JP2011172475A - Battery protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary-battery protection-circuit for protecting a rechargeable battery. <P>SOLUTION: The battery protection circuit includes a monitoring circuit, an integrator circuit and a comparator. The monitoring circuit may be used for monitoring a cell of a battery and for generating monitoring signal which indicates a cell voltage of the cell. The integrator circuit accumulates, for a certain period of time, difference between the monitoring signal and a first predetermined threshold value to generate the integration output. The comparator compares the integration output with a second predetermined threshold value to generate control signal. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rechargeable battery. More particularly, the present invention relates to a secondary battery protection circuit that protects a rechargeable battery.

  This application is a continuation-in-part of US patent application Ser. No. 11/774331, filed Jul. 6, 2007, which is hereby incorporated by reference in its entirety. As such, it is a continuation of U.S. Patent Application No. 10/879655 filed on June 29, 2004, and U.S. Patent Application No. 10/879655 itself is U.S. Patent Application No. 10/879655 filed on April 27, 2004. U.S. Application No. 10/832620 is now a U.S. Patent No. 7589499, which is the priority of U.S. Provisional Application No. 60/556254 filed on March 25, 2004. Is an insistence.

  Various electronic devices can use rechargeable batteries. Such electronic devices can include notebook computers, mobile phones, personal digital assistants, power tools, and the like. A variety of rechargeable batteries, such as lithium ion batteries, nickel cadmium batteries, and nickel metal hydride batteries can be utilized in such devices. Some rechargeable batteries, such as lithium ion batteries, can be dangerous under certain conditions, including over voltage conditions. Accordingly, various battery protection circuits may be utilized in such rechargeable battery packs.

  In some examples, a secondary battery protection circuit may be used in addition to the primary battery protection circuit. The secondary battery protection circuit can provide an output to the fuse element to permanently disable the fuse element in response to a sustained overvoltage condition.

  However, such secondary protection circuits do not protect against short overvoltage spikes. In addition, once the fuse element becomes non-conductive, it cannot return to the conductive state (i.e., once tripped, the fuse element will need to be replaced), so the fuse element is in the conductive state. And not transitionable between non-conducting states.

  Furthermore, the conventional secondary battery pack protection circuit may not detect a relatively high voltage attack that occurs in a relatively short time period.

  The battery circuit includes a monitoring circuit, an integrator circuit, and a comparator. The monitoring circuit can be used to monitor the cell and generate a monitoring signal indicative of the cell voltage of the cell. The integrator circuit accumulates the difference between the monitoring signal and the first predetermined threshold over a period of time to produce an integrated output. The comparator compares the integrated output with a second predetermined threshold value and generates a control signal.

  As the following detailed description proceeds, and with reference to the drawings, in which like parts are designated with like numerals, the features and advantages of the claimed subject matter will become apparent.

It is a block diagram of the electronic device which has a secondary battery protection circuit with overvoltage transient protection. FIG. 2 is a block diagram of an embodiment of the battery pack of FIG. FIG. 3 is a block diagram of an embodiment of a secondary battery protection circuit with overvoltage transient protection that can be utilized in the electronic device and battery pack of FIGS. 1 and 2. FIG. 3 is a block diagram of another embodiment of a secondary battery protection circuit with overvoltage transient protection that can be utilized in the electronic device and battery pack of FIGS. 1 and 2. FIG. 5 is a graph of cell voltage over time showing a short overvoltage spike and a sustained overvoltage condition with associated control signals for the embodiment of FIG. FIG. 6 shows a graph of voltage over time showing battery protection, eg, overvoltage transient protection, using multiple voltage thresholds, according to one embodiment of the invention. FIG. 6 shows a graph of voltage over time showing battery protection, eg, under voltage transient protection, using multiple voltage thresholds according to one embodiment of the present invention. 1 is a block diagram of a battery pack having a battery protection circuit according to an embodiment of the present invention. FIG. 8 shows a waveform of a signal generated or received by the battery protection circuit of FIG. 7, according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail. 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 those 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, one of ordinary skill in the art will appreciate that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.

  FIG. 1 is a block diagram of an electronic device 100 having a DC power source 104 and a battery pack 102 for supplying power to the system 110. In the absence of a DC power source 104 (eg, an ACDC adapter), power can be supplied from the battery pack 102 to the system 110. If a DC power source 104 is present, it can provide power to the system 110 and power to charge the battery cells 120. In one battery charging mode, in one example, the switch S1 may be closed and the switch S2 may be opened. In this example, a current can then flow through the closed switch S1 and the diode D2 in parallel with the open switch S2, thereby supplying a charging current to the cell 120. In another battery charging mode, both switches S1 and S2 may be closed to reduce losses due to diode D2. In one battery supply mode, in one example, the switch S1 may be opened and the switch S2 may be closed. Thereafter, current from the battery cell 120 to the system 110 can flow through the closed switch S2 and the diode D1 in parallel with the open switch S1. In another battery supply mode, both switches S1 and S2 may be closed to reduce losses due to diode D1.

