U.S. patent application number 10/737021 was filed with the patent office on 2005-06-16 for power fault battery protection circuit.
Invention is credited to Boyer, Roger L., Collier, Jenny, Geren, Michael D., Herrmann, John E..
Application Number | 20050127878 10/737021 |
Document ID | / |
Family ID | 34523137 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050127878 |
Kind Code |
A1 |
Geren, Michael D. ; et
al. |
June 16, 2005 |
POWER FAULT BATTERY PROTECTION CIRCUIT
Abstract
A battery protection circuit is provided that includes a safety
circuit and an overpower circuit. The safety circuit monitors the
voltage and current of at least one rechargeable cell within the
battery pack, and disconnects the cell(s) from the external
terminals of the battery pack when either the voltage becomes too
high or low, or when excessive current is being drawn from the
battery pack. The overpower circuit monitors the power being
delivered to or sourced from the battery pack to the load. The
overpower circuit actuates when the power exceeds a predetermined
threshold, thereby simulating an overcurrent condition in the
safety circuit. The overcurrent condition causes a disconnect
means, like a transistor, to open, thereby disconnecting the
cell(s) from the external terminals. The battery protection circuit
then latches in this disconnected state until a load is removed
from the terminals of the battery pack.
Inventors: |
Geren, Michael D.; (Suwanee,
GA) ; Boyer, Roger L.; (Snellville, GA) ;
Herrmann, John E.; (Sugar Hill, GA) ; Collier,
Jenny; (Dunsany, IE) |
Correspondence
Address: |
MOTOROLA, INC.
1303 EAST ALGONQUIN ROAD
IL01/3RD
SCHAUMBURG
IL
60196
|
Family ID: |
34523137 |
Appl. No.: |
10/737021 |
Filed: |
December 16, 2003 |
Current U.S.
Class: |
320/134 |
Current CPC
Class: |
H02J 7/00304 20200101;
H02J 7/0031 20130101 |
Class at
Publication: |
320/134 |
International
Class: |
H02J 007/00 |
Claims
1. A battery protection circuit, comprising: a. at least one
rechargeable cell; b. a safety circuit coupled to the at least one
rechargeable cell, the safety circuit comprising a means for
monitoring a voltage across the at least one rechargeable cell,
further comprising a means for monitoring a current flowing through
the at least one rechargeable cell; c. at least one disconnect
means coupled serially with the at least one rechargeable cell; d.
a means of monitoring power being delivered either to or from the
at least one rechargeable cell; and e. a means for simulating an
overcurrent condition within the safety circuit when the means for
monitoring power determines that the power being delivered either
to or from the at least one rechargeable cell exceeds a
predetermined threshold.
2. The circuit of claim 1, wherein the means of monitoring power
monitors the power being delivered from the at least one
rechargeable cell.
3. The circuit of claim 2, further comprising at least a second
disconnect means, the at least a second disconnect means being
responsive to the means for monitoring power being delivered from
the at least one rechargeable cell.
4. The circuit of claim 3, further comprising a leakage current
path in parallel with the at least a second disconnect means, the
leakage current path having a resistance in excess of one hundred
thousand Ohms.
5. The circuit of claim 1, further comprising at least an
additional disconnect means coupled between the at least one
rechargeable cell and the means of monitoring power delivered to or
from the at least one rechargeable cell, wherein when the
overcurrent condition is simulated, the safety circuit actuates the
at least an additional disconnect means to deactivate the means for
monitoring power delivered to or from the at least one rechargeable
cell.
6. The circuit of claim 1, wherein the at least one disconnect
means arc selected from the group consisting of transistors,
switches, relays, circuit breakers, and fuses and positive
temperature coefficient devices.
