Note: Descriptions are shown in the official language in which they were submitted.
CA 02344753 2001-07-17
TITLE OF THE INVENTIC)N
Method For Extending The Usefu! Life Of A Cordless Telephone Backup Battery
During
A Power Outage Condition
BACKGROUND OF THE INVENTION
Cordless telephones have become a common fixture in the modern household,
to the extent that many consumers now have few, if any, conventional corded
telephones. While the convenience, mobility, and high sound quality of
cordless
1 Q telephones have attracted many consumers, one of their drawbacks is that
they
consume more power than can be provided by a conventional telephone tine.
Consequently, modern cordless telephones must be plugged infio a power outlet
for
operatior.~.
One significant drawback of wail-powered cordless telephones is that such
telephones commonly become inoperative during a power outage. If the telephone
consumer does not also own a conventional corded telephone that operates on
telephone line power, the consumer is then unable to place a telephone call
reporting
the power outage, or otf~er emergencies. As a result, consumers must either
keep an
unwanted conventional telephone in service, or risk elimination of telephone
services in
the event o. a power o~itage. Even if a consumer does keep a corded telephone
in
service, they will be inc~cnvenienced by having to locate and utilize the
corded telephone
while power is out.
Some prior art cordless telephone designs have addressed this problem by
including a rechargeable battery pack in the cordless telephone base unit,
which can
CA 02344753 2001-07-17
temporarily provide power to the base unit when the wall power supply fails,
However,
the effectiveness of this solution is limited by the significant power
consumption of a
typical cordless telephony system, resulting in limited battery life.
It i: therefore an object of this invention to maximize cordless telephone
utilization dime following .a power outage by placing the system into a sleep
mode,
during which power con~~umption is reduced.
It is another object of this invention to periodically check for incoming or
outgoing
calls such that the syste« retains functionality during the power outage.
It is yet another object of this invention to control the frequency,with which
the
'l Q system checks for calf a~~ivity based upon the power Level remaining in
the
rechargeable batteries.
SUMMARY OF THE IN'JENTION
The invention involves a cordless telephone system, including 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.
In accordance with the method of the invention, the base unit detects when the
extemat~source of pow~:~r fails. If the telephone system is not currently
handling a call,
the portable unit is placed into a mode in which its power consumption is
reduced. The
base unit is also places.( into a mode of reduce power consumption, during
which time
calls cannot be proces >ed. The length of the sleep period can be fixed at a
predetermined interval. Alternatively, the period length can vary based on the
amount
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CA 02344753 2001-07-17
of power remaining in the base unit battery. fn one embodiment, the sleep
period is
interrupted immediately upon receipt of an incoming call on the telephone fine
to which
the base unit is connected.
After sleeping for ~.~ period of time, the base unit circuits are awakened.
The base
unit,then determines whether the telephone system is active. The telephone
system will
be deemed active if, for example, a telephone caI! is being placed by a user
of the
handset, or an incoming cal! is being received on the telephone line into
which the base
unit is connected. l~ the telephone system is active, the base unit handles
the call.
Fimahy, when the telephone system is not active, and power is still not being
'l 0 supplied by the external power source, the base unit is placed back into
the state of
reduced power consumrtion, and the cycle is repeated.
BRIEF DESCRIPTION ~:JF THE DRAWf(~CS
Figure 1 of the drawings is a schematic diagram of one embodiment of the
'! 5 invention.
Figure 2 of the drawings is a flowchart describing the operation of one
embodiment of the invention.
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CA 02344753 2001-07-17
~ETAtLEC~ DESCRfPTIO!~ OF THE INVENTION
While this invention is susceptible to embodiment in many forms, there is
shown
in the drawings and will herein be described in detail specific embodiments,
with the
understanding that the present disclosure is to be considered as an
exemplification of
the principles of the invention and is not intended to limit the invention to
embodiments
illustrated,
The present invention comprises a method and apparatus for extending the
duration over which a cordless telephone can operate after its external power
source
has faiied. The inventio~~ places both the base unit and portable unit of the
cordless
'10 telephone into a low-povaer mode while inactive and operating on battery
power.
In the ernbodimeot of Figure 1, a primary externs( power source is applied to
the
base unit at the external power source input, Vunreg. in this embodiment,
approxin~sately +9VDC i:; applied to Vunreg, typically converted from a wall
outset AC
voltage by an AC-to-DG converter, which can be either internal to the base
unit or
'i 5 external. During nom~a~~ operation, regulator U1 converts the Vunreg
voltage level to +5
VDG. Regulator U2 then regulates the voltage level down to +3 VDG for
distribution to
the remaining active components in the base unit.
T'.;~e external po~rver source also charges batteries B1 and B2. Base unit
battery
B1 is charged through ~.;urrent limiting resistor R1 and diode D1. Diode D1
prevents the
20 reverse flow of current fram battery B1 to Vunreg in the event of a failure
of the primary
power source, The external power source charges portable unit battery B2 when
the
portable unit is electrically engaged with the base unit. Current flows from
Vunreg,
through~diode D2 and ~;;urrent limiting resistor R6, into B2. Diode D2
prevents the
CA 02344753 2001-07-17
reverse flow of current from battery B2 to Vunreg in the event of a failure of
the primary
power source.