  The battery pack 102 may also include a primary battery protection circuit 122, a filter 128, a secondary safety circuit 130, a fuse element 132, and a secondary battery protection circuit 126 with overvoltage transient (OVT) protection consistent with the embodiment. it can. The primary battery protection circuit 122 monitors a plurality of states including the respective voltage levels of the cell 120, as well as the charge current level and the discharge current level, and outputs the charge control signal (CHG_IN) and the discharge control signal (DSG_IN). Can be supplied. The respective voltage level of the cell 120 can also be monitored by the secondary safety circuit 130 via the filter 128. Filter 128 serves to filter out shorter duration overvoltage transient spikes. The secondary safety circuit 130 monitors the voltage level of each of the cells 120, and if a voltage level of one of the cells is higher than the overvoltage threshold level for some sustained time interval, the fuse element A signal is provided to fuse element 132 to blow 132, ie open. Thus, the filter 128 serves to prevent the fuse element 132 from being destroyed by a shorter duration overvoltage transient spike.

  The battery pack 102 also includes an overvoltage transient protection circuit to protect the cell when the voltage level of any one of the cells 120 is higher than the overvoltage threshold level for a time interval less than or equal to the transient time interval. A secondary battery protection circuit 126 may be included. As used herein, a “transient time interval” is a permanent protection mechanism, eg, an associated battery pack, in one example, the fuse 132 is activated in the event of a sustained overvoltage condition. It is the time interval required for The transient time interval may vary based on the specific cell chemistry, the specific permanent protection mechanism, and other considerations. In one embodiment, the transient time interval may be about 10 microseconds (μs). Thus, the secondary battery protection circuit 126 protects the cell 120 from shorter overvoltage spikes that would otherwise not work with any other more permanent protection mechanism. For example, the secondary battery protection circuit 126 can protect the cell 120 from short overvoltage spikes that are only 1 millivolt (mV) in magnitude and only 1 μs in duration.

  In addition to protecting the cell 120 from overvoltage transients, the secondary battery protection circuit 126 can also protect the cell 120 from sustained overvoltage conditions that last longer than the transient time interval. With this function, the secondary battery protection circuit 126 can partially provide the overlapping function of the secondary safety circuit 130. Accordingly, one or more of the filter 128, the secondary safety circuit 130, and the fuse element 132 can be removed within the battery pack 102, saving component cost and space. Alternatively, such components 128, 130, 132 may be retained, and this sustained overvoltage protection feature of the secondary battery cell protection circuit 126 can provide an additional layer of reliability. .

  FIG. 2 is a block diagram of an embodiment of a battery pack 102a that can be used in the electronic device 100 of FIG. The battery cell 120a can include a cell 1, a cell 2, and a cell 3. Each battery cell may be coupled with a primary battery protection circuit 122, an RC filtering network 128a, and a secondary battery protection circuit 126. RC filtering network 128a may include resistors R5, R7, and R8 and capacitors C2, C3, and C4. In one embodiment, resistors R5, R7, and R8 may further be equal to 1 kiloohm (kΩ), and capacitors C2, C3, and C4 may all be equal to 0.1 microfarads (μF).

  The RC filtering network 128a can filter out short duration overvoltage transients and provide an input representing the respective voltage level of the cell 120a to the secondary safety circuit 130a. If the voltage level of any one of the cells (cell 1, cell 2, or cell 3) exceeds the overvoltage threshold level, e.g., 4.2 volts, for longer than the transient time interval, the secondary safety circuit 130 A control signal can be supplied to the control terminal of Q7, whereby transistor Q7 is turned on and fuse F1 is destroyed. An additional thermal fuse F2 may be coupled in series with the fuse F1.

  The functionality of the charge switch S1 and the discharge switch S2 in FIG. 1 can be implemented using transistors Q1-Q6, as shown in FIG. The transistors Q1 to Q6 may be any type of transistor including a field effect transistor (FET) such as a metal oxide semiconductor field effect transistor (MOSFET) and a bipolar junction transistor. A battery gas gauge circuit 230 is also included in the battery pack 102a to monitor the capacity of the cell 120a and provide an output signal representative of the remaining capacity of the cell 120a based on various monitored conditions. be able to. The detection resistor 234 can supply current information to the primary battery protection circuit 122.

