U.S. patent application number 11/371686 was filed with the patent office on 2006-07-13 for over-voltage protection circuit.
Invention is credited to Michael F. Habicher, Quang A. Luong, Richard C. Madter, Roshy Stan Mathew, Carl D. Schaaff, Andrew D. Shiner.
Application Number | 20060152873 11/371686 |
Document ID | / |
Family ID | 23268352 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060152873 |
Kind Code |
A1 |
Shiner; Andrew D. ; et
al. |
July 13, 2006 |
Over-voltage protection circuit
Abstract
An over-voltage protection circuit is disclosed herein for
protection against over-voltage of an energy storage device while
charging. The circuit operates within the operational limits of a
battery-operated device, such as a mobile or handheld device. The
over-voltage protection circuit comprises an over-voltage
protection device, and an over-voltage protection controller. The
controller allows current to flow to the over-voltage protection
device only when an energy storage device is experiencing
over-voltage. In allowing current to flow to the over-voltage
protection device only when the voltage across the energy storage
device is above a predetermined voltage, power conservation is
achieved
Inventors: |
Shiner; Andrew D.; (Whitby,
CA) ; Schaaff; Carl D.; (Guelph, CA) ; Madter;
Richard C.; (Puslinch, CA) ; Mathew; Roshy Stan;
(Waterloo, CA) ; Habicher; Michael F.; (Cambridge,
CA) ; Luong; Quang A.; (Mississauga, CA) |
Correspondence
Address: |
Joseph M. Sauer, Esq.
Jones Day, North Point
901 Lakeside Avenue
Cleveland
OH
44114
US
|
Family ID: |
23268352 |
Appl. No.: |
11/371686 |
Filed: |
March 9, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10261038 |
Sep 30, 2002 |
7035070 |
|
|
11371686 |
Mar 9, 2006 |
|
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|
60325551 |
Oct 1, 2001 |
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Current U.S.
Class: |
361/91.1 |
Current CPC
Class: |
H02J 7/0031 20130101;
H02J 7/00302 20200101; H02J 7/00308 20200101 |
Class at
Publication: |
361/091.1 |
International
Class: |
H02H 9/04 20060101
H02H009/04 |
Claims
1. An over-voltage protection circuit for connection to a charging
circuit for maintaining a voltage across an energy storage device
at or below a predetermined voltage during charging, comprising: an
over-voltage protection device; and an over-voltage protection
controller for connecting said over-voltage protection device in
parallel with said energy storage device only when the voltage
across the energy storage device exceeds said predetermined
voltage, so as to draw excess charge from said energy storage
device.
2. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection controller comprises a switch actuated
in response to an over-voltage condition at said energy storage
device.
3. An over-voltage protection circuit according to claim 2 wherein
said over-voltage protection controller further comprises an
over-voltage detector coupled to said energy storage device and to
said switch, which causes the switch to be actuated when a voltage
measured across said energy storage device exceeds said
predetermined voltage.
4. An over-voltage protection circuit according to claim 3 wherein
said over-voltage detector and said switch are integral with one
another.
5. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection device dissipates excess charge drawn
from the energy storage device.
6. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection controller comprises a zener
diode.
7. An over-voltage protection circuit according to claim 6 wherein
said over-voltage protection controller further comprises a switch
connected to the zener diode, which is closed during charging and
open otherwise.
8. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection device comprises a resistor.
9. An over-voltage protection circuit according to claim 6 wherein
said over-voltage protection controller and said over-voltage
protection device are integral with one another.
10. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection circuit comprises a zener diode
connected in series with a resistor.
11. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection controller comprises a shunt
regulator.
12. An over-voltage protection circuit according to claim 11
wherein said over-voltage protection device comprises a resistor
connected in series with said shunt regulator.
13. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection device temporarily stores excess
charge drawn from the energy storage device.
14. An over-voltage protection circuit according to claim 13
wherein said over-voltage protection controller further comprises a
dissipation controller for dissipating the excess charge stored in
said over-voltage protection device.
15. An over-voltage protection circuit according to claim 14
wherein said dissipation controller comprises a dissipation switch
that connects said over-voltage protection device to ground in
order to dissipate the stored voltage.
