GB2582447A

GB2582447A - Balance circuits for battery cells

Info

Publication number: GB2582447A
Application number: GB2002152.3A
Authority: GB
Inventors: Li Guoxing
Original assignee: O2Micro Inc
Current assignee: O2Micro Inc
Priority date: 2018-04-09
Filing date: 2018-04-09
Publication date: 2020-09-23
Anticipated expiration: 2038-04-09
Also published as: GB2582447B; GB202002152D0

Abstract

A balance circuit 200A for a set of battery cells 220 includes a set of switch circuits 212A and control circuitry coupled to the switch circuits. Each switch circuit of the switch circuits is coupled to a corresponding battery cell of the battery cells, and enables a bypass current to flow out from a positive tenninal of the corresponding battery cell if the switch circuit is turned on The switch circuit includes a first switch having a first diode, and includes a second switch having a second diode reversely coupled to the first diode. The second switch disables the bypass current if the second switch is turned off. The switch circuit coupled to the first cell Cell4 is configured to block a current from the adjacent cell Cell3 to the capacitor connected to the positive terminal Cc when the first and second switches of the first circuit are turned off.

Description

BALANCE CIRCUITS FOR BATTERY CELLS

BACKGROUND

FIG. 1 illustrates a battery pack 100 including a conventional balance circuit 112 for a set of battery cells 110. The balance circuit 112 includes current limit resistors Ro, RI, R), R3 and R4, switches SI, 52, S3 and S4, and a controller 102. The controller 102 monitors cells voltages of the battery cells 110 and balance the batten' cells 110 based on the monitored information. For example, during a charging process, if a battery cell Cell1 (NI=1, 2, 3 or 4) of the battery cells 110 has a cell voltage greater than a balance threshold, then the controller 102 turns on a corresponding switch SM (M=1, 2, 3 or 4) to bypass a portion 1PT of the charging current of the battery cell Cellm, and therefore the increasing rate of the cell voltage of the battery cell Cellm is lower than that of the other battery cells. For another example, similarly, if a battery cell CellN (N=1, 2, 3 or 4) has a cell voltage greater than the cell voltages of the other battery cells by an amount, and the amount exceeds a voltage reference, then the controller 102 turns on a corresponding switch SN (N=1, 2, 3 or 4) to bypass a portion In-of the charging current of the battery cell CellN. As a result, differences between the cell voltages of the battery cells 110 are reduced, and therefore the battery cells 110 are balanced.

However, the conventional balance circuit 112 has some shortcomings. For example, if a battery cell Cellx (X=1, 2, 3 or 4) of the battery cells 110 is reversely connected to the other battery cells, then a body diode of the switch Sx (X=1, 2, 3 or 4) is turned on to cause a leakage current IRV to discharge the battery cell Cellx. The leakage current IRv flowing through the body diode may cause plenty of heat to damage the balance circuit 112 and/or damage the whole integrated circuit (IC) package that includes the balance circuit 112. For another example, if a battery cell, e.g., Cello, of the battery cells 110 is disconnected from the balance circuit 112, then a body diode of the switch S4 is turned on, which causes a leakage current to flow from the battery cells Celli, Cell, and Gelb, through the body diode of the switch S4, to charge a filter capacitor Cc that is coupled to a positive terminal PACK+ of the battery pack 100. Such leakage current is relatively large and may damage the switch S4 More specifically, FIG. 1A illustrates a battery pack 100A including the conventional balance circuit 112, in which a battery cell Cell, of the battery cells 110 is reversely connected to the other battery cells. As shown in FIG. 1A, the reversely connected battery cell Cell, applies a forward-bias voltage to the body diode of the switch S2, and therefore the body diode of the switch 5, is turned on to discharge the battery cell Cell,. The leakage current 1RV of the battery cell Ce112 may not only over discharge the battery cell Cell, but also cause plenty of heat to damage the whole IC package.

