Note: Descriptions are shown in the official language in which they were submitted.
CA 02275041 1999-06-17
TITLE OF THE INVENTION
Method And Apparatus Of Extending Useful Life Of A Cordless Telephone During a
Power Outage Condition
BACKGROUND OF THE INVENTION
Cordless telephones have become a common fixture in the modern household,
to the extent that they now often constitute the sole household telephone
device for
many consumers. Consumers have found it quite desirable to have a portable
wireless
handset unit which may be moved about, often great distances from the
stationary
baseset unit which is electrically connected to the telephone company network.
While
the convenience, mobility, and high sound quality of the battery operated
wireless
handset unit has attracted many consumers, one drawback of common cordiess
telephones is that they require more electrical power than can be provided via
a
conventional telephone line and consequently, cordless telephones,
specifically the
baseset unit, must be connected to a household power outlet for operation. The
external electric power source serves to power the radio module and other
circuitry
located in the baseset unit toward being able to communicate with the battery
operated
portable handset unit as well as toward being able to recharge the handset
battery
when the handset unit is returned to its charging cradle located within the
baseset unit.
One significant drawback of such externally powered cordless telephones is
that
they commonly become inoperative during a power outage since even though the
handset unit battery may still contain sufficient charge to operate the
baseset unit
typically ceases to operate when the external power source is interrupted. If
the
telephone consumer does not also own a conventional corded telephone that
operates
1
CA 02275041 1999-06-17
on telephone line power alone, the consumer is unable to place a telephone
call to
report the power outage or, more importantly, to summon assistance in
emergency
situations. As a result, consumers must keep an unwanted and inconvenient
corded
telephone in service, or risk completely losing telephone service in the event
of a power
outage.
At least one prior art cordiess telephone design has addressed this
shortcoming
by incorporating a rechargeable battery pack in the cordiess telephone baseset
unit
which can temporarily provide electoral power to the base unit when the
external power
supply fails. With such a prior art device the consumer may continue to use
the
cordless telephone to both receive and initiate telephone calls during a power
outage for
as long as both the handset unit and baseset unit internal batteries retain
sufficient
electrical charge to operate the handset and baseset units, respectively.
While the backup battery located in the baseset unit is typically at its
maximum
charge state given its continued connection to the external source of
electrical power,
the handset unit, however, is not typically at a full charge state when a
power outage
occurs given that consumers commonly utilize a cordiess telephone handset in
its
mobile capacity, and consequently typically store the handset in locations
other than on
the baseset recharging cradle. Thus when a power outage occurs, the handset
battery
will commonly be discharged to varying degrees while the base unit battery is
often fully
charged. Consequently, the handset battery may become fully discharged long
before
the base backup battery, and backup battery power feature provided by the
baseset unit
cannot be optimally utilized.
2
CA 02275041 1999-06-17
It is therefore an object of this invention to maximize cordless telephone
utilization time in the event of a power outage.
These and other objects of the present invention will become apparent in light
of
the present specification and drawings.
3
CA 02275041 1999-06-17
SUMMARY OF THE INVENTION
The invention involves a base unit and a portable unit, each capable of
operating
from a rechargeable battery pack as a power source. The base unit is further
capable
of operating on power supplied by an external source, such as a wall outlet
and AC to
DC converter.
The base unit normally charges the portable unit battery pack by applying
energy
from the external power source. Energy can be applied to the portable unit
either by an
electrically conductive connection, or through inductive coupling. When the
external
power source fails, both the base unit and portable unit continue operation on
their
respective battery pack power sources. If the portable unit battery nears
depletion, the
invention can act to transfer energy from the base unit to the portable unit.
4
CA 02275041 1999-06-17
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of one embodiment of the invention, showing the
relationship between the base unit and handset unit.
Fig. 2 is a schematic block diagram of one embodiment of the base unit power
supply circuit.
Fig. 3 is a schematic block diagram of the power switch circuit, which selects
between a primary power source and a secondary power source to provide
uninterrupted output voltage to the base unit circuitry.
Fig. 4 is a schematic diagram of a primary power supply failure alarm circuit.
Fig. 5 is a schematic block diagram of one embodiment of the charging circuit.
Fig. 6 is a schematic block diagram of one embodiment of the handset unit.
Fig. 7 is a schematic block diagram of a second embodiment of the invention,
in
which the status of the handset battery is communicated via a conductive
contact.
Fig. 8 is a schematic block diagram of a third embodiment of the invention in
which the handset is charged via an inductive charging system.
5
CA 02275041 1999-06-17
DETAILED DESCRIPTION OF THE INVENTION
While this invention is susceptible to embodiment in many different forms,
there
are shown in the drawings and will be described in detail herein several
specific
embodiments, with the understanding that the present disclosure is to be
considered as
an exemplification of the principle of the invention and is not intended to
limit the
invention to embodiments illustrated. Furthermore, while the invention is
described in
the context of a cordless telephone system, it is envisioned that the
invention could be
incorporated into any electronic device comprised of a first portable battery-
powered
unit and a second externally powered unit with battery backup.