7. The circuit of claim 1, wherein the means for monitoring power
being delivered comprises: a. a means for measuring the voltage
across the at least on rechargeable cell; b. a means for measuring
the current flowing through the at cast on rechargeable cell; c. a
means of determining whether the product of the voltage across the
at least one rechargeable cell and the current flowing through the
at least one rechargeable cell exceeds the predetermined threshold,
and d. a comparator, wherein an output of the comparator is in a
first state when a product of the voltage across the at least one
rechargeable cell and the current flowing through the at least one
rechargeable cell is below the predetermined threshold; further
wherein the output of the comparator is in a second state when a
product of the voltage across the at least one rechargeable cell
and the current flowing through the at least one rechargeable cell
is above the predetermined threshold.
8. The circuit of claim 1, wherein the predetermined threshold is
nine watts.
9. The circuit of claim 1, wherein the safety circuit comprises: a.
an overcharge detector; b. an undercharge detector; and c. an
overcurrent detection circuit.
10. The circuit of claim 9, wherein the overcurrent situation is
simulated by sourcing current into the overcurrent detection
circuit.
11. A rechargeable battery pack comprising the circuit of claim
1.
12. A battery protection circuit having a power monitoring circuit,
wherein the power monitoring circuit determines when power exceeds
a predetermined threshold, comprising: a. at least one rechargeable
cell; b. at least one safety circuit coupled to the at least one
rechargeable cell; c. at least one disconnect means coupled
serially with the at least one rechargeable cell; and d. at least
one means for simulating an overcurrent condition within the safety
circuit when the power monitoring circuit determines that power
exceeds the predetermined threshold.
13. The circuit of claim 12, wherein when the at least one means
for simulating an overcurrent condition within the safety circuit
simulates an overcurrent condition, the at least one disconnect
means enters a high impedance state.
14. The circuit of claim 13, wherein the at least one disconnect
means are selected from the group consisting of transistors,
switches, relays, circuit breakers, and fuses and positive
temperature coefficient devices.
15. The circuit of claim 14, wherein power monitoring circuit
comprises: a a means for sensing the voltage across the at least on
rechargeable cell; b. a means for sensing the current flowing
through the at least on rechargeable cell; c. a means of
determining whether the product of the voltage across the at least
one rechargeable cell and the current flowing through the at least
one rechargeable cell exceeds the predetermined threshold; and d. a
comparator, wherein an output of the comparator is in a first state
when a product of the voltage across the at least one rechargeable
cell and the current flowing through the at least one rechargeable
cell is below the predetermined threshold; further wherein the
output of the comparator is in a second state when a product of the
voltage across the at least one rechargeable cell and the current
flowing through the at least one rechargeable cell is above the
predetermined threshold.
16. The circuit of claim 15, wherein the predetermined threshold is
nine watts.
17. The circuit of claim 16, wherein the safety circuit comprises:
a. an overcharge detector; b. an undercharge detector; and c. an
overcurrent detection circuit.
18. The circuit of claim 17, wherein the overcurrent situation is
simulated by sourcing current into the overcurrent detection
circuit.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This invention relates generally to protection circuits for
rechargeable battery packs, and more specifically to protection
circuits that disable a rechargeable battery pack due to an
excessive amount of power being drawn by the load.
[0003] 2. Background Art
[0004] Portable electronic devices, like cellular telephones,
pagers and two-way radios for example, derive their portability
from rechargeable batteries. Such batteries allow these devices to
slip the surly bonds of wall mounted power supplies and wirelessly
touch the hand of the user wherever he may be.
[0005] While many people may think that a rechargeable battery is
simply a cell and a plastic housing, nothing could be further from
the truth. Rechargeable battery packs often include circuit boards,
electronic circuitry, mechanical assemblies and electromechanical
protection components. The circuits employed in rechargeable
battery packs include charging circuits that start, ramp, taper and
stop current, fuel gauging circuits, temperature measurement
circuits and indicator circuits, just to name a few. Simply put, a
battery pack is a complex system of components working in harmony
to safely deliver power to a portable electronic device.