16. An over-voltage protection circuit according to claim 15
wherein said dissipation controller comprises a dissipation control
mechanism that actuates said dissipation switch so as to connect
and disconnect the over-voltage protection device from said
dissipation controller.
17. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection device comprises a capacitor.
18. An over-voltage protection circuit according to claim 17
wherein said energy storage device comprises first and second
energy storage components and wherein said over-voltage protection
controller comprises first and second switches coupled to said
first and second energy storage components, respectively, and
connected in series to either end of the capacitor.
19. An over-voltage protection circuit according to claim 18
wherein said switches are actuated, during over-voltage, so as to
connect or disconnect the capacitor to each energy storage
component in order to balance charge between them.
20. An over-voltage protection circuit according to claim 18
wherein said over-voltage protection controller further comprises
an actuating means that actuates the connection or disconnection of
the capacitor to each energy storage component at a regular time
interval.
21. An over-voltage protection circuit according to claim 18
wherein said over-voltage protection controller further comprises
an over-voltage detector coupled to said first and second energy
storage components.
22. An over-voltage protection circuit according to claim 21
wherein said over-voltage detector controls actuation of said
switches.
23. An over-voltage protection circuit according to claim 1 wherein
said over-voltage protection device comprises an inductor.
24. An over-voltage protection circuit according to claim 23
wherein said energy storage device comprises first and second
energy storage components and wherein said over-voltage protection
controller comprises first and second switches coupled to said
first and second energy storage components, respectively, and
connected in series with the inductor with respect to said charging
circuit.
25. An over-voltage protection circuit according to claim 24
wherein said over-voltage protection controller further comprises
first and second diodes connected in parallel with said first and
second switches, respectively.
26. An over-voltage protection circuit according to claim 24
wherein said switches are actuated, during over-voltage, to connect
or disconnect the inductor to each energy storage component in
order to balance charge between them.
27. An over-voltage protection circuit according to claim 24
wherein said over-voltage protection controller further comprises
an actuating means that actuates the connection and disconnection
of the inductor to each energy storage component at a regular time
interval.
28. An over-voltage protection circuit according to claim 25
wherein said over-voltage protection controller further comprises
an over-voltage detector coupled to said first and second energy
storage components.
29. An over-voltage protection circuit according to claim 28
wherein said over-voltage detector controls actuation of said
switches.
30. An over-voltage protection circuit for connection to a charging
circuit for use with a handheld device for maintaining a voltage
across an energy storage device at or below a predetermined voltage
so as to avoid over-voltage during charging, comprising: an
over-voltage protection device; and an over-voltage protection
controller for connecting said over-voltage protection device in
parallel with said energy storage device in response to an
over-voltage condition at the energy storage device, so as to draw
excess charge from said energy storage device, wherein said
over-voltage protection circuit is connected to charging leads
which are connected to the charging circuit.
31. An over-voltage protection circuit according to claim 30
wherein the over-voltage protection circuit operates within the
operational limits of the handheld device.
Description
[0001] This application claims the benefit of priority from U.S.
patent application Ser. No. 60/325,551 filed on Oct. 1, 2001. By
this reference, the full disclosure, including the drawings, of
U.S. provisional application Ser. No. 60/325,551 is incorporated
herein.
FIELD OF THE INVENTION
[0002] The present invention relates to energy storage components
used in battery-operated devices. In particular, the present
invention relates to protection against over-voltage of such energy
storage components within the operational limits of a
battery-operated device while charging.
BACKGROUND OF THE INVENTION
[0003] Many mobile devices, such as cellular telephones, personal
digital assistants (PDAs), and other handheld computing and
communicating devices, rely upon standard energy storage devices,
such as battery cells, for providing power on which to operate.
[0004] Though disposable battery cells, such as alkaline cells, are
a well-known and reliable technology, it is common in such mobile
devices to employ rechargeable battery cells. These rechargeable
batteries depend on a number of known cell types, including Ni-Cad,
Ni-MH, and Li-Ion cells. All these cells are known to those of
skill in the art, as are some of their deficiencies.
[0005] Although some mobile devices are able to function with
standard off-the-shelf rechargeable batteries, many use a
specialised rechargeable battery made particularly for that make
and model of mobile device. A charging device is necessary in order
to recharge the mobile device's battery. Such a charging device may
be a dedicated device, or may be integrated into an existing
accessory, such as a cradle. The life of the battery can be
drastically curtailed by improperly charging, or over discharging
the battery.