In the embodiment of Figure 1, base unit 100 is shown connected to external
electrical line power 101 at the primary power source input, terminal 102. In
this
embodiment, approximately +9VDC is applied to terminal 102, typically
converted from
a wall outlet AC voltage by an AC to DC converter (not shown) which can be
either
external to the base unit or internal. Base unit 100 can be operably
electrically
connected to or disconnected from handset unit 200 via contacts 143 and 243,
respectively. Contacts 143 and 243 may be comprised of one of a number of
possible
means of coupling electric energy, such as direct electrical conduction or
inductive
coupling, as further described hereinbelow.
Figure 2 depicts one embodiment of the power circuitry within base unit 100.
During normal operation, when the primary external electrical power source 101
is
present, current flows into terminal 102 to power switch circuit 110. Power
switch circuit
110 regulates the voltage to a desired level, and passes electrical current
via output
6
CA 02275041 1999-06-17
113. Output 113 provides power to the additional circuits which comprise the
wireless
telephone base unit.
The primary power source at terminal 102 also charges base unit battery pack
B1 during normal operation. Current from terminal 102 flows through current-
limiting
resistor RI and diode D1. Diode Dl prevents the reverse flow of current from
battery
B1 to terminal 102 in the event of a failure of the primary power source 101
thereby
preventing electrical charge stored within battery B1 from being dissipated.
The embodiment of Figure 2 includes primary power failure alarm circuit 120,
shown in Figure 4. Alarm circuit 120 is comprised of comparator U4 and
resistors R7,
R8, R9, and R10. The values of the resistors are chosen so that the comparator
U4
output occupies a first state when voltage from the primary power source 101
is present
at terminal 102, and a second state when the primary power source 101 voltage
is not
present and voltage from battery pack B1 is present. Comparator output 123 is
connected to microprocessor U3, whereby U3 detects whether voltage from the
primary
power source 101 is present, such as during normal operation, or absent, such
as
during a power outage. While the illustrated embodiments utilize a
microprocessor to
detect the presence of the primary power source, it is also envisioned that
this function,
as well as the additional functions that are assigned to the microprocessor
and
described herein, can optionally be implemented by other means, including
discrete
logic circuits and/or ASICs.
Figure 3 shows one embodiment of power switch 110. During normal operation,
when the primary power source 101 is present on terminal 102, regulator U1
regulates
the terminal 102 voltage down to +5VDC. The +5VDC is applied to regulator U2,
which
7
CA 02275041 1999-06-17
further regulates down to a +3VDC output voltage. The output of regulator U2
is applied
to terminal 113 for powering base unit circuitry.
Power switch circuit 110 of Figure 3 also acts to automatically switch between
the primary (line) 101 and secondary (B1) base unit power sources. It is
comprised of
transistors Q1, Q2, and Q3, along with resistors R2, R3, R4, and R5. When
proper
voltage is present at terminal 102, regulator U2 receives current solely from
terminal
102 through U1. The voltage present at 102 turns on Q2, which pulls the base
of Q3
low, thereby turning Q3 off. With Q3 pulling no current from the base of Q1,
Q1 is
turned off, disconnecting regulator U2 from battery connection 122.
When the primary power source voltage at terminal 102 is removed such as
during a power outage, Q2 is turned off. Battery connection 122 biases the
base of Q3,
causing it to pull current from the base of Q1. Q1 is thereby turned on.
Battery B1
supplies current to regulator U2 (and consequently the remaining base
circuitry) through
connection 122 and transistor Q1.
The handset battery is charged by charging circuit 140 via connection 143.
Figure 5 shows one possible embodiment of charging circuit 140 when connection
143
consists of a conductive electrical connection. Connection 143 in this
embodiment
consists of electrically conductive terminals on base unit 100, which are
designed to
operatively engage associated electrically conductive terminals 243 on handset
200
when handset 200 is placed in a predetermined position adjacent to base unit
100.
During normal operation, when voltage from the primary power source is present
at
terminal 102, current flows from terminal 102 through diode D2, current
limiting resistor
R6, and current sensor 144 to handset connection 143. Current sensor 144
provides a
s
CA 02275041 1999-06-17
signal on output 142 to microprocessor U3 indicating whether or not current is
flowing to
terminal 143, and hence whether or not a handset is in an engaged position and
capable of being charged. Current from terminal 102 does not flow backwards
into line
141 through R9 because switch SW1 is in the open position.