[0006] One of the most fundamental circuits in a battery pack is
the protection circuit. Rechargeable battery performance,
especially with respect to those having cells constructed of
lithium-based materials, may be severely compromised if the cell
within the battery pack is over or under charged. For this reason,
most all battery packs today include one form of safety circuit or
another.
[0007] Typical safety circuits include voltage and current limits.
As such, when the voltage across the cell in a battery pack becomes
too high or too low, the safety circuit will open switches within
the pack, thereby "turning off" the battery pack. Similarly, if the
current flowing either into or out of the cell gets too high, the
safety circuit will turn off the battery pack.
[0008] Despite these voltage and current safety mechanisms, new
concerns are arising from "over power" situations. These situations
arise when a battery pack is operating within its voltage and
current limits, but the total power--the product of voltage and
current--becomes too high for a particular electronic device. The
concern is that the over power situation may cause components
within the electronic device to generate excessive heat.
[0009] There is thus a need for an improved battery safety circuit
that turns off the battery not only due to excessive voltage or
current, but for excessive power dissipation as well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates a block diagram of a safety circuit
IC.
[0011] FIG. 2 illustrates a protection circuit having a safety
circuit and overpower circuit in accordance with the invention.
[0012] FIG. 3 illustrates one embodiment of a power meter in
accordance with the invention.
[0013] FIG. 4 illustrates one embodiment of an analog multiplier in
accordance with the invention.
[0014] FIG. 5 illustrates a protection circuit having a plurality
of safety circuits and overpower circuits in accordance with the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] 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."
[0016] This invention provides a overpower protection circuit that
may be used in conjunction with an existing battery safety circuit
to offer an additional level of protection. The overpower circuit
monitors the power being delivered to or from the cells in a
battery pack. When the power exceeds a predetermined threshold, the
overpower circuit simulates an overcurrent condition with respect
to the safety circuit. This overcurrent simulation causes the
protection circuit to open one or more serial pass elements,
thereby isolating the cells from the external terminals of the
battery pack. The overpower circuit then resets itself when the
load is removed from the battery pack. The combination of the
overpower circuit with the conventional battery safety circuit
provides a system that protects not only from excessive voltages
and currents, but from excessive power dissipation levels as
well.
[0017] Prior to understanding the overpower circuit, a brief
overview of battery safety circuits is warranted. As used herein, a
"safety circuit" is any circuit capable of monitoring the voltage
across at least one rechargeable cell, in addition to being capable
of monitoring the current flowing through the cell or cells. One
example of such a circuit is the S8232 series of safety circuits
manufactured by Seiko Instruments, Inc. For discussion and
exemplary purposes, such a circuit will be discussed herein. It
will be clear to those of ordinary skill in the art who have the
benefit of this disclosure, however, that the invention is not so
limited. Discrete circuits, application specific circuits and
safety circuits manufactured by other companies, including Ricoh
and Mitsumi for example, may be equally substituted for the Seiko
circuit.
[0018] By way of background, referring now to FIG. 1, illustrated
therein is a block diagram of an S-8232 safety circuit 100. The
S-8232 safety circuit is designed to be used with two, serial,
lithium-based cells. Again, it will be clear to those of ordinary
skill in the art with the benefit of this disclosure that the
invention is not so limited. The overpower circuit discussed herein
may be equally applied to any combination of serial or parallel
cells.
[0019] The safety circuit 100 may be as simple as a single
integrated circuit (IC) that provides a means for monitoring of
cell voltage and current, and thereby controls the charging and
discharging of the cells within a battery pack. Discrete
equivalents of the IC may also be substituted. The safety circuit
100 includes an overcharge detector 101 that monitors the voltages
across the corresponding cells. The overcharge detector 101
compares these voltages to a predetermined maximum cell voltage.