  The secondary battery protection circuit 126 can be disposed between the primary battery protection circuit 122 and the transistors Q1 to Q6. The secondary battery protection circuit 126 receives the charge control signal (CHG_IN) and the discharge control signal (DSG_IN) from the primary battery protection circuit 122, and outputs the output charge control signal (CHG) and the output discharge control signal (DSG) to the transistor Q1. Can be supplied for ~ Q6. Secondary battery protection circuit 126 may also receive signals representative of the voltage level of cell 120a from terminals 270, 272, 274, and 276. In general, the secondary battery protection circuit 126 monitors each voltage level of the cell 120a, and supplies an output signal to the transistors Q1 to Q6 to protect the cell 120a in the case of an overvoltage transient. Can do.

  FIG. 3 is a block diagram of one embodiment of a secondary overvoltage transient protection circuit 126a. Circuit 126a may include an overvoltage detector circuit 302. Overvoltage detector circuit 302 monitors the cell voltage of each cell 350, 352, 354, and 356, thereby allowing all cell voltage levels that exceed the overvoltage threshold level to have any duration, including a short duration. Detect about. The overvoltage detector circuit 302 can then provide an output signal that indicates whether the voltage level of any of the cells 350, 352, 354, and 356 is higher than an overvoltage threshold level, eg, 4.2 volts.

  If the overvoltage detector circuit 302 provides an output signal that indicates that one voltage level of the cell is higher than the overvoltage threshold level, then the secondary battery protection circuit 126a will cause the cell 350, Measures can be taken to protect 352, 354, and 356. Such protection can include opening an appropriate switch S1 or S2 to isolate the cell from overvoltage conditions. Such protection can also include increasing the internal resistance of the appropriate switch S1 or S2 in order to limit the voltage level to the cell to an appropriate level when conducting.

  The switches S1 and S2 may be any type of transistor such as field effect transistors (FETs) 340, 342, and the secondary battery protection circuit 126a supplies a control signal to the gates of these FETs. This control signal may be a digital signal or an analog signal. The digital signal can be used to drive an appropriate switch (switch S1 or S2) to an open state to isolate the cell from overvoltage transients. Analog signals can also be used to control the ON resistance value of the switch (when the switch is conductive) to limit the voltage level to the cell to an appropriate level. For example, if the switch is a FET, the FET can be driven to saturation with an analog signal to operate the FET as a variable resistor. Thus, the ON resistance value of the FET can be controlled to a desired level with an analog signal to limit the voltage level encountered by the cell to an appropriate safety level.

  Referring to FIG. 4, another embodiment of the secondary battery protection circuit 126b is shown. In addition to providing temporary protection for the cell from overvoltage transients, the secondary battery protection circuit 126b may also be able to provide permanent protection for the cell from sustained overvoltage conditions. is there. Secondary battery protection circuit 126b may also be able to provide permanent protection for the cell from other adverse conditions such as over temperature conditions.

  The secondary battery protection circuit 126b includes a cell overvoltage detector circuit 402, a cell overvoltage (COV) stretch circuit 404, a low-pass filter 408, a fuse latch 406, a charge driver 412, a discharge driver 410, a switch disable circuit 416, and an overheat detector. 418 may be included. The charge switch S1 and the discharge switch S2 in FIG. 1 can be implemented as FETs 440 and 442, respectively.

  The overvoltage detector circuit 402 monitors the cell voltage of each cell 450, 452, 454, and 456, thereby allowing all cell voltage levels that exceed the overvoltage threshold level to have a short duration for any duration. Even detect. In one embodiment, the overvoltage detector circuit 402 may include a switch network to couple each cell to one input of the comparator. The other input of the comparator may be at a voltage level equal to the overvoltage threshold level. The comparator can then compare the individual voltage level of the cell to the overvoltage threshold level and provide an output representative of the result of the comparison.

  The overvoltage detector circuit 402 can then provide a cell overvoltage (COV) digital signal to the COV stretch circuit 404. If the COV digital signal represents an overvoltage transient, the COV stretch circuit 404 maintains that COV signal in that state for a minimum time interval. The COV stretch circuit 404 also passes a low pass filter 408 to the COV signal to discard short duration events and outputs a FUSE_BLOW signal if the COV signal remains high for longer than the transient time interval. Can do. The FUSE_BLOW signal can be generated internally as an output of the low-pass filter 408 or generated externally, and can be input to the circuit 126b at the terminal 435.