Figure 6 shows handset circuitry related to charging battery B2. Charging
interface 210 connects terminal 243 to battery B2, providing any interface
circuitry that
is desired. For example, interface 210 may comprise a series resistor, thereby
providing a current-limiting function. Interface 210 could alternatively
consist of a
constant current source, or include overvoltage or electrostatic discharge
protection, or
other circuitry as required for a particular design. Such circuits for
charging
rechargeable battery packs are well known in the art.
Upon failure of the primary power supply, output 123 of primary failure alarm
120
changes from a first to a second state, thereby indicating to microprocessor
U3 that the
primary power supply has failed. Power switch circuit 110 switches base unit
operation
from primary power source 101 operation to backup battery operation by turning
on
transistor Q1. Thereafter, both base unit 100 and handset 200 operate on
battery
power. When the remaining energy level in handset battery B2 falls below a
threshold
level, the handset can request that the base unit transfer electric energy
from base
battery B1 to handset battery B2. One possible way in which the request can be
made
is shown in the embodiment of Figure 6, where battery level detect circuit 220
indicates
the low state of battery B2 to handset transceiver 230. Handset transceiver
230 then
transmits a wireless data message, which is received by base unit transceiver
150
(shown in Figure 2.) Transceiver 150 relays the request to microprocessor U3.
9
CA 02275041 1999-06-17
When microprocessor U3 receives an indication that both 1) the primary power
supply has failed, and 2) the handset battery energy level is low,
microprocessor U3
closes switch SW1 by toggling the state of connection 124. When SW1 is closed,
current flows from base battery B1 into charging circuit 140. The current
flows through
current limiting resistor R9 and current sensor 144 to terminal 143, where the
current
can be conducted into the handset charging interface.
One method of controlling the amount of energy that is transferred from base
battery B1 to handset battery B2 is by a timer function integral to
microprocessor U3. In
such an embodiment, U3 detects the initiation of current flow from B1 to B2 by
the state
of current sensor output 142. U3 can then keep switch SW1 in the closed
position for a
predetermined period of time before toggling the state of line 124, thereby
opening
switch SW1. Other methods of controlling the amount of energy transferred from
B1 to
B2, such as integrating current flow or monitoring voltage levels, can be
easily
implemented and are considered to be within the scope of the invention.
Other methods may also be used by the handset to notify the base unit that the
handset battery requires charging. For example, Figure 7 depicts an embodiment
in
which the handset's request for energy transfer is conveyed by an electrically
conductive connection that is engaged when handset 400 is placed in a
predetermined
position adjacent to base unit 300. In this embodiment, rather than conveying
a
wireless radio message from the handset transceiver to the base transceiver to
signal a
low battery condition, handset battery level detect 420 detects the energy
level of
battery B4 and toggles the state of line 403, which is conducted onto line 303
(when the
handset is in position) and received by microprocessor U303. Alternatively,
the handset
CA 02275041 1999-06-17
could transmit an indication of the remaining energy in the handset battery,
such that
the base unit can determine when an energy transfer should occur. The base
unit could
make this determination based upon, for example, the energy levels remaining
in both
the handset battery and base battery.
Different methods of charging the handset battery are also envisioned, and
considered within the scope of the invention. For example, the embodiment of
Figure 8
utilizes an inductive charging system, whereby handset 600 does not
necessarily need
to be in physical contact with base unit 500, but rather must only be
positioned
proximately to base unit 500. Such a charging system eliminates charging
problems
that might occur when a handset is left slightly ajar on the base unit, or
when electrical
contacts become dirty. In this embodiment, charging circuit 540 is placed into
an
activated or deactivated state depending upon the state of line 524 from
microprocessor
U503. When charging circuit 540 is in an activated state, it draws DC current
in, and
energizes inductive coil L500. When voltage from the primary power source 101
is
present on terminal 102, charging circuit 540 draws current from 101. If the
primary
power source 101 has failed and U503 activates charging circuit 540, circuit
540 draws
DC current from base battery pack B5 through line 522. The magnetic field
generated
by L500 is coupled onto handset coil L600 when the handset is positioned
proximately
to the base unit. Handset charging interface 610 converts the coupled energy
into a DC
current, which operates to charge battery pack B6 and power the handset
circuitry. This
inductive charging system embodiment of Figure 8 can determine when the
handset is
proximately positioned, and hence when a charge transfer can take place, by
performing "test bursts" to determine the coupling efficiency between L500 and
L600.
11
CA 02275041 1999-06-17
For example, transceivers 550 and 630 can communicate to coordinate a
predetermined energy pulse on L500, which can be compared to the received
energy
pulse on L600 to determine the coupling efficiency. Charging would typically
only take
place when the coupling efficiency exceeds a minimum threshold level.
The foregoing description and drawings merely explain and illustrate the
invention
and the invention is not limited thereto except insofar as the appended claims
are so
limited, inasmuch as those skilled in the art, having the present disclosure
before them will
be able to make modifications and variations therein without departing from
the scope of
the invention.
12