[0006] Over-voltage protection circuits are commonly used to
prevent a voltage across an energy storage device, such as a
battery, from exceeding a set predetermined, or threshold, voltage.
Such an energy storage device can comprise a plurality of energy
storage components. Presently, over-voltage protection is typically
achieved by connecting resistors in parallel with the energy
storage device. In such over-voltage circuits, current continuously
flows through the resistors whether the terminal voltage is above
or below the set predetermined voltage, resulting in significant
wasted power. Such a conventional configuration is illustrated in
FIG. 1.
[0007] The energy storage devices 102, 104 illustrated in FIG. 1
are super capacitors, showing an example of a particular energy
storage device. However, those of skill in the art will appreciate,
the energy storage devices can be any suitable device, such as
Ni-Cad, Ni-MH, and Li-Ion cells, for example.
[0008] FIG. 1 shows a typical over-voltage protection circuit that
is well known in the art. In this circuit 100, energy storage
devices 102, 104 are connected in series. Each energy storage
device has a parasitic internal leakage current. The magnitude of
the leakage current may vary over a range of values, even among
energy storage devices from the same manufacturing batch. These
varying leakage rates result in the voltage across different energy
storage devices decreasing at different rates. When the energy
storage devices 102, 104 are charged, the energy storage device
with the lower leakage rate, and hence the greater voltage, can
exceed the maximum voltage specified for that energy storage device
before the combined voltage of both energy storage devices reaches
a desired terminal voltage. Resistors 106, 108 are placed in
parallel with energy storage devices 102, 104 respectively in order
to equalise the respective voltage drops across each energy storage
device. Charging leads 110 are shown in the drawing, for connecting
a charging circuit (not shown) to the energy storage devices.
[0009] As one skilled in the art can appreciate, the resistors act
to increase the total current flowing through each energy storage
device, since the resistors are effectively in parallel with the
parasitic resistance of the energy storage devices. This causes the
energy storage devices to discharge any excess charge faster than
if the resistors were not present. The resistor values are normally
chosen so that the current in each resistor is much greater than
the largest specified internal leakage current of the individual
energy storage device. Given that the resistors typically come from
the same manufacturing batch and are quite closely matched in value
(within a few percent), the rate at which the voltage of the energy
storage devices decrease is therefore more closely matched than if
the resistors were absent.
[0010] However, this configuration results in continually wasted
power since current is constantly flowing through the resistors and
the current in each resistor is greater than the leakage current of
the capacitor. A more power-efficient solution is required.
[0011] It is therefore desirable to provide a configuration that
allows current to flow only when an energy storage component is
above a predetermined voltage and thereby conserve power.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to obviate or
mitigate at least one disadvantage of previous over-voltage
protection circuits, particularly those provided for use with
handheld or mobile devices.
[0013] In an aspect of the invention, a protection circuit to
prevent over-voltage of an energy storage device while being
charged is provided. The energy storage device can be, for example,
a super capacitor, or a lithium-ion battery.
[0014] In a first aspect, the present invention provides an
over-voltage protection circuit for connection to a charging
circuit for maintaining a voltage across an energy storage device
at or below a predetermined voltage during charging. The circuit
comprises an over-voltage protection device and an over-voltage
protection controller. The over-voltage protection controller
connects the over-voltage protection device in parallel with the
energy storage device only when the voltage across the energy
storage device exceeds the predetermined voltage, so as to draw
excess charge from the energy storage device.
[0015] The over-voltage protection controller can comprise a switch
actuated in response to an over-voltage condition at the energy
storage device. The controller can further comprise an over-voltage
detector coupled to the energy storage device and to the switch,
which causes the switch to be actuated when a voltage measured
across the energy storage device exceeds the predetermined voltage.
This over-voltage detector and switch can be integral with one
another.
[0016] In general, the over-voltage protection device either
dissipates excess charge drawn from the energy storage device, or
temporarily stores the excess charge.