  The FUSE_BLOW signal is latched by the fuse latch 406 and can be used to permanently disable the charge FET 440 and / or the discharge FET 442 by the FUSE_BLOWN control signal. The fuse latch 406 is self-resetting and can be persistent as long as power is supplied to the circuit, or it can be permanent by some method, such as destroying a zener zap diode. In one example, disabling FETs 440 and 442 can be accomplished by shorting the gate and source terminals of each FET. For example, this can be accomplished by the switch disable circuit 416 closing the switch 437, thereby shorting the gate and source terminals of the charge FET 440, or closing the switch 439, thereby causing the source terminal and gate of the discharge FET 442. This can be realized by short-circuiting the terminals. For additional protection, FET drivers 412 and 410 can be disabled by the FUSE_BLOWN control signal. The FUSE_BLOWN signal can be output at terminal 441 of the secondary battery protection circuit 126b to provide an indication of such a state.

  Additional protection features can also be implemented by providing an additional input to the fuse latch 406 that represents other adverse conditions that can trigger the FET440 and 442 to be permanently disabled. it can. Such an adverse condition may be, for example, an elevated temperature condition from the overheat detector 418. This may be an elevated temperature of cell 120, switches S1 and S2, or other components. The secondary battery protection circuit 126b can be used together with the thermal fuse F2 in the battery pack (see FIG. 2). The circuit 126b may be able to protect the cell 120 from high temperature conditions before the thermal fuse F2 is disconnected, thereby preventing the more expensive thermal fuse F2 from being disconnected and replacing it. Save.

  The COV signal from overvoltage detector circuit 402 can also be used to temporarily protect cells 450, 452, 454, and 456 during an overvoltage transient that is too short to trigger the FUSE_BLOW signal. In one example, the COV signal can be input to the COV stretch circuit 404 so that the COV signal representing an overvoltage transient is stretched or maintained for a minimum time interval. This prevents a vibration state between the opening operation and the closing operation of either the charge FET 440 or the discharge FET 442 when a short overvoltage spike occurs in the vicinity.

  FIG. 5 shows a graph 502 of cell voltage versus time, along with the COV signal, COV stretch signal, and FUSE_BLOW signal of FIG. 4, to further explain the operation of the secondary battery protection circuit 126b of FIG. As long as the cell voltage is below the overvoltage threshold level (Vov), the overvoltage detector circuit 402 can provide a digital zero COV signal.

  Between times t1 and t2 and between times t3 and t4, an overvoltage transient is shown in which the voltage level of a particular cell exceeds Vov. Accordingly, the overvoltage detector circuit 402 detects this condition and provides a digital one COV signal between times t1 and t2 and between times t3 and t4. The COV stretch circuit 404 also applies a digital, high-level COV stretch signal that starts at time t1 and continues until time t5 to prevent the sudden opening and closing of the charge FET 440 and / or discharge FET 442. Can be supplied. For example, to protect the cell from overvoltage transients during the time interval between times t1 and t5, the COV stretch signal can be digitally maintained and the charge FET 440 and / or the discharge FET 442 The open state can be maintained during this time interval.

  The overvoltage transient between times t1 and t2 and between times t3 and t4 may not be long enough to trigger the FUSE_BLOW signal. That is, the time interval between times t1 and t2 and between times t3 and t4 may be less than or equal to the transient time interval. However, the overvoltage condition starting at time t6 may be longer than the transient time interval (time between times t6 and t7) so as to induce a permanent protection mechanism. For example, the FUSE_BLOW signal can be digitally provided as a signal at time t7, ie, at the end of the transient time interval. This can then trigger an external fuse element (eg, fuse element 132 of FIG. 1) and / or trigger switch disable circuit 416 to permanently disable FETs 440 and 442.

  Therefore, the secondary battery protection circuit 126b can protect the cell from an overvoltage transient state, from a sustained overvoltage state, and from other adverse conditions such as overtemperature. Accordingly, one or more of secondary safety circuit 130, filter 128, and fuse element 132 can be removed (see FIG. 1), saving component cost and space. Alternatively, such components 130, 128, 132 may be retained, and this sustained overvoltage protection feature of the secondary battery protection circuit 126 provides an additional layer of reliability for the cell. can do.

  In summary, a secondary battery protection circuit is provided. The circuit is configured to monitor the voltage level of the associated cell of the rechargeable battery and provide an output signal to the switch in response to comparing the cell voltage level to the overvoltage threshold level. An overvoltage detector circuit may be included. The switch can be coupled between the rechargeable battery and the DC power source and can be transitionable between a conducting state and a non-conducting state. The switch also protects the rechargeable battery in response to the output signal when the cell voltage level is above the overvoltage threshold level for a time interval less than or equal to the transient time interval.