FIG. 1B illustrates a situation in which a battery cell Celt' of the battery cells 110 is disconnected from the conventional balance circuit 112. For example, during an assembling process of the battery pack 100B, the battery cells Celli, Cell?, Ce113 and Cella may be connected to (e.g., welded to) the balance circuit 112, one by one, from the bottom to the top. When the battery cells Celli, Cell? and Celli are connected to the switches SI, S2, and S3, and the battery cell Cella is not connected to the switch S4 yet, a voltage Vc across the series-coupled battery cells Celli, Celle and Ce113 is applied to the switch S4, the resistor Itt, and the capacitor Cc:. Because the voltage Vc is relatively large, the body diode of the switch S4 is forward biased, e.g., turned on, and a leakage current ILK flowing from the battery cells Celli, Ce112 and Ce113, through the body diode of the switch S4 and the resistor I14, to charge the capacitor Cc is relatively large. The relatively large leakage current ILK may cause damage to the switch S4. For another example, when the battery pack 100B is already assembled into a package, one or more of the battery cells 110 may have a loose connection with the balance circuit. If a battery cell, e.g., Celli, has a loose connection with the balance circuit, then a voltage across the series-coupled battery cells Celli and Ce112 is applied to the switches S3 and S4, the resistor R.4, and the capacitor Cc. Similarly, the body diodes of the switches S3 and S4 are turned on and a relatively large leakage current flows through the body diodes to charge the capacitor Cc, which may also cause damage to the switches S3 and S4.

Thus, a balance circuit that addresses the abovementioned shortcomings would be beneficial.

SUMMARY

In one embodiment, a balance circuit for a set of battery cells includes a set of switch circuits and control circuitry coupled to the switch circuits. Each switch circuit of the switch circuits is coupled to a corresponding battery cell of the battery cells, and can enable a bypass current to flow out from a positive terminal of the corresponding battery cell if the switch circuit is turned on. The switch circuit includes a first switch having a first diode, and includes a second switch having a second diode reversely coupled to the first diode. The second switch can disable the bypass current if the second switch is turned off The control circuitry can balance the battery cells by controlling the switch circuits.

In one embodiment, a method comprises balancing a plurality of battery cells by controlling a plurality of switch circuits, wherein each switch circuit is coupled to a corresponding battery cell of said battery cells, wherein said switch circuit comprises a first switch having a first diode, and comprises a second switch having a second diode reversely coupled to said first diode. Said balancing comprises: enabling a bypass current to flow out from a positive terminal of said corresponding battery cell by turning on said switch circuit; and disabling said bypass current by turning off said second switch.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matter will become apparent as the following detailed description proceeds, and upon reference to the drawings, wherein like numerals depict like parts, and in which: FIG. 1 illustrates a battery pack including a conventional balance circuit for a set of battery cells.

FIG lA illustrates a battery pack including a conventional balance circuit, in which a battery cell of a set of battery cells is reversely connected to the other battery cells.

FIG. 1B illustrates a situation in which a battery cell of a set of battery cells is disconnected from a conventional balance circuit.

FIG. 2A illustrates a circuit diagram of an example of a balance circuit for a set of battery cells in a battery pack, in an embodiment of the present invention.

FIG. 2B illustrates a circuit diagram of an example of a balance circuit for a set of battery cells in a battery pack, in an embodiment of the present invention.

FIG. 2C illustrates a circuit diagram of an example of a balance circuit for a set of battery cells in a battery pack, in an embodiment of the present invention.

FIG. 2D illustrates a circuit diagram of an example of a balance circuit for a set of battery cells in a battery pack, in an embodiment of the present invention.

FIG. 3A illustrates a circuit diagram of an example of a balance circuit for a set of battery cells in a battery pack, in an embodiment of the present invention.

FIG. 3B illustrates a circuit diagram of an example of a balance circuit for a set of battery cells in a battery pack, in an embodiment of the present invention.

FIG. 4 illustrates a flowchart of examples of operations performed by a balance circuit for a set of battery cells, in an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the present invention. While the invention will be described in conjunction with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.

Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.