[0017] A resistor is an example of an over-voltage protection
device that dissipates excess charge drawn from the energy storage
device. A zener diode or a shunt resistor may also be used as a
dissipating over-voltage protection device, with the added
advantage that each of these components can also act as the
over-voltage protection controller. If either of these two is used
in the over-voltage protection circuit, the use of a resistor or
other over-voltage protection device is optional since the zener
diode and shunt resistor act as both over-voltage protection
controller and over-voltage protection device. In the case of the
zener diode, a switch is preferably connected to the zener diode;
the switch is closed during charging and open otherwise.
[0018] In a particular embodiment, an over-voltage protection
circuit comprises a shunt regulator (occasionally called a voltage
reference) in series with a resistor, and these are in parallel
with an energy storage device. The shunt regulator prevents the
voltage of the energy storage device from rising above a set
predetermined voltage and only allows current to flow through it
and the resistor when the voltage of the energy storage device is
at or above the predetermined voltage, thereby conserving
power.
[0019] A capacitor and an inductor are both examples of an
over-voltage device that temporarily stores excess charge drawn
from the energy storage device. Since these devices do not
generally dissipate charge, a dissipation controller is preferably
used in such configurations to dissipate the excess charge stored
in the over-voltage protection device. The dissipation controller
can comprise a dissipation switch that connects the over-voltage
protection device to ground in order to dissipate the stored
charge. Preferably, the dissipation controller also comprises a
dissipation control mechanism that actuates the dissipation switch
so as to connect and disconnect the over-voltage protection device
from the dissipation controller.
[0020] There are alternative embodiments of the present invention
that can be used in situations where the energy storage device
comprises a plurality of energy storage components. An over-voltage
device that temporarily stores excess charge is advantageously used
in such instances to avoid over-voltage by balancing charge between
the plurality of energy storage components.
[0021] Consider the exemplary case of a capacitor being used as an
over-voltage protection device for two energy storage components.
The over-voltage protection controller then comprises first and
second switches coupled to the first and second energy storage
components, respectively, and connected in series to either end of
the capacitor. The switches are actuated, during over-voltage, so
as to connect or disconnect the capacitor to each energy storage
component in order to balance charge between them. One or more
over-voltage detectors may be used in order to detect when
over-voltage occurs. This detector can also control the actuation
of the switches. Alternatively, an actuating means can be provided
that actuates the connection or disconnection of the capacitor to
each energy storage component at a regular time interval.
[0022] Next, consider the exemplary case of an inductor being used
as an over-voltage protection device for two energy storage
components. The over-voltage protection controller comprises first
and second switches coupled to the first and second energy storage
components, respectively, and connected in series with the inductor
with respect to the charging circuit. The over-voltage protection
controller preferably further comprises first and second diodes
connected in parallel with the first and second switches,
respectively. The switches are actuated, during over-voltage, to
connect or disconnect the inductor to each energy storage component
in order to balance charge between them. One or more over-voltage
detectors may be used in order to detect when over-voltage occurs.
This detector can also control the actuation of the switches.
Alternatively, an actuating means can be provided that actuates the
connection or disconnection of the capacitor to each energy storage
component at a regular time interval.
[0023] In another aspect of the invention, an over-voltage
protection circuit is provided for connection to a charging circuit
for use with a handheld device for maintaining a voltage across an
energy storage device at or below a predetermined voltage so as to
avoid over-voltage during charging. The circuit comprises an
over-voltage protection device and an over-voltage protection
controller. The over-voltage protection controller connects the
over-voltage protection device in parallel with the energy storage
device in response to an over-voltage condition at the energy
storage device, so as to draw excess charge from the energy storage
device. The over-voltage protection circuit is connected to
charging leads, which are connected to the charging circuit.
[0024] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached figures,
wherein:
[0026] FIG. 1 illustrates a typical over-voltage protection
circuit;
[0027] FIG. 2 illustrates a block diagram of an embodiment of the
invention;
[0028] FIG. 3 illustrates an embodiment of the invention;
[0029] FIG. 4 illustrates an embodiment of the invention;
[0030] FIG. 5 illustrates an alternative embodiment of the
invention; and
[0031] FIG. 6 illustrates a further alternative embodiment of the
invention.