  A battery pack is also provided that includes a primary battery protection circuit configured to monitor the state of the rechargeable battery and provide charge and discharge signals. The battery pack may also include a secondary battery protection circuit configured to receive the charge signal and the discharge signal from the primary circuit and to supply the charge drive output signal and the discharge drive output signal. The secondary battery protection circuit can be configured to monitor the voltage level of at least one cell of the rechargeable battery. The battery pack may also include a charge switch coupled between the rechargeable battery and the DC power source and capable of transitioning between a conductive state and a non-conductive state. The charge switch responds to the charge drive output signal from the secondary battery protection circuit when the cell voltage level is higher than the overvoltage threshold level during the battery charge mode for a time interval less than or equal to the transient time interval. And rechargeable batteries can be protected. An electronic device including such a battery pack is also provided.

  Advantageously, the secondary battery protection circuit protects the cells of the rechargeable battery from overvoltage transients that would otherwise be encountered by the cells. Such overvoltage transients include any small increase in cell voltage above the overvoltage threshold level for a short duration less than the transient time interval. The secondary battery protection circuit can also provide a backup permanent protection mechanism for rechargeable battery cells in the event of a sustained overvoltage condition with a duration longer than the transient time interval. This may allow other circuitry that provides similar sustained overvoltage protection to be eliminated or retained for additional redundancy.

FIG. 6A shows a graph of cell voltage over time showing battery protection, eg, overvoltage transient protection, using multiple voltage thresholds, according to one embodiment of the present invention. In one embodiment, V _OV1 , V _OV2 and V _OV3 are overvoltage thresholds and may be V _OV3 > V _OV2 > V _OV1 . In the example of FIG. 6A, for purposes of illustration, the cell voltage is monitored and compared to a voltage threshold. However, the present invention is not so limited. The battery voltage or average cell voltage can also be compared to a corresponding voltage threshold.

In one embodiment, to protect the battery from undesired conditions, e.g., overvoltage transients, when the cell voltage exceeds the voltage threshold, i.e. above the voltage threshold, during the corresponding time interval. In addition, a protective action is triggered. For example, cell voltage, when it exceeds the threshold V _OV1 for a predetermined time period T _OV1, undesirable condition can be detected, for example, over-voltage transients can induce protective operation. Cell voltage, when it exceeds the threshold V _OV2 for a predetermined time period T _OV2, undesirable condition can be detected, for example, over-voltage transients can induce protective operation. Cell voltage, when it exceeds the threshold V _OV3 for a predetermined time period T _OV3, undesirable condition can be detected, for example, over-voltage transients can induce protective operation. In one embodiment, T _OV1 > T _OV2 > T _OV3 . In one embodiment, each product of an overvoltage threshold and a corresponding predetermined time period is the same, eg, V _OV1 T _OV1 = V _OV2 T _OV2 = V _OV3 T _OV3 .

During the first time interval t1, the cell voltage exceeds the first overvoltage threshold V _OV1 . If t1 is greater than or equal to the predetermined time period T _OV1 , an overvoltage transient is detected and a protective action can be triggered. During the second time interval t2, the cell voltage exceeds the first overvoltage threshold V _OV1 . If t2 is less than the predetermined time period T _OV1 , there is no overvoltage transient. During the third time interval t3, the cell voltage exceeds the second overvoltage threshold V _OV2 . If t3 is greater than or equal to the predetermined time period T _OV2 , an overvoltage transient is detected and a protective action can be triggered. During the fourth time interval t4, the cell voltage exceeds the third overvoltage threshold V _OV3 . If t4 is _greater than or _equal to the predetermined time period T _OV3 , an overvoltage transient is detected and a protective action can be triggered accordingly.

  Use multiple thresholds and multiple predetermined time periods, and monitor the time period when the cell voltage (or battery voltage or average cell voltage) exceeds the threshold, during a relatively short time interval The high voltage spike that occurs can be detected. In FIG. 6A, three voltage thresholds are shown, but other numbers of voltage thresholds can be used.

Similarly, FIG. 6B illustrates a voltage (e.g., cell voltage, battery voltage or average cell voltage) illustrating battery protection, e.g., undervoltage transient protection, using multiple voltage thresholds, according to one embodiment of the invention. ) Shows a graph over time. In one embodiment, V _UV1 , V _UV2, and V _UV3 are undervoltage thresholds, where V _UV3 <V _UV2 <V _UV1 .