FIG. 2A illustrates a circuit diagram of an example of a balance circuit 212A for a set of battery cells 220 in a battery pack 200A, in an embodiment of the present invention. In an embodiment, the battery cells 220 are coupled in series. Although FIG. 2A shows four battery cells in the battery pack 200A, the invention is not so limited. In another embodiment, the battery pack 200A can include another number, e.g., 2, 3, 5, 6, 7 or the like, of battery cells. In an embodiment, the battery cells 220 include rechargeable battery cells such as lithium-ion battery cells. In other embodiments, the battery cells 220 may include nickel-cadmium battery cells, lead-acid battery cells, solar battery cells, or the like.

In an embodiment, the balance circuit 212A includes a set of switch circuits and control circuitry 202A. Each switch circuit is coupled to a corresponding battery cell of the battery cells 220, and can enable a bypass current to flow out from a positive terminal of the corresponding battery cell if the switch circuit is turned on. Additionally, each switch circuit includes a first switch having a first body diode, and includes a second switch having a second body diode reversely coupled to the first body diode. If the second switch if turned off, the second switch can disable the abovementioned bypass current. As used herein, "a second diode is reversely coupled to a first diode" means that either both the cathodes of the diodes are coupled to a connection node therebetween or both the anodes of the diodes are coupled to a connection node therebetween.

For example, as shown in FIG. 2A, the switch circuit coupled to the battery cell Celli (hereinafter, switch circuit QN11-QN12) includes a first switch QN11 having a first body diode, and includes a second switch QN12 having a second body diode. The anode of the first body diode and the anode of the second body are coupled to a connection node 222 therebetween. h) an embodiment, this kind of switch circuit is referred to as a "back-to-back switch." If the first switch QNI I and the second switch Q1412 are turned on, then the switch circuit QN11-QN12 is turned on, and a bypass current luy can be enabled to flow out from a positive terminal 228 of the battery cell Celli, through the switch circuit QN11-QN12, to a negative terminal 226 of the battery cell Celli. In a charging process of the battery cells 220, the bypass current luy can reduce an increasing rate of a cell voltage Valk' of the battery cell Celli. If the battery cells 220 is neither charged nor discharged, then the bypass current 'By can discharge the battery cell Cell, to reduce the cell voltage VcEnt. If the second switch QN12is turned off, then the second switch QN12 can disable/block the bypass current 'By. Similarly, if the first switch ()Nal is turned off, then the first switch QNi i can disable/block a current flowing from the terminal 226 to the terminal 228. If the first switch QN11 and the second switch QN12 are turned off, then no current flows through the switch circuit QN11-QN12. In an embodiment, the circuit structures and functions of the switch circuits Qv [-Qv?, QN2 i-QN32, and QN41-QN42, coupled to the battery cells Celle, Cella and Cell) respectively, are similar to that of the switch circuit QN11-QN12. The switches QN21, QN31 and QN41 can be referred to as the first switches of the switch circuits QN21-QN72, QN31-QN32, and QN41-QN42, respectively. The switches QN22, QN32 and QN42 can be referred to as the second switches of the switch circuits QN2I-QN22, QN3I-QN32, and QN-4I-QN42, respectively.

Accordingly, if a battery cell Celli( (K=1, 2, 3 or 4) is reversely connected to the other battery cells, then a leakage current (e g, similar to the leakage current IRv mentioned in relation to FIG. 1A) of the battery cell CelIK can be blocked/disabled by turning off the first switch (e.g., QN11, QN21, QN31 and QN41) of the corresponding switch circuit. For example, if the battery cell Cell), is reversely connected to the battery cells Celli,Celli and Cella, then turning off the switch ()Npi can disable/block a leakage current of the battery cell Cell). Because all the switches QN11, QN12, QN21, QN22, QN31, Q1,122, Q1,14 I and QN42 are initially off, the balance circuit 212A and/or the IC package that includes the balance circuit 212A can be protected from being damaged by a leakage current IRy mentioned in relation to FIG. IA.