Cornparator U4, ir~ combination with resistors R7, R6, R9, and R10, detects
failure of the primary pov~,~er source by comparing the Vunreg voltage to the
voltage at
battery B'., . When the primary power source fails, the output of U4
transitions from high
to iow. The state of the ~:omparator U4 output is detected by microcontroller
U3.
Transistors Q1, D 2, and Q3, along with resistors R2, R3, R4, and R5, form a
power sv~itch circuit which automatically provides power to the base unit
circuitry from
Vunreg when Vunreg is present; and from battery B1, if Vunreg fails. As was
stated,
during normal operation Vunreg supplies current to regulators U1 and U2 for
distFibution
to the base unit circuitry. Vunreg also biases resistors R2 and R3, turning on
transistor
Q3. Q3 1?ulls the base of Q2 low, thereby turning Q2 off. When Q2 is off, it
draws no
current from the base ov' Q1, thereby turning transistor Q1 off. Because Q1 is
ofd, the
battery B1 is disconnected from the rest of the circuitry during normal
operation.
When Vunreg fails, Q3 is turned off. Battery B1 biases the base of Q2, causing
Q2 to turn on Q1. Therefore, current flows from battery B1 through transistor
C~'i , far
regulation by U2 and subsequent distribution to the base unit circuitry 100.
The embodiment of f=igure 1 further includes circuitry for charging the
battery of
the portable unit when the portable unit and the base unit are engaged and the
prirt~ary
power source has faile~~. If battery B2 nears depletion while base unit
battery l31 has
power remaining, microcontroller U3 can temporarily close switch SW1 to
transfer
energy between batteries B1 and B2 through current-limiting resistor R11.
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CA 02344753 2001-07-17
The: operation of the invention when the primary power source has failed is
explained in the flow chaff t of Figure 2, When the primary power source fails
and a call
is not in progress, step 10, the base unit sends a sleep command to the
handset, step
'i 1. The base unit then ~~laces its own circuitry into a sleep mode in step
12. The sleep
mode constitutes a model of operation in which power consumption is decreased,
while
the functionality of many circuits is suspended or reduced. In the preferred
embodiment, the transmitter and receiver circuits are powered off.
Microcontroifers are
either placed into a steady state, or operated with clock freguencies reduced
from, for
example, 8 MHz to 32 kr~z. .When a devices awakens from a sleep mode, its
circuits
typically resume their vormal functionality.
During the steep mode, both the base unit and the portable unit awaken
periodically. (n one emhodiment, each unit awakens once every 1.5 seconds. The
precise ti'rne between awakenings can be varied to suit particular design
goats. As the
period increases, energy use is reduced, but unit responsiveness is also
reduced,
forcing a user to wait a:~ much as a full period before the handset responds
to an
incoming call, or the base responds to the user's attempt to initiate a calf.
in another
embodiment, the period varies in accordance with the level of energy remaining
in the
backup ioattery. While she battery is highly charged, the sleep period may be
comparatively short, such as .5 seconds, thereby providing a high level of
2~ responsiveness to the user during shorter power outages. As the battery
charge falls,
the period between awakenings increases to avoid complete operation outage.
in step 13, the vase unit starts a timer during which duration the base ur~4t
circuits
remain in sleep mode. An interrupt is provided by step 14, such that if the
bass detects
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CA 02344753 2001-07-17
an incoming telephone ca.Ul on the telephone line to which the base unit is
connected,
the base unit circuits are awoken immediately, step 18, and the call is
handled, step 19.
athervvise, after the timer has completed its duration, step 15, the tease
unit circuits are
awoken ira step 16.
WElen the base ur~if awakens from the power-conserving mode of operation, its
receiver scans for radio ~:ransmissions emanating from the portable unit which
would
indicate that the portable unit is initiating a telephone call, or engaging in
some other
communication which reguires base unit participation. Similarly, when the
portabie unit
awakens, its receiver scans for radio transmissions emanating from the base
unit that
'10 would indicate a teiephc~ne. call is being received. 'his steep mode
operation of the
porfiable unit may differ ~drom conventional power-consenting handset
operation in that
the time period between awakenings can be increased from the typical .5
seconds or
less to match the base unit and further reduce power consumption.
In step 17, the base unit receiver then scans for radio transmissions
emanating
'E 5 from the:portabfe unit which would indicate that the portable unit is
paging the base unit
to initiate a telephone calf, or engaging in some other communication which
reguires
base unit participation, such as an intercom connection. if the base unit
detects paging
by the handset, the base unit handles the calf, step 'f 8. If the base unit
does nvt detect
any paging by the handset in step 'f7, the base unit returns to the start of
the power-
2D failure operation cycle ~.>f Figure 2.
'T'he foregoing d~:acriptions and drawings merely explain and illustrate the
invention and the invention is not Vimited thereto except insofar as the
appended claims
are so limited, as those; skilled in the art who have the disclosure before
them will be
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CA 02344753 2001-07-17
at~fe to make modificatiorss or variations therein without departing firom the
scope of the
invention.