When the cell voltage exceeds this threshold, the overcharge
detector 101, via some internal logic circuitry 103, causes a
push-pull output stage 114 to actuate the charge pin 107. When the
charge pin 107 is coupled to a disconnect means, like a transistor
acting as a switch in its non-linear region, actuation will prevent
any further charging of the cells.
[0020] Similarly, the safety circuit includes an overdischarge
detector 102 that ensures that the voltage across the cells does
not fall below a predetermined threshold. If it does, the
overdischarge detector 102 causes an output stage 113 to actuate
the discharge pin 106. When the discharge pin 106 is coupled to a
disconnect means, like a serial transistor, actuation prevents any
further discharge.
[0021] Cell current is monitored by way of an overcurrent detection
pin 108 coupled to an overcurrent detection circuit 104. The
overcurrent detection pin 108 senses the voltage between the Vss
pin 112 and the overcurrent detection pin 108. When this voltage
exceeds a predetermined threshold, as will be explained in more
detail later, the overcurrent circuit 104 causes the discharging
pin 106 to actuate, thereby stopping the flow of current in the
discharge direction. In some situations, with some safety circuits,
the charging pin 107 may also actuate.
[0022] When the load is removed, as evidenced by an impedance
greater than 200 M.OMEGA. appearing between the Sens pin 110 and
the overcurrent pin 108, the safety circuit 100 resets, thereby
deactuating the discharge pin 106. This action will be more evident
with the discussion of FIG. 2 below.
[0023] Other components of the safety circuit 100 include a Vcc pin
109, a center tap pin 111, and a Vss pin 112, that monitor the
voltage at the cathode, between, and at the anode of serial cells,
respectively. Additionally, a delay circuit 105 provides some
hysteresis and transient immunity.
[0024] Referring now to FIG. 2, illustrated therein is one
preferred embodiment of a battery protection circuit in accordance
with the invention. The safety circuit 100 from FIG. 1 is coupled
to a pair of rechargeable cells 201, 202. The charge pin 107 and
the discharge pin 106 are coupled to disconnect means 203, 204,
respectively, which are in turn coupled serially with the cells
201, 202. The disconnect means 203, 204 in this exemplary
embodiment are field effect transistors (FETs), although other
devices, including switches, relays, circuit breakers and
controllable fuses may be substituted, depending upon the
application.
[0025] The overcurrent pin 108 is coupled to the low side 205
of-the circuit, such that the overcurrent pin 108 may work in
conjunction with the Vss pin 112 to sense the voltage across the
FETs 203, 204. When this voltage becomes too high, the safety
circuit 100 knows that the current being drawn from the cells 201,
202 is correspondingly too high. When this occurs, the discharge
pin 106 causes the FETs 203 to open, thereby preventing current
from flowing to the external terminals 206, 207. The safety circuit
100 resets, and thus closes the FET 203, when an impedance greater
than 200 M.OMEGA. is sensed between the Sens pin 110 and the
overcurrent pin 108. This occurs when a load (not shown) is removed
from the terminals 206, 207, thereby creating an open circuit
between the terminals 206, 207.
[0026] The overpower circuit 208 includes a power meter 209 that
acts as a means of monitoring power being delivered to or from the
cells 201, 202. The power meter 209, explained in more detail with
the discussion of FIG. 3, is any circuit that is capable of
determining whether the product of the voltage across the at least
one rechargeable cell and the current flowing through the at least
one rechargeable cell exceeds the predetermined threshold. It may
include a circuit that generates a signal that is proportional to
the product of the voltage across the cells and the current flowing
through the cells. It may also be a circuit that simply generates a
binary, up or down signal that indicates whether the power is above
or below the threshold. The power meter 209 may be an accurate,
linear power meter, or may be a simpler circuit that approximates
power, for example by way of piecewise linear or other
approximation means.