DETAILED DESCRIPTION
[0032] Generally, the present invention provides an over-voltage
protection circuit for protection against over-voltage of an energy
storage device while charging. The circuit advantageously operates
within the operational limits of a battery-operated device, such as
a mobile or handheld device.
[0033] An over-voltage protection circuit according to the present
invention comprises an over-voltage protection device, and an
over-voltage protection controller. The controller allows current
to flow to the over-voltage protection device only when an energy
storage device is experiencing over-voltage. In allowing current to
flow to the over-voltage protection device only when the voltage
across the energy storage device is above a predetermined voltage,
power conservation is achieved.
[0034] FIG. 2 illustrates an embodiment of the present invention in
block diagram form. In particular, an over-voltage protection
circuit 112 is illustrated, which is preferably connected in
parallel to a charging circuit (not shown) via charging leads 110.
The over-voltage protection circuit 112 is used during battery
charging for maintaining a voltage across an energy storage device,
such as a battery, below a predetermined voltage. The over-voltage
protection circuit 112 comprises an over-voltage protection
controller 114 and an over-voltage protection device 116.
[0035] The over-voltage protection controller 114 can comprise any
device that is actuated in response to a voltage measured between
nodes A and C that meets or exceeds a predetermined voltage, and
connects the over-voltage protection device 116 in parallel with
the energy storage device 102 when actuated. Consequently, current
is conducted to the over-voltage protection device 116 and charge
drawn from the energy storage device 102 only when over-voltage
occurs. The over-voltage protection controller 114 can comprise a
switch, which is actuated in response to a voltage measured between
nodes A and C that meets or exceeds the predetermined voltage. When
the switch is actuated in response to an over-voltage condition,
current is conducted to the over-voltage protection device 116 and
charge is drawn from the energy storage device 102. The switch can
be, for example, a field effect transistor (FET), relay switch,
bipolar junction transistor (BJT) or multiplexer (MUX). The switch
preferably intrinsically comprises an over-voltage detector that
causes the switch to be actuated when a voltage measured between
nodes A and C exceeds a predetermined voltage. Alternatively, a
separate over-voltage detector can be used in conjunction with the
switch.
[0036] The over-voltage protection device 116 draws charge from the
energy storage device 102 experiencing over-voltage. The
over-voltage protection device 116 can comprise any device that is
able to accept the drawn excess charge and dispose of it. The
over-voltage protection device 116 can dissipate the energy itself,
for example if a resistor is used. Alternatively, the over-voltage
protection device 116 may temporarily store the excess charge, for
example if a capacitor or inductor is used, then transfer it
elsewhere to be dissipated. In the latter case, the over-voltage
protection device 116 may temporarily store such charge until it is
connected to a dissipation controller (not shown), at which time
the charge stored therein may be dissipated in an appropriate
manner, as will be well known to one skilled in the art.
[0037] For example, the dissipation controller can comprise a
circuit having a dissipation switch that connects said over-voltage
protection device to ground in order to dissipate the stored
voltage. Preferably, this dissipation controller will also comprise
a dissipation control mechanism that actuates the dissipation
switch so as to connect and disconnect the over-voltage protection
device 116 from the dissipation controller according to appropriate
conditions.
[0038] Of course, the energy storage device 102 may, in fact,
comprise a plurality of energy storage components connected in
series. In such a case, a separate over-voltage protection circuit
112 can be connected in parallel to the terminals of each energy
storage component in order to achieve a similar result as described
in the embodiments above.
[0039] FIG. 3 illustrates a presently preferred embodiment of the
present invention, showing an over-voltage protection circuit 112.
In the embodiment shown in FIG. 3, a shunt regulator 118 is used as
the over-voltage protection controller 114. The use of a shunt
regulator is advantageous in that shunt regulators have very sharp
`turn-on` characteristics. Suppose, for example, that a shunt
regulator is chosen whose rated threshold voltage is below, but
preferably near, the maximum specified voltage of the energy
storage device 102. When the voltage measured across the energy
storage device 102 is below the threshold voltage of shunt
regulator 118, negligible current will flow through the shunt
regulator 118. If the voltage of the energy storage device 102
rises during charging to the threshold voltage of the shunt
regulator 118, the shunt regulator causes current to flow through
it and through resistor 120. Any excess energy is dissipated
primarily across the resistor 120, which is employed in this
example as the over-voltage protection device 116. Current
continues to flow through the shunt regulator 118 until the voltage
of the energy storage device 102 falls below the threshold voltage
of the shunt regulator. The shunt regulator 118, therefore, acts as
both a switch and an over-voltage detector in this embodiment. If
the leakage resistance in the shunt regulator 118 is suitable, the
shunt regulator 118 can also perform the function of the
over-voltage protection device 116, thereby obviating the need for
resistor 120.