Additionally, in an embodiment, the battery pack 200A includes a capacitor Cc coupled to a positive terminal PACK+ of the battery pack 200A. The capacitor Cc can filter out, e.g., voltage spikes and/or current spikes, at the terminal PACK+. In an embodiment, if a top battery cell, e.g., Cello, of the battery cells 220 is disconnected from or has a loose connection with a top switch circuit, e.g., QN41-QN42, of the switch circuits, then turning off the top switch circuit QN41-QN42 can block a current flowing from an adjacent battery cell Ce113, adjacent to the top battery cell Ce114, to charge the capacitor Cc. As a result, the balance circuit 212A can protect the switch circuit QN41QN42 from being damaged by a relative large leakage current, e.g., similar to the leakage current ILK mentioned in relation to FIG. I B, from the battery cells Celli, Gelb and Cella.

Moreover, in an embodiment, the control circuitry 202A can balance the battery cells 220 by controlling, e.g., selectively turning on or off, the switch circuits Q.Ni-Q2,112, QN21-QN22, QN31-QN32, and QN41-QN42, thereby extending the battery life of the battery cells. For example, the control circuitry 202A can monitor a status, e.g., including cell voltages, of the battery cells 220. If the control circuitry 202A detects that a battery cell Ce11Q (Q=1, 2, 3 or 4) of the battery cells 220 has a cell voltage greater than a balance reference, then the control circuitry 202A turns on a corresponding switch circuit of the switch circuits by turning on the first switch and the second switch in the corresponding switch circuit. In an embodiment, the balance reference is a preset voltage reference. In another embodiment, the balance reference is determined by a minimum cell voltage of the cell voltages of the battery cells 220. For example, the balance reference can be equal to the minimum cell voltage plus a preset voltage. In yet another embodiment, the balance reference is determined by an average voltage of the cell voltages of the battery cell 220. As a result, the battery cells 220 can be balanced.

In an embodiment, the switches QN1 1, QN12, QN9 1, Q12121, QN3 1, QN32, QN41 and QN42 of the switch circuits are metal-oxide-semiconductor field-effect transistors (MOSFETs) The connection node 222 between the anode of the body diode of the first MOSFET Qmi and the anode of the body diode of the second MOSFET QN12 includes a connection node between a source of the first MOSFET QNi I and a source of the second MOSFET In the example of FIG. 2A, anodes of the body diodes of each switch circuit of the switch circuits are coupled to a corresponding connection node. However, the invention is not so limited. In other embodiments, e.g., as shown in FIG. 2B and FIG. 2D, cathodes of the body diodes of each switch circuit of the switch circuits are coupled to a corresponding connection node therebetween. For example, in FIG. 2B, the cathode of the body diode of the first switch QNI I and the cathode of the body diode of the second switch QN12 are coupled to a connection node 224 therebetween.

Additionally, in the example of FIG. 2A, the switches in the switch circuits include n-channel MOSFETs. However, the invention is not so limited. In other embodiments, the switches in the switch circuits include p-channel MOSFETs, e.g., as shown in FIG. 2C and FIG. 2D.

In the examples of FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D, each switch circuit of the switch circuits includes a first MOSFET and a second MOSFET. The switch circuit can be turned on by turning on both the MOSFETs, and power consumption of the switch circuit is relatively small due to the low-power consumption feature of MOSFETs. However, the invention is not limited. In other embodiments, the switch circuit includes a transistor such as a NIOSFET and a regular PN junction diode.

By way of example, as shown in FIG. 3A, the switch circuit (hereinafter, switch circuit QN12-D11) coupled to the battery cell Celli includes a transistor QN12 and a diode DI i, e.g., a regular PN junction diode. In an embodiment, the transistor QNi2 can function as a switch under control of the control circuitry 302A, and the diode D11 can function as a switch under control of the transistor QN12. In the example of FIG. 3A, the transistor QNi2 includes an n-channel MOSFET. Thus, the control circuitry 302A can control the driver circuit 304A to pull up a voltage at the gate terminal of the transistor QN12 to turn on the transistor QN12, or pull down the voltage at the gate terminal of the transistor QNi2 to turn off the transistor QNi2. If the transistor QNi2 is turned on, then the battery cell Cell, can apply a forward bias voltage to the diode D,,, through the resistors R0 and R1 and the transistor QNi2, to turn on the diode D11. The switch circuit QN12-Diu can also be turned on. If the transistor QN12 is turned off, then the diode Di i, as well as the switch circuit QN12-D,1, can be turned off.