[0027] The power signal 210 is then coupled to a comparator 211
that has a signal 212 (like a reference voltage) that is
proportional to the predetermined threshold of power. When the
power signal 210 exceeds the predetermined threshold 212, the
comparator 211 actuates. The predetermined threshold may be set to
any level required by the application. One exemplary threshold for
a two-serial-cell configuration, that is intended to comply with a
corresponding temperature threshold limit set forth by the
Atmospheric Explosive (ATEX) directive set forth by the European
Union, is nine watts. In any event, when the signal proportional to
power is below the predetermined threshold, the output 216 of the
comparator 211 is in a first state. The output 216 of the
comparator 211 switches to a second state when the signal
proportional to power exceeds the predetermined threshold.
[0028] When the power sourced from the cells 201, 202 exceeds the
predetermined threshold, the overpower circuit 208 simulates an
overcurrent condition within the safety circuit 100, causing the
FET 203 to open or enter a high impedance state, thereby preventing
current from flowing from the cells 201, 202. The overcurrent
condition is simulated by sourcing current into the overcurrent pin
108 (as a result of increased voltage at the overcurrent pin 108),
and thus into the overcurrent detection circuit within the safety
circuit 100.
[0029] Such an overpower condition would arise as follows: The
power meter 209 would be continually monitoring the power sourced
from the cells 201, 202. The load connected to the terminals 206,
206 would begin drawing power in excess of the predetermined
threshold. The power meter 209 determines that this is the case,
causing the power signal 210 to rise above the power threshold
signal 212. This, in turn, actuates the comparator 211.
[0030] A switch 219, shown here as a FET, is responsive to the
comparator and closes upon actuation of the comparator 211. This
pulls the overcurrent pin 108 to the cell voltages, thereby causing
current to flow into the overcurrent pin 108 through a current
limiting resistor 213. To the safety circuit 100, this appears to
be an overcurrent situation. The safety circuit 100 then opens the
discharge FET 203, thereby preventing any current from flowing out
of the cells 201, 202. As such, the cells 201, 202 are disconnected
from the terminals 206, 207 as a result of power dissipation
exceeding the predetermined threshold. An optional delay circuit
218, for example a R-C filter, may be coupled between the
comparator 211 and the switch 219 where a delay prior to opening
the FET 203 is desired. Such a delay may be desirable when a host
device needs time to complete an operation prior to power down.
[0031] In parallel, an optional second disconnect means 214, shown
here as a FET, may be coupled to the comparator 211 so as to be
responsive to the comparator 211. The second disconnect means 214,
coupled serially between the terminals 206, 207 and the cells 201,
202, operates as a secondary circuit breaker and opens when the
comparator 211 is actuated. As such, if the discharge FET 203
fails, the second disconnect means will still disconnect the cells
201, 202 from the terminals 206, 207 when an overpower condition
occurs.
[0032] Note that this second disconnect means 214 is optional, as
it is advantageous in some designs. For example, in circuits where
redundancy is needed for reliability, a designer may decide to
employ two separate safety circuits, using the second safety
circuit to control a second discharge FET, which would thus serve
as the optional second disconnect means. In such a case, one
example of which is illustrated in FIG. 5, either the overpower
circuit 208, or a redundant overpower circuit 501, would be
connected to the overcurrent pin 502 of a second safety circuit
503, with the charge and discharge FETs 504, 505 of the second
safety circuit 503 being coupled serially with the terminals 206,
207, the cells 201, 202, and the first charge and discharge FETs
203, 204. Other designs may need neither the second safety circuit
nor the second disconnect means.
[0033] A leakage current path in parallel with the second
disconnect means 214 is provided by a resistor 215. The resistor
215 provides a latching mechanism that causes the safety circuit
100 to remain in the simulated overcurrent condition. Recall that
the safety circuit 100 resets when the impedance between the sense
pin 110 and the overcurrent pin 108 exceeds 200 M.OMEGA.. This
would be the case when the second disconnect means 214 opens. As
such, a leakage path provided by the resistor 215 ensures that the
safety circuit 100 stays latched in the simulated overcurrrent
condition until the load is removed from the terminals 206, 207.