In one embodiment, if the cell voltage is below the voltage threshold during the corresponding time interval, a protective action will be triggered to protect the battery from undesirable conditions, such as undervoltage transients. . For example, the cell voltage is lower than the threshold V _UV1 is for a predetermined time period T _UV1, can be under voltage transient condition is detected, induces protective operation. Cell voltage is lower than the threshold V _UV2 is for a predetermined time period T _UV2, it is possible to undervoltage transient condition is detected, induces protective operation. Cell voltage is lower than the threshold V _UV3 is for a predetermined time period T _UV3, can be under voltage transient condition is detected, induces protective operation. In one embodiment, T _UV1 > T _UV2 > T _UV3 .

  FIG. 7 shows a block diagram of a battery pack including a battery protection circuit according to an embodiment of the present invention. The battery pack includes one or more battery cells, a charge switch 740, a discharge switch 742, and a battery protection circuit 126C. In the example of FIG. 7, battery cells 750, 752, 754 and 756 are coupled in series for purposes of illustration. The charge switch 740 and discharge switch 742 may be various types of switches such as field effect transistors (FETs).

  Battery protection circuit 126C is coupled to the battery cell, charge switch 740, and discharge switch 742. The battery protection circuit 126C can monitor the cell voltage and compare the cell voltage with a predetermined threshold value. In one embodiment, the battery protection circuit 126C can be used to detect an overvoltage transient or an undervoltage transient in a battery cell and trigger a protective action. The battery protection circuit 126C can include a cell voltage monitor 702, a selection circuit 704, an integrator circuit 706, a comparator 708, a charge driver 712, and a discharge driver 710.

  The cell voltage monitor 702 can receive the cell terminal voltage of each battery cell 750, 752, 754 and 756 and provide the cell voltage of the battery cells 750, 752, 754 and 756, respectively. The selection circuit 704, in one embodiment, can receive the cell voltages of the cells 750, 752, 754, and 756 from the cell voltage monitor 702 and select the cell voltage. The selection circuit 704 may include a winner-take-all circuit in one embodiment. In one embodiment, the selection circuit 704 can select the highest cell voltage of the cells 750, 752, 754, and 756 to detect overvoltage transients. In another embodiment, the selection circuit 704 can select the lowest cell voltage of the cells 750, 752, 754, and 756 to detect an undervoltage transient.

Integrator circuit 706 receives a selected voltage V _SEL , eg, the highest cell voltage of the cell or the lowest cell voltage of the cell. Integrator circuit 706 also receives a first predetermined threshold V _TH1 . In one embodiment, for overvoltage protection, the first predetermined threshold V _TH1 represents an overvoltage threshold, eg, 4.2V. In another embodiment, for undervoltage protection, the first predetermined threshold V _TH1 represents an undervoltage threshold, eg, 3.0V. The integrator circuit 706 can integrate the difference between the selected voltage V _SEL and the first predetermined threshold V _TH1 over a period of time to produce an integrated output V _INT . In one embodiment, integrator circuit 706 can be implemented by a switching capacitor integrator.

Comparator 708 receives the output V _INT of integrator circuit 706 and a second predetermined threshold V _TH2 . The comparator compares the output V _INT of the integrator circuit 706 with a second predetermined threshold value V _TH2 and outputs a control signal CTR. In one embodiment, for overvoltage protection, when the integrator circuit output V _INT exceeds a second predetermined threshold V _TH2 , the comparator 708 controls to indicate that an overvoltage transient occurs. A signal CTR can be generated. The output control signal CTR can be utilized to turn off the charge switch 740 via the charge driver 712, and thus the battery charge can be terminated to protect the battery cell from overvoltage transients. it can. In another embodiment, for undervoltage protection, if the integrator circuit output V _INT exceeds a second predetermined threshold V _TH2 , the comparator 708 causes an undervoltage transient to occur. A control signal CTR indicating can be generated. The output control signal CTR can be utilized to turn off the discharge switch 742 via the discharge driver 710, and thus the discharge of the battery can be terminated to protect the battery cell from undervoltage transients. Can do.

FIG. 8 shows a waveform of a signal generated or received by the battery protection circuit of FIG. 7, according to an embodiment of the present invention. FIG. 8 is described in combination with FIG. For illustrative purposes, FIG. 8 shows an example for overvoltage detection. During the first time interval t1, the selected cell voltage V _SEL from the selection circuit 704 exceeds a first predetermined threshold V _TH1 . The integrator circuit 706 accumulates the difference between the selected cell voltage V _SEL and the first predetermined threshold V _TH1 . As shown in FIG. 8, when the output signal V _INT of the integrator circuit 706 exceeds the second predetermined threshold V _TH2 , an overvoltage transient is detected and the control signal CTR output by the comparator 708 is detected. Thus, the charging switch 740 can be turned off to end the charging of the battery.

