltage. In this
system,
step-up switcher 21 selects one of two output voltages. In the preferred
embodiment, the two output voltages are 3.3V and 4.6V. The voltage regulators
56
are powered by the super capacitors 24 or alternatively by the primary cell 12
via
the step-up switcher 21. Likewise, switcher 21 charges super capacitors 24 or
them
power voltage regulator 56. In most circumstances, the super cap 24 supplies
the
power to voltage regulator 56. This is efficient since the load current is
comparable
CL 408472v1
Optimizing Battery Life-RIM
CA 02523091 1999-06-29
to the quiescent current of the switcher 28. When the load current is higher,
such
as the case when the radio is active or the user is typing a message, the
voltage
regulators 56 are powered from the switcher 28 operating at 3.3 V. In this
case the
super caps 24 are disconnected via the FET switch 21 and are able to power the
PA 39. In addition the voltage drop across the voltage regulators 31 is much
less
and hence the system efficiency is much higher. The super capacitors 24 are
preferably charged after a data transmission or communication.
Fig. 8 is illustrative of a circuit implementation of the system disclosed
in Fig. 6. This particular circuit is utilized for power supply within a two-
way wireless
communications device that has a predetermined packet size for response
messages, such as the case for acknowledgement pagers, which have a fixed
packet size for all responses. In this embodiment, the secondary power source
cell
24 is composed of two super capacitors 24. The super capacitors 24 provide
power
to the voltage regulators 56 and power amplifier. The super capacitors 24
supply
the large current required by the power amplifier. Any time the load is on,
the output
voltage of the integrated circuit 51 is set to a predetermined voltage defined
by
voltage drop of the voltage regulator 56, preferably 3.3 V, which minimizes
the
voltage drop across the voltage regulators 56. This minimization of the
voltage drop
is designed to increase efficiency. When the voltage of integrated circuit 51
is set
to 3.3 V the super capacitors 24 are disconnected from the circuit via the FAT
switch 52. When the load is off (or the load current is very low) the output
of
integrated circuit 51 is set to 4.6 V and the FET switch 52 is closed. This
allows the
super capacitors 24 to charge. Integrated circuit 54 monitors the voltage of
the
CL 408472v1
Optimizing Battery Life-RIM
11
CA 02523091 1999-06-29
super capacitors 24 and turns the step-up switcher (the integrated circuit 51
) on and
off. It is to be appreciated that this example can be extended to function
when a
single super capacitor is used.
It will be appreciated that the above description relates to the
preferred embodiment by way of example only. Many variations on the invention
will be appreciated to those knowledgeable in the field, and such variations
are
within the scope of the invention as described and claimed, whether or not
expressly described.
CL 408472v1
Optimizing Battery Life-RIM
12