Resistance values for resistor 215 range from 100 k.OMEGA. to 500
k.OMEGA., preferably about 200 k.OMEGA.. Note that when a second
safety circuit is used to control the second disconnect means 214,
the leakage current path may not be necessary, as the second safety
circuit provides an internal leakage path.
[0034] As stated, when the overpower, and thus the simulated
overcurrent, condition is initiated, the cells 201, 202 are
disconnected from the terminals 206, 207 by way of the FET 203. In
such a state, it is not desirable to have electrical components
within the battery pack discharge the cells 201, 202. As such, the
invention provides a means of disabling the overpower circuit 208.
Disablement is accomplished by a switch coupled between the high
side terminal 206 of the circuit and the overpower circuit 208.
This switch 217, shown for exemplary purposes as a FET, is coupled
to the discharge pin 106 of the safety circuit 100.
[0035] When the discharge pin 106 is actuated, the switch 217 turns
off, thereby blocking current from flowing to the overpower
circuit. Thus, in an overpower condition, the overpower circuit 208
first simulates an overcurrent condition in the safety circuit 100,
thereby causing the discharge pin 106 to actuate. This, in turn,
causes the switch 217 to open, thereby deactivating the overpower
circuit 208.
[0036] Such a scenario is perfectly acceptable, in that the
overpower circuit 208 is no longer needed to monitor power being
delivered from the cells 201, 202, as there is no power being
delivered from the cells 201, 202 since the charge and discharge
FET 203 is open. Upon removal of the load, however, the safety
circuit 100 resets, thereby causing closure of the FET 203, thereby
closing the switch 217, thereby reactivating the overpower circuit
208. The safety circuit will then revert back to normal
operation.
[0037] Referring now to FIG. 3 illustrated therein is one example
of a power meter 209 in accordance with the invention. The power
meter 209 includes a means for measuring or sensing the voltage
across the cells, as well as a means for measuring or sensing the
current flowing through the cells. Both the means of measuring
voltage and current may comprise analog amplifiers 301, 302 coupled
to the cells. In the case of voltage, the amplifier 301 may have
inputs coupled across the cells to measure the voltage. The gain of
the amplifier 301 would be scaled such that the product output is
at a level that is acceptable by the comparator.
[0038] In the case of current, the amplifier 302 input may be
coupled to a means of sensing current, like a current sense
resistor for example. As with the voltage amplifier 301, the gain
of the current amplifier 302 would be scaled such that the product
output is at a level that is acceptable by the comparator.
[0039] The outputs of the amplifiers 301, 302 are then fed into an
analog multiplier 303. The analog multiplier produces a product
output 304 that is proportional to the product of voltage and
current. This output 304 is then fed to the comparator 211. One
example of an analog multiplier is shown in FIG. 4, and is also
taught in U.S. Pat. No. 3,562,553, entitled "Multiplier Circuit,
issued to Roth, which is incorporated herein by reference for all
purposes.
[0040] Note that the power meter of FIG. 2 and the multiplier
circuit of FIG. 3 are but one exemplary embodiment of a power meter
in accordance with the invention. It will be clear to those of
ordinary skill in the art who have the benefit of this disclosure
that the invention is not so limited. Numerous other power
measurement circuits, including those employing logarithmic
amplifiers, microprocessors with analog to digital converters, hall
effect multipliers, and other analog and digital circuits may be
equally substituted. The only requirement is that the power
measurement circuit be capable of producing a signal proportional
to the amount of power being sourced from, or delivered to, the
cells.
[0041] 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. For example, while
one preferred embodiment of the invention is a rechargeable battery
pack comprising the battery protection circuit taught in FIG. 2,
the invention is not so limited. It may be applied to any power
source, including power supplies, fuel cells, solar cells and the
like. Additionally, it may be incorporated into the host device as
well as within the battery pack.
* * * * *