During the second time interval t2, the second time interval t2 is shorter than the first time interval t1, but during the second time interval t2, the selected cell voltage V _SEL from the selection circuit 704 is It is higher than the selected cell voltage V _SEL from the selection circuit 704 during the first time interval t1. Accordingly, the integrator circuit output signal V _INT may still exceed the second predetermined threshold V _TH2 . As a result, an overvoltage transient is detected, and the charge switch 740 can be turned off by the control signal CTR to terminate battery charging.

During the third time interval t3, the selected cell voltage V _SEL exceeds the first predetermined threshold V _TH1 . However, since the time period during which the selected cell voltage exceeds the first predetermined threshold V _TH1 is relatively short, as shown in FIG. 8, the output V _INT of the integrator circuit 706 is equal to the second _{Below a} predetermined threshold V _TH2 . Accordingly, there is no overvoltage transient and charging switch 740 can remain on.

During the fourth time interval t4, the time period during which the selected cell voltage V _SEL exceeds the first predetermined threshold V _TH1 is relatively short. However, since the selected cell voltage V _SEL from the selection circuit 704 during t4 is relatively high (e.g., voltage spike), as shown in FIG. 8, the output V _INT of the integrator circuit 706 is The second predetermined threshold V _TH2 may still be exceeded. Therefore, an overvoltage transient can still be detected and the charge switch 740 can be turned off in order to terminate the battery charging by the control signal CTR.

  Thus, a battery circuit including a monitoring circuit, an integrator circuit, and a comparator can detect an undesirable condition, such as an overvoltage condition or an undervoltage condition, and can trigger a corresponding protective action. A monitoring circuit can be used to monitor the cell voltage. The integrator circuit may receive a monitoring signal indicative of the cell voltage and accumulate the difference between the monitoring signal and a predetermined threshold over a period of time to produce an integrated output. it can. The comparator compares the integrated output with a second predetermined threshold value and generates a control signal. The control signal can be used to trigger a protective action, such as terminating the charging or discharging of the battery. As a result, the accuracy of the battery protection circuit can be improved. Further, the present invention is not limited to overvoltage or undervoltage protection. A battery circuit including a monitoring circuit, an integrator circuit, and a comparator also determines whether the battery cell voltage, battery pack voltage, or average cell voltage is above or below one or more predetermined thresholds. Can be used to detect.

  The terms and expressions used herein are to be used as descriptive terms and not as limiting terms, and in the use of these terms and expressions are shown and described. It is understood that no equivalents (or portions thereof) of features are intended to be excluded, and that various modifications are possible within the scope of the claims. Other variations, changes, and alternative methods are also possible. Accordingly, the claims are intended to cover all these equivalents.

  While the foregoing description and drawings illustrate embodiments of the present invention, various additions may be made therein without departing from the spirit and scope of the principles of the invention as defined in the appended claims. It will be understood that changes and substitutions may be made. For those skilled in the art, the present invention is used in the practice of the present invention, and is specifically adapted to the particular environment and operational requirements without departing from the principles of the present invention. It will be appreciated that elements, parts and others can be used with numerous modifications. The embodiments disclosed herein are, therefore, to be considered in all respects as illustrative and not restrictive, and the scope of the present invention is defined by the appended claims and their legal equivalents. And is not limited to the above description.

100 electronics
102, 102a battery pack
104 DC power supply
110 system
120, 120a cell, battery cell
122 Primary battery protection circuit
126 Secondary battery protection circuit, secondary battery cell protection circuit
126a Secondary overvoltage transient protection circuit, secondary battery protection circuit, circuit
126b Secondary battery protection circuit, circuit
126C battery protection circuit
128 filters
128a RC filtering network
130, 130a Secondary safety circuit
132 Fuse elements, fuses
230 Battery gas gauge circuit
234 Sense resistor
270, 272, 274, 276 terminals
302 Overvoltage detector circuit
340, 342 FET
350, 352, 354, 356 cells
402 cell overvoltage detector circuit, overvoltage detector circuit
404 cell overvoltage stretch circuit, COV stretch circuit
406 Fuse latch
408 Low-pass filter
410 Discharge driver, FET driver
412 Charge driver, FET driver
416 Switch disable circuit
418 Overheat detector
435 terminals
437, 439 switch
440 FET, charging FET
441 terminal
442 FET, discharge FET
450, 452, 454, 456 cells
502 graph
702 cell voltage monitor
704 Selection circuit
706 Integrator circuit
708 comparator
710 discharge driver
712 charger driver
740 charge switch
742 Discharge switch
750, 752, 754, 756 battery cells, cells
C2, C3, C4 capacitors
CHG output charge control signal
CHG_IN Charge control signal
CTR control signal, output control signal
D1, D2 diode
DSG output discharge control signal
DSG_IN Discharge control signal
F1 fuse
F2 thermal fuse
Q1-Q7 transistors
R5, R7, R8 resistors
S1 switch, charge switch
S2 switch, discharge switch
Vov overvoltage threshold level