[0040] Although FIG. 3 illustrates an exemplary embodiment of the
invention, many alternative embodiments are possible. The energy
storage device 102 may comprise a plurality of energy storage
components connected in series and a separate over-voltage
protection circuit 112 can be connected in parallel to the
terminals of each energy storage component in order to achieve a
similar result as described in the embodiments above.
[0041] FIG. 4 illustrates an example of such an alternative
embodiment. In FIG. 4, a zener diode 122 can be used instead of the
shunt regulator 118 as the over-voltage protection controller 114.
The zener diode 122 is advantageously chosen such that its
threshold voltage is equal to or slightly less than the
predetermined voltage at or over which over-voltage will occur. In
this embodiment, it is preferable to have a switch 124 disposed
between the zener diode 122 and node C. The switch 124 is closed
during charging and open otherwise, so that power is dissipated in
the zener diode 122 only while charging the energy storage device
102. As one skilled in the art can appreciate, little current flows
through the zener diode 122 as long as the voltage of the energy
storage device 102 remains below the threshold voltage of the zener
diode. If the voltage rises above the threshold voltage of the
zener diode 122, exponentially greater current flows through the
zener diode. Either the zener diode itself, or a combination of the
zener diode 122 and a series resistor or resistors (not shown in
FIG. 4), dissipates this excess energy. In the case of using the
zener diode 122 by itself, it is both over-voltage protection
controller 114 and over-voltage protection device 116. Where the
zener diode 122 is used in conjunction with a resistor, or a
plurality of resistors, (not shown in FIG. 4) the over-voltage
protection device 116 functionally comprises both the zener diode
122 and the resistor.
[0042] There are, however, further alternative embodiments that may
be considered in the case where the energy storage device comprises
a plurality of energy storage components. Such embodiments cannot
be implemented with the energy storage device comprising only one
energy storage component. FIGS. 5 and 6 illustrate such exemplary
alternative embodiments. Although these figures illustrate an
energy storage device comprising two energy storage components, the
designs may be employed in circuits having more than two energy
storage components, with appropriate modifications being apparent
to one of ordinary skill in the art. For example, if energy storage
components are provided in multiples of two, circuits such as those
illustrated in FIGS. 5 and 6 may be connected in parallel with each
pair of energy storage components. Alternatively, the over-voltage
protection device may be suitably connected to more than two energy
storage components, as long as the properties of the over-voltage
protection device are selected such that it can handle possible
over-voltage from each of the energy storage components to which it
is connected.
[0043] FIG. 5 illustrates an alternative embodiment of the
invention. In this figure, energy storage device 126 comprises the
energy storage components 102, 104, which are connected to the
over-voltage protection circuit 112. In FIG. 5, the over-voltage
protection controller 114 comprises switches 128, 130, and the
over-voltage protection device 116 comprises capacitor 132. These
switches 128, 130 could be, for example, FETs, relay switches,
BJTs, MUXs, or any other suitable means as described earlier. The
switches 128, 130 are connected to a capacitor 132 in order to
protect against over-voltage by balancing the charge between the
energy storage components. When the energy storage components 102,
104 are charged and one energy storage component is at or above the
predetermined voltage, the switches 128, 130 are actuated and
connect or disconnect the capacitor 132 to each energy storage
component 102, 104 in order to balance the charge between them.
[0044] In this embodiment, the switches 128, 130 are actuated in
phase with one another as long as over-voltage occurs. Over-voltage
detectors 134 and 136 preferably control such actuation for
switches 128, 130 respectively. In this case, the over-voltage
detector performs the functions of both detecting when over-voltage
occurs, and controlling the actuation of the switch. A single
integral over-voltage detector can alternatively perform the
functions of the two over-voltage detectors 134 and 136.