In an embodiment, the diode Dii can be referred to as a first switch of the switch circuit QN12-D II, and the transistor QN12 can be referred to as a second switch of the switch circuit QN12-D11. In an embodiment, the circuit structures and functions of the switch circuits QN22-D21, QN32-D31, and QN42-D41, coupled to the battery cells Ce112, Celli and Celli respectively, are similar to that of the switch circuit QN12-Dil. The diodes D21, D31 and D41 can be referred to as the first switches of the switch circuits QN22-D21, ON32-Ds1, and QIN42-D41, respectively. The transistors QN22, QN17 and QN42 can be referred to as the second switches of the switch circuits QN22-D21, QN32-D31, and c1/442-D41, respectively.

In an embodiment, the diodes D11, D21, D31 and D41 are unidirectional conducting devices, and they block currents flowing from their cathodes to their anodes. Thus, if a battery cell Celli; (K=1, 2, 3 or 4) is reversely connected to the other battery cells, the diode DKi can block a leakage current, e.g., similar to the leakage current II/v mentioned in relation to FIG. 1A, flowing out from the battery cell CellK. In other words, the balance circuit 312A and/or the IC package that includes the balance circuit 312A can be protected from being damaged by a leakage current IRy mentioned in relation to FIG. 1A.

Additionally, in an embodiment, if the top battery cell Celli of the battery cells 220 is disconnected from or has a loose connection with the top switch circuit Qniii-D41, the diode D41 can block a leakage current, e.g., similar to the leakage current ILK mentioned in relation to FIG. 1B, flowing from the battery cells Celli, Ce112 and Cell; to the capacitor Cc. Thus, the switch circuit QN42-D41 can be protected from being damaged by the leakage current ILK.

In the example of FIG. 3A, each of the switch circuits includes an n-channel MOSFET and a diode. However, the invention is not so limited. In another embodiment, each of the switch circuits can include a p-channel MOSFET and a diode, e.g., as shown in FIG. 3B. Operations and functions of the balance circuit 312B in FIG. 3B are similar to that of the balance circuit 312A in FIG. 3A.

FIG. 4 illustrates a flowchart of examples of operations performed by a balance circuit for a set of battery cells, in an embodiment of the present invention. FIG. 4 is described in combination with FIG. 2A, FIG. 2B, FIG. 2C and FIG. 2D. Although specific steps are disclosed in FIG. 4, such steps are examples for illustrative purposes.

That is, embodiments according to the present invention are well suited to performing various other steps or variations of the steps recited in FIG. 4.

At step 402, the control circuitry (e.g., 202A, 202B, 202C, 202D, 302A or 302B) balances a set of battery cells 220 by controlling a set of switch circuits (e.g., QNii-QN[2, QN21-QN22, QN11-QN32, and On41-QN42 in FIG. 2A; QN12-QN11, QN22-QN21, QN3))-QN31, and QN42-QN41 in FIG. 2B C) -cP11-QP12, QP21-QP22, QP31-QP32, and QP41-QP42 in FIG. 2C; QP12-QP11, QP22-QP21, QP12-QP11, and QP42-QP41 in FIG. 2D; QN12-D11, QN22-D21, QN32-D31, and Oivaa-D41 in FIG. 3A; or Dii-Qp12, Q11-QP32, and D41-QP47 in FIG. 3B). Each switch circuit of the switch circuits is coupled to a corresponding battery cell of the battery cells. Each switch circuit includes a first switch having a first diode, and 13 includes a second switch having a second diode reversely coupled to the first diode. In an embodiment, the control circuitry balances the battery cells 220 by enabling or disabling a bypass current of a battery cell of the battery cells 220.

For example, at step 404, the control circuitry, e.g., 202A in FIG. 2A, can enable a bypass current fay to flow out from a positive terminal of the battery cell Celli by turning on the switch circuit QN11-QN12.

At step 406, the control circuitry 202A can disable the bypass current 13y by turning off the second switch QN11 or turning off the switches Qmi and QN12.