Claims (18)

A circuit,
A monitoring circuit operable to monitor the cell and generate a monitoring signal indicative of the cell voltage of the cell;
Accumulating the difference between the monitoring signal and the first predetermined threshold over a period of time to receive the monitoring signal and the first predetermined threshold and generate an integrated output An integrator circuit coupled to the monitoring circuit, operable to perform:
A comparator coupled to the integrator circuit operable to compare the integral output with a second predetermined threshold and generate a control signal;
A circuit comprising:   2. The circuit according to claim 1, wherein the monitoring circuit includes a selection circuit operable to select the monitoring signal from a plurality of monitoring signals each indicating a plurality of cell voltages. The monitoring signal indicates the highest cell voltage of the cell voltage;
3. The circuit according to claim 2, wherein the first predetermined threshold value indicates an overvoltage threshold value. The supervisory signal indicates the lowest cell voltage of the cell voltage;
3. The circuit according to claim 2, wherein the first predetermined threshold value indicates an undervoltage threshold value.   In response to the control signal, a switch in series with the cell is turned off to protect the battery from undesirable conditions when the integrated output exceeds the second predetermined threshold. The circuit according to claim 1, wherein the circuit is characterized. Monitoring a plurality of cell voltages;
Accumulating the difference between the monitoring signal indicative of the cell voltage and the first predetermined threshold to produce an integrated output over a period of time;
Generating a control signal in response to a comparison between the integrated output and a second predetermined threshold;
A method comprising the steps of:   7. The method of claim 6, further comprising selecting the monitoring signal from a plurality of monitoring signals each indicating the cell voltage. The monitoring signal indicates the highest cell voltage of the cell voltage;
7. The method of claim 6, wherein the first predetermined threshold indicates an overvoltage threshold. The monitoring signal indicates the lowest voltage of the cell voltage;
7. The method of claim 6, wherein the first predetermined threshold indicates an undervoltage threshold.   Responsive to the control signal to turn off a switch in series with the battery to protect the battery from undesirable conditions when the integrated output exceeds the second predetermined threshold. 7. The method of claim 6, comprising: A battery pack,
Multiple cells,
A switch coupled in series with the cell;
Storing the difference between a first signal indicative of the cell voltage and a predetermined overvoltage threshold over a period of time to couple to the cell and generate an integral output; and the integral output And a battery protection circuit operable to generate a control signal in response to a comparison between the second predetermined threshold and
With
The switch is turned off in response to the control signal to protect the battery pack from an overvoltage transient when the integrated output exceeds the second predetermined threshold. Battery pack.   12. The battery protection circuit of claim 11, wherein the battery protection circuit is further operable to select the first signal from a plurality of signals each indicating a plurality of cell voltages of the cell. Battery pack.   13. The battery pack according to claim 12, wherein the first signal indicates a cell voltage having the highest cell voltage.   12. The battery pack according to claim 11, wherein the charging of the battery pack is terminated when the switch is turned off. A method for protecting a battery, comprising:
Monitoring a cell voltage of a cell in the battery;
Comparing the cell voltage to a first predetermined threshold and a second predetermined threshold;
When the cell voltage exceeds the first predetermined threshold, a first duration in which the cell voltage exceeds the first predetermined threshold is compared with a first predetermined time period. Steps,
Detecting a first undesirable condition if the first duration exceeds the first predetermined time period;
When the cell voltage exceeds the second predetermined threshold, a second duration for which the cell voltage exceeds the second predetermined threshold is compared with a second predetermined time period. Steps,
Detecting a second undesirable condition if the second duration exceeds the second predetermined time period;
Including
The method of claim 1, wherein the first predetermined threshold is higher than the second predetermined threshold, and the first predetermined time period is shorter than the second predetermined time period.   The product of the first predetermined threshold value and the first predetermined time period is equal to the product of the second predetermined threshold value and the second predetermined time period. The method according to claim 15. Ending charging of the battery if the first undesirable condition is detected; and
Ending charging of the battery if the second undesirable condition is detected; and
16. The method of claim 15, further comprising: The first predetermined threshold represents a first overvoltage threshold;
16. The method of claim 15, wherein the second predetermined threshold represents a second overvoltage threshold.

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