[0045] An advantage of this embodiment is that any excessive charge
is transferred from the energy storage component with greater
charge to the energy storage component with lesser charge and such
excessive charge is not dissipated as it is across the resistors in
FIG. 1. For example, if energy storage component 102 were at or
over the predetermined voltage, switches 128 and 130 would connect
capacitor 132 in parallel to energy storage component 102, so that
the charge is then transferred to the capacitor 132. Later,
switches 128 and 130 would connect capacitor 132 to energy storage
component 104 and charge would transfer to energy storage component
104 since its voltage is lower that that of energy storage
component 102. Once again, the actuation of the switches is
preferably controlled as described above.
[0046] Alternatively, instead of using the over-voltage detectors
134 and 136, the circuit can comprise an actuating means (not shown
in FIG. 5) that actuates the connection and disconnection of the
capacitor 132 to each energy storage component 102, 104 at a
regular time interval. This provides for automatic charge balancing
without the need for the over-voltage detectors 134, 136.
[0047] In a case such as in FIG. 5 where the over-voltage
protection device 116 temporarily stores charge associated with
drawn excess charge, a dissipation controller 138 is preferably
provided as part of the over-voltage protection circuit 114. This
dissipation controller 138 enables the charge stored in the
over-voltage protection device 116 to be dissipated in an
appropriate manner, as will be well known to one skilled in the
art. For example, the dissipation controller can comprise a circuit
having a dissipation switch that connects said over-voltage
protection device to ground in order to dissipate the stored
voltage. Preferably, this dissipation controller will also comprise
a dissipation control mechanism that actuates the dissipation
switch so as to connect and disconnect the over-voltage protection
device 116 from the dissipation controller according to appropriate
conditions. In an alternative embodiment, a single integral
controller may perform all the functions of over-voltage detectors
134, 136 as well as those of the dissipation controller 138.
[0048] FIG. 6 is another alternative embodiment of the invention.
This figure illustrates a circuit that operates similarly to the
circuit in FIG. 5, but has an improved efficiency over the
embodiment in FIG. 5. In FIG. 6, energy storage device 126
comprises the energy storage components 102, 104, which are
connected to the over-voltage protection circuit 112. Each energy
storage component 102, 104 is connected to switch 128, 130. The
switches 128, 130 alternatively connect the respective energy
storage component to an inductor 140, thus moving any excess charge
between the energy storage components. In this embodiment, the
switches 128, 130 are actuated out of phase with one another and
cannot both be closed at the same time.
[0049] Diodes 142 and 144 conduct during the brief interval when
one switch has opened and the other has not yet closed while there
is energy stored in inductor 140. When an energy storage component
charges to (or just over) the predetermined voltage, the factor
affecting which switch will close first is which energy storage
component has the greater voltage.
[0050] For example, consider the situation where, within the
circuit in FIG. 6, energy storage component 104 is at or just above
the predetermined voltage and has a greater voltage than energy
storage component 102. Then, switch 130 closes for a period of time
to energize, but not saturate, inductor 140. Later, switch 130
opens and diode 142 immediately begins to conduct, because there is
energy stored in inductor 140. Switch 128 subsequently closes,
short-circuiting diode 142 to improve efficiency, since switch 128
has a lower voltage across it than diode 142 when it is closed, and
thereby transferring charge to energy storage component 102.
[0051] In FIG. 6, since the over-voltage protection device 116
temporarily stores charge associated with drawn excess charge, a
dissipation controller 138 is preferably provided as part of the
over-voltage protection circuit 114. This dissipation controller
138 enables the charge stored in the over-voltage protection device
116 to be dissipated in an appropriate manner, as will be well
known to one skilled in the art. For example, the dissipation
controller can comprise a circuit having a dissipation switch that
connects said over-voltage protection device to ground in order to
dissipate the stored voltage. Preferably, this dissipation
controller will also comprise a dissipation control mechanism that
actuates the dissipation switch so as to connect and disconnect the
over-voltage protection device 116 from the dissipation controller
according to appropriate conditions. In an alternative embodiment,
a single integral controller may perform all the functions of
over-voltage detectors 134, 136 as well as those of the dissipation
controller 138.
[0052] The above-described embodiments of the present invention are
intended to be examples only. Alterations, modifications and
variations may be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
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