While the foregoing description and drawings represent embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the principles of the present invention as defined in the accompanying claims. One skilled in the art will appreciate that the invention may be used with many modifications of form, structure, arrangement, proportions, materials, elements, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and their legal equivalents, and not limited to the foregoing description.

Further aspects of the present invention are set out in the following numbered Clauses: Clause 1: A balance circuit for a plurality of battery cells, said balance circuit comprising: a plurality of switch circuits, each switch circuit of said switch circuits coupled to a corresponding battery cell of said plurality of battery cells and operable for enabling a bypass current to flow out from a positive terminal of said corresponding battery cell if said switch circuit is turned on, wherein said switch circuit comprises a first switch having a first diode and a second switch having a second diode reversely coupled to said first diode, and wherein said second switch is configured to disable said bypass current if said second switch is turned off; and control circuitry, coupled to said switch circuits, operable for balancing said battery cells by controlling said switch circuits.

Clause 2: The balance circuit of clause 1, wherein a first cathode of said first diode and a second cathode of said second diode are coupled to a connection node therebetween.

Clause 3: The balance circuit of clause 2, wherein said first switch comprises a first metal-oxide-semiconductor field-effect transistor (MOSFET), and said second transistor comprises a second MOSFET, and wherein said connection node between said first and second cathodes comprises a connection node between a source of said first MOSFET and a source of said second MOSFET.

Clause 4: The balance circuit of clause 1, wherein an anode of said first diode and an anode of said second diode are coupled to a connection node therebetween.

Clause 5: The balance circuit of any of clauses 1 to 4, wherein said control circuitry is configured to monitor a status of said battery cells, and wherein if said control circuitry detects that a battery cell of said battery cells comprises a cell voltage greater than a balance reference, then said control circuitry is configured to turn on a corresponding switch circuit of said switch circuits by turning on the first switch and the second switch in said corresponding switch circuit.

Clause 6: The balance circuit of any of clauses 1 to 5, wherein said battery cells are coupled in series.

Clause 7: A battery pack comprising a balance circuit as clauseed in any of clauses 1 to 5 and a plurality of battery cells.

Clause 8: The battery pack of clause 7, wherein said battery cells are coupled in series.

Clause 9: The battery pack of clause 8, further comprising a capacitor coupled to a positive terminal of said battery pack, wherein said battery cells comprise a top battery cell and an adjacent battery cell adjacent to said top battery cell, and wherein said switch circuits comprise a top switch circuit, coupled to said top battery cell, and operable for blocking a current from said adjacent battery cell to said capacitor if said top switch circuit is turned off.

Clause 10: A method comprising: balancing a plurality of battery cells by controlling a plurality of switch circuits, wherein each switch circuit is coupled to a corresponding battery cell of said battery cells, wherein said switch circuit comprises a first switch having a first diode, and comprises a second switch having a second diode reversely coupled to said first diode, and wherein said balancing comprises: enabling a bypass current to flow out from a positive terminal of said corresponding battery cell by turning on said switch circuit; and disabling said bypass current by turning off said second switch.

Clause 11: The method of clause 10, wherein a first cathode of said first diode and a second cathode of said second diode are coupled to a connection node therebetween.

Clause 12: The method of clause 11, wherein said first switch comprises a first metal-oxide-semiconductor field-effect transistor (MOSFET), and said second switch comprises a second MOSFET, and wherein said connection node between said first and second cathodes comprises a connection node between a source of said first MOSFET and a source of said second MOSFET.

Clause 13: The method of clause 10, wherein an anode of said first diode and an anode of said second diode are coupled to a connection node therebetween.

Clause 14: The method of any of clauses 10 to 13, further comprising: monitoring a status of said battery cells; and if a battery cell of said battery cells comprises a cell voltage greater than a balance reference, then turning on a corresponding switch circuit of said switch circuits by turning on the first switch and the second switch in said corresponding switch circuit.

Clause 15: The method of any of clauses 10 to 14, wherein said battery cells are coupled in series.

Clause 16: The method of clause 15, wherein said battery cells are assembled in a battery pack having a capacitor coupled to a positive terminal of said battery pack, wherein said battery cells comprise a top battery cell and an adjacent battery cell adjacent to said top battery cell, wherein said switch circuits comprise a top switch circuit coupled to said top battery cell, and wherein said method further comprises: blocking a current from said adjacent battery cell to said capacitor by turning off said top switch circuit.

Claims

WE CLAIM: 1. A battery pack comprising: a positive terminal; a capacitor coupled to the positive terminal; a plurality of battery cells coupled in series, wherein the plurality of battery cells comprises: a first battery cell, at an end of the series, coupled to the positive terminal via the capacitor; and a second battery cell adjacent to the first battery cell; a plurality of resistors; and a plurality of switch circuits, wherein each switch circuit of the plurality of switch circuits comprises a first switch having a first diode and a second switch having a second diode reversely coupled to the first diode, wherein each switch circuit of the plurality of switch circuits is coupled between positive and negative terminals of a corresponding battery cell of the plurality of battery cells via a corresponding resistor of the plurality of resistors, and wherein that switch circuit is configured to: enable a bypass current to flow through the corresponding resistor when the first and second switches of that switch circuit are turned on, and disable the bypass current when the second switch of that switch circuit is turned off, and wherein the plurality of switch circuits comprises a first switch circuit that is coupled to the first battery cell and configured to block a current from the adjacent second battery cell to the capacitor when the first and second switches of the first switch circuit are turned off.
2. The battery pack of claim 1, further comprising: control circuitry, coupled to the plurality of switch circuits, and configured to balance the plurality of battery cells by selectively: turning on the first and second switches of that switch circuit to enable the bypass current to flow out from the positive terminal of the corresponding battery cell to the negative terminal of the corresponding battery cell via the corresponding resistor; and turning off the second switch of that switch circuit to disable the bypass current in that switch circuit.
3. The battery pack of claim 2, wherein the control circuitry is configured to monitor a status of the plurality of battery cells, and wherein if the control circuitry detects that a battery cell of the plurality of battery cells comprises a cell voltage greater than a balance reference, then the control circuitry is configured to turn on the first and second switches in a corresponding switch circuit of the plurality of switch circuits.
4. The battery pack of any of claims 1 to 3, wherein an anode of the first diode and an anode of the second diode are coupled to a connection node therebetween.
5. The battery pack of claim 4, wherein the first switch comprises a first n-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and the second switch comprises a second n-channel MOSFET, and wherein the connection node between the anodes of the first and second diodes comprises a connection node between a source of the first n-channel MOSFET and a source of the second n-channel MOSFET.
6. The battery pack of claim 4, wherein the first switch comprises a first p-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and the second switch comprises a second p-channel MOSFET, and wherein the connection node between the anodes of the first and second diodes comprises a connection node between a drain of the first p-channel MOSFET and a drain of the second p-channel MOSFET.
7. The battery pack of any of claims 1 to 3, wherein a cathode of the first diode and a cathode of the second diode are coupled to a connection node therebetween.
8. The battery pack of claim 7, wherein the first switch comprises a first n-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and the second switch comprises a second n-channel MOSFET, and wherein the connection node between the cathodes of the first and second diodes comprises a connection node between a drain of the first n-channel MOSFET and a drain of the second n-channel MOSFET.
9. The battery pack of claim 7, wherein the first switch comprises a first p-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and the second switch comprises a second p-channel NIOSFET, and wherein the connection node between the cathodes of the first and second diodes comprises a connection node between a source of the first p-channel MOSFET and a source of the second p-channel MOSFET.
10. The battery pack of any of claims 1 to 3, wherein the second switch comprises an n-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and wherein an anode of the first diode is coupled to the positive terminal of the corresponding battery cell, and a cathode of the first diode is coupled to a drain of the n-channel MOSFET.
11. The battery pack of any of claims 1 to 3, wherein the second switch comprises a p-channel metal-oxide-semiconductor field-effect transistor (MOSFET), and wherein a cathode of the first diode is coupled to the negative terminal of the corresponding battery cell, and an anode of the first diode is coupled to a drain of the p-channel MOSFET